conceptual erosion and sediment control plan and stormwater quality management plan ... · 2011. 5....

Conceptual Erosion and Sediment

Control Plan and Stormwater Quality

Management Plan

Lot 200 on SP195706 Malanda

CLIENT:

Atherton Tableland Developments

STATUS:

Final

REPORT NUMBER:

SC-R00848b

ISSUE DATE:

December 2010

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page i

Atherton Tableland Developments SC_R00848b

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CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page ii


O2 Environmental Pty Ltd t/as O2 ABN 79 136 340 924

Originating Office – Sunshine Coast

8 Grebe St Peregian Beach Qld

PO Box 1384 Noosaville BC Qld 4566

T 61 7 5448 3288 | F 61 7 5448 3288 | [email protected]

Version Register

Issue Author Reviewer Change Notes Authorised for Release

Signature Date

SC_R00848 Kyle Robson Steve Dudgeon

17 Aug 2010

SC_R00848a Kyle Robson Steve Dudgeon

27 Oct 2010

Transmission Register

Controlled copies of this document are issued to the persons/companies listed below. Any copy of this

report held by persons not listed in this register is deemed uncontrolled. Updated versions of this report if

issued will be released to all parties listed below via the email address listed.

Name Email Address

Mr Grant McAuliffe [email protected]

Mr Simon Danielson [email protected]

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page iii


Table of Contents

1. Introduction 1 1.1. Background 1

2. Site Description 2 2.1. Location 2 2.2. Topography 2 2.3. Soils and Geology 2 2.4. Fauna 3 2.5. Climate 3

3. Erosion Risk Assessment 4

4. Design Standards and Technique Selection 6 4.1. Drainage Control 6

4.1.1. Flow Diversion 7 4.1.2. Spacing of Lateral Drains Down Long Continuous Slopes 7 4.1.3. Low Gradient Drainage Techniques 8 4.1.4. Drainage Down Slope 9 4.1.5. Outlet Structures for Temporary Drainage Systems 9 4.1.6. Velocity Control Structure 9 4.1.7. Selection of Channel and Chute Linings 10

4.2. Erosion Control Measures 10 4.2.1. Best Practice Erosion Requirements 11 4.2.2. Soil Stabilisation and Protection 12

4.3. Sediment Control Measures 13 4.3.1. Sediment Control Standard 13 4.3.2. Sediment Control Measures in Areas of Sheet Flow 15 4.3.3. Sediment Control Structures in Areas of Minor Concentrated Flow 16 4.3.4. Sediment Basin 17

5. Technical Notes 18 5.1. General 18 5.2. Land Clearing 18 5.3. Site Access 18 5.4. Soil and Stockpile Management 18 5.5. Site Management 19 5.6. Drainage Control 20 5.7. Erosion Control 21 5.8. Sediment Control 21 5.9. Site Rehabilitation 21 5.10. Sediment Basin Rehabilitation 22 5.11. Site Monitoring 23 5.12. Site Maintenance 23

6. Roles and Responsibilities 24

7. Monitoring Program 25 7.1. Surface Water 25

8. Auditing, Corrective and Preventative Action 26 8.1. Audit Reporting 27

9. Operational Phase Water Quality 28 9.1. Introduction 28 9.2. Objectives 28

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page iv


9.3. Existing environmental condition 28 9.4. MUSIC Modelling 29

9.4.1. Catchments 29 9.4.2. Rainfall Data 30 9.4.3. Source Node Parameters 30 9.4.4. Treatment Node Parameters 31 9.4.5. Model setup 32

9.5. Results 32

10. Operational Phase Water Quantity 34 10.1. Frequent Flow Management 34 10.2. Waterway Stability Management 35

11. Reference List 36

Tables

Table 1 – Soil Types and Characteristics 2 Table 2 – Soil Texture and Sodicity 2 Table 3 – Rainfall and Temperature for Malanda 3 Table 4 – Monthly Erosivity (R-Factor) values for Cairns 4 Table 5 – Recommended “Maximum” Drain or Bench Spacing on Non-Vegetated Slopes 7 Table 6 – Recommended “Maximum” Drain or Bench Spacing on Vegetated Slopes 8

Table 7 − Low Gradient Drainage Techniques 8

Table 8 − Steep-Gradient Flow Diversion Techniques 9 Table 9 – Outlet Structures 9 Table 10 – Chute and Channel Linings 10 Table 11 – Erosion Risk Rating for Cairns Based on Monthly Rainfall Depth 11 Table 12 – Best Practice Land Clearing and Rehabilitation Requirements 11 Table 13 – Summary of Erosion Control Techniques 12 Table 14 – Application of Erosion Control Measures to Soil Slopes 13 Table 15 – Sediment Control Standard Based on Soil Loss Rate 13 Table 16 – Sheet Flow Sediment Control Techniques 15 Table 17 – Minor Concentrated Flow Sediment Control Techniques 16 Table 18 – Type D/F Sediment Basin Design Requirements 17 Table 19 – Roles and Responsibilities 24 Table 20 – Surface Water Monitoring Program (excluding Sediment Basin) 25 Table 21 – Water Quality Objectives 25 Table 22 – Operational Phase Water Quality Objectives – Wet Tropics 28 Table 23 – MUSIC Catchments 30 Table 24 – MUSIC Rainfall-Runoff Parameters 30 Table 25 – MUSIC Pollutant Export Parameters 31 Table 26 – MUSIC Rainwater Tank Parameters 31 Table 27 – MUSIC Buffer Parameters 32 Table 28 – MUSIC Results (Annual Pollutant Loads) 32

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page v


Figures

Figure 1 – Erosion Risk Assessment 5

Figure 2 – Treatment Selection by Slope 14

Figure 3 – Existing Dam Banks and Lantana Growth 29

Figure 4 – Pre and Post Development MUSIC Models 32

Annexures

Annexure A Site Locality Plan A

Annexure B Site Plan B

Annexure C Soils Data C

Annexure D Concept ESC Plan D

Annexure E Design Calculations E

Annexure F Fact Sheets F

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page 1


1. Introduction

O2 was commissioned by Atherton Tableland Developments (the Client) to prepare a conceptual Erosion

and Sediment Control Plan (cESCP) and conceptual Stormwater Quality Management Plan (cSWQMP) in

support of the proposed subdivision of Lot 200 on SP195706 (the site). The site is located at Lot 200 Davies

Road, Malanda, and comprises an area of approximately 126 hectares. A site locality plan is provided in

Annexure A.

It is understood that the site is to be subdivided into 123 residential lots with a minimum size of 5,000m2.

A significant portion of the site is to be dedicated as Johnstone River Nature Refuge.

1.1. Background

A ‘Request for Additional Information’ was issued by the Department of Environment, Water, Heritage and

the Arts (DEWHA) on 21 October 2009 (ref. 2009/5080) following assessment of the proposed development

under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). In assessing the

proposed development under the EPBC Act, DEWHA has identified the requirement for a sediment and

erosion management plan, and stormwater management plan for the site, for both during and after

construction.

This report has been produced to provide a conceptual Erosion and Sediment Control Plan and conceptual

Stormwater Quality Management Plan for the proposed development site. A detailed ESCP and SWQMP

will need to be undertaken at the detailed design stage of the development.



2. Site Description

2.1. Location

The site is located approximately 3km east of the Malanda Township and is surrounded by existing or

future rural residential allotments. The site is also bound by the Johnstone River on the eastern boundary

of the site.

The site is predominantly clear of vegetation with the portion of vegetation bordering Johnstone River to

be dedicated as Nature Refuge. An unnamed creek/dam system traverses the site in a south-north

direction.

2.2. Topography

Site slopes vary from approximately 4% to in excess of 20%. The majority of the site grades to the central

creek/dam system prior to discharging to the Johnstone River to the north of the site. A portion of the site

grades directly into the Johnstone River to the east.

2.3. Soils and Geology

A site assessment undertaken by Walker Environmental Consultants indicates the site has been categorised

as being predominantly ‘Pin Gin’ soil profile classes. The Department of Natural Resources and Mines

findings on the ‘Pin Gin’ SPC are shown below in Table 1.

Table 1 – Soil Types and Characteristics

Soil Profile Class Australian Soil

Classification (ASC)

Australian Soil

Classification

(ASC)

Principle

Profile Form

(PPF)

Geology

Pin Gin Dystrophic Red Ferrosol Krasnozem Uf6.31 Atherton Basalt

The sodic properties of the Pin Gin SPC were determined from the main chemical attributes detailed in

Annexure C of the Walker Environmental site assessment, and are detailed below in Table 2.

Table 2 – Soil Texture and Sodicity

Depth (cm) Soil texture Exchangeable Sodium

Percentage (ESP)

Properties

0 – 10 Light Clay 2.3% Not Sodic

20 – 30 Light Clay 3.7% Not Sodic

50 – 60 Light Medium Clay 7.5% Sodic

80 – 90 Light Medium Clay 16.7% Extremely Sodic

110 – 120 Medium Clay 17.1% Extremely Sodic

Table 2 above indicates that subsoils found within the site are highly sodic. Site specific erosion and

sediment control measures will be required during the construction phase of the development to ensure

adequate treatment of sodic soils is undertaken. It should also be noted that soils on the site are highly

acidic with the majority of testing undertaken indicating a ph level below 5.



2.4. Fauna

There are several species listed as endangered under the EPBC Act, and have been identified by the DEWHA

as potentially occurring within the adjacent Johnstone River and within the creek running through the

centre of the site. These include the Lake Eacham Rainbowfish (Melanoaenia eachamensis), Aponogeton

bullosos, and Lace-eyed Tree Frog (Nyctimystes dayi).

2.5. Climate

Climate data was obtained from the Bureau of Meteorology website using the closest stations to the site –

Malanda Post Office (Rainfall data only - Station number: 031038), Kairi Research Station (Temperature

data only – Station number: 031034). Climate data is summarised below in Table 3.

Table 3 – Rainfall and Temperature for Malanda

Annual Rainfall

(mm)

Maximum

Temperature

(ºC)

Mean 1675.1 25.3

Highest 2718.1 26.5

Lowest 864.4 24.4

Median 1591.9 25.4



3. Erosion Risk Assessment

A quantitative erosion risk assessment for the site has been conducted using the Revised Universal Soil Loss

Equation (RUSLE). RUSLE aims to predict the potential long term average soil loss rate from a given site

based on the following parameters.

RUSLE A = K x R x LS x P x C

Where:

A is the predicted soil loss per hectare per year

K is the soil erodibility factor

R is the rainfall erosivity factor

LS is the slope length/gradient factor

P is the erosion control practice factor

C is the ground cover and management factor

Application of the RUSLE is based on the following site and soil characteristics.

Soil erodibility (K value) for the materials encountered have been assessed against Table E4 of the IECA

manual (2008) as 0.018, which is typical of Light medium clays that will be exposed during construction.

Monthly rainfall erosivity factors (R value) for nearby Cairns are presented below in Table 4.

Table 4 – Monthly Erosivity (R-Factor) values for Cairns

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec TOTAL

4727 5186 4516 1320 402 134 57.4 76.5 115 191 727 1665 19118

Sourced from Table E1 of IECA (2008)

Industry accepted and site indicative P and C values have been applied to the erosion risk assessment, with

adopted values shown below in Figure 1.

Figure 1 presents an erosion risk matrix for the site, indicating potential volumes of soil loss for any given

slope and period of disturbance.

Slope analysis undertaken by Walker Environmental Consultants indicate that significant areas of land

proposed for development have slopes greater than 8%, therefore having extremely high erosion risk

during the summer and low risk during the winter.


Atherton Tableland Developments SC_R00848a

Slope Gradient Soil Loss (tonnes/ha/yr)

Ratio % Degrees Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec

1 in 100 1 0.9 226 248 216 63 19 6 3 4 5 9 35 79

1 in 50 2 1.8 451 495 431 126 38 13 5 7 11 18 69 159

1 in 33 3 2.7 703 772 672 196 60 20 9 11 17 28 108 248

1 in 25 4 3.6 969 1,063 926 271 82 27 12 16 24 39 149 341

1 in 20 5 4.5 1,261 1,383 1,205 352 107 36 15 20 31 51 194 444

1 in 16.6 6 5.4 1,566 1,718 1,496 437 133 44 19 25 38 63 241 552

1 In 12.5 8 7.2 2,190 2,403 2,092 612 186 62 27 35 53 88 337 771

1 in 10 10 9 3,013 3,306 2,879 841 256 85 37 49 73 122 463 1,061

1 in 8.3 12 10.8 4,009 4,398 3,830 1,119 341 114 49 65 98 162 617 1,412

1 in 7.1 14 12.6 5,004 5,490 4,781 1,397 426 142 61 81 122 202 770 1,763

1 in 6.3 16 14.4 6,026 6,611 5,757 1,683 512 171 73 98 147 243 927 2,123

1 in 5.5 18 16.2 7,048 7,733 6,734 1,968 599 200 86 114 171 285 1,084 2,483

1 in 5 20 18 8,070 8,854 7,710 2,254 686 229 98 131 196 326 1,241 2,843

1 in 4 25 22.5 10,579 11,606 10,107 2,954 900 300 128 171 257 427 1,627 3,726

1 in 3.3 30 27 13,008 14,271 12,427 3,632 1,106 369 158 211 316 526 2,001 4,582

1 in 2.5 40 36 17,428 19,120 16,650 4,867 1,482 494 212 282 424 704 2,680 6,139

1 in 2 50 45 21,131 23,183 20,188 5,901 1,797 599 257 342 514 854 3,250 7,443

Notes on Table

Low erosion risk - soil loss less than 225 t/ha/yr

Medium erosion risk - soil loss between 225 - 500 t/ha/yr

High erosion risk - soil loss greater than 500 tonnes/ha/yr

Soil loss rates calculated using RUSLE

Soil Erodibility factor (K) estimated to be 0.018

Cover and Management Factor adopted (C) = 1

Erosion Control Practice Factor (P) = 1.3

Slope length = 80m

Figure 1 – Erosion Risk Assessment



4. Design Standards and Technique Selection

The subject site is located within Tablelands Regional Council LGA and as such reference has been made to

the Far North Regional Organisation of Councils (FNQROC) Development Manual, specifically design

guideline D5 – Stormwater Quality Management. The FNQROC Development Manual states:

“The requirements for implementation of management practices applies to all sites (i.e. subdivision

and building sites) that involve disturbing of earth irrespective of size, timing for construction and /

or the approval processes which preceded the construction. The extent of the management

practices required will be influenced by consideration of the risk, which will take into account the

scope of the works, the timing of works and other site specific factors”. And;

“Construction phase water quality works relate to temporary works and management measures

required to manage a development site during periods when the site is disturbed to minimise the

potential for release of Pollutants / Contaminants / Sediments to downstream properties and / or

receiving waters”.

To address the above requirements a Conceptual Erosion and Sediment Control Plan (cESCP) has been

developed for the site and is presented within Annexure D. Supporting design calculations and required

sizing is provided in Annexure E.

Standard design drawings and factsheets for nominated erosion and drainage controls are presented in

Annexure F.

The application of best practice erosion and sediment control is based upon the appropriate integration of

three groups of control measures:

• Drainage control measures;

• Erosion control measures (including revegetation measures); and

• Sediment control measures.

Wherever reasonable and practical, control measures from all three groups must be integrated in a total

treatment system.

4.1. Drainage Control

The IECA guideline (2008) recommend the following design standard for temporary drainage works:

• Less than 12 months 1 in 2 year ARI;

• Between 12 -24 months 1 in 5 year ARI; and

• Greater than 24 months 1 in 10 year ARI.

In the case of the subject development it is considered that application of drainage design standards for

events up to a 2 year ARI be adopted. It should be noted that the design capacity excludes a minimum

150mm freeboard.



4.1.1. Flow Diversion

Where possible, provision for the diversion of up-slope stormwater runoff for catchments above temporary

stockpile locations and excavations for road and service installation shall be made.

4.1.2. Spacing of Lateral Drains Down Long Continuous Slopes

Long unstable slopes must be divided into manageable drainage areas to prevent the formation of rill

erosion. Catch drains or flow diversion banks should be placed at regular intervals down the slope to collect

and divert surface runoff to a stable outlet.

Table 5 provides the recommended maximum drain, bank and bench spacing down long exposed, non

vegetated slopes.

Table 5 – Recommended “Maximum” Drain or Bench Spacing on Non-Vegetated Slopes

Batter Slope Horizontal

Spacing (m)

Vertical

Spacing (m) Percentage Degrees (H):(V)

1% 0.57 100:1 90 0.9

2% 1.15 50:1 60 1.2

4% 2.29 25:1 40 1.6

6% 3.43 16.7:1 32 1.9

8% 4.57 12.5:1 28 2.2

10% 5.71 10:1 25 2.5

12% 6.84 8.33:1 22 2.6

15% 8.53 6.67:1 19 2.9

20% 11.3 5:1 16 3.2

25% 14.0 4:1 14 3.5

30% 16.7 3.33:1 12 3.5

35% 19.3 2.86:1 10 3.5

40% 21.8 2.5:1 9 3.5

50% 26.6 2:1 6 3.0



Table 6 provides the recommended maximum spacing of benching down well grassed, low to moderately

erodible soil slopes.

Table 6 – Recommended “Maximum” Drain or Bench Spacing on Vegetated Slopes

Batter Slope Horizontal

Spacing (m)

Vertical

Spacing (m) Percentage Degrees (H):(V)

<10% 5.71 10:1 Site specific Site specific

12% 6.84 8.33:1 100 12

15% 8.53 6.67:1 80 12

20% 11.3 5:1 55 11

25% 14.0 4:1 40 10

30% 16.7 3.33:1 30 9

>36% >19.8 2.78:1 Site specific Site specific

4.1.3. Low Gradient Drainage Techniques

The recommended usage of various low gradient drainage control techniques is provided in Table 7.

Techniques are taken from the IECA (2008) guidelines. Only applicable and feasible techniques that have

availability of materials are presented.

Table 7 −−−− Low Gradient Drainage Techniques

Technique Typical Use

Catch Drain • The collection and diversion of sheet flow across a slope or

around soil disturbances.

• Best use in non-dispersive soils, otherwise the drain must be

lined with non-dispersive soils (minimum 100m thick) prior to

placement of channel liner.

Compost Berm • Primarily used as a sediment filter berm, but can be used as a

Flow Diversion Bank.

• Used when onsite land clearing produces sufficient quantities of

organic matter.

Flow Diversion Banks

(earth, sandbags, etc)

• Flow diversion at the base of fill slopes.

• Cross drainage on unsealed roads.

• Flow diversion up-slope of excavations and trenches.



4.1.4. Drainage Down Slope

The recommended usage of drainage controls on steep slopes is provided in Table 8.

Table 8 −−−− Steep-Gradient Flow Diversion Techniques


Chute • Discharge of concentrated flows down steep slopes.

• Temporary drainage down the face of newly formed road

embankments.

Level Spreader • Conversion of minor concentrated flows back to sheet flows.

• Discharge of flows down grassed slopes.

• Discharge of sheet flow into bushland

Slope Drain • Discharge of minor flows down steep slopes.

• Discharge of minor flows through bushland and other areas

where it is essential to minimize disturbance to vegetation and

soil.

4.1.5. Outlet Structures for Temporary Drainage Systems

The recommended usage of outlet structures for chute and slope drains is provided in Table 9.

Table 9 – Outlet Structures


Level Spreader • Used at the end of flow diversion banks and catch drains to

discharge minor concentrated flows down stable, grassed slopes.

• Discharge into bushland or grass filter zones.

Outlet Structure • Used at the end of chutes and slope drains to dissipate flow

energy and control scour.

• Used as a permanent energy dissipater on pipe and culvert

outlets.

4.1.6. Velocity Control Structure

Wherever reasonable and practicable, drainage channels, whether temporary or permanent, should be

designed and constructed at a gradient that limits the maximum flow velocity to a value not exceeding the

maximum allowable flow velocity for the given surface material.

Excessive flow velocities can cause channel erosion, usually along the invert (bottom) of the drain. Such

erosion is most prominent in newly formed or recently seeded drains.



The flow velocity can be reduced by either:

• Reducing the depth of flow (i.e. increasing the width of the channel);

• Reducing the bed slope;

• Reducing the peak discharge (i.e. reducing the effective catchment area or diverting water away

from the channel); or

• Increasing the channel roughness.

4.1.7. Selection of Channel and Chute Linings

In steep channels it is usually more economical to line the channel or chute with turf, rock or Erosion

Control Mats instead of trying to reduce flow velocities down the slope. Table 10 provides guidance on the

selection of appropriate channel linings. Given the nature of the site the suggested practice is to use ‘soft

natural linings’ such as turf or grass lined chutes for all low to medium velocity channels. These options and

typical use guidance is listed below.

Table 10 – Chute and Channel Linings


Grass Lining • Permanent protection of low to medium velocity chutes and

channels.

Turfing • Permanent lining of low velocity chutes, catch drains and

diversion channels.

Erosion Control Mat • Temporary or permanent scour protection of medium velocity

drains.

• Includes the use of Erosion Control Mesh made from jute or coir.

Rock Lining • High velocity drainage channels.

• Drainage chutes.

• Sediment Basin spillways.

4.2. Erosion Control Measures

Best practice erosion control requires appropriate measures to be employed as soon as reasonable and

practicable to limit soil erosion and, in particular, to protect any and all exposed areas of soil from raindrop

impact erosion. Best practice land clearing, erosion control and site rehabilitation depends on the

likelihood and intensity of expected wind or rainfall. If construction occurs during the dry season when

rainfall is unlikely, then the required erosion protection can be significantly less than if construction occurs

during the wet season.

Unlike the sediment control standard, which is related to the anticipated soil loss, the timing and degree of

land stabilisation measures depends on the expected erosion risk and sensitivity of receiving waters to

turbidity levels within site runoff.



In the absence of a locally adopted risk assessment procedure, the erosion control standard should be

based on either the monthly rainfall erosivity or the average monthly rainfall depth as appropriate.

Alternatively, the erosion control standard can be based on estimated rate of soil loss. Table 11 provides

erosion risk ratings based on monthly erosivity.

Table 11 – Erosion Risk Rating for Cairns Based on Monthly Rainfall Depth

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Risk

Rating

E E E H H M VL L M M H E

Source: Table 4.4.5 IECA (2008)

Key: E = Extreme, H = High, M = Moderate, L = Low, VL = Very low

4.2.1. Best Practice Erosion Requirements

Table 12 provides recommended land clearing and rehabilitation requirements based on erosion risk.

Table 12 – Best Practice Land Clearing and Rehabilitation Requirements

Risk Best Practice Requirements

All cases • All reasonable and practicable steps taken to apply best practice erosion control

measures to completed earth works, or otherwise stabilize such works, prior to

anticipated rainfall – including existing unstable, undisturbed, soil surfaces under

the management or control of the construction works.

Very low • Land clearing limited to 8 weeks of work if rainfall is reasonably possible.

• Disturbed soil surfaces stabilized with minimum 60% cover within 30 days of

completion of works if rainfall is reasonably possible.

• Unfinished earthworks are suitably stabilized if rainfall is reasonable possible, and

disturbance is expected to be suspended for a period exceeding 30 days.

Low • Land clearing limited to a maximum of 8 weeks of work.


completion of works within any area of a work site.



• Appropriate protection of all planned garden beds is strongly recommended.

Moderate • Land clearing limited to a maximum of 6 weeks of work.



• Staged construction and stabilization of earth batters (steeper than 6H:1V) in

maximum 3m vertical increments wherever reasonable and practicable.



High • Land clearing limited to a maximum of 4 weeks of work.







Risk Best Practice Requirements

• The use of turf to form grassed surfaces given appropriate consideration.

• Soil stockpiles and unfinished earthworks are suitably stabilized if disturbance is

expected to be suspended for a period exceeding 10 days.

Extreme • Land clearing limited to a maximum of 2 weeks of work.





• High priority given to the use of turf to form grassed surfaces.

• Soil stockpiles and unfinished earthworks are suitably stabilized if disturbance is

expected to be suspended for a period exceeding 5 days.

Reproduced from table 4.4.7 of IECA (2008)

4.2.2. Soil Stabilisation and Protection

Table 13 provides recommended soil stabilisation techniques that may be applied where such measures

are practicable:

Table 13 – Summary of Erosion Control Techniques


Erosion Control Blanket • Temporary erosion control on exposed soils not subjected to

concentrated flow.

• Temporary control of raindrop impact erosion on earth

embankments before and during the revegetation phase.

Gravelling • Protection of non-vegetated soils from raindrop impact erosion.

• Stabilisation of hardstand areas including site office area, process

areas, temporary car parks and access roads.

Heavy Mulching • Stabilisation of soil surfaces that are expected to remain non-

vegetated for medium to long periods.

• Suppression of weed growth on non-grassed areas.

Light Mulching • Control of raindrop impact erosion on flat and mild slopes. May

be placed on steeper slopes with appropriate anchoring.

• Control water loss and assist seed germination on newly seeded

soil.

Revegetation • Temporary and permanent stabilisation of soil.

• Stabilisation of long-term stockpiles.

• Includes Turfing and temporary seeding.

Reproduced from table 4.4.8 of IECA (2008)

While vegetation is one of the best long-term options, it can also serve as a short-term option if turf is used.

On mild slopes (1 in 10 to 1 in 4) loose organic mulch may not be appropriate if heavy rains are expected, or

if stormwater runoff is allowed to concentrate down the slope. The application of various erosion control

measures to flat, mild and steep slopes subject to “sheet” flow is summarised in Table 14.



Table 14 – Application of Erosion Control Measures to Soil Slopes

Flat Land

(flatter than 1 in 10)

Mild Slopes

(1 in 10 – 1 in 4)

Steep Slopes

(steeper than 1 in 4)

Erosion Control Blankets

Gravelling

Mulching

Revegetation

Rock Mulching

Soil Binder

Turfing

Bonded Fibre Matrix

Compost Blankets

Erosion Control Blankets, Mats

and Mesh

Mulching well anchored

Revegetation

Rock Mulching

Turfing

Bonded Fibre Matrix

Compost Blankets

Erosion Control Blankets, Mats

and Mesh

Revegetation

Rock Armouring

Turfing

4.3. Sediment Control Measures

4.3.1. Sediment Control Standard

The IECA (2008) provides a risk based standard for selection of sediment control techniques. The type of

control is determined depending on soil loss rate and area of disturbance. Analysis of the treatment type

required for the site depending on the estimated soil loss is provided below in Table 15.

Table 15 – Sediment Control Standard Based on Soil Loss Rate

Conservative analysis indicates for the majority of the site and year a Type 1 treatment is required (i.e

sediment basin). Nevertheless it is strongly recommended that development works be limited to the dry

season, in particular June to September.

Area Limit

(m²)

Soil Loss Rate Limit (t/ha/yr) Soil Loss Rate Limit (t/ha/month)

Type 1 Type 2 Type 3 Type 1 Type 2 Type 3

250 N/A N/A Default N/A N/A Default

1000 N/A N/A All cases N/A N/A All cases

2500 N/A >75 75 N/A > 6.5 6.25

>2500 >150 150 75 >12.5 12.5 6.25



Ratio % Degrees Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec

1 in 100 1 0.9 275.8 302.6 263.5 77.0 23.5 7.8 3.3 4.5 6.7 11.1 42.4 97.1

1 in 50 2 1.8 551.6 605.1 527.0 154.0 46.9 15.6 6.7 8.9 13.4 22.3 84.8 194.3

1 in 33 3 2.7 859.8 943.3 821.4 240.1 73.1 24.4 10.4 13.9 20.9 34.7 132.2 302.9

1 in 25 4 3.6 1184.3 1299.3 1131.4 330.7 100.7 33.6 14.4 19.2 28.8 47.9 182.1 417.1

1 in 20 5 4.5 1541.2 1690.8 1472.4 430.4 131.1 43.7 18.7 24.9 37.5 62.3 237.0 542.9

1 in 16.6 6 5.4 1914.3 2100.2 1828.9 534.6 162.8 54.3 23.2 31.0 46.6 77.4 294.4 674.3

1 In 12.5 8 7.2 2676.8 2936.7 2557.3 747.5 227.6 75.9 32.5 43.3 65.1 108.2 411.7 942.9

1 in 10 10 9 3682.6 4040.2 3518.3 1028.4 313.2 104.4 44.7 59.6 89.6 148.8 566.4 1297.1

1 in 8.3 12 10.8 4899.4 5375.1 4680.7 1368.1 416.7 138.9 59.5 79.3 119.2 198.0 753.5 1725.7

1 in 7.1 14 12.6 6116.1 6710.0 5843.1 1707.9 520.1 173.4 74.3 99.0 148.8 247.1 940.6 2154.3

1 in 6.3 16 14.4 7365.3 8080.5 7036.5 2056.7 626.4 208.8 89.4 119.2 179.2 297.6 1132.8 2594.3

1 in 5.5 18 16.2 8614.4 9450.9 8229.9 2405.6 732.6 244.2 104.6 139.4 209.6 348.1 1324.9 3034.3

1 in 5 20 18 9863.6 10821.4 9423.3 2754.4 838.8 279.6 119.8 159.6 240.0 398.6 1517.0 3474.3

1 in 4 25 22.5 12929.8 14185.3 12352.6 3610.6 1099.6 366.5 157.0 209.3 314.6 522.4 1988.6 4554.3

1 in 3.3 30 27 15898.6 17442.4 15188.9 4439.6 1352.1 450.7 193.1 257.3 386.8 642.4 2445.2 5600.0

1 in 2.5 40 36 21300.9 23369.2 20350.1 5948.2 1811.5 603.8 258.7 344.7 518.2 860.7 3276.0 7502.8

1 in 2 50 45 25827.1 28335.0 24674.3 7212.1 2196.4 732.1 313.6 418.0 628.3 1043.6 3972.1 9097.1

Notes on Table

Type 3 treatment soil loss less than 75 tonnes/ha/yr

Type 2 treatment - soil loss greater than 76 but less than 150 tonnes/ha/yr

Type 1 treatment - soil loss greater than 151 tonnes/ha/yr

Soil loss rates calculated using RUSLE

Soil Erodibility factor (K) estimated to be 0.022. Assuming light medium clays (K factor of 0.018) with adjustment of 20% for presence of dispersive subsoils

Cover and Management Factor adopted (C) = 1

Erosion Control Practice Factor (P) = 1.3

Slope length = 80m

Slope Gradient Soil Loss (tonnes/ha/yr)

Figure 2 – Treatment Selection by Slope



4.3.2. Sediment Control Measures in Areas of Sheet Flow

Table 16 outlines the typical use of various sheet flow sediment control techniques.

Table 16 – Sheet Flow Sediment Control Techniques


Buffer Zones • Type 3 sediment trap.

• Most suited to sandy soils.

• Generally only suitable for rural and rural-residential

building/construction sites.

• Can provide some degree of turbidity control while the Buffer

Zone remains unsaturated.

Compost Berm • Type 2 sediment trap.

• Suitable for all soil types.

Fibre Roll • Supplementary sediment trap.

• Most suited to sandy soils.

• Suitable for minor flows only.

Filter Fence • Type 3 sediment trap.

• Very small catchment areas (e.g. stockpiles).

• Better capture of the finer (sand/silt) sediments compared to

woven Sediment Fence.

Mulch Berm • Type 2 sediment trap.


Sediment Fence - woven fabric • Type 3 sediment trap.


• Long duration construction sites likely to experience several

storm events.

Sediment Fence -

non-woven composite fabric

• Type 3 sediment trap.


• Preferred type of Sediment Fence when placed adjacent critical

habitats such as waterways.

• Short duration construction sites or sites likely to experience only

a few storm events.



4.3.3. Sediment Control Structures in Areas of Minor Concentrated Flow

Table 17 outlines the typical use of sediment control techniques for minor concentrated flows, such as

roadside drains.

Table 17 – Minor Concentrated Flow Sediment Control Techniques

Technique Typical use

Check Dam Sediment Trap • Supplementary sediment trap.

• Trapping sediment in table drains and other minor drainage lines.

• Check dams may be constructed from rock, sand bags, or

compost filled socks.

• Compost-filled socks can adsorb some dissolved and fine

particulate matter.

Coarse Sediment Trap • Type 3 sediment trap.

• Best used on sandy soils.

• Commonly used as sediment trap at the low point of a Sediment

Fence.

• Used as an alternative to a spill through weir on a Sediment

Fence.

Filter Tube Dam • Type 2 sediment trap.

• Trapping sediment in minor drainage lines.

• Generally provides greater treatment of low flows than a U-

shaped Sediment Trap.

• Filter Tubes can be integrated into a variety of Type 2 and 3

sediment traps (such as rock check dam, U-shaped sediment trap,

rock filter dam and sediment weir) to improve efficiency during

minor flows.

Modular Sediment Trap • Type 3 sediment trap.

• Modern replacement for straw bale barriers.

• Capability of accepting concentrated flows depends on

construction technique.

U-Shaped Sediment Trap • Type 3 sediment trap.

• Minor concentrated flows such as table drains.

• The sediment fence must be constructed in a U-shape with an

appropriate spill through weir.

• Filter tubes can be integrated into a U-shaped sediment trap to

increase the effective hydraulic capacity and to improve the

treatment of low flows.



4.3.4. Sediment Basin

The selection of the type of sediment basin is governed by the soil properties present at the site. A type D/F

basin will be required. Conceptual design of the sediment basin has been undertaken based on the

following minimum design criteria, as per the IECA (2008) best practice guideline (refer Annexure C).

� A sensitive receiving environment

� Sized to capture the 85th

percentile five day duration event

� For a five-day management period. Adjustment factors to the five-day volumes for alternate

management periods are 85% for two-days, 125% for 10 days and 170% for 20 days.

Management of the basin requires draining or pumping out within the adopted management period

following rainfall (commonly within a five-day period).

Design of the sediment basin will be based on the desired design requirements outlined in Table 18.

Table 18 – Type D/F Sediment Basin Design Requirements

Parameter Design Requirement

Length to width ratio 3 (L) : 1 (W)

Sediment storage volume 50% of settling volume

Basin batter slopes 2 (H) : 1 (V)

Freeboard from maximum pond water level to top

of fill embankment

300 mm

Minimum spillway chute freeboard 300 mm



5. Technical Notes

The following technical notes apply to the implementation of the erosion and sediment control plan

contained within Annexure D.

5.1. General

1. Additional erosion and sediment control measures must be implemented and a revised Erosion

and Sediment Control Plan (ESCP) must be submitted for approval in the event that site

conditions change significantly from those considered within the ESCP.

5.2. Land Clearing

2. All reasonable and practicable efforts must be taken to delay the removal of, or disturbance to,

existing ground cover (organic or inorganic) prior to land- disturbing activities.

3. No land clearing shall be undertaken unless preceded by the installation of adequate drainage

and sediment control measures, unless such clearing is required for the purpose of installing such

measures, in which case, only the minimum clearing required to install such measures shall occur.

4. All land clearing must be in accordance with the Federal, State and local government Vegetation

Protection/Preservation requirements and/or policies.

5. Land clearing is limited to the minimum practicable during those periods when soil erosion due to

wind, rain or surface water is possible.

5.3. Site Access

6. Site exit points must be appropriately managed to minimise the risk of sediment being tracked

onto sealed, public roadways.

7. Stormwater runoff from access roads and stabilised entry/exit points must drain to an

appropriate sediment control device.

5.4. Soil and Stockpile Management

8. All reasonable and practicable measures must be taken to obtain the maximum benefit from

existing topsoil, including:

(i) Where the proposed area of soil disturbance does not exceed 2500m2, and the topsoil does not

contain undesirable weed seed, the top 100mm of soil located within areas of proposed soil

disturbance (including stockpile areas) must be stripped and stockpiled separately from the

remaining soil.

(ii) Where the proposed area of soil disturbance exceeds 2500m2, and the topsoil does not contain

undesirable weed seed, the top 50mm of soil must be stripped and stockpiled separately from

the remaining topsoil, and spread as a final surface soil.

(iii) In areas where the topsoil contains undesirable weed seed, the affected soil must be suitably

buried or removed from the site.



9. Stockpiles of erodible material that has the potential to cause environmental harm if displaced,

must be:

(i) Appropriately protected from wind, rain, concentrated surface flow and excessive up-slope

stormwater surface flows.

(ii) Located at least 2m from any hazardous area, retained vegetation, or concentrated drainage line.

(iii) Located up-slope of an appropriate sediment control system.

(iv) Provided with an appropriate protective cover (synthetic, mulch or vegetative) if the materials

are likely to be stockpiled for more than 28 days.

(v) Provided with an appropriate protective cover (synthetic, mulch or vegetative) if the materials

are likely to be stockpiled for more than 10 days during those months that have a high erosion

risk.

(vi) Provided with an appropriate protective cover (synthetic, mulch or vegetative) if the materials

are likely to be stockpiled for more than 5 days during those months that have a extreme erosion

risk.

10. A suitable flow diversion system must be established immediately up-slope of a stockpile of

erodible material that has the potential to cause environmental harm if displaced, if the up-slope

catchment area draining to the stockpile exceeds 500m.

5.5. Site Management

11. All office facilities and operational activities must be located such that any liquid effluent (e.g.

process water, wash-down water, effluent from equipment cleaning, or plant watering), can be

totally contained and treated within the site.

12. The construction schedule must aim to minimise the duration that any and all areas of soil are

exposed to the erosive effects of wind, rain and surface water.

13. Land-disturbing activities must be undertaken in accordance with the Erosion and Sediment

Control Plan (ESCP) and associated development conditions.

14. Land-disturbing activities must be undertaken in such a manner that allows all reasonable and

practicable measures to be undertaken to:

(i) allow stormwater to pass through the site in a controlled manner and at non- erosive flow

velocities up to the specified design storm discharge;

(ii) minimise soil erosion resulting from rain, water flow and/or wind;

(iii) minimise adverse effects of sediment runoff, including safety issues;

(iv) prevent, or at least minimise, environmental harm resulting from work-related soil erosion and

sediment runoff;

(v) ensure that the value and use of land/properties adjacent to the development (including roads)

are not diminished as a result of the adopted ESC measures.



15. All erosion and sediment control measures must conform to the standards and specifications

contained in:

(i) the development approval condition issued by CCRC; and

(ii) the approved ESCP and supporting documentation.

16. Any works that may cause significant soil disturbance and are ancillary to any activity for which

regulatory body approval is required, must not commence before the issue of that approval.

17. Additional and/or alternative ESC measures must be implemented in the event that site

inspections, the site's Monitoring and Maintenance Program, or the regulatory authority,

identifies that unacceptable off-site sedimentation is occurring as a result of the work activities.

18. Land-disturbing activities must not cause unnecessary soil disturbance if an alternative

construction process is available that achieves the same or equivalent outcomes at an equivalent

cost.

19. Sediment (including clay, silt, sand, gravel, soil, mud, cement and ceramic waste) deposited off

the site as a direct result of an on-site activity, must be collected and the area appropriately

cleaned/rehabilitated as soon as reasonable and practicable, and in a manner that gives

appropriate consideration to the safety and environmental risks associated with the sediment

deposition.

20. Adequate waste collection bins must be provided on-site and maintained such that potential and

actual environmental harm resulting from such material waste is minimised.

21. Trenches not located within roadways must be backfilled, capped with topsoil, and compacted to

a level at least 75mm above adjoining ground level and appropriately stabilised.

22. Site spoil must be lawfully disposed of in a manner that does not result in ongoing soil erosion or

environmental harm.

23. All fill material placed on site must comprise only natural earth and rock, and is to be free of

contaminants, be free draining, and be compacted in layers not exceeding 300mm to 90%

modified maximum dry density in accordance with AS 1289.

5.6. Drainage Control

24. All drainage control measures must be applied and maintained in accordance with the ESCP.

25. To the maximum degree reasonable and practicable, all waters discharged during the

construction phase must discharge onto stable land, in a non-erosive manner, and at a legal point

of discharge.

26. Wherever reasonable and practicable, "clean" surface waters must be diverted away from

sediment control devices and any untreated, sediment-laden waters.

27. During the construction period, roof water must be managed in a manner that minimises soil

erosion throughout the site, and site wetness within active work areas.



5.7. Erosion Control

28. All erosion control measures must be applied and maintained in accordance with the ESCP.

29. All temporary earth banks, flow diversion systems, and embankments associated with

constructed sediment basins must be machine-compacted, seeded and mulched for the purpose

of establishing a temporary vegetative cover within 10 days after grading.

30. The construction and stabilisation of earth batters steeper than 6:1 (H:V) must be staged such

that no more than 3 vertical-metres of any batter is exposed to rainfall at any instant.

31. Synthetic reinforced erosion control mats and blankets must not be placed within, or adjacent to,

riparian zones and watercourses if such materials are likely to cause environmental harm to

wildlife or wildlife habitats.

32. A minimum 60% ground cover must be achieved on all non-completed earthworks exposed to

accelerated soil erosion if further construction activities or soil disturbances are likely to be

suspended for more than 30 days during those months when the expected rainfall erosivity is less

than 30mm; minimum 70% cover within 30 days if between 30 and 45mm; minimum 70% cover

within 20 days if between 45 and 100mm; minimum 75% cover within 10 days if between 100

and 225mm; and minimum 80% cover within 5 days if greater than 225mm.

5.8. Sediment Control

33. All sediment control measures must be applied and maintained in accordance with the ESCP.

34. Optimum benefit must be made of every opportunity to trap sediment within the work site, and

as close as practicable to its source.

35. Sediment traps must be installed and operated to both collect and retain sediment.

36. All reasonable and practicable measures must be taken to prevent, or at least minimise, the

release of sediment from the site.

37. Sediment control devices must be de-silted and made fully operational as soon as reasonable and

practicable after a sediment-producing event, whether natural or artificial, if the device's

sediment retention capacity falls below 75% of its design retention capacity.

38. Materials, whether liquid or solid, removed from sediment control devices during maintenance

or decommissioning, must be disposed of in a manner that does not cause ongoing soil erosion or

environmental harm.

39. Settled sediment must be removed from sediment basins when the volume of the sediment

exceeds the designated sediment storage volume, or the design maximum sediment storage

elevation.

5.9. Site Rehabilitation

40. All disturbed areas identified as very low, low, medium, high, or extreme erosion risk must be

suitably stabilised within 30, 30, 20, 10 or 5 days respectively, or prior to anticipated rainfall,

whichever is the greater, from the day that soil disturbances on the area have been finalised.

41. No completed earthwork surface must remain denuded for longer than 60 days.



42. The type of ground cover applied to completed earthworks is compatible with the anticipated

long-term land use, environmental risk, and site rehabilitation measures.

43. Unless otherwise directed by the approved revegetation plan, topsoil must be placed at a

minimum depth of 75mm on slopes 4:1 (H:V) or flatter, and 50mm on slopes steeper than 4:1.

44. The pH level (soil:water 1:5) of topsoil must be adequate to enable establishment and growth of

the specified vegetation.

45. Soil ameliorants must be added to the soil in accordance with the approved

landscape/revegetation plans and/or soil analysis.

46. Temporary site stabilisation procedures must commence at least 30 days prior to the nominated

site shutdown date. At least 70% stable cover of all unstable and/or disturbed soil surfaces must

be achieved prior to the start of shutdown. The stabilisation works must not rely upon the

longevity of non- vegetated erosion control blankets, or temporary soil binders.

5.10. Sediment Basin Rehabilitation

47. Required drainage, erosion and sediment control measures during the decommissioning and

rehabilitation or a sediment basin must comply with same standards specified for the normal

construction works.

48. Upon decommissioning of a sediment basin, all water and sediment must be removed from the

basin prior to removal of the embankment (if any). Any such material, liquid or solid, must be

dispose of in a manner that will not create an erosion or pollution hazard.

49. A basin's catchment conditions associated with the staged decommissioning of the basin from a

Type 1 to a Type 2 sediment trap must comply with the specified sediment control standard.

50. The permanent stormwater treatment features (e.g. vegetation and filtration media) must be

appropriately protected from the adverse effects of sediment runoff.

51. Sediment basin must not be decommissioned until all up-slope site stabilisation measures have

been implemented and are appropriately working to control soil erosion and sediment runoff in

accordance with the specified ESC standard.

52. Immediately prior to the construction of the permanent stormwater treatment device,

appropriate flow bypass conditions must be established to prevent sediment-laden water

entering the device.

53. Immediately following the construction of the filter media of the permanent stormwater

treatment device, the filter media must be covered by heavy-duty filter cloth (minimum bidum

A44 or equivalent) and a minimum 200mm layer of earth or sacrificial filter media. Such earth

and filter cloth must not be removed from the device until suitable surface conditions being

achieved within the basin's catchment area.

54. Upon suitable conditions being achieved within the basin's catchment area, the operational

features of the permanent stormwater treatment system must be made fully operational (i.e.

maintenance and/or reconstruction as required).



5.11. Site Monitoring

55. All water quality data, including dates of rainfall, dates of testing, testing results and dates of

water release, must be kept in an on-site register. The register is to be maintained up to date for

the duration of the approved works and be available on-site for inspection by the regulatory

authority on request.

56. Sediment basin water quality samples must be taken at a depth no greater than 200mm above

the level of settled sediment.

57. All environmentally relevant incidents must be recorded in a field log that must remain accessible

to all relevant regulatory authorities.

5.12. Site Maintenance

58. All erosion and sediment control measures, including drainage control measures, must be

maintained in proper working order at all times during their operational lives.

59. All temporary erosion and sediment control measures, including drainage control measures, must

be fully operational and maintained in proper working order at all times during the maintenance

period as specified by CCRC.

60. All drainage, erosion and sediment control measures must be inspected:

(i) at least daily (when work is occurring on-site);

(ii) at least weekly (when work is not occurring on-site);

(iii) within 24 hours of expected rainfall; and

(iv) within 18 hours of a rainfall event of sufficient intensity and duration to cause runoff on-site.

61. Sediment removed from sediment traps and places of sediment deposition must be disposed of

in a lawful manner that does not cause ongoing soil erosion or environmental harm.

62. Maintenance mowing of all road shoulders, table drains, batters and other surfaces likely to

experience accelerated soil erosion must aim to leave the grass length no shorter than 50mm

where reasonable and practicable.

63. Maintenance mowing must be done in a manner that will not damage the profile of formed, soft

edges, such as the crest of earth embankments.



6. Roles and Responsibilities

Table 19 outlines the responsibilities of parties with respect to ESC.

Table 19 – Roles and Responsibilities

Role Responsibility

Developer/Contractor

• Ensure the prompt implementation of measures to mitigate

erosion and sediment generation;

Managing Engineer

• Provide design information as required;

• Assist site foreman in tasks.

Site Foremen

• Monitor daily rainfall;

• Notify Environmental Consultant when runoff generating rainfall

occurs in the previous 24 hours;

• Treat, test and dispose of captured runoff as per operating

procedures;

• Maintain current records of rainfall, storage volumes, water

quality, treatment practices, discharge volumes.

Environmental

Consultant/Representative

• Conduct in-situ monitoring;

• Collect and submit samples to laboratory;

• Collate results and prepare reports as required.



7. Monitoring Program

7.1. Surface Water

The requirements of the surface water quality monitoring program are stipulated below in Table 20 and

Table 21. A sediment basin operating procedure should be developed for the site and monitoring

conducted in accordance with this.

Table 20 – Surface Water Monitoring Program (excluding Sediment Basin)

Responsibility Contractor to carry out sampling.

Analytes As per Table 20

Monitoring Locations • Upstream and downstream of works;

• Drainage discharge points; and

• Sediment basin discharge points

Timing On any day when stormwater run-off discharges from the site.

Methodology Samples are to be collected by a suitably qualified party and

submitted to NATA accredited laboratory for analysis.

Samples to be collected in accordance with Qld EPAs “Water Quality

Sampling Manual” December 1999 (or later version).

The following water quality objectives have been adopted, with consideration of the recently published

Queensland Water Quality Guidelines (DERM, 2009). Comparative water quality objectives as per the

guideline are also presented for freshwater lowland stream environments of the Wet Tropics Region.

Table 21 – Water Quality Objectives

Parameter Target (IECA, 2008) Qld Water Quality Guidelines

(DERM, 2009)

TSS 50mg/L No data

pH 6.5 – 7.5 6.0 – 8.0

Turbidity 75 NTU 15 NTU



8. Auditing, Corrective and Preventative Action

Best practice site management requires all ESC measures to be inspected by the Contractors nominated

representative at least daily when rain is occurring, within 24 hours prior to expected rainfall, and within 18

hours of a rainfall event of sufficient intensity and duration to cause onsite runoff (IECA, 2008). Such

inspections must check:

• Daily site inspections (during periods of runoff producing rainfall)

o All drainage, erosion and sediment control measures

o Occurrences of excessive sediment deposition (whether on-site or off-site)

o All site discharge points

o Occurrences of construction materials, litter or sediment placed, deposited, washed or

blown from the site, including deposition by vehicular movements

• Prior to anticipated runoff producing rainfall


o All temporary flow diversion and drainage works

• Following runoff producing rainfall

o Treatment and de-watering requirements of sediment basins

o Sediment deposition within sediment basins and the need for its removal


o Occurrences of excessive sediment deposition (whether on-site or off-site)

o Occurrences of construction materials, litter or sediment placed, deposited, washed or

blown from the site, including deposition by vehicular movements

o Occurrences of excessive erosion, sedimentation, or mud generation around the site office,

car park and/or material storage areas.

During construction the on-ground controls are to be audited against the requirements of the Site

Inspection Checklist provided on page 7.19 – 7.31 of the IECA 2008 Best Practice Erosion and Sediment

Control Guidelines (November 2008) by the Contractors nominated representative or a Certified

Practitioner in Erosion and Sediment Control (CPESC).

Compliance auditing is to be conducted on a monthly basis and include:

• Copies of all original completed ESC site audit checklists, non-conformance and corrective action

reports;

• Rainfall records, sediment basin flocculation and water quality results, site discharge water quality

monitoring results and interpretation of results against the Site Water Quality Objectives;

• A current ESC Plan showing those areas of site stabilization and the percentage completion of all

soil stabilization/erosion control works;

• A table showing the completion of all actions (or percentage thereof) required by the compliance

program;



• Representative date-stamped color photographs, clearly identifying and locating each primary ESC

device on the site and showing its condition and use including, as a minimum (where relevant):

o Sediment basin embankments, basin water levels, inflow points, depth marker and

emergency spillway outlets

o Sediment fencing

o Each catch drain and diversion channel

o Stormwater inlet and outlet protection

o Stabilized site entry/exit point/s

o All ESC related corrective action requests

o Ground stabilization areas and the stabilization media used, such as sheet mulching,

hydromulching, concrete etc.

8.1. Audit Reporting

Audit reports are to be compiled within 5 business days of completion of the site inspection and made

available upon request of the regulatory authority.



9. Operational Phase Water Quality

9.1. Introduction

MUSIC Version 3.01 was utilised to determine pollutant loadings associated with site for the existing and

post development scenarios.

Due to no local or state government guidelines being available at the time of the assessment, the industry

standard Gold Coast City Council ‘MUSIC Modelling Guidelines 2006’ was utilised for the analysis.

9.2. Objectives

The Draft Queensland Water Quality Guidelines (DERM 2009) detail the design objectives for management

of stormwater quality during the operational phase of development (post-construction). Figure 2.5 of the

DERM Queensland Water Quality Guidelines indicates the site is located within the Wet Tropics sub-region

of Queensland.

Table 2.1b of the Draft Queensland Water Quality Guidelines details the load-based reduction

requirements for an urban development within the Wet Tropics region. The load based reduction

requirements are detailed below in Table 22.

Table 22 – Operational Phase Water Quality Objectives – Wet Tropics

Location TSS

(% Reduction)

TP

(% Reduction)

TN

(% Reduction)

Wet Tropics 80 65 40

The SEQ Implementation Guideline No. 7 indicates that load based reduction requirements are only

applicable for developments with a total fraction impervious of greater than 25%. The site proposal will

only achieve a total fraction impervious of approximately 5.5%. The load based reduction targets detailed

in Table 23 are not applicable to the proposed development site.

MUSIC models were undertaken for the pre and post development scenarios to approximate pollutant

loadings associated with the site for the existing agricultural and proposed rural residential use.

9.3. Existing environmental condition

The undeveloped site is predominantly used for agricultural purposes. For the existing scenario, the site

was analysed as a single agricultural node of 126 ha.

The existing dam/creek system is currently degraded due to the existing agricultural use and the

unconstrained access to the dam banks causing turbidity and destabilisation of the dam and dam

surroundings. The banks of the existing dams are also heavily infested by the Class 3 declared weed

Lantana (Lantana camara) in numerous locations (refer to Figure 3).

It is understood that rehabilitation works of the dam banks will be undertaken with the development

proposal. The proposed vegetated buffer zone to be provided will significantly aid in water quality

treatment of all runoff discharging to the internal dam/creek system.



Figure 3 – Existing Dam Banks and Lantana Growth

9.4. MUSIC Modelling

9.4.1. Catchments

For the post development scenario the site was divided into numerous catchments:

• Road - Approx 3,900m with average road reserve of 20m: 7.80 ha (pavement width 6.6m – fi = 0.33)

• Roof to Tank – 125m2/allotment: 1.54 ha (minimum requirements in accordance with QDC)

• Roof to bypass Tank – 125m2/allotment: 1.54 ha

• Other Impervious Area (driveway/courtyard etc.) – 100m2/allotment: 1.23ha

• Remaining Rural Residential area – 113.9 ha

Details of the pre and post development catchments are shown in Table 23.



Table 23 – MUSIC Catchments

Scenario Catchment Name Catchment

Area (ha)

% Impervious MUSIC Source

Node

Pre Development Existing Agricultural

Use

126 0 Agriculture

Post

Development

Road 7.80 33 Urban – Road

Roof to Tank 1.54 100 Urban – Roof

Roof bypass Tank 1.54 100 Urban – Roof

Other Impervious

Area

1.23 100 Urban – Ground

Level

Remaining Area 113.9 0 Rural Residential

9.4.2. Rainfall Data

The site was analysed using rainfall data from BOM Station Number 31034 (Kairi Research Centre) being

approximately 18km from the site location. The MUSIC analysis was undertaken for a 10 year period from

01/01/1980 to 31/12/1989 utilising a 6 minute time step.

9.4.3. Source Node Parameters

MUSIC source node parameters were taken from the Gold Coast City Council ‘MUSIC Modelling Guidelines

2006’ and are detailed below in Table 24 and Table 25.

Table 24 – MUSIC Rainfall-Runoff Parameters

Parameter Urban Residential Rural Residential

Rainfall Threshold 1 1

Soil Storage Capacity (mm) 400 120

Initial Storage (% capacity) 10 25

Field Capaacity (mm) 200 80

Infiltration Capacity Coefficient a 50 200

Infiltration Capacity Exponent b 1 1

Initial Depth (mm) 50 50

Daily Recharge Rate (%) 25 25

Daily Baseflow Rate (%) 5 5

Daily Deep Seepage Rate (%) 0 0



Table 25 – MUSIC Pollutant Export Parameters

Flow Type Surface Type TSS log10

values TP log10

values TN log10

values

Mean St. Dev. Mean St. Dev. Mean St. Dev.

Baseflow

Parameters

Urban Roof N/A N/A N/A N/A N/A N/A

Urban Roads 1.00 0.34 -0.97 0.31 0.20 0.20

Urban Ground

Level

1.00 0.34 -0.97 0.31 0.20 0.20

Agriculture 1.40 0.13 -0.88 0.13 0.074 0.13

Rural

Residential

0.53 0.24 -1.54 0.38 -0.52 0.39

Stormflow

Parameters

Urban Roof 1.30 0.39 -0.89 0.31 0.26 0.23

Urban Roads 2.43 0.39 -0.30 0.31 0.26 0.23

Urban Ground

Level

2.18 0.39 -0.47 0.31 0.26 0.23

Agriculture 2.30 0.31 -0.27 0.30 0.59 0.26

Rural

Residential

2.26 0.51 -0.56 0.28 0.32 0.30

9.4.4. Treatment Node Parameters

MUSIC treatment node parameters were determined in accordance with the Gold Coast City Council

‘MUSIC Modelling Guidelines 2006’ and are detailed below in Table 25 and Table 26.

Rainwater Tanks

A roof area of 250m2/allotment was assumed for the analysis. Only 50% of the roof area was assumed to

discharge to the rainwater tank (5kL tank/allotment) in accordance with QDC minimum requirements. The

re-use rate applied to the rainwater tank node is detailed below in accordance with the GCCC MUSIC

Modelling Guidelines.

0.326kL/day x 123 allotments = 40.1 kL/day

Table 26 – MUSIC Rainwater Tank Parameters

Parameter Rainwater Tank

Low Flow Bypass (m3/s) 0

High Flow Bypass (m3/s) 100

Volume Below Overflow Pipe (kL) 615

Depth Above Overflow (m) 0.20

Surface Area (m2) 308

Overflow Pipe Diameter (mm) 998

Daily Demand (kL/day) 40.1



Buffers

All runoff from the site will be significantly buffered prior to discharging to the existing dam/creek system.

Details on the buffer parameters utilized for the MUSIC analysis are shown below in Table 27.

Table 27 – MUSIC Buffer Parameters

Parameter Buffer

Percentage of Upstream Area Buffered (%) 100

Buffer Area (% of Upstream Impervious Area) 50

Seepage Loss (mm/hr) 0.00

9.4.5. Model setup

The MUSIC model analysed for the pre and post development scenarios detailed below in Figure 4

Figure 4 – Pre and Post Development MUSIC Models

9.5. Results

The MUSIC results for the pre and post development scenarios are shown below in Table 28.

Table 28 – MUSIC Results (Annual Pollutant Loads)

TSS

(kg/year)

TP

(kg/year)

TN

(kg/year)

Pre Development 51,100 145 991

Post Development 58,400 76.4 599



As can be seen in Table 28 above, the pollutant loadings (Total Phosphorus and Total Nitrogen) have been

significantly reduced due to the proposed WSUD treatment measures, and site use change from

agricultural to rural residential.

With the proposed rehabilitation of the existing degraded dam banks and erosion locations, and the large

amount of buffering to be provided to the internal road and impervious areas, TSS pollutant loadings from

the proposed development site are likely to be well below that for the existing scenario.

The proposed Erosion and Sediment Control measures will ensure impacts to the surrounding environment

during the construction phase of the development will be kept to a minimum.



10. Operational Phase Water Quantity

In accordance with the Draft Queensland Water Quality Guidelines (DERM 2009), a site discharging to an

unlined channel, creek or non-tidal river is to achieve the following water quantity objectives:

1. Frequent Flow Management

2. Waterway Stability Management

10.1. Frequent Flow Management

In accordance with the Frequent Flow Management objective, the site is to capture 10mm/day from all

impervious areas, and must be capable of draining the captured stormwater within 24 hours.

Compliance with this objective can be demonstrated by providing a total stormwater capture volume (m3)

calculated as follows:

Total Capture Volume (m3) = Site Impervious area (m2) x 10 (mm/day) x 0.001

= 68,400 m2 (approximately) x 10 x 0.001

= 684 m3

Assuming the proposed rainwater tanks capture and re-use the required volume from the proposed roof

areas, the remaining volume to be captured on site is detailed below:

Remaining Capture Volume (m3) = Remaining Impervious area (m2) x 10 (mm/day) x 0.001

= 37,650 m2 (approximately) x 10 x 0.001

= 377 m3

The 377m3 of storage volume required on site could be implemented via the following:

• localised depressed areas/small basins at stormwater outlets

• swale systems with raised outlets

• Infiltration pits

• Bio-retention filters

The actual design, location and size of the capture systems to be implemented are to be determined at the

detailed design stage of the development. The systems are to be designed to ensure they are capable of

capturing and draining the required stormwater within a 24 hour period.



10.2. Waterway Stability Management

In accordance with the Waterway Stability Management objective, the site is to limit the post-development

peak 1 year ARI event discharge within receiving waterways to the pre development peak 1 year ARI event

discharge.

Compliance with the design objective can be demonstrated using one of the following methods depending

on the scale of the development:

• Method A (developments < 10 ha gross site area) – calculate required detention storage using the

simple hydrograph method in QUDM (1994, Equation 6.01)

• Method B (developments > 10 ha gross site area) – calculate required detention storage runoff

routing model

Due to the low density proposal of the site, an initial estimate on the required storage detention volume

has been calculated utilising Method A. A detailed runoff routing model in accordance with Method B will

need to be undertaken at the detailed design stage of the development.

The following assumptions have been made:

• C1 (pre development) = 0.56

• C1 (post development) = 0.57

• t’c = 60 minutes

• I1 = 40mm/hr

Required Storage Volume m3 (Vs) = Vi (1 - 0.5Qo/Qi)

= 638.4 x (1 – 0.5 x 0.98)

= 325m3

The storage volume required to achieve the Waterway Stability Management objective will be catered for

in the proposed capture measures required for the Frequent Flow Management objective.



11. Reference List

Department of Environment and Resource Management (DERM) (2009), Queensland Water Quality

Guidelines 2009, Version 3

IECA (2008), Best Practice Erosion and Sediment Control, International Erosion Control Association

(Australasia), Picton, NSW

Murtha, G.G (1986), Soils of the Tully-Innisfail Area, North Queensland, CSIRO Division of Soils, Division

Report No.

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page A


Annexure A Site Locality Plan

Legend

Property

¹

Locality Map

Atherton Tableland Developments Drawn: SDDrawing No. SC10-0020-0001

10 Kilometers

@ A41:200,000

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page B


Annexure B Site Plan

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page C


Annexure C Soils Data

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page D


Annexure D Concept ESC Plan

SB9

SB8

SB7

SB6

SB5

SB4

SB3

SB2

SB1

C1

C5

C8

C2

C9

C4

C7

C10

C6

C3

CW

D13

CW

D5

CW

D10

CW

D4

CW

D18

CWD16

CWD1

CW

D2

CWD14

CW

D8

CWD17

CWD11

CW

D7CWD12CW

D9

CW

D6

CWD15

CWD19

CWD3

Legend

Catchments

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

! Sediment Basin

˃ ˃ Clean Water Diversion

¹

Concept ESC Plan

Atherton Tableland Developments Drawn: SDDrawing No. SC10-0020-002

500 Meters

@ A31:4,500

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page E


Annexure E Design Calculations

Type D and F Sediment Basin Sizing

Basin volume = settling zone volume + sediment storage zone volume

Vset = 10 x Cv x A x R y%ile,x-day Equation B7, IECA (2008)

where:

Vset = Settling Volume (m3)

Cv= The volumtric runoff coefficient (dimensionless)

A= Area (hectare)

Ry%ile,x-day= Design rainfall event. (mm)

Vstor = 0.5 x Vset Table B8, IECA (2008)

Total Basin Volume Calculations

Description

Volumetric

Runoff

Coefficient

Catchment

Area (ha)

Design

Rainfall

Event

Settling

Zone

Volume

(m3)

Sediment

Storage

Volume (m3)

Total

Volume

Depth

(m)

Pond length

width ratio

(L/W)

Batter Slope Length

(m)

Width

(m)

Label Cv A R85%ile, 5-day Vset Vstor Vtotal d L/W a L w

SB-C1 0.67 1.444 74.1 716.7 358.4 1,075.1 1.0 3.0 2.0 63.0 21.0

SB-C2 0.67 0.822 74.1 407.9 203.9 611.8 1.0 3.0 2.0 49.1 16.4

SB-C3 0.67 0.128 74.1 63.6 31.8 95.4 1.0 3.0 2.0 23.5 7.8

SB-C4 0.67 0.772 74.1 383.4 191.7 575.1 1.0 3.0 2.0 47.8 15.9

SB-C5 0.67 1.258 74.1 624.4 312.2 936.6 1.0 3.0 2.0 59.2 19.7

SB-C6 0.67 0.291 74.1 144.5 72.2 216.7 1.0 3.0 2.0 31.9 10.6

SB-C7 0.67 0.570 74.1 283.2 141.6 424.8 1.0 3.0 2.0 42.0 14.0

SB-C8 0.67 0.762 74.1 378.3 189.2 567.5 1.0 3.0 2.0 47.5 15.8

SB-C9 0.67 0.777 74.1 385.7 192.8 578.5 1.0 3.0 2.0 47.9 16.0

SB-C10 0.67 0.750 74.1 372.4 186.2 558.5 1.0 3.0 2.0 47.2 15.7

Notes: Volumetric runoff coefficient (Cv) of 0.67 adopted for Group C soils (loamy clay) with moderate to high runoff potential.

Design rainfall event conservatively adopted for published location of Cairns (Table B5, IECA 2008)

Given a sensitive receiving environment a design rainfall event equal to the 85%ile, 5 day is appropriate (Table B4, IECA 2008)

Potential exists for a reduction in sediment storage volume on basis of detailed soil loss calculations once further soil sampling and construction scheduling are known.

INPUTS OUTPUTS Inputs Outputs

L

1

a

Cross-section A

1

a

W

Cross-section B

CONCEPTUAL EROSION AND SEDIMENT CONTROL PLAN AND STORMWATER QUALITY MANAGEMENT PLAN Page F


Annexure F Fact Sheets

© Catchments & Creeks Pty Ltd September 2009 Page 1

Catch Drains Part 4: Geotextile-lined

DRAINAGE CONTROL TECHNIQUE

Low Gradient 6 Velocity Control Short Term 6

Steep Gradient Channel Lining Medium-Long Term 6

Outlet Control Soil Treatment Permanent [1]

[1] The design of permanent catch drains requires consideration of issues not discussed within this factsheet, such as maintenance requirements. This fact sheet should not be used for the design ofpermanent drains.

Symbol

Photo 11 – Roadside table drain lined witha temporary jute erosion control mat

Photo 12 – Roadside catch drain linedwith an erosion control mat sealed with

bitumen

Key Principles

1. Catch drains typically have standardised cross-sectional dimensions. Rather than uniquelysizing each catch drain to a given catchment, standard-sized drains are used based on amaximum allowable catchment area for a given rainfall intensity.

2. The maximum recommended spacing of catch drains down slopes (Table 3, Part 1 –General information) is based on the aim of avoiding rill erosion within the up-slopedrainage slope. It should be noted that the actual spacing of catch drains down a givenslope may need to be less than the specified maximum spacing if the soils are highlyerosive soils, or if rilling begins to occur between two existing drains.

3. The critical design parameters are the spacing of the drains down a slope, the maximumallowable catchment area, the choice of lining material (e.g. earth, turf, rock or erosioncontrol mats), and the required channel gradient.

Design Information

The following information must be read in association with the general information presented inPart 1 – General information. These design tables specifically address catch drains lined withnon-vegetated erosion control mats. The design tables are also applicable to the initialestablishment of mat-protected catch drains prior to development of the grass cover.

The design procedure outlined within this fact sheet has been developed to provide a simplifiedapproach suitable for appropriately trained persons involved in the regular design of temporarycatch drains. The procedure is just one example of how catch drains can be designed.Designers experienced in hydraulic design can of course, design a catch drain using thegeneral principles of open channel hydrologic/hydraulic as outlined in Appendix A –Construction site hydrology and hydraulics.

* These facts sheets have been purchased for the sole use of Atherton Tableland Developments for Lot 200 on SP195706 Malanda ESC and should not be copied or reproduced


Common Problems

Erosion control mats can be incorrectlyinstalled with the adjoining matsoverlapping against the direction of flow.This can cause the mats to be torn from thechannel bed during moderate flows.

Damage to associated flow diversion bank(rutting) caused by vehicles.

Catch drains not discharging to a stableoutlet either causing downstream erosion,or initiating scour within the drain.

‘Plastic’ reinforced mats can entangleground-dwelling wildlife such as lizards,snakes and birds.

Temporary mats can fail before adequategrass cover is established.

Special Requirements

The dispersive nature of the local subsoilsshould be investigated before planning ordesigning any excavated drains.

Straw bales or other sediment traps shouldnot be placed within these drains due to therisk of causing surcharging of the drain.

Catch drain should drain to a suitablesediment trap if the diverted water isexpected to contain sediment. “Clean”water should divert around sediment traps.

The drain must have positive gradient alongits full length to allow free drainage.

Sufficient space must be provided to allownecessary maintenance access.

Site Inspection

Check the direction of overlap of the matsand the spacing of anchor pins (staples).

Check that the drain has a stable, positivegrade along its length.

Check for a stable drain outlet.

Check if the associated flow diversion bank(if any) is free of damage, i.e. damagecaused by construction traffic.

Check that the drain has adequatehydraulic capacity given the catchment area(general observations based on pastexperience).

Check if rill erosion is occurring within thecatchment area up-slope of the drain. Ifrilling is occurring, then the lateral spacingof the drains will need to be reduced.However, some degree of rill erosion maybe expected if recent storms exceeded theintensity of the nominated design storm.

Inspect for evidence of water spilling out(overtopping) of the drain, or erosion down-slope of the drain.

Inspect for erosion along the bed of thedrain (i.e. damage to the mat). Investigatethe reasons for any erosion beforerecommending solutions. Bed (invert)erosion can result from either excessivechannel velocities, or an unstable outlet,which causes bed erosion (head-cut) tomigrate up the channel.

Possible solutions to channel erosion:

• reduce effective catchment area;

• increase channel width;

• increase channel roughness;

• replace erosion control mats;

• stabilise the outlet.

Installation (drain formation)

1. Refer to approved plans for location,extent, and construction details. Ifthere are questions or problems withthe location, extent, or method ofinstallation, contact the engineer orresponsible on-site officer forassistance.

2. Clear the location for the catch drain,clearing only what is needed to provideaccess for personnel and equipment forinstallation.

3. Remove roots, stumps, and otherdebris and dispose of them properly.Do not use debris to build the bank.

4. Grade the drain to the specified slopeand form the associated embankmentwith compacted fill. Note that the draininvert must fall 10cm every 10m foreach 1% of channel gradient.

5. Ensure the sides of the cut drain are nosteeper than a 1.5:1 (H:V) slope andthe embankment fill slopes no steeperthan 2:1.

6. Ensure the completed drain hassufficient deep (as specified for the typeof drain) measured from the drain invertto the top of the embankment.

7. Ensure the drain has a constant fall inthe desired direction free ofobstructions.

8. Ensure the drain discharges to a stableoutlet such that soil erosion will beprevented from occurring. Ensure thedrain does not discharge to an unstablefill slope.



Installation (mat placement)The method of mat installation varies withthe type of mat. Installation proceduresshould be provided by the manufacturer ordistributor of the product. A typicalinstallation procedure is described below,but should be confirmed with the productmanufacturer or distributor.

1. Erosion control mats must be storedaway from direct sunlight or coveredwith ultraviolet light protective sheetinguntil the site is ready for theirinstallation.

2. Vehicles and construction equipmentmust not be permitted to manoeuvreover the geotextile unless it has beencovered with a layer of soil or gravel atleast 150mm thick. Fill material shallnot be mixed over the geotextile.

3. If the channel is to be grassed, preparea smooth seed bed of approximately75mm of topsoil, seed, fertilise, waterand rake to remove any remainingsurface irregularities.

4. Excavate a 300mm deep by 150mmwide anchor trench along the full widthof the upstream end of the area to betreated.

5. At least 300mm of the mat must beanchored into the trench with the roll ofmatting resting on the ground up-slopeof the trench.

6. Staple the fabric within the trench at200 to 250mm spacing using 100mmwide by 150mm penetration length U-shaped, 8 to 11 gauge wire staples.Narrower U-sections may easily tearthe matting when placed under stress.

7. When all mats have been anchoredwithin the trench across the full width ofthe treated area, then the trench isbackfilled and compacted. The matsare then unrolled down the slope suchthat each mat covers and protects thebackfilled trench.

8. When spreading the mats, avoidstretching the fabric. The mats shouldremain in good contact with the soil.

9. If the channel curves, then suitably fold(in a downstream direction) and staplethe fabric to maintain the fabric parallelto the direction of channel flow.

10. Staple the surface of the matting at 1mcentres. On irregular ground, additionalstaples will be required wherever themat does not initially contact the groundsurface.

11. At the end of each length of mat, a newtrench is formed at least 300mm up-slope of the end of the mat such thatthe end of the mat will be able to fullycover the trench. A new roll of mattingis then anchored within this trench asper the first mat. After this new mat hasbeen unrolled down the slope, the up-slope mat may be pinned in place fullycovering the new trench and at least300mm of the down-slope mat. Theprocess is continued down the slopeuntil the desired area is fully covered.

12. In high-velocity channels, intermediateanchor slots may be required at 10mintervals down the channel.

13. Anchor the outer most edges (top andupper most sides) of the treated area ina 300mm deep trench and staple at 200to 250mm centres.

14. If the channel was grass seeded priorto placement of the mats, then the matsmay be rolled with a suitable rollerweighing 60 to 90 kg/m, then watered.

15. The installation procedure must ensurethat the mat achieves and retains goodcontact with the soil.

16. Damaged matting must be repaired orreplaced.

Additional instructions for the installation ofJute Mesh (not jute blankets):

1. Ensure the jute mesh is laid on a firmearth surface that has been trimmed,topsoiled, watered, sown with seed andfertiliser.

2. The jute mesh is then either tamped orrolled firmly onto the prepared surface,avoiding stretching, watered toencourage the penetration of thebitumen emulsion, and finally sprayedwith a top layer of bitumen at 1 to 3litres per square metre.

3. The rate of emulsion application shouldbe adjusted such that the emulsion juststarts to pond in the mesh squares.



Additional requirements associated withuse near airport pavements

1. Only erosion mats that are doublenetted shall be allowed within 3.0m ofany airport pavement used by aircraftwith the exception of airports classifiedas air carrier or corporate/transport. Ifthe airport is classified as an air carrieror corporate/transport, there will be noerosion mats allowed within 9.0m ofpavement used by aircraft.

2. Only biodegradable anchoring devicesshall be allowed in the installation ofany erosion mat for airport applications.No metal staples will be allowed.

Maintenance

1. Inspect all catch drains at least weeklyand after runoff-producing storm eventsand repair any slumps, bank damage,or loss of freeboard.

2. Ensure fill material or sediment is notpartially blocking the drain. Wherenecessary, remove any depositedmaterial to allow free drainage.

3. Dispose of any sediment or fill in amanner that will not create an erosionor pollution hazard.

Removal

1. When the soil disturbance above thecatch drain is finished and the area isstabilised, the drain and any associatedbanks should be removed, unless it isto remain as a permanent drainagefeature.

2. Dispose of any sediment or earth in amanner that will not create an erosionor pollution hazard.

3. Grade the area and smooth it out inpreparation for stabilisation.

4. Stabilise the area by grassing or asspecified within the approved plan.

Figure 7(1) – Parabolic catch drain with bank

Figure 8(2) – Triangular V-drain with down-slope bank



Hydraulic design of mat-lined catch drains (using the Rational Method approach):

Step 1 Choose the preferred surface condition of the catch drain (in this case lined with aspecified erosion control mat). With experience, the choice of erosion control matcan be based on the required allowable flow velocity determined from a quickreview of the following design tables, but gaining this experience take time!

Step 2 Determine the allowable flow velocity (Vallow) for the chosen type of mat. Theallowable flow velocity can be determined from Tables 28 and 29, or Tables 30 and31 if the mat Class and/or allowable shear stress are known.

Step 3 Nominate the catch drain profile: parabolic or triangular (V-drain). Parabolic drainshave a greater hydraulic capacity and are generally less susceptible to inverterosion, but can be slightly more time-consuming to construct.

Step 4 Choose a trial catch drain size (flow top width ‘T’, and depth ‘Y’) from Table 32(parabolic drains), or Table 37 (triangular drains).

Step 5 Determine Manning's roughness (n) and required longitudinal gradient (S%) for thecatch drain type, mat type, and allowable flow velocity from Tables 33 or 38.

Step 6 Determine the required Average Recurrence Interval (ARI) of the design storm forthe given catch drain (i.e. 1 year, 2 year, 5 year, etc. – refer to Table 4.3.1 inChapter 4, or Table A1 in Section A2 of Appendix A). Note, if a locally adopteddesign standard exists, then the ARI must be determined from that standard.

Step 7 Determine the appropriate time of concentration (tc) for the catch drain (refer toStep 4 in Section A2 of Appendix A).

It is usually sufficient to assume a 5-minute time of concentration (conservativeapproach), otherwise use the locally adopted hydrologic procedures for determiningthe time of concentration, or the procedures presented in Appendix A.

Step 8 Given the design storm ARI, and duration (tc), determine the Average RainfallIntensity (I) for the catch drain (refer to Step 6 in Section A2 of Appendix A).

To determine the average rainfall intensity it will be necessary to obtain the relevantIntensity-Frequency-Duration (IFD) chart for the given site location.

Step 9 Determine the maximum unit catchment area (A*) of the catch drain using Tables34 to 36, or Tables 39 to 41 depending on the chosen drain type and profile.

The maximum unit catchment area (A*) is the maximum allowable catchment areabased on a coefficient of discharge of unity (i.e. C = 1.0).

Step 10 Determine the actual Coefficient of Discharge (C) for the catchment contributingrunoff to the catch drain (refer to Step 3 in Section A2 of Appendix A).

Note, it will be necessary to first determine the Coefficient of Discharge for a 10year storm (C10), and then the Frequency Factor (FY) for the nominated designstorm frequency from Table A7 in Step 3, Section A2 of Appendix A, such that:

C = C10 . FY ≤ 1.0

Step 11 Determine the maximum allowable catchment area (A) for the catch drain based onthe Coefficient of Discharge (C) determined in Step 10:

A = (A*)/C (hectares)

Step 12 Determine the maximum allowable horizontal spacing of the catch drains down theslope from Table 3 (Catch Drain Part 1: General information).

Step 13 If the actual catchment area of the catch drain (measured from the Erosion andSediment Control Plan) is greater than the maximum allowable area determined inStep 11, then return to Step 4 and select a larger catch drain profile.

If the actual catchment area of the catch drain is less than the maximum allowablearea determined in Step 11, then either return to Step 4 and select a smaller catchdrain profile; or determine the minimum allowable drain slope (Smin) which is limitedby the maximum allowable flow depth (y), and maximum allowable drain slope(Smax) which is limited by the maximum allowable flow velocity Vallow.



Explanation of the design philosophy adopted within this fact sheet:

Given the cross-sectional dimensions of a given catch drain (A & R), its surface roughness (n),gradient (S), and required freeboard, it is possible (using Manning’s equation) to determine thehydraulic capacity (Q) of the drain, as presented in Equation 1.

Manning’s equation: Qn

A R S=1 2 3 1 2. . ./ /

(Eqn 1)

where: A = cross-sectional flow area of the catch drain

The Rational Method (Equation 2) can be rearrange to form Equation 3:

Q = (C.I.A)/360 (Eqn 2)

A.C = 360(Q / I) (Eqn 3)

where: A = catchment area (ha) of the catch drain (not the cross-sectional area of the drain)

If we define a new term called ‘the unit catchment area’ (A*) as the effective catchment areabased on an assumed coefficient of discharge of unity (i.e. C = 1.0), then:

Maximum unit catchment area: A* = 360(Q / I) (Eqn 4)

The relationship between flow velocity (V) and channel slope (S) is given by a modification ofthe Manning’s equation (Equation 5):

Vn

R S=1 2 3 1 2. ./ /

(Eqn 5)

For a given catch drain profile (represented by the hydraulic radius, R), and surface lining(represented by the Manning’s roughness, n) we can determine the required drain slope (S) fora given allowable flow velocity. This information is presented in Tables 33 and 38. It is notedthat at this channel slope, the maximum allowable flow velocity (Vallow) will be achieved when thechannel is flowing at the maximum allowable flow depth (Y).

Also, for a given catch drain cross-sectional area (A), hydraulic radius (R), and maximumallowable flow velocity (V), we can determine the maximum allowable discharge (Q) from

Equation 1. With this discharge, and the nominated design rainfall intensity (I), we candetermine the maximum unit catchment area (A*) from Equation 4. This information is presentedin Tables 34 to 36 for parabolic drains, and Tables 39 to 41 for drains with a triangular profile.

This means Tables 34 to 36 and 39 to 41 are independent of location, and thus can be used

anywhere in the world. Rainfall intensity, I (mm/hr) being the only parameter that is locationspecific.

In order to determine the maximum allowable catchment area (A), it is necessary to determinethe actual coefficient of discharge (C) for the adopted storm frequency (ARI), and catchmentconditions (i.e. soil porosity). The maximum allowable catchment area (A) is determined fromEquation 6.

Maximum allowable catchment area: A = A*/C (Eqn 6)

Since the coefficient of discharge is always assumed to be less than or equal to unity, themaximum allowable catchment area (A) cannot exceed the maximum unit catchment area (A*).

If the actual catchment area is less than the calculated maximum catchment area (A) fromEquation 6, then the catch drain can be constructed at a range of channel gradients such that:

Smin < S < Smax

where:

• Smin can be determined from Manning’s equation based on the catch drain flowing full, butat a channel-full velocity less than the maximum allowable flow velocity;

• Smax can be determined from Manning’s equation based on the catch drain flowing partiallyfull, and at a velocity equal to the maximum allowable flow velocity.



Design example: Mat-lined catch drain

Design a temporary (< 24 months) jute mesh lined catch drain cut into a non-dispersive loamsoil in Townsville with a desired length of 300m, catchment area of 1.5ha, and an averagecatchment land slope of 6%. The catch drain will be used to divert ‘clean’ water around a soildisturbance. The catchment consists of undisturbed, well-grassed, land, and the ‘time ofconcentration’ (tc) for the catchment is known to be 15 minutes.

Step 1 The catch drain surface condition has been given as jute mesh. For the purpose ofthis example it will be assumed that the jute mesh will not be protected withbitumen emulsion.

Step 2 Given the non-dispersive loam soil is likely to have a low to moderate erosionpotential, nominate an allowable flow velocity (Vallow) of 1.5m/s from Table 28.

Step 3 Choose a parabolic drain profile.

Step 4 Initially try a Type-B catch drain with dimensions: T = 1.8m, Y = 0.3m.

Step 5 Determine the Manning’s roughness (n) and required longitudinal gradient (S) fromTable 33 as S = 1.03% and n = 0.022 for a Type-B drain based on an allowableflow velocity, Vallow =1.5m/s.

Step 6 Nominate a 1 in 5 year ARI design storm from Table 4.3.1 (Chapter 4).

Step 7 The catchment time of concentration (tc) is given as 15 minutes.

Step 8 Determine the average rainfall intensity: I = 132mm/hr for Townsville from TableA11 (Appendix A) for ARI = 5-year, and tc = 15 minutes.

Step 9 Determine the maximum allowable unit catchment area as A* = 1.43ha from Table35, given V = 1.5m/s, and I = 132mm/hr.

Step 10 Determine the coefficient of discharge (CY):

Given the catch drain’s catchment area is open, undisturbed grass with mediumpermeability, 100% pervious surface area, and given that Townsville’s 10 minute, 1-year rainfall intensity (

1I10) is 91.9mm/hr, the 10-year coefficient of discharge, C10 =

0.70 from Table A5 (Appendix A – Construction site hydrology and hydraulics).

Determine the frequency factor, FY = 0.95 for the 1 in 5-year ARI storm from TableA7 (Appendix A).

Calculate the effective coefficient of discharge (C) for the 1 in 5-year event usingEquation A4 (Appendix A):

C = C5 = FY .C10 = 0.95 x 0.70 = 0.665 ≤ 1.0 (OK)

Step 11 Calculate the maximum allowable catchment area (A) for the catch drain:

A = (A*)/C = 1.43/0.665 = 2.15ha

Thus the maximum allowable catchment area is greater than the actual catchmentarea of 1.5ha, OK.

Step 12 Because this catch drain is being used to collect and divert ‘clean’ water from anundisturbed catchment there is no need (in this case) to determine the maximumallowable spacing of the catch drains down the catchment slope.

So, a Type-B catch drain formed at a gradient of 1.03% will have a flow capacitysignificantly greater than is required for the specified 1.5ha catchment. At this pointin the analysis we have the following options:

(i) stay with the current design (Type-B, 1.03% grade, lined with jute mesh);

(ii) stay with a Type-B drain, but calculate a suitable range of channel gradients;

(iii) try a smaller, Type-A catch drain, but this is unlikely to be large enough.



Step 5a For the purpose of this example, option (ii) will be chosen

Given that the actual catchment area is significantly less than the maximumallowable catchment area, the catch drain can be constructed at:

• a flatter gradient (Smin < 1.03%) limited by the maximum flow depth of 0.3m; or

• a steeper gradient (Smax > 1.03%) limited by the allowable velocity of 1.5m/s.

To determined flattest allowable gradient for this catch drain, first calculate thedesign 1 in 5-year flow at the end of the 300m long catch drain.

Q = C I A/360 = (0.665 x 132 x 1.5)/360 = 0.366m3/s

The flattest longitudinal gradient of the catch drain may be determined from theManning's equation (Equation A16 in Appendix A); where the flow top width (T) is1.8m, and the flow depth (Y) is 0.3m.

It should be OK to assume that Manning’s roughness remains close to n = 0.022determined in Step 5, thus:

Q = 0.366 = (1/n).A.R2/3

.S1/2

= (1/0.022)(0.360)(0.186)2/3

.S1/2

Smin = 0.47%

Note, in the above equation, the term ‘A’ is the cross-sectional area of the catchdrain at a depth of y = 0.3m (determined from Table 31), not the catchment area!Also, ‘R’ is the hydraulic radius for the drain flowing full (Y = 0.3m) which is alsoprovided in Table 32.

The steepest longitudinal gradient of the catch drain can also be determined fromManning’s equation (Equation A16 in Appendix A); however, in this case the drainwill be flowing partially full with a flow top width (T) less than 1.8m, and the flowdepth (y) less than 0.3m. (Note, the drain would still be constructed with the samestandard overall physical dimensions specified for all Type-B catch drains.)

Now, for a parabolic Type-B drain the numerical relationship between the flow topwidth (T) and the flow depth (y) is given by the following equation (Table 4):

y = 0.0926 T2

and the cross sectional area of flow (A) is given by (Table A30b, Appendix A):

A = 0.67(T.y) = 0.062 T 3 = Q/V = 0.366/1.5 = 0.244m

2

Therefore, the flow top width, T = 1.581m; the flow depth, y = 0.231m; and thehydraulic radius (R) may be determined from (Table A29b, Appendix A):

RT y

T ym=

+=

×+

=2

3 8

2 1581 0 231

3 1581 8 0 2310 146

2

2 2

2

2 2

. ( . ) .

( . ) ( . ).

The maximum catch drain slope is given by rearranging the Manning’s equation:

Smax = 100 x (V 2 . n

2)/R

4/3 = 100 x (1.5

2 x 0.022

2)/0.146

4/3 = 1.42%

Therefore, the Type-A catch drain can be constructed at any longitudinal gradientbetween 0.47% (maximum flow depth) and 1.42% (maximum flow velocity), and stillprovide the required hydraulic capacity for the 1 in 5 year design storm. It is notedthat constructing the drain at the steeper gradient will result in a construction sitewith maximum drainage capacity.



Tables 28 and 29 provide guidance on the selection of an allowable flow velocity for varioustypes of temporary and permanent erosion control mats. Wherever possible, the allowablevelocity and/or allowable shear stress should be obtained from the manufacturer/distributor ofthe chosen product.

In circumstances where the manufacturer/distributor supplies only the allowable shear stress,then an equivalent allowable flow velocity may be determined from Table 31.

Table 28 – Allowable flow velocity for various erosion control mats

Type DescriptionAllowablevelocity Comments

Thick juteblankets

1.4m/s • Typical design life of around 3 months.

Coir blankets Medium, say1.5m/s

• Design life of 1 to 2 years depending ondegree and duration of water saturation.

Erosioncontrol

blankets

Blanketsreinforced

with non UV-stabilisedsynthetic

mesh

1.6 to

3.6m/s

• Allowable flow velocity depends on soilerodibility and strength of the mat.

• Warning: wildlife (e.g. birds and reptiles) canbecome entangled in the mesh.

Jute mesh 1.3 to1.7m/s

• Typical design life of 1 year.

Jute meshsprayed with

bitumen

Refer toTable 28

• Typical design life of 1 year.

• Allowable flow velocity depends on the soil’serosion resistance.

Erosioncontrolmesh

Coir mesh 1.7m/s • Typical design life of 1 to 2 years.

• Biodegradable after 4 to 10 years.

Open face2D synthetic

mats

2.4 to

3.0m/s

• Refer to manufacturer’s data.

Bio-degradablemulch matsreinforcedwith UV-stabilised

mesh

2.1 to

6.0m/s


• Long-term reinforcement of grass, but canbe subject to damage during periods ofdrought if the grass surface is damaged orlost.

Turfreinforcing

mats(TRMs)

3D, fullysynthetic,

UV-stabilisedmats on

vegetatedground

5.5m/s for30min

duration to3m/s for 50

hoursduration


• Long-term protection of soil surface.

Table 29 – Allowable flow velocity for temporary channel linings [1]

Anticipated inundation = Less than 6 hours Less than 24 hours

Soil erodibility = Low Medium High Low Medium High

Jute or coir mesh sprayedwith bitumen, and

Coconut/jute fibre mats

2.3 2.0 1.7 1.7 1.5 1.3

[1] Sourced from Landcom (2004)



Erosion control blanket/mat classification system

A classification system for erosion control blankets and mats (e.g. Class 1, Type A) is providedin Table 30. In general terms, this classification system is based on the following distinctions.

Class 1 includes those temporary, light-duty Rolled Erosion Control Products (RECPs) that areprimarily used in areas of ‘sheet’ flow, and thus are termed Erosion Control Blankets.

Class 2 includes those temporary, heavy-duty Rolled Erosion Control Products (RECPs) thatare primarily used in areas of medium shear stress such as drainage channels. These productsmay be termed Erosion Control Blankets or Mats depending on their use.

Class 3 comprises permanent, heavy-duty Rolled Erosion Control Products (RECPs) that areprimarily used in areas of high shear stress such as drainage channels and spillways/chutes.

Class 3 - Type B, C and D "Turf Reinforcement Mats" (TRM) are permanent, 100% synthetic,open-weaved mats that shall be continuously bonded at the filament intersections.

Table 30 presents the flow stability properties of erosion control blankets and mats in terms ofpermissible shear stress measured in units of Pascals (Pa). Permissible shear stress isconsidered a more reliable measure of blanket’s resistance to damage by water flow and is themeasure typically used within Europe and USA; however, allowable flow velocity is morecommonly used within Australia.

Table 3 defines the relationship between allowable shear stress (Pa) and allowable flow velocity(m/s) for various values of hydraulic radius (R) and assumed Manning’s n roughness presentedwithin the table. The table is therefore appropriate for non-vegetated, three-dimensional turfreinforcement mat (TRM) such as Class 3, Types B, C and D mats.

Table 30 – Classification of erosion control mats

Class 1 2 3

Type A B C AU BU CU A B C A B C D

Permissible shearstress (Pa)

N/A 50 70 N/A 50 70 N/A 95 95 95 95 170 240

[1] For more information on this classification system, refer to the fact sheet on Erosion Control Mats.

Table 31 – Equivalent allowable flow velocity (m/s) for a given permissible shear stress(Pa) for non-vegetated turf reinforcement mats

Permissible shear stress (Pa)AssumedManning’sroughness

Hydraulicradius (m)

50 70 95 100 150 170 240

0.06 0.05 0.65 0.72 0.79 0.85 0.91 0.97 1.02

0.04 0.10 1.09 1.22 1.33 1.44 1.54 1.63 1.72

0.036 0.15 1.29 1.45 1.58 1.71 1.83 1.94 2.05

0.033 0.20 1.48 1.66 1.81 1.96 2.09 2.22 2.34

0.031 0.25 1.64 1.83 2.00 2.16 2.31 2.45 2.59

0.029 0.30 1.80 2.02 2.21 2.38 2.55 2.70 2.85

0.026 0.40 2.11 2.36 2.58 2.79 2.98 3.16 3.33

0.023 0.50 2.47 2.77 3.03 3.27 3.50 3.71 3.91

0.02 1.0 3.19 3.57 3.91 4.23 4.52 4.79 5.05

0.02 1.5 3.42 3.82 4.19 4.52 4.83 5.13 5.40

0.02 2.0 3.59 4.01 4.39 4.74 5.07 5.38 5.67

0.02 2.5 3.72 4.16 4.56 4.92 5.26 5.58 5.88

0.02 3.0 3.84 4.29 4.70 5.07 5.43 5.75 6.07



Table 32 – Dimensions of standard parabolic catch drains

Catchdrain type

Max topwidth offlow (T)

Maximumflow depth

(y)

Top widthof formed

drain [1]

Depth offormeddrain

Hyd. rad.(R) at maxflow depth

Area (A) atmax flow

depth

Type-A 1.0m 0.15m 1.6m 0.30m 0.094m 0.100m2

Type-B 1.8m 0.30m 2.4m 0.45m 0.186m 0.360m2

Type-C 3.0m 0.50m 3.6m 0.65m 0.310m 1.000m2

[1] Top width of the formed drain assumes the upper bank slope is limited to a maximum of 2:1.

Table 33 – Required longitudinal gradient (%) for parabolic cross-section catch drainslined with Erosion Control Mats/Mesh

Allowable flow velocity along catch drain (m/s)

1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.0 3.5 4.0Manning's

roughness (n)

Type-A catch drain: flow width (T) = 1.0 m and flow depth (Y) = 0.15 m

Jute/Coir Meshn=0.022

1.13 1.62 2.21 2.89 3.65 4.51 7.04 10.1 13.8 18.0

TRM withoutgrass n=0.026

1.57 2.27 3.09 4.03 5.10 6.30 9.84 14.2 19.3 25.2

Straw mulchpinned with

mesh n=0.0332.54 3.65 4.97 6.49 8.22 10.1 15.9 22.8 31.1 40.6

Wood shavingblanket n=0.035

2.85 4.11 5.59 7.30 9.24 11.4 17.8 25.7 34.9 45.6

Type-B catch drain: flow width (T) = 1.8 m and flow depth (Y) = 0.3 m


0.46 0.66 0.89 1.17 1.47 1.82 2.84 4.10 5.58 7.28


0.64 0.92 1.25 1.63 2.06 2.54 3.97 5.72 7.79 10.2


mesh n=0.0331.02 1.47 2.01 2.62 3.32 4.10 6.40 9.22 12.6 16.4


1.15 1.66 2.26 2.95 3.73 4.61 7.20 10.4 14.1 18.4

Type-C catch drain: flow width (T) = 3.0 m and flow depth (Y) = 0.5 m


0.23 0.33 0.45 0.59 0.75 0.92 1.44 2.07 2.82 3.69


0.32 0.46 0.63 0.82 1.04 1.29 2.01 2.90 3.94 5.15


mesh n=0.0330.52 0.75 1.02 1.33 1.68 2.07 3.24 4.66 6.35 8.29


0.58 0.84 1.14 1.49 1.89 2.33 3.64 5.25 7.14 9.33



Table 34 – Maximum allowable unit catchment area (A*, hectares)

Type-A Catch Drain: Parabolic cross section

Dimensions: Flow top width = 1.0 m Flow depth = 0.15 m

Allowable flow velocity along catch drain (m/s)Rainfallintensity(mm/hr) 1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.0 3.5 4.0

15 2.400 2.880 3.360 3.840 4.320 4.800 6.000 7.200 8.400 9.600

20 1.800 2.160 2.520 2.880 3.240 3.600 4.500 5.400 6.300 7.200

25 1.440 1.728 2.016 2.304 2.592 2.880 3.600 4.320 5.040 5.760

30 1.200 1.440 1.680 1.920 2.160 2.400 3.000 3.600 4.200 4.800

35 1.029 1.234 1.440 1.646 1.851 2.057 2.571 3.086 3.600 4.114

40 0.900 1.080 1.260 1.440 1.620 1.800 2.250 2.700 3.150 3.600

45 0.800 0.960 1.120 1.280 1.440 1.600 2.000 2.400 2.800 3.200

50 0.720 0.864 1.008 1.152 1.296 1.440 1.800 2.160 2.520 2.880

55 0.655 0.785 0.916 1.047 1.178 1.309 1.636 1.964 2.291 2.618

60 0.600 0.720 0.840 0.960 1.080 1.200 1.500 1.800 2.100 2.400

65 0.554 0.665 0.775 0.886 0.997 1.108 1.385 1.662 1.938 2.215

70 0.514 0.617 0.720 0.823 0.926 1.029 1.286 1.543 1.800 2.057

75 0.480 0.576 0.672 0.768 0.864 0.960 1.200 1.440 1.680 1.920

80 0.450 0.540 0.630 0.720 0.810 0.900 1.125 1.350 1.575 1.800

85 0.424 0.508 0.593 0.678 0.762 0.847 1.059 1.271 1.482 1.694

90 0.400 0.480 0.560 0.640 0.720 0.800 1.000 1.200 1.400 1.600

95 0.379 0.455 0.531 0.606 0.682 0.758 0.947 1.137 1.326 1.516

100 0.360 0.432 0.504 0.576 0.648 0.720 0.900 1.080 1.260 1.440

105 0.343 0.411 0.480 0.549 0.617 0.686 0.857 1.029 1.200 1.371

110 0.327 0.393 0.458 0.524 0.589 0.655 0.818 0.982 1.145 1.309

115 0.313 0.376 0.438 0.501 0.563 0.626 0.783 0.939 1.096 1.252

120 0.300 0.360 0.420 0.480 0.540 0.600 0.750 0.900 1.050 1.200

125 0.288 0.346 0.403 0.461 0.518 0.576 0.720 0.864 1.008 1.152

130 0.277 0.332 0.388 0.443 0.498 0.554 0.692 0.831 0.969 1.108

135 0.267 0.320 0.373 0.427 0.480 0.533 0.667 0.800 0.933 1.067

140 0.257 0.309 0.360 0.411 0.463 0.514 0.643 0.771 0.900 1.029

145 0.248 0.298 0.348 0.397 0.447 0.497 0.621 0.745 0.869 0.993

150 0.240 0.288 0.336 0.384 0.432 0.480 0.600 0.720 0.840 0.960

155 0.232 0.279 0.325 0.372 0.418 0.465 0.581 0.697 0.813 0.929

160 0.225 0.270 0.315 0.360 0.405 0.450 0.563 0.675 0.788 0.900

165 0.218 0.262 0.305 0.349 0.393 0.436 0.545 0.655 0.764 0.873

170 0.212 0.254 0.296 0.339 0.381 0.424 0.529 0.635 0.741 0.847

175 0.206 0.247 0.288 0.329 0.370 0.411 0.514 0.617 0.720 0.823

180 0.200 0.240 0.280 0.320 0.360 0.400 0.500 0.600 0.700 0.800

185 0.195 0.234 0.272 0.311 0.350 0.389 0.486 0.584 0.681 0.778

190 0.189 0.227 0.265 0.303 0.341 0.379 0.474 0.568 0.663 0.758

200 0.180 0.216 0.252 0.288 0.324 0.360 0.450 0.540 0.630 0.720

210 0.171 0.206 0.240 0.274 0.309 0.343 0.429 0.514 0.600 0.686

220 0.164 0.196 0.229 0.262 0.295 0.327 0.409 0.491 0.573 0.655

230 0.157 0.188 0.219 0.250 0.282 0.313 0.391 0.470 0.548 0.626

240 0.150 0.180 0.210 0.240 0.270 0.300 0.375 0.450 0.525 0.600

250 0.144 0.173 0.202 0.230 0.259 0.288 0.360 0.432 0.504 0.576

Q (m3/s) 0.100 0.120 0.140 0.160 0.180 0.200 0.250 0.300 0.350 0.400




Type-B Catch Drain: Parabolic cross section



15 8.640 10.368 12.096 13.824 15.552 17.280 21.600 25.920 30.240 34.560

20 6.480 7.776 9.072 10.368 11.664 12.960 16.200 19.440 22.680 25.920

25 5.184 6.221 7.258 8.294 9.331 10.368 12.960 15.552 18.144 20.736

30 4.320 5.184 6.048 6.912 7.776 8.640 10.800 12.960 15.120 17.280

35 3.703 4.443 5.184 5.925 6.665 7.406 9.257 11.109 12.960 14.811

40 3.240 3.888 4.536 5.184 5.832 6.480 8.100 9.720 11.340 12.960

45 2.880 3.456 4.032 4.608 5.184 5.760 7.200 8.640 10.080 11.520

50 2.592 3.110 3.629 4.147 4.666 5.184 6.480 7.776 9.072 10.368

55 2.356 2.828 3.299 3.770 4.241 4.713 5.891 7.069 8.247 9.425

60 2.160 2.592 3.024 3.456 3.888 4.320 5.400 6.480 7.560 8.640

65 1.994 2.393 2.791 3.190 3.589 3.988 4.985 5.982 6.978 7.975

70 1.851 2.222 2.592 2.962 3.333 3.703 4.629 5.554 6.480 7.406

75 1.728 2.074 2.419 2.765 3.110 3.456 4.320 5.184 6.048 6.912

80 1.620 1.944 2.268 2.592 2.916 3.240 4.050 4.860 5.670 6.480

85 1.525 1.830 2.135 2.440 2.744 3.049 3.812 4.574 5.336 6.099

90 1.440 1.728 2.016 2.304 2.592 2.880 3.600 4.320 5.040 5.760

95 1.364 1.637 1.910 2.183 2.456 2.728 3.411 4.093 4.775 5.457

100 1.296 1.555 1.814 2.074 2.333 2.592 3.240 3.888 4.536 5.184

105 1.234 1.481 1.728 1.975 2.222 2.469 3.086 3.703 4.320 4.937

110 1.178 1.414 1.649 1.885 2.121 2.356 2.945 3.535 4.124 4.713

115 1.127 1.352 1.578 1.803 2.029 2.254 2.817 3.381 3.944 4.508

120 1.080 1.296 1.512 1.728 1.944 2.160 2.700 3.240 3.780 4.320

125 1.037 1.244 1.452 1.659 1.866 2.074 2.592 3.110 3.629 4.147

130 0.997 1.196 1.396 1.595 1.794 1.994 2.492 2.991 3.489 3.988

135 0.960 1.152 1.344 1.536 1.728 1.920 2.400 2.880 3.360 3.840

140 0.926 1.111 1.296 1.481 1.666 1.851 2.314 2.777 3.240 3.703

145 0.894 1.073 1.251 1.430 1.609 1.788 2.234 2.681 3.128 3.575

150 0.864 1.037 1.210 1.382 1.555 1.728 2.160 2.592 3.024 3.456

155 0.836 1.003 1.171 1.338 1.505 1.672 2.090 2.508 2.926 3.345

160 0.810 0.972 1.134 1.296 1.458 1.620 2.025 2.430 2.835 3.240

165 0.785 0.943 1.100 1.257 1.414 1.571 1.964 2.356 2.749 3.142

170 0.762 0.915 1.067 1.220 1.372 1.525 1.906 2.287 2.668 3.049

175 0.741 0.889 1.037 1.185 1.333 1.481 1.851 2.222 2.592 2.962

180 0.720 0.864 1.008 1.152 1.296 1.440 1.800 2.160 2.520 2.880

185 0.701 0.841 0.981 1.121 1.261 1.401 1.751 2.102 2.452 2.802

190 0.682 0.819 0.955 1.091 1.228 1.364 1.705 2.046 2.387 2.728

200 0.648 0.778 0.907 1.037 1.166 1.296 1.620 1.944 2.268 2.592

210 0.617 0.741 0.864 0.987 1.111 1.234 1.543 1.851 2.160 2.469

220 0.589 0.707 0.825 0.943 1.060 1.178 1.473 1.767 2.062 2.356

230 0.563 0.676 0.789 0.902 1.014 1.127 1.409 1.690 1.972 2.254

240 0.540 0.648 0.756 0.864 0.972 1.080 1.350 1.620 1.890 2.160

250 0.518 0.622 0.726 0.829 0.933 1.037 1.296 1.555 1.814 2.074

Q (m3/s) 0.360 0.432 0.504 0.576 0.648 0.720 0.900 1.080 1.260 1.440




Type-C Catch Drain: Parabolic cross section



15 24.00 28.80 33.60 38.40 43.20 48.00 60.00 72.00 84.00 96.00

20 18.00 21.60 25.20 28.80 32.40 36.00 45.00 54.00 63.00 72.00

25 14.40 17.28 20.16 23.04 25.92 28.80 36.00 43.20 50.40 57.60

30 12.00 14.40 16.80 19.20 21.60 24.00 30.00 36.00 42.00 48.00

35 10.29 12.34 14.40 16.46 18.51 20.57 25.71 30.86 36.00 41.14

40 9.00 10.80 12.60 14.40 16.20 18.00 22.50 27.00 31.50 36.00

45 8.00 9.60 11.20 12.80 14.40 16.00 20.00 24.00 28.00 32.00

50 7.20 8.64 10.08 11.52 12.96 14.40 18.00 21.60 25.20 28.80

55 6.55 7.85 9.16 10.47 11.78 13.09 16.36 19.64 22.91 26.18

60 6.00 7.20 8.40 9.60 10.80 12.00 15.00 18.00 21.00 24.00

65 5.54 6.65 7.75 8.86 9.97 11.08 13.85 16.62 19.38 22.15

70 5.14 6.17 7.20 8.23 9.26 10.29 12.86 15.43 18.00 20.57

75 4.80 5.76 6.72 7.68 8.64 9.60 12.00 14.40 16.80 19.20

80 4.50 5.40 6.30 7.20 8.10 9.00 11.25 13.50 15.75 18.00

85 4.24 5.08 5.93 6.78 7.62 8.47 10.59 12.71 14.82 16.94

90 4.00 4.80 5.60 6.40 7.20 8.00 10.00 12.00 14.00 16.00

95 3.79 4.55 5.31 6.06 6.82 7.58 9.47 11.37 13.26 15.16

100 3.60 4.32 5.04 5.76 6.48 7.20 9.00 10.80 12.60 14.40

105 3.43 4.11 4.80 5.49 6.17 6.86 8.57 10.29 12.00 13.71

110 3.27 3.93 4.58 5.24 5.89 6.55 8.18 9.82 11.45 13.09

115 3.13 3.76 4.38 5.01 5.63 6.26 7.83 9.39 10.96 12.52

120 3.00 3.60 4.20 4.80 5.40 6.00 7.50 9.00 10.50 12.00

125 2.88 3.46 4.03 4.61 5.18 5.76 7.20 8.64 10.08 11.52

130 2.77 3.32 3.88 4.43 4.98 5.54 6.92 8.31 9.69 11.08

135 2.67 3.20 3.73 4.27 4.80 5.33 6.67 8.00 9.33 10.67

140 2.57 3.09 3.60 4.11 4.63 5.14 6.43 7.71 9.00 10.29

145 2.48 2.98 3.48 3.97 4.47 4.97 6.21 7.45 8.69 9.93

150 2.40 2.88 3.36 3.84 4.32 4.80 6.00 7.20 8.40 9.60

155 2.32 2.79 3.25 3.72 4.18 4.65 5.81 6.97 8.13 9.29

160 2.25 2.70 3.15 3.60 4.05 4.50 5.63 6.75 7.88 9.00

165 2.18 2.62 3.05 3.49 3.93 4.36 5.45 6.55 7.64 8.73

170 2.12 2.54 2.96 3.39 3.81 4.24 5.29 6.35 7.41 8.47

175 2.06 2.47 2.88 3.29 3.70 4.11 5.14 6.17 7.20 8.23

180 2.00 2.40 2.80 3.20 3.60 4.00 5.00 6.00 7.00 8.00

185 1.95 2.34 2.72 3.11 3.50 3.89 4.86 5.84 6.81 7.78

190 1.89 2.27 2.65 3.03 3.41 3.79 4.74 5.68 6.63 7.58

200 1.80 2.16 2.52 2.88 3.24 3.60 4.50 5.40 6.30 7.20

210 1.71 2.06 2.40 2.74 3.09 3.43 4.29 5.14 6.00 6.86

220 1.64 1.96 2.29 2.62 2.95 3.27 4.09 4.91 5.73 6.55

230 1.57 1.88 2.19 2.50 2.82 3.13 3.91 4.70 5.48 6.26

240 1.50 1.80 2.10 2.40 2.70 3.00 3.75 4.50 5.25 6.00

250 1.44 1.73 2.02 2.30 2.59 2.88 3.60 4.32 5.04 5.76

Q (m3/s) 1.000 1.200 1.400 1.600 1.800 2.000 2.500 3.000 3.500 4.000



Table 37 – Dimensions of standard triangular V-drains

Catchdrain type

Max topwidth offlow (T)

Maximumflow depth

(y)

Top widthof formed

drain

Depth offormeddrain

Hyd. rad.(R) at maxflow depth

Area (A) atmax flow

depth

Type-AV 1.0m 0.15m 2.0m 0.30m 0.072m 0.075m2

Type-BV 1.8m 0.30m 2.7m 0.45m 0.142m 0.270m2

Type-CV 3.0m 0.50m 3.9m 0.65m 0.237m 0.750m2

Table 38 – Required longitudinal gradient (%) for triangular cross-section V-drains linedwith Erosion Control Mats/Mesh

Allowable flow velocity along catch drain (m/s)

1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.0 3.5 4.0Manning's

roughness (n)

Type-AV catch drain: flow width (T) = 1.0 m and flow depth (Y) = 0.15 m


1.62 2.33 3.18 4.15 5.25 6.48 10.1 14.6 19.9 25.9


2.26 3.26 4.44 5.80 7.33 9.05 14.1 20.4 27.7 36.2


mesh n=0.0333.65 5.25 7.15 9.34 11.8 14.6 22.8 32.8 44.7 58.3


4.10 5.91 8.04 10.5 13.3 16.4 25.6 36.9 50.3 65.6

Type-BV catch drain: flow width (T) = 1.8 m and flow depth (Y) = 0.3 m


0.65 0.94 1.28 1.67 2.11 2.61 4.07 5.86 7.98 10.42


0.91 1.31 1.78 2.33 2.95 3.64 5.69 8.19 11.15 14.56


mesh n=0.0331.47 2.11 2.87 3.75 4.75 5.86 9.16 13.19 17.96 23.45


1.65 2.37 3.23 4.22 5.34 6.60 10.31 14.84 20.20 26.38

Type-CV catch drain: flow width (T) = 3.0 m and flow depth (Y) = 0.5 m


0.33 0.47 0.65 0.84 1.07 1.32 2.06 2.97 4.04 5.27


0.46 0.66 0.90 1.18 1.49 1.84 2.88 4.14 5.64 7.37


mesh n=0.0330.74 1.07 1.45 1.90 2.40 2.97 4.64 6.68 9.09 11.9


0.83 1.20 1.64 2.14 2.70 3.34 5.22 7.51 10.2 13.4




Type-AV Catch Drain: V-drain cross section



15 1.800 2.160 2.520 2.880 3.240 3.600 4.500 5.400 6.300 7.200

20 1.350 1.620 1.890 2.160 2.430 2.700 3.375 4.050 4.725 5.400

25 1.080 1.296 1.512 1.728 1.944 2.160 2.700 3.240 3.780 4.320

30 0.900 1.080 1.260 1.440 1.620 1.800 2.250 2.700 3.150 3.600

35 0.771 0.926 1.080 1.234 1.389 1.543 1.929 2.314 2.700 3.086

40 0.675 0.810 0.945 1.080 1.215 1.350 1.688 2.025 2.363 2.700

45 0.600 0.720 0.840 0.960 1.080 1.200 1.500 1.800 2.100 2.400

50 0.540 0.648 0.756 0.864 0.972 1.080 1.350 1.620 1.890 2.160

55 0.491 0.589 0.687 0.785 0.884 0.982 1.227 1.473 1.718 1.964

60 0.450 0.540 0.630 0.720 0.810 0.900 1.125 1.350 1.575 1.800

65 0.415 0.498 0.582 0.665 0.748 0.831 1.038 1.246 1.454 1.662

70 0.386 0.463 0.540 0.617 0.694 0.771 0.964 1.157 1.350 1.543

75 0.360 0.432 0.504 0.576 0.648 0.720 0.900 1.080 1.260 1.440

80 0.338 0.405 0.473 0.540 0.608 0.675 0.844 1.013 1.181 1.350

85 0.318 0.381 0.445 0.508 0.572 0.635 0.794 0.953 1.112 1.271

90 0.300 0.360 0.420 0.480 0.540 0.600 0.750 0.900 1.050 1.200

95 0.284 0.341 0.398 0.455 0.512 0.568 0.711 0.853 0.995 1.137

100 0.270 0.324 0.378 0.432 0.486 0.540 0.675 0.810 0.945 1.080

105 0.257 0.309 0.360 0.411 0.463 0.514 0.643 0.771 0.900 1.029

110 0.245 0.295 0.344 0.393 0.442 0.491 0.614 0.736 0.859 0.982

115 0.235 0.282 0.329 0.376 0.423 0.470 0.587 0.704 0.822 0.939

120 0.225 0.270 0.315 0.360 0.405 0.450 0.563 0.675 0.788 0.900

125 0.216 0.259 0.302 0.346 0.389 0.432 0.540 0.648 0.756 0.864

130 0.208 0.249 0.291 0.332 0.374 0.415 0.519 0.623 0.727 0.831

135 0.200 0.240 0.280 0.320 0.360 0.400 0.500 0.600 0.700 0.800

140 0.193 0.231 0.270 0.309 0.347 0.386 0.482 0.579 0.675 0.771

145 0.186 0.223 0.261 0.298 0.335 0.372 0.466 0.559 0.652 0.745

150 0.180 0.216 0.252 0.288 0.324 0.360 0.450 0.540 0.630 0.720

155 0.174 0.209 0.244 0.279 0.314 0.348 0.435 0.523 0.610 0.697

160 0.169 0.203 0.236 0.270 0.304 0.338 0.422 0.506 0.591 0.675

165 0.164 0.196 0.229 0.262 0.295 0.327 0.409 0.491 0.573 0.655

170 0.159 0.191 0.222 0.254 0.286 0.318 0.397 0.476 0.556 0.635

175 0.154 0.185 0.216 0.247 0.278 0.309 0.386 0.463 0.540 0.617

180 0.150 0.180 0.210 0.240 0.270 0.300 0.375 0.450 0.525 0.600

185 0.146 0.175 0.204 0.234 0.263 0.292 0.365 0.438 0.511 0.584

190 0.142 0.171 0.199 0.227 0.256 0.284 0.355 0.426 0.497 0.568

200 0.135 0.162 0.189 0.216 0.243 0.270 0.338 0.405 0.473 0.540

210 0.129 0.154 0.180 0.206 0.231 0.257 0.321 0.386 0.450 0.514

220 0.123 0.147 0.172 0.196 0.221 0.245 0.307 0.368 0.430 0.491

230 0.117 0.141 0.164 0.188 0.211 0.235 0.293 0.352 0.411 0.470

240 0.113 0.135 0.158 0.180 0.203 0.225 0.281 0.338 0.394 0.450

250 0.108 0.130 0.151 0.173 0.194 0.216 0.270 0.324 0.378 0.432

Q (m3/s) 0.075 0.090 0.105 0.120 0.135 0.150 0.188 0.225 0.263 0.300




Type-BV Catch Drain: V-drain cross section



15 6.480 7.776 9.072 10.368 11.664 12.960 16.200 19.440 22.680 25.920

20 4.860 5.832 6.804 7.776 8.748 9.720 12.150 14.580 17.010 19.440

25 3.888 4.666 5.443 6.221 6.998 7.776 9.720 11.664 13.608 15.552

30 3.240 3.888 4.536 5.184 5.832 6.480 8.100 9.720 11.340 12.960

35 2.777 3.333 3.888 4.443 4.999 5.554 6.943 8.331 9.720 11.109

40 2.430 2.916 3.402 3.888 4.374 4.860 6.075 7.290 8.505 9.720

45 2.160 2.592 3.024 3.456 3.888 4.320 5.400 6.480 7.560 8.640

50 1.944 2.333 2.722 3.110 3.499 3.888 4.860 5.832 6.804 7.776

55 1.767 2.121 2.474 2.828 3.181 3.535 4.418 5.302 6.185 7.069

60 1.620 1.944 2.268 2.592 2.916 3.240 4.050 4.860 5.670 6.480

65 1.495 1.794 2.094 2.393 2.692 2.991 3.738 4.486 5.234 5.982

70 1.389 1.666 1.944 2.222 2.499 2.777 3.471 4.166 4.860 5.554

75 1.296 1.555 1.814 2.074 2.333 2.592 3.240 3.888 4.536 5.184

80 1.215 1.458 1.701 1.944 2.187 2.430 3.038 3.645 4.253 4.860

85 1.144 1.372 1.601 1.830 2.058 2.287 2.859 3.431 4.002 4.574

90 1.080 1.296 1.512 1.728 1.944 2.160 2.700 3.240 3.780 4.320

95 1.023 1.228 1.432 1.637 1.842 2.046 2.558 3.069 3.581 4.093

100 0.972 1.166 1.361 1.555 1.750 1.944 2.430 2.916 3.402 3.888

105 0.926 1.111 1.296 1.481 1.666 1.851 2.314 2.777 3.240 3.703

110 0.884 1.060 1.237 1.414 1.591 1.767 2.209 2.651 3.093 3.535

115 0.845 1.014 1.183 1.352 1.521 1.690 2.113 2.536 2.958 3.381

120 0.810 0.972 1.134 1.296 1.458 1.620 2.025 2.430 2.835 3.240

125 0.778 0.933 1.089 1.244 1.400 1.555 1.944 2.333 2.722 3.110

130 0.748 0.897 1.047 1.196 1.346 1.495 1.869 2.243 2.617 2.991

135 0.720 0.864 1.008 1.152 1.296 1.440 1.800 2.160 2.520 2.880

140 0.694 0.833 0.972 1.111 1.250 1.389 1.736 2.083 2.430 2.777

145 0.670 0.804 0.938 1.073 1.207 1.341 1.676 2.011 2.346 2.681

150 0.648 0.778 0.907 1.037 1.166 1.296 1.620 1.944 2.268 2.592

155 0.627 0.753 0.878 1.003 1.129 1.254 1.568 1.881 2.195 2.508

160 0.608 0.729 0.851 0.972 1.094 1.215 1.519 1.823 2.126 2.430

165 0.589 0.707 0.825 0.943 1.060 1.178 1.473 1.767 2.062 2.356

170 0.572 0.686 0.800 0.915 1.029 1.144 1.429 1.715 2.001 2.287

175 0.555 0.667 0.778 0.889 1.000 1.111 1.389 1.666 1.944 2.222

180 0.540 0.648 0.756 0.864 0.972 1.080 1.350 1.620 1.890 2.160

185 0.525 0.630 0.736 0.841 0.946 1.051 1.314 1.576 1.839 2.102

190 0.512 0.614 0.716 0.819 0.921 1.023 1.279 1.535 1.791 2.046

200 0.486 0.583 0.680 0.778 0.875 0.972 1.215 1.458 1.701 1.944

210 0.463 0.555 0.648 0.741 0.833 0.926 1.157 1.389 1.620 1.851

220 0.442 0.530 0.619 0.707 0.795 0.884 1.105 1.325 1.546 1.767

230 0.423 0.507 0.592 0.676 0.761 0.845 1.057 1.268 1.479 1.690

240 0.405 0.486 0.567 0.648 0.729 0.810 1.013 1.215 1.418 1.620

250 0.389 0.467 0.544 0.622 0.700 0.778 0.972 1.166 1.361 1.555

Q (m3/s) 0.270 0.324 0.378 0.432 0.486 0.540 0.675 0.810 0.945 1.080




Type-CV Catch Drain: V-drain cross section



15 18.00 21.60 25.20 28.80 32.40 36.00 45.00 54.00 63.00 72.00

20 13.50 16.20 18.90 21.60 24.30 27.00 33.75 40.50 47.25 54.00

25 10.80 12.96 15.12 17.28 19.44 21.60 27.00 32.40 37.80 43.20

30 9.00 10.80 12.60 14.40 16.20 18.00 22.50 27.00 31.50 36.00

35 7.71 9.26 10.80 12.34 13.89 15.43 19.29 23.14 27.00 30.86

40 6.75 8.10 9.45 10.80 12.15 13.50 16.88 20.25 23.63 27.00

45 6.00 7.20 8.40 9.60 10.80 12.00 15.00 18.00 21.00 24.00

50 5.40 6.48 7.56 8.64 9.72 10.80 13.50 16.20 18.90 21.60

55 4.91 5.89 6.87 7.85 8.84 9.82 12.27 14.73 17.18 19.64

60 4.50 5.40 6.30 7.20 8.10 9.00 11.25 13.50 15.75 18.00

65 4.15 4.98 5.82 6.65 7.48 8.31 10.38 12.46 14.54 16.62

70 3.86 4.63 5.40 6.17 6.94 7.71 9.64 11.57 13.50 15.43

75 3.60 4.32 5.04 5.76 6.48 7.20 9.00 10.80 12.60 14.40

80 3.38 4.05 4.73 5.40 6.08 6.75 8.44 10.13 11.81 13.50

85 3.18 3.81 4.45 5.08 5.72 6.35 7.94 9.53 11.12 12.71

90 3.00 3.60 4.20 4.80 5.40 6.00 7.50 9.00 10.50 12.00

95 2.84 3.41 3.98 4.55 5.12 5.68 7.11 8.53 9.95 11.37

100 2.70 3.24 3.78 4.32 4.86 5.40 6.75 8.10 9.45 10.80

105 2.57 3.09 3.60 4.11 4.63 5.14 6.43 7.71 9.00 10.29

110 2.45 2.95 3.44 3.93 4.42 4.91 6.14 7.36 8.59 9.82

115 2.35 2.82 3.29 3.76 4.23 4.70 5.87 7.04 8.22 9.39

120 2.25 2.70 3.15 3.60 4.05 4.50 5.63 6.75 7.88 9.00

125 2.16 2.59 3.02 3.46 3.89 4.32 5.40 6.48 7.56 8.64

130 2.08 2.49 2.91 3.32 3.74 4.15 5.19 6.23 7.27 8.31

135 2.00 2.40 2.80 3.20 3.60 4.00 5.00 6.00 7.00 8.00

140 1.93 2.31 2.70 3.09 3.47 3.86 4.82 5.79 6.75 7.71

145 1.86 2.23 2.61 2.98 3.35 3.72 4.66 5.59 6.52 7.45

150 1.80 2.16 2.52 2.88 3.24 3.60 4.50 5.40 6.30 7.20

155 1.74 2.09 2.44 2.79 3.14 3.48 4.35 5.23 6.10 6.97

160 1.69 2.03 2.36 2.70 3.04 3.38 4.22 5.06 5.91 6.75

165 1.64 1.96 2.29 2.62 2.95 3.27 4.09 4.91 5.73 6.55

170 1.59 1.91 2.22 2.54 2.86 3.18 3.97 4.76 5.56 6.35

175 1.54 1.85 2.16 2.47 2.78 3.09 3.86 4.63 5.40 6.17

180 1.50 1.80 2.10 2.40 2.70 3.00 3.75 4.50 5.25 6.00

185 1.46 1.75 2.04 2.34 2.63 2.92 3.65 4.38 5.11 5.84

190 1.42 1.71 1.99 2.27 2.56 2.84 3.55 4.26 4.97 5.68

200 1.35 1.62 1.89 2.16 2.43 2.70 3.38 4.05 4.73 5.40

210 1.29 1.54 1.80 2.06 2.31 2.57 3.21 3.86 4.50 5.14

220 1.23 1.47 1.72 1.96 2.21 2.45 3.07 3.68 4.30 4.91

230 1.17 1.41 1.64 1.88 2.11 2.35 2.93 3.52 4.11 4.70

240 1.13 1.35 1.58 1.80 2.03 2.25 2.81 3.38 3.94 4.50

250 1.08 1.30 1.51 1.73 1.94 2.16 2.70 3.24 3.78 4.32

Q (m3/s) 0.750 0.900 1.050 1.200 1.350 1.500 1.875 2.250 2.625 3.000


© Catchments & Creeks Pty Ltd V2 February 2010 Page 1

Flow Diversion Banks: General


Low Gradient ᅛ Velocity Control Short Term ᅛ

Steep Gradient Channel Lining Medium-Long Term ᅛ

Outlet Control Soil Treatment Permanent [1]

[1] Flow diversion banks are not commonly used as permanent drainage structures.

Symbol

Photo 1 – Flow diversion bank down-slope of a future pipeline installation

Photo 2 – Flow diversion bank up-slope ofa building site

Key Principles

1. Key design parameters are the effective flow capacity of the structure, and the scourresistance of the embankment material.

2. The critical operational issue is usually preventing structural damage to the embankment asa result of high velocity flows or construction traffic.

3. Flow diversion banks are often favoured over Catch Drains in areas containing dispersivesubsoil because their construction does not require exposure of the subsoils.

Design Information

Dimensional requirements of flow diversion banks and berms vary with the type of embankment.The recommended values are outlined in Table 1.

Table 1 – Recommended dimensional requirements of flow diversion banks/berms

Parameter Earth banks Compost berms [1]

Sandbag berms

Height (min) 500mm 300mm (450mm) N/A

Top width (min) 500mm [2]

100mm (100mm) N/A

Base width (min) 2500mm [2]

600mm (900mm) N/A

Side slope (max) 2:1 (H:V) 1:1 (H:V) N/A

Hydraulic freeboard 150mm (300mm) [3]

100mm 50mm

[1] Values in brackets apply to berms placed across land slopes steeper than 4:1 (H:V).

[2] Top width may be reduced in non-critical situations in which overtopping will not cause excessiveerosion and the banks are unlikely to experience damage from construction equipment.

[3] A minimum freeboard of 300mm applies to non-vegetated earth embankments.



Free standing earth embankments may be stabilised with rock, vegetation, or Erosion ControlBlankets; however, unprotected topsoil embankments are also acceptable for short-termapplications.

Maximum recommended spacing of flow diversion banks down long continuous slopes isprovided in Table 2. The actual spacing specified for a given site may need to be less than thatpresented in Table 2 if the soils are highly susceptible to erosion, or if intense storm events areexpected (i.e. northern parts of Australia during the wet season).

Table 2 – Maximum recommended spacing of flow diversion banks down slopes

Open Earth Slopes Vegetated Slopes

Slope Horiz. Vert. Slope Horiz. Vert. Slope Horiz. Vert.

1% 80m 0.9m 15% 19m 2.9m < 10% No maximum

2% 60m 1.2m 20% 16m 3.2m 12% 100m 12m

4% 40m 1.6m 25% 14m 3.5m 15% 80m 12m

6% 32m 1.9m 30% 12m 3.5m 20% 55m 11m

8% 28m 2.2m 35% 10m 3.5m 25% 40m 10m

10% 25m 2.5m 40% 9m 3.5m 30% 30m 9m

12% 22m 2.6m 50% 6m 3.0m > 36% Case specific

Photo 3 – Flow diversion berm used tominimise road runoff flowing down a steep,

unstable section of the embankment

Photo 4 – Sandbag flow diversion bermused to minimise surface flow over a

recently seeded embankment

Photo 5 – Earth flow diversion bank usedto direct runoff towards the entrance of a

Slope Drain

Photo 6 – Turf-lined flow diversion bankwith grass-lined outlet chutes at regular

intervals along the embankment



Figure 1 – Profile of “back-push” bank

The hydraulic capacity of a flow diversion bank normally needs to be assessed on a case-by-case basis; however, the associated fact sheets subtitled “On earth slope” and “On grassedslope” provide the hydraulic capacity for drains with a standard triangular profile established onearth and grassed slopes respectively.

The geometric properties of triangular drainage channels formed by the construction of a flowdiversion bank are provided in Table 3.

Table 3 – Geometric properties of triangular drainage profiles

Area (A):

A T y= 0 5.

Wetted perimeter (P):

P T y= +2 24

Symmetrical or asymmetric V-drain:

Hydraulics radius (R):

RTy

T y=

+2 42 2

Area (A):

Aa b

y=+⎛

⎝⎜⎞⎠⎟2

2

Wetted perimeter (P):

P y a b= + + +⎡⎣⎢

⎤⎦⎥

( ) ( )1 12 2

Asymmetric V-drain:

where flow top width, T = y(a + b)

Hydraulics radius (R):

Ra b y

a b=

+

+ + +

0 5

1 12 2

. ( )

( ) ( )



Figure 2 – Flow diversion bank formed from earth

Photo 7 – Flow diversion banks placed each side of drainage line passing through roadconstruction site

Types of flow diversion banks:

The following provides a brief description of some of the flow diversion banks used within ruraland construction land management.

Absorption bank A level bank turned up at each end to promote water infiltration.

Back-push bank A bank formed by moving in-situ earth up a slope.

Conventional bank A bank formed by moving in-situ earth down thus forming an excavateddrain up-slope of the bank. Also known as a “catch bank”.

Diversion bank A graded bank used to collect and divert water away from a soildisturbance, or to a dam, drainage channel, or sediment trap.

Graded bank A bank constructed with a positive gradient to promote water movement.

Level bank A bank constructed along a contour. Discharge usually occurs at eachend of the bank.

Perimeter bank A bank located along the upper or lower perimeter of a well-defined area,such as a building site, or along the top edge of a batter.

Trainer bank A bank used to divert water away from unstable land.

Water-spreadingbank

Banks used to collect and distribute surface runoff over an increased flowwidth. Typically used on low-gradient, marginal arable land.



Description

Flow diversion banks typically consist of araised earth embankment normally placedalong level or near level ground. Minor flowdiversion berms can also be formed fromtightly packed sandbags, or compost.

Short-term flow diversion banks can also beconstructed from tightly packed straw bales.Such banks are often constructed prior toan impending storm.

The term perimeter bank is often used todescribe an embankment constructedaround the “perimeter” of a work site.These are used to either prevent cleanwater entering the site, or to prevent theuncontrolled release of dirty water from asite.

The term back-push bank is used todescribe an embankment formed bypushing in-situ soils up a slope to from anearth embankment.

Purpose

Flow diversion banks and berms are usedas temporary drainage systems to:

• collect sheet runoff (clean or dirty) fromslopes and transport it across the slopeto a stable outlet (Photo 1);

• divert up-slope runoff around astockpile or soil disturbance (Photo 2);

• divert stormwater away from anunstable slope (Photos 3 & 4);

• direct water to the inlet of a Chute orSlope Drain (Photos 5 & 6);

• control the depth of ponding around asediment trap such as a stormwaterdrop (field) inlet.

Flow diversion banks can also act as a formof topsoil stockpile. Topsoil can be strippedfrom a site and used to form flow diversionbanks either up-slope and/or down-slope ofthe soil disturbance (Photo 1). Such apractice can be very space effective whenconducting “strip” construction such asroadways and pipeline installation.

Limitations

Catchment area is limited by the allowableflow capacity of the diversion bank and theallowable flow velocity of the surfacematerial.

Not used on slopes steeper than 10%(10:1).

Advantages

Quick to establish or re-establish ifdisturbed.

Generally inexpensive to construct andremove.

Allows for the management of stormwaterflow without the need to excavate adrainage channel. This can be a significantadvantage in areas that have highly erosiveor dispersive subsoils.

Disadvantages

Can cause sediment problems and flowconcentration if overtopped during a severestorm.

Can restrict the movement of equipmentaround the site.

Can be highly susceptible to damage byconstruction equipment.

Common Problems

Damaged by construction traffic.

Scour along the base of the embankmentcaused by excessive flow velocity or anunstable outlet.

Overtopping flows caused by the depositionof sediment up-slope of the bank.


All flow diversion banks must have a stableoutlet.

Flow diversion banks should be seeded andmulched if their working life is expected toexceed 30 days, or as required by theerosion control standard.

Banks should not be constructed ofunstable, non-cohesive, or dispersive soil.

Location

When flow diversion banks are requiredand their locations are not shown on theapproved plans, their location on theground should be determined after takinginto consideration the following:

• the bank must discharge to a stabilisedoutlet;

• the bank should drain to a sedimenttrap if the diverted water is expected tobe contaminated with sediment;

• stormwater must not be unnaturallydiverted or concentrated onto anadjacent property.



Site Inspection

Check for slumps, wheel track damage, orloss of freeboard.

Check for excessive sediment deposition.

Check for erosion along the bank.

Installation

1. Refer to approved plans for location,extent, and construction details. Ifthere are questions or problems withthe location, extent, or method ofinstallation, contact the engineer orresponsible on-site officer forassistance.

2. Clear the location for the bank, clearingonly the area that is needed to provideaccess for personnel and equipment.

3. Remove roots, stumps, and otherdebris and dispose of them properly.Do not use debris to build the bank.

4. Form the bank from the material, and tothe dimension specified in the approvedplans.

5. If earth is used, then ensure the sidesof the bank are no steeper than a 2:1(H:V) slope, and the completed bankmust be at least 500mm high.

6. If formed from sandbags, then ensurethe bags are tightly packed such thatwater leakage through the bags isminimised.

7. Check the bank alignment to ensurepositive drainage in the desireddirection.

8. The bank should be vegetated (turfed,seeded and mulched), or otherwisestabilised immediately, unless it willoperate for less than 30 days or ifsignificant rainfall is not expectedduring the life of the bank.

9. Ensure the embankment drains to astable outlet, and does not discharge toan unstable fill slope.

Maintenance

1. Inspect flow diversion banks at leastweekly and after runoff-producingrainfall.

2. Inspect the bank for any slumps, wheeltrack damage or loss of freeboard.Make repairs as necessary.

3. Check that fill material or sediment hasnot partially blocked the drainage pathup-slope of the embankment. Wherenecessary, remove any depositedmaterial to allow free drainage.

4. Dispose of any collected sediment or fillin a manner that will not create anerosion or pollution hazard.

5. Repair any places in the bank that areweakened or in risk of failure.

Removal

1. When the soil disturbance above thebank is finished and the area isstabilised, the flow diversion bankshould be removed, unless it is toremain as a permanent drainagefeature.

2. Dispose of any sediment or earth in amanner that will not create an erosionor pollution hazard.


4. Stabilise the area by grassing or asspecified in the approved plan.



Level Spreaders DRAINAGE CONTROL TECHNIQUE

Low Gradient 6 Velocity Control Short Term 6

Steep Gradient [1] Channel Lining Medium-Long Term 6

Outlet Control 6 Soil Treatment Permanent 6

[1] Level spreaders can release sheet flow down steep slopes, but the level spreader itself must be constructed across a level gradient.

Symbol

Photo 1 – Diversion drains (centre) collect stormwater from roadside table drains,

then releases the water as sheet flow via a level spreader

Photo 2 – Level spreader established to discharge stormwater from a diversion

drain into the roadside property

Key Principles

1. Flow must be released from the level spreader as sheet flow.

2. Flow must be released over a stable, well-grassed surface that will maintain suitable flow conditions down the slope.

3. Critical design parameter is the length of the outlet sill.

4. Critical operational parameter is the level construction of the outlet sill. Design Information

The length of the outlet sill (weir) of the level spreader is governed by the design discharge, and the allowable flow velocity of the down-slope area.

Allowable flow velocity for grassed surfaces can be determined from Table 1.

Minimum dimension can be determined from Tables 2 and 3.

Minimum sill length is 4 metres.

Maximum sill length is 25 metres. If a longer sill length is required, then the inflow must be spilt and released through more than one level spreader.

Up-slope channel grade should not exceed 1% for the last 6 metres before entering the level spreader.

Discharge must release evenly along a level surface (sill) of 0% cross gradient.

Caution the use of a design discharge exceeding 0.85 m 3/s.

Caution the release of water onto grass slopes steeper than 10%.



Table 1 – Allowable flow velocity (m/s) for grassed surfaces [1]

Percentage grass cover

Gradient of grass surface (%)

1 2 3 4 5 6 8 10 15 20

70% [2]

2.0 1.8 1.7 1.6 1.6 1.5 1.5 1.4 1.3 1.3

100% [3]

2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.9 1.8 1.7

Poor soils [3]

1.5 1.4 1.3 1.2 1.2 1.1 1.1 1.1 1.0 0.9

[1] Maximum allowable flow velocity limited to 2.0m/s due to shallow water flow and resulting high shear stress. High flow velocities are allowable on reinforced grass.

[2] 70% cover would be typical for most grasses recently established by seed, but only when there is sufficient plant establishment time.

[3] “Poor soils” refers to the soil’s high erosion potential, such as dispersive clays (Emerson Class 1 and 2) such as sodic, yellow and red soils. Unstable, dispersible clayey sands and sandy clays, such as yellow and grey massive earths formed on sandstones and some granites. Highly erodible soils may include: lithosols, alluvials, podzols, siliceous sands, soloths, solodized solonetz, grey podzolics, some black earths, fine surface texture-contrast soils, and Soil Groups ML and CL.

Table 2 – Level spreader sill length metres per unit discharge (m per m /s) [1]

Land slope (%)

Allowable down-slope velocity over well grassed surface (m/s)

1.0 1.2 1.5 1.8 2.0 2.2 2.5

1.0 3.5* 2.5* 1.6* 1.1* 0.9* 0.8* 0.6*

2.0 5.2 3.8* 2.5* 1.8* 1.4* 1.2* 0.9*

3.0 6.6 4.8 3.2* 2.3* 1.8* 1.5* 1.2*

4.0 7.7 5.6 3.8* 2.7* 2.2* 1.8* 1.4*

5.0 8.7 6.3 4.3* 3.1* 2.5* 2.1* 1.6*

6.0 9.5 7.0 4.7 3.4* 2.8* 2.3* 1.8*

7.0 10.3 7.6 5.2 3.7* 3.1* 2.6* 2.0*

8.0 11.0 8.2 5.6 4.0* 3.3* 2.8* 2.2*

9.0 11.8 8.7 6.0 4.3* 3.5* 3.0* 2.4*

10.0 12.4 9.2 6.3 4.6* 3.8* 3.2* 2.5*

Caution the release of water onto grass slopes steeper than 10%.

15.0 15.2 11.3 7.8 5.7 4.8 4.0* 3.2*

20.0 17.4 13.1 9.1 6.7 5.6 4.7 3.7*

25.0 19.4 14.6 10.3 7.6 6.3 5.3 4.3*

33.3 22.1 16.8 11.9 8.8 7.4 6.2 5.0

50.0 26.6 20.3 14.5 10.8 9.1 7.8 6.3

* Sill length limited to minimum 4m for discharges less than 0.85m3/s.

Design example:

Design a level spreader to release a flow rate of 0.5m3/s down a 10% slope containing a good

(70%) grass cover on moderately erodible soil. Solution:

From Table 1, choose a maximum flow velocity of 1.4m/s as best representative of a good grass cover on a moderately erodible soil.

From Table 2, select a sill width per unit flow rate of 7.3m/m3/s.

Therefore, the sill length would need to be 0.5 x 7.3 = 3.65m < 4m (minimum).

Conclusion, specify a sill length of 4m.



The minimum sill lengths presented in Table 2 have been determined assuming a Manning’s roughness for 50-150mm (Class D) grassed surfaces based on Equation 1. The sill length is sensitive to the selection of Manning’s roughness. Variations between Table 2 and other published design tables for is due to variations in the assumed Manning’s roughness, which is highly variable depending on the type and length of grass, and local growing conditions. Class D roughness: (Eqn 1)

Table 3 – Minimum dimension of level spreader

Discharge (m3/s) Entrance width (m) Depth (m) End width (m)

0 to 0.28 3.0 0.15 0.9

0.29 to 0.57 4.9 0.18 0.9

0.58 to 0.85 7.3 0.21 0.9

Construction of a level spreader may require formation of flow control banks as shown in Figures 1 to 3.

Figure 1 – Example of a level spreader used for flow diversion around a soil disturbance

Figure 2 – Typical layout of level spreader

nR

R S=

+

1 6

101 4 0 45124 20 77

/

. .. . log ( . )



Description

Level spreaders consist of a level, grassed, side-flow weir (i.e. water discharges at 90 degrees to the inflow direction) constructed along the contour. Purpose

Used to allow concentrated inflow to be released as sheet flow down a stable, vegetated slope.

Can be used as an outlet for Catch Drains and Flow Diversion Banks.

Level spreaders are commonly used in rural areas to discharge stormwater from roadside table drains into an adjacent property (Photos 1 & 2). Limitations

Minimum sill length of 4m.

Maximum sill length of 25m.

Maximum discharge of around 0.85 m3/s.

Must only be used where the outflow can be discharged to an undisturbed, stable, grassed surface.

Construction traffic should be prohibited from the area of the level spreader.

Not suitable for highly erosive soils, dispersive soils, or soils with poor vegetation cover. Advantages

Inexpensive to construct and maintain. Disadvantages

Can be difficult to construct the outlet sill to the required precision.

May require a considerable width of undisturbed land.

May require the land to be free of trees, shrubs and other surface irregularities to avoid local erosion problems. Common Problems

The most common problems result from damage to the outlet sill either from erosion, sedimentation, or stock.

Other problems can result from water flow concentrating below the level spreader due to the existence of a concave surface, vehicular tracks, or uneven vegetation cover.


Outlet area must be free of depressions that may concentrate the outflow.

Extra erosion protection using jute mesh, Erosion Control Mats, turf, rock etc. may be required at the sill (Figure 4).

Generally constructed by bozers no larger than D5 or equivalent.

Extreme caution must be exercised when attempting to discharge sheet flow down a steep gradient (>10%) to ensure that the sedimentation or damage to the outlet sill does not concentrate the outflow. Site Inspection

Check for sediment build-up on the sill, or the concentration of outflow.

Check for erosion down-slope of the sill. Installation

1. Refer to approved plans for location, dimensions and construction details. If there are questions or problems with the location, dimensions, or method of installation contact the engineer or responsible on-site officer for assistance.

2. Wherever practical, locate the level spreader on undisturbed, stable soil.

3. Ensure flow discharging from the level spreader will disperse across a properly stabilised slope not exceeding 10:1 (H:V) and sufficiently even in grade across the slope to avoid concentrating the outflow.

4. The outlet sill of the spreader should be protected with erosion control matting to prevent erosion during the establishment of vegetation. The matting should be a minimum of 1200mm wide extending at least 300mm upstream of the edge of the outlet crest and buried at least 150mm in a vertical trench. The downstream edge should be securely held in place with closely spaced heavy-duty wire staples at least 150mm long.

5. Ensure that the outlet sill (crest) is level for the specified length.

6. Immediately after construction, turf, or seed and mulch where appropriate, the level spreader.



Maintenance

1. Inspect the level spreader after every rainfall event until vegetation is established.

2. After establishment of vegetation over the level spreader, inspections should be made on a regular basis and after runoff-producing rainfall.

3. Ensure that there is no soil erosion and that sediment deposition is not causing the concentration of flow.

4. Ensure that there is no soil erosion or channel damage upstream of the level spreader, or soil erosion or vegetation damage downstream of the level spreader.

5. Investigate the source of any excessive sedimentation.

6. Maintain grass in a health condition with no less than 90% cover unless current weather conditions require otherwise.

7. Grass height should be maintained at a minimum 50mm blade length within the level spreader and downstream discharge area, and a maximum blade length no greater than adjacent grasses.

Removal

1. Temporary level spreaders should be decommissioned only after an alternative stable outlet is operational, or when the inflow channel is decommissioned.

2. Remove collected sediment and dispose of in a suitable manner that will not cause an erosion or pollution hazard.

3. Remove and appropriately dispose of any exposed geotextile.

4. Grade the area and smooth it out in preparation for stabilisation.

5. Stabilise the area as specified on the approved plan.

Figure 3 – Alternative level spreader layout

Figure 4 – Cross-sectional profile of end sill



Construction Exits – Rock pads

SEDIMENT CONTROL TECHNIQUE

Type 1 System Sheet Flow Sandy Soils ᅛ

Type 2 System Concentrated Flow [1] Clayey Soils ᅛ

Type 3 System Supplementary Trap ᅛ Dispersive Soils

[1] Minor concentrated flows passing down the access track towards the rock pad must be diverted offthe rock pad towards a suitable sediment trap (Photo 3).

Symbol or

Photo 1 – Stabilised rock padconstruction exit

Photo 2 – Stabilised rock padconstruction exit

Key Principles

1. Rock pad dimensions and rock specifications are different for small building sites comparedto construction sites.

2. Rock pads on small building sites primarily act as all-weather parking surfaces that aim tominimise the initial placement of dirt and mud on tyres.

3. Rock pads on construction sites primarily act as sediment traps aiming to strip from vehicletyres any dirt and mud generated from soil disturbances elsewhere on the site.

4. Sediment trapping ability is directly related to the ‘volume’ of open voids between the rocks,which is related to the uniformity of the rock size, and the length and depth of rock. Thewidth of the rock pad is less important, so long as it is greater than the width of the trucks.

Design Information

Table 1 provides the recommended dimensions of rock pads.

Table 1: Rock pad dimensions

Parameter Construction Sites Building Sites

Minimum width 3m (single lane) or 2.5m per lane 2m

Minimum length (where practical) 15m 10m

Minimum thickness of rock 200mm 150mm

Rock size (avoid 75–100mm) 50–75mm, or 100–150mm 40–75mm



Figure 1 shows the typical layout of a rock pad suitable for construction sites. Guidelines on thedesign of entry/exit rock pads for small building sites are provided in the separate fact sheet forBuilding Sites.

Figure 1 – Rock pad construction exit for civil construction sites

(a) Specification of rock

To the maximum degree practical, the rock size must be near uniform to maximise the availablevoid spacing. Rock size of 50 to 75mm is best used only for small soil disturbances and lowtruck volumes. For larger sites a rock size of 100 to 150mm is preferred. It is considered thatrocks of 75 to 100mm is size have a higher risk of being hooked up between dual tyres.

The rock must be placed on filter cloth (minimum bidim A24 or equivalent) if located on clayeyor unstable soils.

Figure 2: Good rock selection Figure 3: Poor rock selection

Photo 3 – Example of suitable rocks forconstruction site rock pads

Photo 4 – Warning sign for truck driversregarding rocks hooked up in dual tyres



(b) Drainage control

In circumstances where surface runoff from the work site is directed towards the rock pad (i.e.where the rock pad is down-slope of the soil disturbance), a drainage berm (bund) must beconstructed across the rock pad to direct this runoff to a suitable sediment trap. The type ofsediment trap being appropriate for the catchment area and erosion hazard.

The location of this flow control berm (up-slope end, middle, or down-slope end) depends onsite topography and the location of the associated sediment trap.

The mountable flow control berm should have side slopes not exceeding 5:1 (H:V) batters.

Figure 4: Rock Pad without flow diversion Figure 5: Rock Pad with flow diversion

Photo 5 – Flow control berm Photo 6 – Passing site runoff under a rockpad

Photo 7 – Drain down-slope of rock paddirecting sediment-laden runoff to a nearby

sediment trap.

Photo 8 – Rock pad with adjacent,gravelled site entry footpath


Sediment Basins SB-01Feb-10Drawn: Date:

GMW

Inflow

Inflow

Emergency

spillway

Fill embankment

Maximum water level

Bottom of settling zone

Length (L)

Width (W)

Energy

dissipater

(d) Type C (dry) basin with riser pipe outlet system

OutletInflow

(a)

Baffle

L2

L1

AS

Inflow

Outlet

Baffle

In case (b) it is important

to place the baffle so that

L1 = L2

(b)

ASL1

L2

L2

L1

Inflow

(c) AS

Outlet

L2

AS

L4

L3

L1

Inflow

Inflow

(d)Cases (a), (b), (c): We = AS/(L1 + L2)

Cases (d): We = AS/(L1 + L2 + L3 + L4)

Where: We = Effective width

AS = Pond surface area

(c) Typical arrangement of internal flow control baffles

(after USDA, 1975)

Maximum water level

Sediment storage zone

Settling zone

Spillway crest

300mm (min)

600mm

(min)

(b) Typical profile of Type F/D (wet) basin

Maximum water level

Sediment storage zone

Settling zone

Riser pipe outlet

Spillway crest

300mm

(min)

300mm (min)

Debris screen

Anti-flotation weight

Anti-seep collars

600mm

(min)

(a) Type C (dry) basin with riser pipe outlet system

Ca

tchm

ents

& C

reeks P

ty L

td



Slope Drains


Low Gradient Velocity Control Short Term 6

Steep Gradient 6 Channel Lining Medium-Long Term 6

Outlet Control [1] Soil Treatment Permanent

[1] Slope drains can act as outlet structures for Catch Drains, Flow Diversion Banks.

Symbol

Photo 1 – Flexible, plastic slope drain Photo 2 – Corrugated, steel pipe slopedrain

Key Principles

1. Critical design parameter is the hydraulic capacity of the pipe’s inlet, which is governed bythe pipe diameter (D) and the relative upstream water level (H).

2. Critical operational factor is the control of leakages and flow bypassing around the pipeentrance. It is essential for adequate flow controls (e.g. Flow Diversion Banks) to exist at thepipe’s entrance to control water movement and prevent wash-outs.

3. The pipe must not release the water part way down the embankment, but must release thewater at a stable outlet (e.g. Outlet Structure), at the base of the slope.

Design Information

The material contained within this fact sheet has been supplied for use by persons experiencedin hydraulic design.

The hydraulic capacity of a drop pipe is normally controlled by the inlet hydraulics. The inletcapacity is normally limited by either:

• the maximum allowable water level elevation at the entrance to the drop pipe, which iscontrolled by the height of the associated Flow Diversion Bank, and the required freeboardfor this bank; or

• flow restrictions at the pipe’s entrance (inlet control hydraulics), which may result from eitherweir flow conditions (H<D), or orifice flow conditions (H>D).

In the latter case, hydraulic capacity may be determined using a standard pipe culvert “inlet-control” design chart. Inlet control conditions are normally based on the design line (3) for asocket-end projecting pipe.

Table 1 provides inlet flow capacities for two standard pipe sizes of 300 and 375mm.

Tables 2 and 3 provide mean rock size, d50 (mm) and length, L (m) of rock protection required atthe outlet of the slope drain.



Table 1 – Hydraulic capacity (L/s) of slope drains with 300 and 375mm diameter pipe [1]

Upstream water level “H” (m) relative to the slope drain invert at its inletPipedia “D” 0.20 0.25 0.30 0.32 0.34 0.36 0.38 0.40 0.45 0.50 0.55 0.60 0.70

300mm 36 49 62 67 72 76 81 85 96 106 115 123 138

375mm 43 63 82 89 96 104 11 118 134 150 166 180 207

[1] Tabulated flow rate assumes partial full flow conditions exist within the pipe. If the inlet and outlet aredrowned, full-pipe siphon flow conditions may commence within the pipe, in which case the flow ratewill be governed by the total fall in water level from inlet to outlet. In such cases, “gulping” (airentrainment) can occur at the inlet causing highly irregular flow conditions and highly variableupstream water levels.

Details of associated Flow Diversion Bank:

Minimum 500mm high, and 2:1(H:V) side slopes (maximum grade).

Embankment crest at least 300mm above inlet pipe obvert (not to be confused with “freeboard”).

Minimum hydraulic freeboard of 300mm for non-vegetated embankments, otherwise 150mm.

Well-compacted (at least by hand-tamping around the pipe) and in 100mm layers.

Pipe inlet:

Inlet section laid at a minimum 3% slope.

An excavated sediment trap may be constructed at the pipe entrance to reduce sedimentationproblems within the pipe.

Pipe geometry:

Bends in the pipe should be avoided down the slope.

Anchor points provided at approximately 3m intervals.

Outlets should (ideally) extend at least 1.5m on a grade no steeper than 1%.

Slope drains must not discharge onto a fill slope or unstable ground.

Typical outlet structure (energy dissipater):

Level bed of rock (Rock Pad).

Minimum bed thickness of 250mm, but at least 1.5 times the nominal d50 rock size.

Refer to Tables 2 and 3 for design information.

In theory, the required rock size and length of rock protection decreases with the increasinglength of a low gradient section of pipe at the toe of the embankment (as seen in Photo 2).

Additional design notes:

Debris collection bars or trash racks may need to be considered on the entrance of some slopedrains to avoid blockage of the inlet. If required, debris bars typically should be placed at leastthree pipe diameters away from the pipe entrance, with scour protection placed between thebars and pipe entrance.

Collapsible or “lay-flat” pipes (Figure 2) should be securely attached to a solid, ribbed pipeembedded within the Flow Diversion Bank. The pipe may need to be secured at regularintervals down the slope. At the outlet, the lay-flat pipe may need to be modified to dissipateoutflow energy (e.g. a perforated pipe outlet manifold), otherwise the outlet will need to beanchored to a standard Outlet Structure.



Table 2 – Mean rock size (mm) and length (m) of rock pad outlet structure for smoothinternal sidewall slope drain

Pipe diameter: 300 and 375mm Smooth internal sidewall: n = 0.01

Pipe discharge (L/s)Pipeslope(X:1) 30 40 50 60 70 80 100 120 140 160 180 200 220

10 150 150 150 150 150 150 200 200 200 200 200 300 300

8 150 150 150 150 150 150 200 200 200 200 300 300 300

7 150 150 150 150 150 150 200 200 200 300 300 300 300

6 150 150 150 150 150 200 200 200 300 300 300 300 300

5 150 150 150 150 200 200 200 200 300 300 300 300 300

4 150 150 150 200 200 200 200 300 300 300 300 300 300

3 150 150 200 200 200 200 300 300 300 300 300 300 300

2 150 200 200 200 200 300 300 300 300 300 400 400 400

1 200 200 300 300 300 300 300 400 400 400 400 400 400

L [1]

1.1 1.2 1.5 1.5 1.5 1.5 1.7 2.0 2.0 2.0 2.1 2.1 2.5

[1] Recommended minimum length (m) of rock pad outlet structure.

Table 3 – Mean rock size (mm) and length (m) of rock pad outlet structure for roughinternal sidewall slope drain

Pipe diameter: 300 and 375mm Rough internal sidewall: n = 0.03

Pipe discharge (L/s)Pipeslope(X:1) 30 40 50 60 70 80 100 120 140 160 180 200 220

10 150 150 150 150 150 150 150 150 150 150 150 150 150

8 150 150 150 150 150 150 150 150 150 150 150 150 150

7 150 150 150 150 150 150 150 150 150 150 150 150 150

6 150 150 150 150 150 150 150 150 150 150 150 150 150

5 150 150 150 150 150 150 150 150 150 150 150 150 150

4 150 150 150 150 150 150 150 150 150 150 150 150 200

3 150 150 150 150 150 150 150 150 150 150 200 200 200

2 150 150 150 150 150 150 150 150 200 200 200 200 200

1 150 150 150 150 150 150 200 200 200 200 300 300 300

L [1]

1.6 1.8 1.9 2.1 2.2 2.3 2.5 2.6 2.8 2.9 3.1 3.2 3.3

[1] Recommended minimum length (m) of rock pad outlet structure.

Technical Note – Development of Tables 2 and 3

Many of the rock sizing charts traditionally presented for the design outlet structures canattribute their origins to the published work of Bohan (1970). This research work was based onlow gradient flow conditions where the pipe is flowing full just upstream of the outlet, and duringlow tailwater conditions, the flow passed through critical depth at or near the outlet of the pipe.Such flow conditions are not consistent with the high-velocity, partial-full flow expected at thebase of a slope drain.

The rock sizes and pad lengths presented in Tables 2 and 3 have been determined by firstlydetermining the partial-full, supercritical flow velocity expected at the base of a slope drain for agiven discharge, internal pipe roughness, and slope gradient. Secondly an equivalent pipediameter was determined that would have a full-pipe discharge and velocity equivalent to thatdetermined above. Using this equivalent pipe diameter and actual discharge velocity, the designcharts presented by Bohan for low tailwater conditions were used to determine the requiredmean rock size and length of rock protection. The rock sizes where then rounded up to thenearest 100mm rock size, with a minimum rock size set as 150mm.



Figure 1 shows the typical layout of solid wall, flexible pipe, slope drains. These pipes areusually available in sizes of 300 and 375mm. Larger diameter, steel wall pipes (Photo 2) canalso be used.

Figure 1 – Slope drain formed from flexible PVC pipe

Figure 2 and Photo 3 show examples of lay-flat pipes, which can also be used as slope drains.

Figure 2 – Slope drain formed from lay-flat pipe

Design example:

Design a slope drain to carry a flow rate of 100L/s down a 1 in 4 slope.

Solution:

Choose a 500mm high earth embankment to collect and direct stormwater runoff towards thedrop pipe/s. Choosing a 300mm pipe and allowing 300mm freeboard, the maximum upstreamwater level (H) relative to the pipe invert would be 500 - 300 = 200mm. From Table 1 the flowcapacity for a 300mm pipe with H = 0.2m is 36L/s. Therefore, three pipes will be required totake the required flow rate of 100L/s.

Also, if we assume a rough internal wall PVC pipe, Table 3 indicates a rock pad outlet structurewith mean rock of 150mm, a length of 1.8m, and a depth of rock protection of at least 225mm.



Photo 3 – Lay-flat pipe Photo 4 – Slope drains (right) used as anoutlet structure for a sediment trap

Photo 5 – Inlet sediment trap Photo 6 – Flow diversion bank

Photo 7 – Pipe directing flow to asediment basin

Photo 8 – Outlet sediment trap

Photo 9 – Inappropriate flow release Photo 10 – Inappropriate flow release



Description

Slope drains (also known as Drop Pipes)consist of a flexible, prefabricated, solid-wall or lay-flat pipe, anchored to the side ofan embankment, with a stabilised inlet andoutlet (Outlet Structure).

Flow Diversion Banks are normally used todirect water to the slope drain.

Purpose

Typically used to:

• transportation of concentrated flowdown embankments usually greaterthan 3m in height;

• diversion of “clean” water around awork site;

• movement of stormwater down newlyformed earth embankments prior toinstallation of the permanent drainagesystem.

Limitations

Up-slope topography must allow collectionof surface water at the pipe inlet withoutcausing traffic safety (flooding) problems orflow bypassing.

Usually only economical for low flows.Chutes are preferred in high flow situations.

Commercially available flexible pipes areusually limited to around 300 to 375mmdiameter.

Advantages

Very effective for the temporary diversion ofwater through bushland where sitedisturbance is to be minimised.

Economical for low flows and high, irregulardrops.

Can be relocated with relative ease.

The pipes are generally reusable.

Disadvantages

High rise of theft or vandalism when used insome urban areas.

Pipe entrance may be subject to blockageby sediment and debris.

Wash-outs during severe storms.

Only suitable as a temporary structure.


Slope drains must be adequately size toavoid flow bypassing (wash-outs).

Slope Drains must be securely anchoreddown the slope to avoid movement.

Trash racks/bars may need to beconsidered at the entrance of the pipe toavoid debris blockage.

Soil around the inlet must be wellcompacted and stabilised.

Most outlets require an energy dissipatersuch as a rock pad.

Location

Located at regular intervals along the roadembankment where runoff can successfullycollect and enter the pipe.

Site Inspection

Check for adequate freeboard at the inlet.

Check for obstructions or damage at theinlet.

Check for watertightness.

Check for excessive sedimentation at theinlet and outlet.

Check for excessive erosion at the outlet.



Materials (Outlet rock pads)

• Rock: hard, angular, durable, weatherresistant and evenly graded with 50%by weight larger than the specifiednominal rock size and sufficient smallrock to fill the voids between the largerrock. The diameter of the largest rocksize should be no larger than 1.5 timesthe nominal rock size. Specific gravityto be at least 2.5.

• Geotextile fabric: heavy-duty, needle-punched, non-woven filter cloth,minimum bidim A24 or equivalent.

Installation

1. Refer to approved plans for locationand installation details. If there arequestions or problems with the location,extent, or method of installation contactthe engineer or responsible on-siteofficer for assistance.

2. Place pipes on undisturbed soil or well-compacted fill at locations shown on theapproved plan.

3. Excavate suitable bedding for the slopedrain inlet. If it is necessary to cutthrough a flow diversion bank at the topof the slope, then limit the disturbanceto the absolute minimum.

4. Slightly grade (minimum 3% slope inthe direction of flow) the section of pipeup-slope of the crest of theembankment.

5. Re-establish the flow diversion bank soas to firmly anchor the inlet of the slopedrain. Firmly hand-tamp the soil underand around the inlet section of pipe inlifts not to exceed 100mm. Ifnecessary, drive stakes on both sidesof the inlet a minimum of 450mm intothe ground. Secure the pipe to thestakes with wire or cord.

6. Ensure that the embankment (flowdiversion bank) formed over the inlet ofthe pipe has minimum dimensions of500mm height, 300mm clearance overpipe obvert, and maximum 2:1(H:V)side slopes.

7. Extend the slope drain down the slopeensuring that it is placed perpendicularto the slope contours.

8. Ensure that all pipe connections arewatertight.

9. Ensure that all fill material is well-compacted.

10. Securely fasten the pipe down theslope with anchors spaced no morethan 3m apart.

11. Extend the pipe beyond the toe of theslope and adequately protect the outletof the pipe from erosion. Do not directthe outlet to a fill slope or unstableground.

12. Construct a stabilised outlet structure,such as a rock pad (as detailed on theplans), to control soil scour.

13. Immediately stabilise all disturbedareas following installation of the slopedrain.

Maintenance

1. While construction works continue onthe site, inspect all slope drains prior toforecast rainfall, daily during extendedperiods of rainfall, after significantrunoff producing rainfall, and on aweekly basis.

2. Inspect for:

• soil erosion at the inlet and outlet;

• sediment or debris blockage of the inlet;

• water damage cause by leakage formpipe joints;

• damage or slumping of the associatedinlet control flow diversion bank;

• leakage of water through the flowdiversion bank along the outer surfaceof the pipe.

3. Promptly make all necessary repairs.

Removal

1. Slope drains should be removed onlywhen an alternative, stable, drainagepath is available.

2. Remove all materials and collectedsediment and dispose of in a suitablemanner that will not cause an erosionor pollution hazard.


4. Stabilise the area as specified in theapproved plan.



(c) Alternative designs

An alternative rock pad design is presented in Figure 6. This concept utilises the moderatespeed properties of a traditional rock pad with the low maintenance properties of a vibrationgrid. The intent here is to extend the design life of a rock pad by establishing a large sedimentstorage volume beneath the rocks.

Further alternatives are discussed in the separate fact sheet for Vibration Grids. On-site trials ofthis and other designs are required to develop the optimum high-efficiency, low-maintenancedesign.

Figure 6 – Alternative low-maintenance rock pad design(concept still under development)

(d) Pedestrian safety

The rock pad must be made safe for expected pedestrian traffic, especially if the rock padcrosses an open footpath (Figure 1). This is usually done by covering large rocks (100–150mm)with 25–50mm aggregate/gravel.

Such measures are only required in circumstances where potential risks to pedestrian areconsidered to exit.

(e) Maintenance

All stabilised construction exits require regular maintenance, including sediment removal, androck replacement.

Photo 9 – Heavy sedimentation of rockpad adjacent a vibration grid

Photo 10 – Heavy sedimentation shouldnot be allowed to occur at construction

exits prior to their maintenance



Description

‘Construction exit’ is a general termreferring to rock pads, vibration grids andwash bays.

Rock pads consist of a short length ofroadway covered with crushed rock.

Rock pads have been referred to under avariety of names including stabilisedconstruction exits, entry/exit pads, gravelpads and rumble pads. The term ‘rumblepad’ is a misnomer because few rock padsare able to significantly rumble or vibrateheavy trucks.

Purpose

Rock pads on building sites primarily act asall-weather parking surfaces that aim tominimise the initial placement of dirt andmud on tyres.

Rock pads on construction sites primarilyact as sediment traps aiming to strip fromvehicle tyres any dirt and mud generatedfrom soil disturbances elsewhere on thesite.

Stabilised construction exits are one of thefew sediment control measures that arerequired during both wet and dry weather.

Limitations

A ‘supplementary’ sediment trap typically oflow sediment trapping efficiency.

Sediment trapping efficiency is generallyrelated to the soil type and weatherconditions.

Rock pads can be ineffective if the soils arehighly cohesive (sticky) clays.

Advantages

A sediment control technique that generallydoes not interfere with constructionactivities.

Various alternative designs exist that canbe adapted to the site conditions.

On building site the rock pad can act as anall weather parking area.

Disadvantages

Requires regular maintenance, includingplacement or addition of more rock.

It is common for these systems toexperience less than ideal maintenance.

Rock pads can interfere with roadconstruction if located at the permanent siteentry point.

Location

Located at site entry points, or wherevehicles pass from unsealed roads ontosealed roads.

It is important to locate the construction exitsuch that vehicles cannot bypass the rockpad when exiting the site.

Avoid placing site rock pads on steepgrades.

The construction site entry/exit point maynot necessarily be located at the permanentsite entry/exit point.

Common Problems

Rock size too small, or not uniform ingrading, resulting in rapid sedimentblockage.

‘Gravel’ used instead of uniformly-sized,crushed rock.

Sediment not regularly removed from therock pad.

Drainage not adequately controlled at theentry/exit point, allowing sediment-ladenstormwater runoff to wash onto publicroads.


If the entry/exit point is down-slope of thesoil disturbance or parts of the access road,then the rock pad must contain a flowcontrol berm to deflect sediment-ladenrunoff to an adjacent sediment trap.

The rock pad must not become a source ofsediment runoff onto the adjacent road.

It is noted that even entry only points canstill allow sediment to be washed off site.Thus adequate sediment and drainagecontrols will be required.

A square-edged shovel and large stiff-bristled broom must be available on-site formaintenance.

Site Inspection

Check for excessive sedimentation on therock pad.

Check for sediment tacked onto the road.

Check if an additional layer of rock isrequired.

Ensure surface runoff is directed to asuitable sediment trap.



Materials

• Rock: well graded, hard, angular,erosion resistant rock, nominaldiameter of 50mm to 75mm (smalldisturbances) or 100 to 150mm (largedisturbances). All reasonable measuresmust be taken to obtain rock of nearuniform size.

• Footpath stabilising aggregate: 25 to50mm gravel or aggregate.

• Geotextile fabric: heavy-duty, needle-punched, non-woven filter cloth (bidimA34 or equivalent).

Installation

1. Refer to approved plans for locationand dimensional details. If there arequestions or problems with the location,dimensions, or method of installation,contact the engineer or responsible on-site officer for assistance.

2. Clear the location of the rock pad,removing stumps, roots and othervegetation to provide a firm foundationso that the rock is not pressed into softground. Clear sufficient width to allowpassage of large vehicles, but clearonly that necessary for the exit. Do notclear adjacent areas until the requirederosion and sediment control devicesare in place.

3. If the exposed soil is soft, plastic orclayey, place a sub-base of crushedrock or a layer of heavy-duty filter clothto provide a firm foundation.

4. Place the rock pad forming a minimum200mm layer of clean, open-void rock.

5. If the associated construction site is up-slope of the rock pad, thus causingstormwater runoff to flow towards therock pad, then form a minimum 300mmhigh flow control berm across the rockpad to divert such runoff to a suitablesediment trap.

6. The length of the rock pad should be atleast 15m where practicable, and aswide as the full width of the entry or exitand at least 3m. The rock pad shouldcommence at the edge of the off-sitesealed road or pavement.

7. Flare the end of the rock pad where itmeets the pavement so that the wheelsof turning vehicles do not travel overunprotected soil.

8. If the footpath is open to pedestrianmovement, then cover the coarse rockwith fine aggregate or gravel, orotherwise take whatever measures areneeded to make the area safe.

Maintenance

1. Inspect all site entry and exit pointsprior to forecast rain, daily duringextended periods of rainfall, afterrunoff-producing rainfall, or otherwise atfortnightly intervals.

2. If sand, soil, sediment or mud is trackedor washed onto the adjacent sealedroadway, then such must be physicallyremoved, first using a square-edgedshovel, and then a stiff-bristled broom,and then by a mechanical vacuum unit,if available.

3. If necessary for safety reasons, theroadway shall only be washed cleanafter all reasonable efforts have beentaken to shovel and sweep the materialfrom the roadway.

4. When the voids between the rockbecomes filled with material and theeffectiveness of the rock pad is reducedto a point where sediment is beingtracked off the site, a new 100mm layerof rock must be added and/or the rockpad must be extended.

5. Ensure any associated drainage controlmeasures (e.g. flow control berm) aremaintained in accordance with theirdesired operational condition.

6. Dispose of sediment and debris in amanner that will not create an erosionor pollution hazard.

Removal

1. The rock pad should be removed onlyafter they are no longer needed as asediment trap.

2. Remove materials and collectedsediment and dispose of in a suitablemanner that will not cause an erosionor pollution hazard.

3. Re-grade and stabilise the disturbedground as necessary to minimise theerosion hazard.


conceptual erosion and sediment control plan and stormwater quality management plan ... · 2011. 5....

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