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Farmhill Properties (Pty) Ltd

Feasibility design of the raising of

Farmhill Dam

Report Nr. JB2025-01

Final2019-01-30

Prepared by:

Jan Brink Pr Eng20 Manor RdKingswood Golf EstateGeorge

Executive Summary

Farmhill Dam is a small existing dam owned by Farmhill Properties (Pty) Ltd. The owner plans to raise thedam wall to increase its storage and yield. The existing earthfill dam wall is approximately 5 m high and it willbe raised to a final height of approximately 12 m.

The dam was neglected by the previous owner and the embankment was overtopped and suffered severedamage. The new owner repaired the embankment and excavated a new spillway on the left flank.

This report advises the owner on the engineering and technical requirements for the project, in terms of thetechnical scope of works, regulatory requirements and recommendations on further investigations anddesign.

The dam is approximately 500 m upstream of the Seven Passes provincial road. Due to this, it will beclassified as a Category 2 dam with a “Significant” hazard rating, even if it is lower than the conventional12 m guideline for Category 2 dams. An Approved Professional Person will therefore have to be employed tooversee the design and construction of the dam.

The feasibility design concluded that a new uncontrolled bywash spillway should be constructed on the leftflank. This is the location of the repaired existing spillway as well. The existing dam has no outlet pipe. A newoutlet pipe can only be installed at a high level and will not contribute significantly to the draw down capacityduring an emergency. Installation is therefore not recommended.

No further studies are required for the feasibility design. A geotechnical survey of the site and material will beconducted as part of the detail design phases. The geotechnical investigation will confirm whether sufficientmaterial is available at the borrow areas identified by the owner and at what slopes the embankment can beconstructed safely.

A catchment and dam yield analysis can add value to the project by optimising the storage capacity andheight of the dam.

JB2025-01 - Farmhill Dam – Feasibility Design 2

ContentsExecutive Summary.........................................................................................................................2

Abbreviations and Acronyms............................................................................................................4

1 Introduction...................................................................................................................................51.1 Background............................................................................................................................................ 51.2 Scope of Report..................................................................................................................................... 5

2 Summary of information................................................................................................................5

3 Dam safety legislation...................................................................................................................6

4 Hydrology......................................................................................................................................74.1 Flood Hydrology..................................................................................................................................... 74.2 Catchment Yield..................................................................................................................................... 7

5 Spillway Design.............................................................................................................................75.1 Flow cases and Freeboard.................................................................................................................... 75.2 Spillway Options.................................................................................................................................... 75.3 Return Channel...................................................................................................................................... 8

6 Embankment.................................................................................................................................86.1 Embankment description....................................................................................................................... 86.2 Materials................................................................................................................................................ 96.3 Geotechnical investigation................................................................................................................... 10

7 Outlet pipe...................................................................................................................................10

8 Construction arrangements, Control and Monitoring...................................................................108.1 Site arrangements............................................................................................................................... 108.2 Contracting........................................................................................................................................... 118.3 Specifications and monitoring..............................................................................................................11

9 Further studies.............................................................................................................................11

10 References................................................................................................................................12

Appendix A – Hydrology Calculations.............................................................................................13

Appendix B – Spillway Calculations................................................................................................14

Appendix C – Drawings..................................................................................................................15


Abbreviations and Acronyms

APP .......................................................................................................................APPROVED PROFESSIONAL PERSON

c........................................................................................................................................................................... COHESION

DSE ......................................................................................................................................... DAM SAFETY EVALUATION

DSO ................................................................................................................................................. DAM SAFETY OFFICE

DWS ........................................................................................................... DEPARTMENT OF WATER AND SANITATION

EPP.........................................................................................................................EMERGENCY PREPAREDNESS PLAN

FSL .................................................................................................................................................... FULL SUPPLY LEVEL

FOS ................................................................................................................................................... FACTOR OF SAFETY

FSC ..............................................................................................................................................FULL SUPPLY CAPACITY

HRU ............................................................................................................................ HYDROLOGICAL RESEARCH UNIT

MAP ................................................................................................................................. MEAN ANNUAL PRECIPITATION

NOC ............................................................................................................................................ NON-OVERSPILL CREST

O&M............................................................................................................................... OPERATION AND MAINTENANCE

RBL ........................................................................................................................................................ RIVER BED LEVEL

RDD .................................................................................................................... RECOMMENDED DESIGN DISCHARGE

RDF .............................................................................................................................. RECOMMENDED DESIGN FLOOD

REGULATIONS.....................................................DAM SAFETY REGULATIONS IN TERMS OF NATIONAL WATER ACT

RL ............................................................................................................................................................ REDUCED LEVEL

RMF .................................................................................................................................... REGIONAL MAXIMUM FLOOD

SANCOLD ....................................................................... SOUTH AFRICAN NATIONAL COMMITTEE ON LARGE DAMS

SED ............................................................................................................................SAFETY EVALUATION DISCHARGE

SEF ..................................................................................................................................... SAFETY EVALUATION FLOOD

tc............................................................................................................................................... TIME OF CONCENTRATION

ø ................................................................................................................................................................ PIPE DIAMETER

Φ ....................................................................................................................................................... ANGLE OF FRICTION


1 INTRODUCTION

1.1 BACKGROUND

Farmhill Dam is a small existing dam owned by Farmhill Properties (Pty) Ltd. The owner intends toraise the dam wall to increase its storage and yield. The existing earthfill dam wall is approximately5 m high and it will be raised to a final height of approximately 12 m.

The owner purchased the farm and dam recently. No previous design and construction information isavailable. The dam was neglected by the previous owner and the embankment washed away partly,likely because the spillway was too small. The new owner commenced with repairs to theembankment. This included the excavation of a new spillway on the left flank, stabilising theembankment and levelling the embankment crest.

This report advises the owner on the engineering and technical requirements for the project, in termsof the technical scope of works, regulatory requirements and recommendations on furtherinvestigations and designs.

1.2 SCOPE OF REPORT

In October 2018 the owner appointed Jan Brink Pr. Eng as engineer to complete a feasibility design forthe raising of the dam. The scope of the feasibility design was agreed to include the following:

• Conduct a site inspection and discussion on the requirements for the dam.

• Engaging with other specialists involved to gather all available information that may impact onthe design.

• Discussions with the owner’s preferred contractor to determine available experience andequipment and how the design may have to adapt to suit.

• Compile inception-level calculations and -design of the following:

◦ Layout and footprint of the embankment

◦ Design- and safety flood magnitudes

◦ Spillway options

◦ Outlet requirements and options

• Advise on the scope of further investigations, specifically geotechnical, that should be includedin the detail design phases.

• Engage with the Dam Safety Office to verify the classification of the dam

• Compile an Inception Design Report

2 SUMMARY OF INFORMATION

The following table summarises the data that is recorded in the Dam Safety Office’s database. Thetable should be populated with the correct information in future reports on the dam design.

Name of dam Farmhill Dam

Departmental file reference for dam 12/2/K401/… (number will be assigned by DSO)

Designer/Approve Professional Person Jan Brink Pr Eng (APP approval only at detail design-stage)

Name of Owner Farmhill Properties (Pty) Ltd


Representative of Owner Mr M Rubin

Address of Owner PO Box 100, Hoekwil, 6538

Tel. 044 850 1862

Email [email protected]

Nearest Town (distance) Karatara, Knysna Municipality (2 km)

Province Western Cape

Latitude 33°55'27" S Longitude 22°49'23" E

Wall type Earthfill Wall height t.b.c.

Storage capacity t.b.c. Completion date t.b.c.

Crest length t.b.c. Crest width t.b.c.

Contractor t.b.c.

3 DAM SAFETY LEGISLATION

The raised dam will be higher than 5 m and store more than 50 000 m³. It will therefore be registeredas a dam with a safety risk. All design, construction and operations must comply with the Dam SafetyRegulations (“the Regulations”, Government Notice R.139 of February 2012.)

The owner initially indicated that the dam will likely be less than 12 m high. Generally dams of this sizewill be classified as “Small”. The proximity to the nearby provincial road will, however, result in ahazard potential classification of “Significant”, resulting in a Category 2 classification. There istherefore no motivation to limit the final height to less than the 12 m level generally applied toCategory 1 dams.

Once the project proceeds to detail design, the Regulations require that an Approved ProfessionalPerson (APP) be appointed to oversee the design and construction of the dam. This is not required forthe feasibility phase. It is recommended that the APP be appointed as soon as the decision to proceedwith the project is made.


Figure 1: Location of Farmhill Dam

Farmhill Dam

Karatara

Karatara Rd to N2 (15 km)

Seven Passes Rd to Hoekwil (26 km)

4 HYDROLOGY

4.1 FLOOD HYDROLOGY

Two extreme floods are calculated to determine the required capacity of the spillway. TheRecommended Design Flood (RDF) is used for the design of the spillway and the Safety EvaluationFlood (SEF) is the extreme conditions under which the dam should be on the brink of failure, butwithout actually failing.

The SANCOLD guidelines (SANCOLD, 1991) recommends using the regional maximum flood (RMF)calculated with the method explained the TR137 (Kovacs, 1987) as SEF. The catchment area wasmeasured as 3,2 km². This is too small to use the TR137-method and a simple rational-method wasused. A probable maximum flood (PMF) of 228 m³/s was calculated. The same rational calculation wasused to calculate a 1:100-year flood of 20 m³/s. The calculations are attached as Appendix A. Thecalculation parameters are summarised in the table below.

Recurrence Interval Flow Rate

1:10 7

1:50 15

1:100 - RDF 20

1:200 27

PMF - SEF 228

4.2 CATCHMENT YIELD

The yield and annual flow pattern from the catchment has not been studied. The wall height andstorage capacity was selected by the owner was based on the shape of the site and assumes that theyield is much larger than the dam’s storage capacity. The storage capacity does not have a directimpact on the sizing of the spillway and safety against floods.

As part of the detail design, a catchment yield analysis and dam balance may be done to optimise thestorage capacity.

5 SPILLWAY DESIGN

5.1 FLOW CASES AND FREEBOARD

The spillway must be designed to discharge extreme floods. For the purposes of this report, the SEFand RDF are used as-is. In the further design phases the attenuation of these floods may beconsidered to optimise the spillway capacity.

During the SEF, the upstream water level can be at the non-overspill crest (NOC) level of the dam. Forthe RDF case some freeboard must be allowed to accommodate wave action from e.g. wind over thewater surface, flood surges and earthquake- or landslide-induced waves. An allowance of 0,5 mfreeboard is considered adequate for this feasibility phase.

5.2 SPILLWAY OPTIONS

The spillway selection is dictated by the required discharge capacity, site layout, material availabilityand founding conditions.

The existing embankment disqualifies central concrete spillway options, leaving the two flanks. Theright flank is slightly steeper and also the preferred access route for operations, maintenance and


services to the dam. The left flank is therefore the preferred location for the spillway. This is also thelocation of the existing spillway.

The spillway structure must be excavated into the flank. The excavation depth will depend on thedepth to competent rock. The rock must either be sufficiently strong to not erode during regular spillingor excavated further and built up in concrete again to the desired full supply level (FSL). Even on rocka low concrete sill should be constructed to form a smooth invert at the correct level. This willcontribute to smooth flow conditions and increase the discharge capacity of the structure.

If rock is found to be too deep, a concrete structure might have to be constructed. It will likely take theshape of a thin concrete wall, supported by buttresses.

5.3 RETURN CHANNEL

The return channel conveys water back to the river. Its capacity must be similar to the capacity of thespillway crest. Rapid flow rates in the channel have a high erosion potential. Water must therefore beguided away from the dam embankment. The river bends to the left shortly downstream from the dam.The channel may therefore be aligned to lead perpendicularly away from the dam and straight to theriver. Again, the rock condition will dictate whether any protection of the channel will be required.

6 EMBANKMENT

6.1 EMBANKMENT DESCRIPTION

The existing embankment is approximately 5 m high. It will be contained within the raisedembankment and form the upstream toe of the structure. A ±10 m wide berm was placed against thedownstream toe as part of the rehabilitation works (Figure 3). The berm may be used to form the baseof the (then planned) raising.

The raised embankment will be approximately 12 m high, with upstream slope 1:3 to 1:3,5 anddownstream slope 1:2 to 1:2,5. The slopes will be optimised with slope stability analyses, based onactual material properties. The top width of the embankment will be 4 m and capped with a 150 mmthick gravel layer.

A cut-off trench was excavated below the new berm. To protect against internal erosion and excessiveseepage losses, it is very important that the core of the embankment is water tight, both through thecore material itself and the contact with the foundation. According to the owner the cut-off wasexcavated to rock. Some photographic evidence is available to support this (See Figure 2 below).Methods to determine whether the core was constructed to acceptable specifications will have to bedevised in cooperation with a geotechnical specialist. Methods such as dynamic cone penetrator tests,calibrated against nuclear in situ density tests or laboratory results may be considered.


Figure 2: Construction of cut-off downstream of embankment

6.2 MATERIALS

The raising will be constructed with the material excavated from the spillway and -return channel and aborrow pit in the dam basin. The borrow area was previously investigated by the owner and used forthe repair works to the embankment. The material appears to comply with the clayey sand-requirement for water tight zones. This material should be used for a thick upstream zone in the raisedembankment.

The material from the spillway will likely consist of fine soils and partially- to completely weatheredrock in the form of sand, gravel and boulders. The excavated material should be used in adownstream, more porous zone. If the excavated material can be separated further, fine materialshould be placed against the core zone/upstream zone and rougher materials downstream. A porousdownstream zone has the advantage of lowering the phreatic surface in the embankment and negatesthe need for expensive internal filters, a rock toe or a toe drain (although the latter cannot be ruled out


Figure 3: Berm viewed from right flank

entirely.) The larger gravel and boulders can also be used to provide erosion protection on theupstream slope.

The berm was constructed with the clayey material, rendering it largely impermeable. This will preventa porous zone on top from drawing down the phreatic surface low enough. This may require a flatterdownstream slope, the inclusion of formal filters, or reshaping some of the downstream material. Thefinal cross-section will be determined by the detail design.

6.3 GEOTECHNICAL INVESTIGATION

To optimise the design of the embankment and identify as many of the possible underground risks, ageotechnical investigation of the site must be conducted in the detail design phase. Setting out of thescope for the investigation was included in the scope of this report to inform the client.

The scope of the investigation must include the following:

• Review of available geotechnical information on the area.

• Site inspection to assess general site conditions and general geotechnical risks.

• Subsurface investigations from test pits to determine e.g. local rock and soil types, ground

water table and borrow area materials.

• Soil sampling for embankment materials.

• In situ and laboratory testing of potential construction materials. Testing of factors such as

Atterberg limits, sheer strength parameters and others as advised by specialist.

• Testing of the existing embankment and new berm to confirm the condition of the previous

works, specifically the extent and density of the cut-off core.

• Slope stability analyses to confirm optimum embankment slopes.

• Reporting on findings and recommendations.

7 OUTLET PIPE

The existing dam does not have any outlets. Generally outlets with sufficient capacity to draw downthe water level in an emergency are provided.

It is not desirable to install new outlet pipes through an existing embankment dam, as it would disturbthe integrity of the earthfill. This will increase the risk of failure, rather than contribute to its safety. It ispossible to install an outlet pipe at the existing full supply level. The intake level will be relatively highand therefore both its discharge capacity and lowest draw-down level will not contribute significantlyduring an emergency.

The dam is located at the bottom of farm and water will be abstracted with suction pumps for irrigationor any other demands.

An outlet pipe will therefore not contribute significantly to dam safety an is not required for operations.The benefit of an outlet pipe does not warrant the costs of providing a reliable system.

8 CONSTRUCTION ARRANGEMENTS, CONTROL AND MONITORING

8.1 SITE ARRANGEMENTS

The main access to the site is from the right flank, across the farm. There is sufficient clear area forplant, site office and work area.


Care will have to be taken when moving heavy equipment to the left flank for the excavation of thespillway. Heavy machines may over-compact the top embankment layers. This can be solved byfinding an alternative access via the left flank, using a sacrificial layer on the embankment, orreworking affected material.

8.2 CONTRACTING

A standard form of contract for civil engineering works, such as the latest version of the South AfricanInstitution of Civil Engineers’ General Conditions of Contract (GCC, 2015) can be used for the project.This document is well priced and manages the risk to both Employer and Contractor effectively.

8.3 SPECIFICATIONS AND MONITORING

A set of construction specifications based on the SANS 1200 range of documents should be used. Allcontractors with suitable expertise in dam building will be familiar with the documents. This will simplifycompliance and control.

The level of independent quality control by an engineer’s representative can be negotiated and agreedto between the Employer and Contractor. A project of this scale does not warrant a full time site agent(or “Employer’s Agent’s Representative” per GCC 2015). Critical aspects of the construction that willrequire careful monitoring must be identified by the Engineer and then highlighted in the Contractor’sprogramme to allow the Engineer (or “Employer’s Agent”) to monitor these activities physically. Theseitems may include filter placement, outlet pipe founding and encasement reinforcing, etc. Othermonitoring results may be submitted by the Contractor at agreed intervals or at milestones.

9 FURTHER STUDIES

The geotechnical investigation must be completed as part of the next phase of the design, asdiscussed in paragraph 6.3.

It is recommended that a hydrologist be employed to verify the yield from the dam’s catchment. A moreaccurate flow pattern will allow optimisation of the required storage capacity and therefore the size andcost of the dam. This is a recommendation to the owner and does not impact on the safety of the dam.It can be completed during the detail design-phase.


10 REFERENCES

[1] SAICE (2015), General Conditions of Contract for Construction Works, Third Edition, South

African Institution of Civil Engineering, Midrand, 2015.

[2] SANS 1200, South African Bureau of Standards, Standardized Specifications for Civil

Engineering Construction, SABS, Pretoria

[3] SANCOLD (1991) Safety Evaluation of Dams: Guidelines on Safety in Relation to Floods. Report

No. 4, December 1991. South African National Committee on Large Dams, Pretoria.

[4] SANCOLD (2011) Guidelines on Freeboard for Dams: Volume II. South African National Committee

on Large Dams, Pretoria.


Appendix A – Hydrology Calculations


APPENDIX A

RETURN PERIOD ADJUSTMENT FACTOR

RETURN PERIOD RURAL URBAN [ 0.87*L^3/H]]^0.385

T (years)0.53

2 0.32

5 0.50

GENERAL DATA TOPOGRAPHY AND GEOLOGY 10 0.61 LIGHTNING DENSITY

PROJECT NO. JB2016 3.2 20 0.71 4

RIVER / AREA No. Farmhill LONGEST WATER COURSE (km) 3.65 ### 50 0.83

ANALYSIS BY JB HEIGHT DIFFERENCE (m) 164 ### 100 0.92

DATE 2018-12-03 DOLOMITIC AREA (%) 0 200 1.00

5

AREA WEIGHTING FACTORS % MAP (mm)

URBAN 0 RURAL 100 LAKES 0 300RAINFALL

RETURN PERIOD (years) 5 10 20 50 100 200 PMF

PHYSICAL CHARACTERISTICS RECOMM. RUNOFF COEFF. C POINT RAINFALL DEPTH (mm) 18 23 29 37 46 58 200

STEEPNESS % OF AREAMAP

'C' POINT INTENSITY (mm/h) 35 44 54 70 87 108 376

< 600 600-900 >900 AREA REDUCTION FACTOR % 87 87 87 87 87 87 87

< 3 % 0 0.01 0.03 0.05 0.01 0.000 30 38 47 61 75 94 327

3 to 10% 5 0.06 0.08 0.11 0.06 0.003

10 to 30% 30 0.12 0.16 0.20 0.12 0.036AREA WEIGHTED RUNOFF COEFFICIENT

30 to 50% 60 0.22 0.26 0.30 0.22 0.132

> 50% 5 0.26 0.30 0.34 0.26 0.013 RETURN PERIOD (years) 5 10 20 50 100 200

0.184 RURAL 0.16 0.20 0.23 0.27 0.30 0.33 0.78

URBAN 0.00 0.00 0.00 0.00 0.00 0.00 0.00

PHYSICAL CHARACTERISTICS RECOMM. RUNOFF COEFF. C LAKES 0.00 0.00 0.00 0.00 0.00 0.00 0.00

PERMEABILITY % OF AREAMAP

'C' 0.16 0.20 0.23 0.27 0.30 0.33 0.78

< 600 600-900 >900

VERY PERMEABLE 10 0.03 0.04 0.05 0.03 0.003

PERMEABLE 55 0.06 0.08 0.10 0.06 0.033

SEMI-PERMEABLE 35 0.12 0.15 0.20 0.12 0.042 RETURN PERIOD (years) 5 10 20 50 100 200

IMPERMEABLE 0 0.21 0.26 0.30 0.21 0.0004 7 10 15 20 27 228

0.078

PHYSICAL CHARACTERISTICS RECOMM. RUNOFF COEFF. C

VEGETATION % OF AREAMAP

'C' < 600 600-900 >900

DENSE BUSH, FOREST 15.34 0.03 0.04 0.05 0.03 0.005

CULTIVATED LAND 84.66 0.07 0.11 0.15 0.07 0.059

GRASS LAND 0.00 0.17 0.21 0.25 0.17 0.000

BARE SURFACE 0.00 0.26 0.28 0.30 0.26 0.000

0.064

PHYSICAL CHARACTERISTICS RECOMM. RUNOFF COEFF. C

OCCUPATION % OF AREA 'C' CV

LAWNS, PARKS

SANDY, FLAT < 2 % 0.00 0.05 to 0.10 0.08 0.00

SANDY, STEEP > 7 % 0.00 0.15 to 0.20 0.18 0.00

HEAVY SOIL, FLAT < 2 % 0.00 0.13 to 0.17 0.15 0.00

HEAVY SOIL, STEEP < 7 % 0.00 0.25 to 0.35 0.30 0.00

RESIDENTIAL

SINGLE DWELLING AREA 0.00 0.30 to 0.50 0.40 0.00

FLATS 0.00 0.50 to 0.70 0.60 0.00

INDUSTRIAL

LIGHT INDUSTRIES 0.00 0.50 to 0.80 0.65 0.00

HEAVY INDUSTRIES 0.00 0.50 to 0.90 0.70 0.00

BUSINESS

DOWNTOWN 0.00 0.70 to 0.95 0.83 0.00

NEIGHBOURHOOD 0.00 0.50 to 0.70 0.60 0.00

NEIGHBOURHOOD

STREETS 0.00 0.70 to 0.95 0.83 0.00

0.00

FLOOD FREQUENCY ANALYSISRATIONAL METHOD

(CALCULATION SHEET)

TIME OF CON. Tc (hr)

fT

For return periods equal or greater

than 50 years CT = 1.00

CATCHMENT AREA (km2)

FRANCOU - RODIERREGIONAL COEFF.

CT = fT( CY + CP + CV)

PHYSICAL CHARACTERISTICS AND RECOMMENDED VALUES OF RUNOFFCOEFFECIENTS (RURAL)

POINT RAINFALL FOR TIME OF CONCENTRATION tC

CY

AVERAGE INTENSITY (mm/h) IT

CS =

CP

AREA WEIGHTED AVERAGE CT

PEAK DISCHARGE(m3/ s)

QT = 0.278 CT IT ACP =

CV

CV =

PHYSICAL CHARACTERISTICS AND RECOMMENDED VALUES OF RUNOFF COEFFECIENTS (URBAN)

CU =

RECOMMENDED PROCEDURE

1. Locate the site on 1:50 000 or 1:250 000 topographical maps.

2. Determine the following catchment characteristics for the site:

a) Demarcate the catchment boundary on the 1:50 000 topographical maps, or 1:250000 maps if the catchment covers more than four 1:50 000 sheets.

b) Measure the area of the catchment. Subtract areas of significant internal drainage (eg large pans) if any. Use transparent graph paper with 2mm quares. One hundred squares have an equivalent area of one square kilometer on a 1:50 000 scale map. Count the number of squares to determine the area.

c) Produce a longitudinal profile along the longest tributary from the site to the watershed. Use dividers for measuring the main stream length. These should be set at 0.2 km for 1:50000 maps and 1.0 km for 1:250000 maps. When the latter maps are used the length should be multiplied by a factor 1.2 to correct for a loss of resolution.

The distances along the length of stream where the contour lines are crossed should be used to plot the profile. Where waterfalls and rapids are clearly evident as discontinuities in the profile, the profile should be adjusted downwards to eliminate them.

d) Determine the height difference along the equal area and 1085 slopes.

e) Locate the centroid of the catchment site by eye and measure the distance along the main channel length from the site point to a point opposite the centroid.

3. Determine the MAP over the catchment. The catchment MAP is the average of the quartenary catchments within which the catchment of interest is located as shown in the HRU series of publications.

4. Determine whether the catchment is located in the coastal or inland region.

5. Note the presence of any dams upstream of the site.

6. Identify the RMF region in which the site is located and determine the value of the RMF k- factor.

7. Determine the catchment characteristics required for the rational method as listed on this sheet.

8. Add any other comments relevant.

COMMENTS

Appendix B – Spillway Calculations


APPENDIX B

Page 1

BROAD-CRESTED WEIR

Copied results:

Main SW H = 1.000 m H = 1.500 1.000 2.000 2.500 2.500 2.000 1.500 1.000

b = 79.396 m b = 85.684 157.412 55.654 39.822 20.086 28.071 43.218 79.396

g = 9.810 g = 9.810 9.810 9.810 9.810 9.810 9.810 9.810 9.810

μ = 0.327 μ = 0.327 0.327 0.327 0.327 0.327 0.327 0.327 0.327

Q = 115.000 m³/s Q = 228.000 228.000 228.000 228.000 115.000 115.000 115.000 115.000

Target Q = 115.000 m³/s Target Q = 228.000 228.000 228.000 228.000 115.000 115.000 115.000 115.000

0.000 m³/s 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

OGEE Selected for feasibility design:

Copied results:

Main SW H = 2.500 m H = 1.500 1.000 2.000 2.500 2.500 2.000 1.500 1.000

b = 17.407 m b = 56.930 104.587 36.977 26.459 13.345 18.651 28.715 52.752

C = 2.180 μ = 2.180 2.180 2.180 2.180 2.180 2.180 2.180 2.180

Q = 150.000 m³/s Q = 228.000 228.000 228.000 228.000 115.000 115.000 115.000 115.000

Target Q = 150.000 m³/s Target Q = 228.000 228.000 228.000 228.000 115.000 115.000 115.000 115.000

0.000 m³/s 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

H = 1.000 1.500 2.000 2.500

b = 68.807 37.454 24.327 17.407

C = 2.180 2.180 2.180 2.180

Q = 150.000 150.000 150.000 150.000

Target Q = 150.000 150.000 150.000 150.000

0.000 0.000 0.000 0.000

DQ = DQ =

DQ = DQ =

DQ =

PROJECT: FarmhillPROJECT NUMBER: JB2025DATE: 2018-12-05DESIGN: JAB

Q=0.327∗b∗√2∗g∗H3 /2Q=2,18∗b∗H 3 /2

Appendix C – Drawings


TYPICAL EMBANKMENT SECTION

(N.T.S.)

DOWNSTREAM VIEW

LAYOUT

EXISTING BERM

EXISTING NOC

NEW NOC

NEW FULL SUPPLY LEVEL

EXISTING FSL

4,0 (PROV.)2,50

NEW SPILLWAY

CUT-OFF CORE

(ESTIMATE)

NEW NOC

NATURAL SLOPE

(ESTIMATE)

BASIN CONTOURS

(SURVEYED)

SPILLWAY CREST

(FULL SUPPLY LEVEL)

NEW OUTLET PIPE

CUT-OFF CORE

(ESTIMATE)

ALTERNATIVE SPILLWAYLOCATION

EXISTINGEMBANKMENT

25,00 (Ext.)

NOTES:

1. SIZES AND DIMENSIONS BASED ON FEASIBILITY DESIGN-LEVEL CALCULATIONS AND AVAILABLE SURVEYS

2. ALTERNATIVE SPILLWAY POSITION SHOWN ON LAYOUT ONLY

3. DRAWINGS NOT TO SCALE

EXISTING NOC

SITE OFFICE& PLANT

CLAY BORROW PIT

DAM CENTRE LINE

2.5

1

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