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Cassowary Coast Regional Council Master Drainage Study: Mourilyan Reference: R.B18921.017.02.Mourilyan.docx Date: August 2016 Confidential

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Document: R.B18921.017.02.Mourilyan.docx

Title: Cassowary Coast Regional Council Master Drainage Study: Mourilyan

Project Manager: Michael Hughes

Author: Richard Sharpe

Client: Cassowary Coast Regional Council

Client Contact: Justin Fischer

Client Reference:

Synopsis: This report is a master drainage study of Mourilyan within the Cassowary Coast Regional Council Local Government Area. It outlines the drainage infrastructure within the Mourilyan area that may not be operating optimally. It also proposes an infrastructure upgrade priority list.

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Cassowary Coast Regional Council Master Drainage Study: Mourilyan i Executive Summary


Executive Summary This study forms part of the 2nd stage of a three stage process focused on the management of the urban drainage system in the Cassowary Coast Regional Council (CCRC) Local Government Area. In particular, this assessment presents the methodology and findings of a detailed hydraulic assessment of the Mourilyan (including the Etty Bay Road) urban drainage system. The three aspects of the Master Drainage System study process are outlined below:

(1) Master Drainage System Framework Plan;

(2) Master Drainage System Detailed Hydraulic Assessment; and

(3) Structural Works.

The first stage was undertaken by BMT WBM and is outlined in the report Cassowary Coast Regional Council Master Drainage Study Framework and Priority Plan (BMT WBM, 2012). The report outlines the drainage system assessment methodology and a priority plan for the various urban drainage areas of the CCRC.

This hydraulic assessment report is for the Mourilyan and Etty Bay Road drainage system and is intended to present the current hydraulic capacity of the urban drainage system and, where appropriate, present upgrade options to ensure the system can perform to CCRC’s design standards. In addition, preliminary flood mitigation measures addressing flooding trouble spots not directly associated with the drainage network are also presented.

Infrastructure Capacity Assessment The capacity of the existing urban drainage network was evaluated as part of this assessment and compared to the design capacity recommendations outlined in the Stage 1 report (BMT WBM, 2012). It was found that parts of the Mourilyan stormwater drainage system are undersized when compared to the recommended design capacity guidelines.

Preliminary Flood Mitigation Assessment In addition to the infrastructure capacity assessment, flooding ‘trouble spots’ were identified from the flood modelling assessment and in BMT WBM (2012) and preliminary mitigation measures were investigated. A key finding from the Preliminary Flood Mitigation Assessment was that much of the flooding issues identified in the Mourilyan area are because of elevated tail water levels along Ninds Creek.

Sections of the Etty Bay Road drainage system drain to a wetland to the south (Bulgaroo Swamp). This wetland is slow to drain, which can cause flood waters in the wetland to rise and limit the drainage capacity of the Etty Bay Road urban area. As such, a mitigation strategy that drains stormwater to the northern wetland was investigated.

Upgrade Priority Assessment Results of the infrastructure capacity assessment indicate that the priority upgrade for Mourilyan is the drainage infrastructure that drains the eastern side of Mourilyan (upstream of drain ID L0856). No upgrades have been suggested for Etty Bay Road drainage infrastructure, as Etty Bay Road is largely flood immune in a 10% AEP flood event.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan ii Contents


Contents

Executive Summary i 1 Introduction 1

1.1 Intent/Purpose 1

1.2 Catchment Summary 1 1.2.1 Mourilyan 1 1.2.2 Etty Bay Road 2

2 Methodology 6

2.1 Available Data 6 2.1.1 Topographic Data 6 2.1.2 Stormwater/Infrastructure Details 6 2.1.3 Landuse 7 2.1.4 Rainfall 7 2.1.5 Tailwater Conditions 7

2.2 Hydraulic Model 12 2.2.1 Model Layout 12 2.2.2 Climate Change Assessment 15 2.2.3 Critical Duration Assessment 15

3 Model Results 18

4 Mitigation Options 20

4.1 Cooma and Peregrine Streets, Mourilyan 20 4.1.1 Model Results 20 4.1.2 Mitigation Strategy 21

4.2 Mourilyan Harbour Road, Central Mourilyan 23 4.2.1 Model Results 23

4.3 South Mourilyan 23 4.3.1 Model Results 24 4.3.2 Mitigation Strategy 24

4.4 Back and Mill Street, West Mourilyan 27 4.4.1 Model Results 27 4.4.2 Mitigation Strategy 27

4.5 Mourilyan Primary School Car Park 30 4.5.1 Mitigation Strategy 30

4.6 Bulguru Road, Etty Bay Road 31 4.6.1 Model Results 32

Cassowary Coast Regional Council Master Drainage Study: Mourilyan iii Contents


4.6.2 Mitigation Strategy 32

4.7 Lot RP909310 Etty Bay Road 35 4.7.1 Model Results 35 4.7.2 Mitigation Strategy 35

5 Infrastructure Tables 38

6 Conclusions 42

7 References 43

Appendix A Modelling Methodology A-1

Appendix B Infrastructure Tables B-1

List of Figures Figure 1-1 Catchment Location 3

Figure 1-2 Mourilyan Catchment Features 4

Figure 1-3 Etty Bay Catchment Features 5

Figure 2-1 Mourilyan Topography 8

Figure 2-2 Etty bay Topography 9

Figure 2-3 Mourilyan Drainage Infrastructure 10

Figure 2-4 Etty Bay Drainage Infrastructure 11

Figure 2-5 Mourilyan TUFLOW Model Land Use 13

Figure 2-6 Etty Bay TUFLOW Model Land Use 14

Figure 2-7 Mourilyan Critical Storm Duration 16

Figure 2-8 Etty Bay Critical Storm Duration 17

Figure 4-1 Cooma and Peregrine Streets Existing Results (10% AEP Flood Extent) 20

Figure 4-2 Cooma and Peregrine St Mitigation Layout 21

Figure 4-3 Flood Mitigation Results Cooma Street 22

Figure 4-4 Mourilyan Harbour Road Model Results (10% AEP Flood Extent) 23

Figure 4-5 South Mourilyan Existing Results (10% AEP Flood Event) 24

Figure 4-6 Ninds Creek Mitigation Strategy Layout 25

Figure 4-7 Flood Mitigation Results South Mourilyan 26

Figure 4-8 Back and Mill St Existing Results (10%AEP Flood Extent) 27

Figure 4-9 Back and Mill St Mitigation Strategy Layout 28

Figure 4-10 Flood Mitigation Results Back and Mill St 29

Figure 4-11 Mourilyan Primary School Car Park Results (10% AEP Flood Extent) 30

Figure 4-12 Bulguru Rd Existing Results (18% AEP Flood Extent) 31

Cassowary Coast Regional Council Master Drainage Study: Mourilyan iv Contents


Figure 4-13 Bulguru Rd Mitigation Strategy Layout 33

Figure 4-14 Flood Mitigation Results Bulguru Road 34

Figure 4-15 Mitigation Strategy for Lot RP909310 35

Figure 4-16 Flood Mitigation Results for Lot RP909310 18% AEP Flood Event 37

Figure 5-1 Infrastructure Capacity Assessment, Central Mourilyan 39

Figure 5-2 Infrastructure Capacity Assessment, South and West Mourilyan 40

Figure 5-3 Infrastructure Capacity Assessment, Etty Bay 41

Figure A-1 Mourilyan Intensity Frequency Duration Data A-2

Figure A-2 Etty Bay Intensity Frequency Duration Data A-4

Figure A-3 Design Rainfall Temporal Patterns A-5

Figure A-4 Linking Underground 1D Stormwater Drainage Network to the Overland 2D Domain A-9

Figure A-5 Example Pit Inlet Curve A-10

List of Tables Table A-1 Mourilyan Design Rainfall Intensities (IFD) A-2

Table A-2 Etty Bay Design Rainfall Intensities (IFD) A-3

Table A-3 Mourilyan Manning’s ‘n’ Roughness Coefficients in TUFLOW Model A-7

Table A-4 Etty Bay Manning’s ‘n’ Roughness Coefficients in TUFLOW Model A-7

Table A-5 Kerb Inlet Blockage Factors A-11

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 1 Introduction


1 Introduction

1.1 Intent/Purpose BMT WBM have undertaken a number of flood studies within Cassowary Coast Regional Council (CCRC) area including the CCRC flood study (BMT WBM, 2014) and the Stage 1 report associated with this study (BMT WBM, 2012). This study utilises aspects of the regional flood study and is a direct continuation of the work undertaken as part of the Stage 1 report.

The consequences of an inadequately designed stormwater network or the failure of any part of that network can be severe. In order to minimise the consequences of failure and to identify any areas of high risk, a detailed understanding of the existing Mourilyan and Etty Bay Road stormwater network was undertaken. It is the intent of this report to present the detailed hydraulic assessment of the urban drainage system and identify aspects of the system that do not conform to Councils design requirements.

The design standard for current stormwater infrastructure varies throughout the council area. Phase 1 of this 3 phase process reviewed various drainage system design standards and determined that the FNQROC design standards should be applied to all urban drainage systems within the CCRC area. This approach will guarantee a consistent standard throughout the CCRC area and ensure future development is serviced by an adequate drainage infrastructure.

The intent of this assessment is to determine the suitability of the existing Mourilyan drainage system. Parts of the drainage network that do not meet the FNQROC design standards will be highlighted and upgrade options, that will ensure nonconforming infrastructure meet the design requirements, will be presented. Note that the FNQROC standards are more stringent than QUDM (used by most of the state) for medium to low density urban residential and rural residential property – QUDM specifies 39% AEP and FNQROC specifies 18% AEP. The results of this Stage 2 study will be used by CCRC to guide future maintenance and upgrades of the Mourilyan urban drainage infrastructure.

1.2 Catchment Summary

1.2.1 Mourilyan Mourilyan is located south of Innisfail and lies in the Johnstone River floodplain off the eastern bank of the river. The location of the urban area within the CCRC region is shown in Figure 1-1 and a zoom of the urban area in Figure 1-2. The primary land use surrounding the town is sugar cane plantation. The following sections of Mourilyan are defined for the purposes of discussion in this report:

Central Mourilyan refers to the largest urban portion of the town, bounded by the Cane Railway along the southern edge and the Bruce Highway on the western edge. This area contains a rectangular grid of streets and residential blocks, flanked by open channel drains. The area also has an underground pipe network linking to a large open channel drain that bounds the northern edge of Central Mourilyan.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 2 Introduction


South Mourilyan refers to the urban development south of the Cane Railway and east of the Bruce Highway. This area comprises the Castor Park sub-division and sports fields. The western side of the Castor Park sub-division drains via underground pipes into an open channel drain along the Bruce Highway, and the western side drains into another open channel drain that is linked to the creek via a stormwater pipe under Castor Road.

West Mourilyan comprises the urban development west of the Bruce Highway (Back Street and Mill Street).

The local catchment that drains toward Mourilyan is situated south of the town. The Johnstone River bounds this catchment on the western side and a ridge bounds the southern side, with the Moreseby River catchment on the southern side of the watershed. Two drainage paths discharge local stormwater runoff from Mourilyan:

Ninds Creek flows in a northerly direction through Mourilyan. The creek bisects Central and South Mourilyan and then crosses the Bruce Highway through a set of culverts. A network of cane drains south of Mourilyan feeds the creek. The creek is the primary discharge for stormwater runoff in West and South Mourilyan.

A drain on the north-eastern corner of Central Mourilyan discharges stormwater runoff from Central Mourilyan. The drain flows in an easterly direction towards lower lying land past Graham Road. This drain is referred to as the eastern drain in this report.

1.2.2 Etty Bay Road The Etty Bay Road urban area is situated on a ridge to the east of Mourilyan. The ridge forms a peninsular connected to higher ground to the southeast and bounded by low lying wetlands to the north and south. The southern wetland (Bulgaroo Swamp) is heavily vegetated and drains across Etty Bay Road into the northern wetland on the north eastern side of the ridge. The northern wetland drains through Ninds Creek into the Johnstone River between Innisfail East and Coquette Point.

The area typically comprises rural residential development along Etty Bay Road. Some of this development, surrounding Bulguru Rd, is serviced by open channel drainage system that outflows to the Bulgaroo Swamp.

Previously proposed upgrades to Etty Bay Road has been investigated separately (BMT WBM, 2015). The proposed upgrades were not pursued. Instead, Etty Bay Road was widened, the existing centreline retained and culverts widened.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 6 Methodology


2 Methodology The methodology used in this assessment was derived from the ‘Cassowary Coast Regional Council Master Drainage Study Framework and Priority Plan’ (BMT WBM, 2012). This section is intended to be a summary, for a more complete presentation of the methodology and data used please refer to Appendix A

This section is presented in three parts:

(1) Available data;

(2) Hydrology model; and

(3) Hydraulic model.

2.1 Available Data This section outlines the data used in developing the flood models used in this master drainage assessment. A more detailed presentation of the data used in this assessment is included in Appendix Section A.2.

2.1.1 Topographic Data The underlying topography of the flood model was derived from a LiDAR data set provided to BMT WBM by CCRC. The raw LiDAR data was provided to BMT WBM in the form of a filtered points ‘cloud’ where only laser ground strikes were included. An Inverse Distance Weighting (IDW) interpolation technique was applied to this data set to create a Digital Elevation Model (DEM) for both models. The topography used for this assessment is presented in Figure 2-1 for Mourilyan and Figure 2-2 Etty Bay Road.

2.1.2 Stormwater/Infrastructure Details No survey was undertaken for the Etty Bay Road drainage infrastructure. Details of road cross drainage were extracted from previous modelling (BMT WBM, 2015) and open drainage details were inspected from the DEM.

Survey information of Mourilyan’s urban stormwater network was provided to BMT WBM by CCRC for the purposes of this study. This data was delivered in a geographic information system (GIS) format and includes:

Gully pit dimensions;

○ Lintel length;

○ Grate dimensions (if present);

○ Whether the gully pit is located ‘on grade’ or in a depression (sag pit);

○ Relative elevation of the gully pit opening;

○ Relative elevation of the base of the gully pit chamber.



Culvert network dimensions;

○ Culverts inverts;

○ Culvert type (i.e. circular or box culvert);

○ Culvert dimensions;

○ Number of culverts in a group (if applicable);

○ Embankment and headwall elevations;

○ Locations and size of driveway cross overs.

Open drainage dimensions:

○ Cross-sectional information within open drains.

A map illustrating the location of the urban drainage network in Mourilyan is shown in Figure 2-3.

2.1.3 Landuse Aerial images were used to define landuse within the catchments, which has subsequently been used in the development the Mourilyan and Etty Bay Road flood models..

2.1.4 Rainfall Intensity frequency duration (IFD) data was used to derive design rainfall information for the site. The Bureau of Meteorology (BoM) online IFD calculator was used to derive these values. IFD tables and figures are presented in Section A.2.2 of Appendix A.

2.1.5 Tailwater Conditions Tailwater conditions (downstream boundary) are the water surface levels assumed at the downstream extent of the hydraulic model. For the purposes of this assessment, the tailwater levels were derived from the Cassowary Coast Regional Council Flood Study (BMT WBM, 2014).

It is noted that Mourilyan is inundated in a 5% AEP regional Johnson River flood event and the Etty Bay Road area in a 1% AEP regional Johnson River flood event. However, since the focus of this study is on local catchment flooding, and investigating potential mitigation options for local catchment flooding (drainage design), the Johnstone River was assumed to have a minor flood. A static 2 year ARI Johnstone River flood level (of 1.4mAHD) was adopted for the downstream boundary for both Mourilyan and Etty Bay Road.

For perspective on the adopted tailwater level, the Highest Astronomical Tide (HAT) level is 1.82mAHD and the Mean High Water Spring (MHWS) tide level is 1.01mAHD. The adopted tailwater level lies between these two high tide events. The ground levels in Mourilyan range between 4mAHD to 5mAHD. Therefore, flood levels in Mourilyan in a large flood are unlikely to be sensitive to the tidal conditions.



2.2 Hydraulic Model Because of the complex nature of flow patterns in urban catchments, a computerised modelling approach for the prediction of flood behaviour has been adopted. This computer model is a dynamically linked 2D/1D hydrodynamic numerical model (TUFLOW).

The hydraulic models consist of high resolution 2D domains that are dynamically linked to a series of 1D domains that simulate the drainage characteristics of the stormwater network (i.e. pits and pipes system and open channel drains). For the simulation of the catchment rainfall-runoff processes over the local catchment surrounding the study areas, a direct rainfall-on-grid approach has been adopted. For rainfall coinciding with 1D open channel drainage areas in Mourilyan, the rainfall volume was computed and distributed across the 1D channels. This technique applies rainfall to every location within the model area.

For a more comprehensive overview of the hydraulic modelling undertaken as part of this study refer to Section A.4 in Appendix A.

2.2.1 Model Layout The hydraulic model developed for Mourilyan covers the entire urban area and local catchment draining into Mourilyan. The 1D network is shown in Figure 2-3 and a layout of the hydraulic model land use is presented in Figure 2-5.

A similar approach has been used for the Etty Bay Road urban area. The model layout and landuse for this area is shown in Figure 2-6.



2.2.2 Climate Change Assessment The hydraulic models were run using variations in the inflow and downstream boundary conditions to estimate the likely changes to flooding behaviour due to climate change. The methodology applied in this regard is presented in A.4.6.3.

Results from the climate change scenario are present in the drawing addendum.

2.2.3 Critical Duration Assessment A critical duration assessment was carried out for both the Mourilyan and Etty Bay Road hydraulic models. The results are presented in Figure 2-7 and Figure 2-8. The critical duration assessment was carried out using the 10% AEP (10 year ARI) event and the hydraulic model was simulated using the 0.5, 1, 2, 3, 4.5, 6, 9, 12, 18, 24 and 36 hour duration events.

It can be seen that the dominant rainfall durations in the Mourilyan floodplain area is the 24 hour duration. However, the critical storm duration through the urban Central Mourliyan is shorter, generally 1 hours. The 24 hour and 1 hour events were chosen as the ‘critical’ storm durations for all design flood events for Mourilyan.

The critical duration for Etty Bay Road is mixed. Bulgaroo Swamp has a long critical duration as it stores much of the rainfall that falls in the swamp. The initial critical duration assessment showed the 36 hour storm to be critical in this area. Therefore a 42 hour and 72 hour storm were run. The 72 hour event produced the highest flood levels in Bulgaroo Swamp. The northern wetland has a critical duration of 0.5 hour, and the residential areas of Etty Bay Road have a critical duration of 1.5 hours in general. The 1.5 hour, 24 hour and 72 hour storms were adopted as the critical durations for Etty Bay Road. The adopted critical duration peak water level is generally within 10mm of the actual critical duration peak water level for both Mourilyan and Etty Bay Road.

The design flood event results presented in this report and drawing addendums have been created by merging the adopted critical duration results together to create the peak ‘worst case’ combined result.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 18 Model Results


3 Model Results Flood maps are presented in a drawing addendum accompanying this report. Results are presented for the 63%, 18%, 10%, 2% and 1% AEP events (1, 5, 10, 50, 100 year ARI). Results presented in this regard include:

Peak Water Surface Level;

Peak Depth;

Peak Velocity;

Peak Velocity Depth Product; and

Peak Hazard.

The results from the Mourilyan model indicate that the terrain around the urbanised area of Mourilyan forms a bottleneck on Ninds Creek that causes a backup of floodwater south of Central Mourilyan. Similarly, the terrain that surrounds Ninds Creek further north of Mourilyan, and through the second Bruce Highway crossing, forms another bottleneck that causes floodwaters to backup west of Central Mourilyan.

The primary causes of flooding are:

A lack of capacity in Ninds Creek through Mourilyan and further north;

Inadequate stormwater pipe capacity in Central Mourilyan; and

High flood levels in Bulgaroo Swamp limiting the drainage capacity of residential development in Etty Bay Road.

The following sub-sections comment on results obtained from the hydraulic modelling assessment in relation to the drainage issues identified in the Stage 1 report. A number of potential flood mitigation options were also identified as appropriate to include in the model to test their potential to alleviate flooding within the identified trouble areas.

This is not an exhaustive flood mitigation assessment; rather it is intended as a preliminary investigation to inform any further work. A more comprehensive investigation into flood mitigation would investigate the relative contribution of the individual measures in more detail, and compare the mitigation costs against the benefits to determine the economic viability; this was not part of the scope for this Master Drainage Study.

Flooding ‘trouble spots’ and potential mitigation measures are presented in the following sub-sections:

(1) Cooma and Peregrine Streets, Central Mourilyan;

(2) Mourilyan Harbour Road, Central Mourilyan;

(3) South Mourilyan;

(4) Back and Mill Street, West Mourilyan;

(5) Mourilyan Primary School Car Park;

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 19 Model Results


(6) Bulguru Road, Etty Bay Road; and

(7) Lot RP909310 Etty Bay Road.

All mitigation scenarios have been tested on the 10% AEP event, which is the nominated design event for much of the Mourilyan urban area.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 20 Mitigation Options


4 Mitigation Options

4.1 Cooma and Peregrine Streets, Mourilyan Cooma and Peregrine Streets are located in the north-eastern section of Central Mourilyan. This area is serviced by a combination of a pit and pipe drainage network and open channels (road table drains) that discharges to an open channel to the northeast of the urban area. This open channel falls to the northeast toward a wetland and ultimately drains to Ninds Creek downstream. The Cooma and Peregrine Street area is shown in Figure 4-1.

Potential Issue: The capacity of the existing drainage network may be exceeded in events less than the design flood event.

Figure 4-1 Cooma and Peregrine Streets Existing Results (10% AEP Flood Extent)

4.1.1 Model Results Modelling results indicate that inundation of dwellings is likely in the 18% AEP event and above in the area along Cooma St between Bombala St and Peregrine St. Similarly, some flooding on Peregrine Street occurs in events greater than (and including) the 18% AEP design event due likely to inadequate pipe capacity for the pipe section along Canberra Street. Cooma St is flood free in the 10% AEP event, but is inundated in a 2% AEP event.



4.1.2 Mitigation Strategy The existing pipe sizes range between 450mm and 600mm diameter. A mitigation scenario was modelled where the pipe sizes were increased as per the Infrastructure Table in Appendix B – see Figure 4-2 for location. This test scenario reduced the depth of extent inundation in this area for all design events simulated.

Figure 4-2 Cooma and Peregrine St Mitigation Layout

The results of the mitigation are shown in Figure 4-3. By increasing the drainage pipe sizing the flood inundation on Peregrine St in a 10% AEP event has been mitigated. The ponding on fields near the school on Cooma Street is reduced in depth, but not fully mitigated. This ponding is caused by on site drainage rather than inadequate Council drainage.



4.2 Mourilyan Harbour Road, Central Mourilyan Located adjacent to Mourilyan Harbour Road draining south across the road toward an open channel adjacent to the sports field.

Potential Issue: Floodwaters originating from the southern side of Mourilyan Harbour Road contribute to flooding of dwelling adjacent to the road.

Figure 4-4 Mourilyan Harbour Road Model Results (10% AEP Flood Extent)

4.2.1 Model Results The model results suggest that the Canberra Rd and Mourilyan Harbour Rd intersection, as well as adjacent dwellings, are inundated in a 10% AEP flood event. In a 18% AEP flood event there is some flooding on the road intersection, but the dwellings are flood free.

This flooding is caused by a back flow from the Ninds Creek floodplain on the eastern and southern edges of Central Mourilyan. Little can be done to alleviate this flooding without creek modifications (discussed in the next section).

4.3 South Mourilyan Located on the southern side of the Cane Railway and east of the Bruce Highway. This area comprises development along Castor St.

Potential Issue: Floodwaters from the Ninds Creek floodplain cause flooding on Castor Rd, which is the only access for the local residential properties. Flooding at the Bruce Highway crossing and along the Bruce Highway drain also affects dwellings in this area.



Figure 4-5 South Mourilyan Existing Results (10% AEP Flood Event)

4.3.1 Model Results Flood modelling indicates that the existing hydraulic capacity of Ninds Creek west and further north of Central Mourilyan in combination with the capacity south of Mourilyan in the vicinity of the sports field likely contributes to drainage and flooding issues in South Mourilyan for the 18% AEP flood event. The culverts under the Bruce Highway do not flow at full capacity for the 10% AEP event, which indicates that the Bruce Highway crossing capacity is not causing the flooding.

4.3.2 Mitigation Strategy Improvements to the flow capacity (i.e. increase in the channel cross sectional area) of this section of Ninds Creek will likely alleviate flooding issues upstream. To estimate the likely change in the existing flooding regime due to an increase in channel dimensions the following mitigation scenarios were assessed in combination:

Increase the width of Ninds Creek to 50m from the Bruce Highway crossing at Mourilyan to the Bruce Highway crossing north of Mourilyan;

Increase the width of Ninds Creek to 8m adjacent to the Cane Railway upstream of the Bruce Highway crossing at Mourilyan;

Reduce the hydraulic resistance to flow (Manning’s value) where widening was assumed (i.e. assume the channel is in a ‘maintained’ state). This considers implementation of an ongoing vegetation clearance maintenance program in the widened Ninds Creek;



Increase the size of the Castor Street culverts on Ninds Creek. Existing 3 x Ɵ1.5m RCP were replaced with 3 x 2.1m x 2.4m RCBC. The practicality of undertaking this works given the proximity to the tram line and private property would need to be confirmed as part of detailed design.

A layout of the mitigation strategy is shown in Figure 4-6. While these modifications are considerable and may not be feasible to implement, the exercise demonstrates how much mitigation may be achieved by increasing the flow capacity of Ninds Creek.

Figure 4-6 Ninds Creek Mitigation Strategy Layout

The results (see Figure 4-7) show a large reduction in flood level and inundation extent for the 10% AEP flood event. This flood mitigation strategy alleviates flooding on the southern edge of Central Mourilyan and South Mourilyan. However, the number of properties that benefit is small. The properties that benefit are along Castor Street. The floodwaters on Castor Street could be mitigated further by a bund on the southern edge of Castor Street or near the left bank of Ninds Creek near the sports field. The main benefit is that the Castor Street Road could be made flood immune, thereby maintaining access to the Castor Street properties in a 10% AEP flood event.



4.4 Back and Mill Street, West Mourilyan Residential development extends west of the Bruce Highway along Back St and Mill St.

Potential Issue: This development blocks the natural floodplain flow on Ninds Creek, possibly exacerbating flooding to south and Central Mourilyan.

Figure 4-8 Back and Mill St Existing Results (10%AEP Flood Extent)

4.4.1 Model Results The Bruce Highway road embankment cuts across the Ninds Creek catchment south of Mourilyan. Culverts drain floodwater across the highway (floodwater flows from east to west across the highway). Nevertheless, as shown in Figure 4-8, the highway embankment blocks floodwaters flowing across the floodplain. The highway forces floodwater on the western side of the highway to flow north towards West Mourilyan – alleviating flooding in South Mourilyan. Some of the floodwater on the western side of the highway flows north towards West Mourilyan near Back and Mill Street. The drainage across West Mourilyan, which consists of a system of small open channel drains, may limit the flow of floodwater across this area. Therefore, improving the drainage across West Mourilyan may alleviate flooding on the western side of the highway and, by virtue of reducing the driving head across the highway culverts, reduce the volume of floodwater crossing the highway into Ninds Creek.

4.4.2 Mitigation Strategy The mitigation strategy comprises installation of two drains across West Mourilyan, one of which extends to the south. Additionally, the Bruce Highway cross drainage to the south (just north of the Boogan Road intersection) was blocked. The intention of the strategy was that this would retain flood waters on the western side of the Bruce Highway and thereby reduce the volume of flood



waters to the east of the highway south of Mourilyan. The location of the drains is shown in Figure 4-9. The drains widths are 12m, which is twice the coarser grid cell size. The invert levels of the drains correspond with the existing floodplain levels north and south of West Mourilyan, the open channel drains through West Mourilyan and the cross drainage levels near the Boogan Road intersection.

Figure 4-9 Back and Mill St Mitigation Strategy Layout

The results (see Figure 4-10) show that blocking the culverts significantly lowers flood levels in the drain that runs along the eastern side of the Bruce Highway. This alleviates flooding at a few properties on Castor Street for the 10% AEP flood event. While the proposed mitigation does lower flood levels on Castor Street, inundation of the street still occurs in the 10% AEP flood event. The lower flood levels on Ninds Creek (near Castor Street) south of the Bruce Highway lead to lower flood levels north of the highway as well.

Conversely, flood levels on the western side of the Bruce Highway are higher. This was expected, and the intention of the proposed drain was to direct the floodwater northwards to minimise the adverse flood impact. However, the proposed drain appears to provide little benefit in this regard.



4.5 Mourilyan Primary School Car Park The car park for Mourilyan Primary School is located adjacent to Mourilyan Harbour Road near the Cooma Street intersection. Here, the tramline crosses Mourilyan Harbour Road to run on the northern side of the road east of the car park.

The car park drains towards the east via a drain along the northern side of the tramline. A drain that runs between the tramline and the road also facilitates drainage of water from the car park. These two drains are separated by the tramline embankment and are connected via culverts under the tramline. However, the survey did not extend to this part of Mourilyan. Therefore, details of the infrastructure that links the drains was not known at the time of the study and has not been included in the modelling.

Potential Issue: The car park is low lying and susceptible to flooding. The model results show that the eastern side of the car park becomes inundated in small floods.

Figure 4-11 Mourilyan Primary School Car Park Results (10% AEP Flood Extent)

4.5.1 Mitigation Strategy The drains along the tramline and road run in an easterly direction across Graham Road. Ground levels east of Graham Road drop off steeply. As such, there is potential to improve the drainage of the car park area. Improved drainage could be achieved by one of, or a combination of, the following:



Increasing the size of the drain north of the tramline;

Providing additional culverts under the tramline to improve the link between the two drains; and

Increasing and/or lowering the culverts across Graham Road with corresponding re-profiling of the drains as required.

Modelling of potential mitigation has not been undertaken as drainage infrastructure details in this area were not available at the time of the study and the car park inundation issue was raised after the modelling work had been completed.

4.6 Bulguru Road, Etty Bay Road Residential development surrounding Bulguru Rd, off Etty Bay Road, drains in a south westerly direction through open drains across Jabiru St and Etty Bay Road into Bulgroo Swamp (see Figure 4-12).

Potential Issue: High water levels in Bulgaroo Swamp during a flood limit the drainage capacity of the open channel drains. The model results indicate that the drainage in this area conforms to FNQROC flood immunity requirements. However, there may be an opportunity to improve the drainage capacity.

Figure 4-12 Bulguru Rd Existing Results (18% AEP Flood Extent)



4.6.1 Model Results Two open channel drains that drain the residential development surrounding Bulguru Rd drain across Jabiru St towards Etty Bay Road. The peak flood levels across the road have a flat grade with only 35mm to 65mm drop in flood level across the road in a 10% AEP flood event. The two drainage channels merge before flowing across Etty Bay Road. The drop in flood level across the road is 270mm for the 10% AEP flood event and 80mm for a 1% AEP flood event. Therefore, for some flood events the driving head across Etty Bay Road is small, and for some floods Bulgaroo Swamp may limit the drainage capacity or cause a backup of flood waters up the drains.

The results show flooding on Jabiru St. However, this is due to drainage of runoff on the road, not due to overtopping of the open channel drains. The results show inundation of lots, but not to dwellings for the 18% AEP. Therefore, there is no indication that the open channel drains do not conform to the FNQROC flood immunity requirement.

4.6.2 Mitigation Strategy The mitigation strategy that has been tested is as follows. Additional culverts were inserted at the northern (upstream) ends of the open channel drains. This enables stormwater in the drains to drain across Bulguru Rd to the northern wetland. The existing culverts under Jabiru St that drain to the south are 1.8m wide by 0.6m high double barrel box culverts. The proposed culverts to the north across Bulguru Rd for mitigation were sized at four barrels 1.8m wide and 0.6m high (see Figure 4-13). Simple open channels were inserted into the model to link the proposed culverts to the existing drain north of the residential development area.



Figure 4-13 Bulguru Rd Mitigation Strategy Layout

The results of the mitigation strategy showed minor reductions in flood inundation extent – see . The proposed mitigation culverts flowed at 20% capacity for the 18% AEP event and can, therefore, be reduced in number. Given that the existing flooding conditions conform to FNQROC flood immunity requirements, this mitigation strategy is not required. Nevertheless, this mitigation option was included to check whether there was an opportunity to improve drainage in this area.



4.7 Lot RP909310 Etty Bay Road A residential dwelling is located on lot RP909310 on the southern side of Etty Bay Road on the corner with Daniel Close.

Potential Issue: A drain runs along the southern side of Etty Bay Road and crosses Daniel Close via a culvert. This culvert discharges at the north-eastern corner of the property. The slab on ground dwelling was constructed on one of the lowest parts of the property.

4.7.1 Model Results The model results indicate that runoff collects at the property causing inundation for small flood events; the dwelling is inundated in a 63% AEP flood event, and therefore has not been designed to Council’s required standard.

4.7.2 Mitigation Strategy A mitigation scenario was set up whereby an open channel drain was included around the boundary of the property. The drain links to the culvert under Daniel Close, and then runs along the northern and western boundary of the property toward Bulgaroo Swamp to the south. The drain was sized as a single grid cell wide (6m) and was generally approximately 1m deep.

Figure 4-15 Mitigation Strategy for Lot RP909310



The results indicate that the drain mitigates flooding for small and large events. For the 18% and 1% AEP flood events the dwelling in no longer within the extent of inundation. There is still a small pocket of inundation in the yard of the property.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 38 Infrastructure Tables


5 Infrastructure Tables An Infrastructure table for Mourilyan and Etty Bay Road was produced from hydraulic modelling undertaken as part of this investigation and is presented as Appendix B in this report. The tables summarise the performance of the existing stormwater drainage system for existing and future climate conditions. For each culvert, the following information is presented:

Culvert ID;

Type, dimensions and number of culverts in a set;

Capacity of the culvert (i.e. the largest storm event where the culvert does not exceed its capacity);

Peak flow rates through each culvert for all events modelled (current and future climate scenarios); and

Indicative upgrade culvert dimensions (current and future climate scenarios).

For cross road drainage, the capacity has been assigned based on overtopping of the road.

Note that the proposed upgrades are indicative and only consider pipe sizing upgrades. Indicative upgrades have not always been provided in the infrastructure table, as:

Broader flooding issues (rather than insufficient pipe capacity) cause some noncompliance with immunity requirements. This typically manifests as backwater from the floodplain along a road or at a pipe network outlet;

Inadequate capacity at one part of the network (say near the outlet) can propagate to falsely indicate noncompliance in other parts of the network (further upstream); and

Other aspects, such as shallow grades, can cause flooding rather than pipe size.

Results of the pipe capacity assessment are also presented in Figure 5-1 and Figure 5-2 for Mourilyan and Figure 5-3 for Etty Bay Road. These figures present the pipe identification number referenced in the Appendix B table.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 42 Conclusions


6 Conclusions This Mourliyan hydraulic assessment has highlighted the existing infrastructure does not conform to the FNQROC design guidelines. In particular, sections of the pipe network that are under capacity, with regard to hydraulic conveyance, have been presented in the Infrastructure tables (Appendix B). In addition, the pipe dimensions that will be required to meet the FNQROC design guidelines have also been presented in this table.

Findings of this assessment indicate that parts of the Mourilyan pipe network are under sized when compared to the FNQROC guidelines. Some of the drainage and flooding issues arise from flooding on Ninds Creek, which limits the ability to alleviate urban flooding. The hydraulic models predicted that drowned outlets were likely at a number of locations in along the eastern and southern edges of Central Mourilyan and in South Mourilyan.

This report has presented indicative mitigation strategies and pipe sizing upgrades. However, this is indicative only, and more detailed assessment will be required prior to detailed design or as part as feasibility studies into the flood mitigation strategies.

In terms of identifying priorities, there are two sections of drainage infrastructure where pipe capacity limitations lead to flooding in minor events (i.e. no creek modification required). The priority for upgrades of these drainage infrastructure are (in order of priority):

The drainage along Cooma and Peregrine St (outflow pipe ID: L0856).

The drainage along Peregrine St and Canberra St (outflow pipe ID: L0752).

Cassowary Coast Regional Council Master Drainage Study: Mourilyan 43 References


7 References Benham SA and Rogencamp GJ (2003) Application of 2D Flood Models with 1D Drainage Elements. Flood Mitigation Conference, Forbes.

BMT WBM (2014) Cassowary Coast Regional Council Flood Study, May 2014

BMT WBM (2015) Etty Bay Road Upgrade; Hydraulic Assessment, October 2015

BoM (2014) AR&R87 IFDs: Intensity–Frequency–Duration: Design Rainfalls: Water Information: Bureau of Meteorology. . Available at: http://www.bom.gov.au/water/designRainfalls/ifd-arr87/index.shtml (accessed 20/02/14).

Chow VT (1959) Open Channel Hydraulics. .

DEHP (2009) Draft Queensland Coastal Plan: Draft State Planning Policy Coastal Protection. Queensland Department of Environment and Heritage Protection. Available at: http://www.ehp.qld.gov.au/coastalplan/ (accessed 21/01/14).

DEHP (2010) Climate Change in Queensland – What the Science is Telling Us. Queensland Climate Change Centre of Excellence, Department of Environment and Heitage Protection.

Department of Transport and Main Roads (2014) Queensland Tide Tables 2014. The Chart & Map Shop. Available at: /2805492/Queensland-Tide-Tables-2014/0680569503367 (accessed 20/02/14).

Institution of Engineers, Australia (1987) Australian Rainfall and Runoff: A Guide to Flood Estimation , Vol. 1 (Reprinted edition 1998.).

Stelling GS (1984) On the Construction of Computational Methods for Shallow Water Flow Problems. Rijkswaterstaat Communications No. 35/1984.

Style RG (1979) Model Analysis to Determine Hydraulic Capacities of Kerb Inlets and Gully Pit Gratings. . Available at: http://trid.trb.org/view.aspx?id=142848 (accessed 10/10/13).

Syme WJ (1991) Dynamically Linked Two-Dimensional / One-Dimensional Hydrodynamic Modelling Program for Rivers, Estuaries & Coastal Waters. Dept of Civil Engineering, The University of Queensland.

Syme WJ, Rogencamp GJ and Nielsen CF (1999) Two-Dimensional Modelling of Floodplains – A Powerful Floodplain Management Tool. paper presented at the NSW Flood Mitigation Conference. Tamworth, NSW.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan A-1 Modelling Methodology


Appendix A Modelling Methodology

A.1 Preamble The modelling methodology is presented in three parts:

(1) Data used in the assessment;

(2) Hydrology modelling methodology; and

(3) Hydraulic modelling methodology.

A.2 Data Data used in this assessment is presented in the following sections:

Topographic data

Rainfall data

A.2.1 Topographic Data Topographic data used in this assessment was obtained from CCRC in the form of a LiDAR ‘points cloud’. This information is a highly accurate data set which was flown in 2010. This information was then processed into a Digital Elevation Model (DEM) using an Inverse Distance Weighting (IDW) interpolated technique. The following parameters were used in this regard:

Cell size = 1.5m;

Exponent = 4;

Search radius = 20m; and

Display radius = 20m.

The resultant DEM data set is presented in Figure 2-1 and Figure 2-2.

A.2.2 Rainfall Design rainfall information used in this assessment was derived from the Bureau of Meteorology’s (BoM) Intensity Frequency Duration (IFD) online tool (BoM 2014). This program applies the Australian Rainfall and Runoff (AR&R) method for identifying IFD data based on a sites location (Institution of Engineers, Australia 1987).

The IFD data used in this assessment is presented in Figure A-1. This data is also presented graphically Figure A-1.



Table A-1 Mourilyan Design Rainfall Intensities (IFD)

Duration 63% AEP 39% AEP 18% AEP 10% AEP 5% AEP 2% AEP 1% AEP 30Mins 66.2 83.9 103 114 129 149 163

1Hr 47.2 60 74.1 82.1 93.2 108 118

1.5Hr 37.8 48.3 60.4 67.3 76.7 89.1 98.5

2Hrs 32 41 52 58.3 66.9 78.1 86.8

3Hrs 25.1 32.4 42 47.7 55.2 65.2 72.9

4.5Hr 19.6 25.5 33.9 38.9 45.6 54.5 61.4

6Hrs 16.5 21.6 29.1 33.7 39.8 47.9 54.4

9HR 13 17.2 23.6 27.6 32.8 39.9 45.5

12Hrs 11.1 14.7 20.4 23.9 28.5 34.9 39.9

18HR 9.1 12 16.6 19.6 23.4 28.5 32.6

24Hrs 7.93 10.5 14.4 16.9 20.1 24.5 28

36HR 6.6 8.7 11.8 13.7 16.2 19.6 22.3

Figure A-1 Mourilyan Intensity Frequency Duration Data

3

30

300

0.5 5 50

Rai

nfal

l Int

ensi

ty (m

m/h

r)

Storm Duration (hrs)

63% AEP (1 Year ARI)39% AEP (2 Year ARI)18% AEP (5 Year ARI)10% AEP (10 Year ARI)5% AEP (20 Year ARI)2% AEP (50 Year ARI)1% AEP (100 Year ARI)



Table A-2 Etty Bay Design Rainfall Intensities (IFD)

Duration 63% AEP 39% AEP 18% AEP 10% AEP 5% AEP 2% AEP 1% AEP

30Mins 66.2 84.2 104 116 131 151 167

1Hr 47.1 60.0 74.7 83.1 94.5 109 121

1.5Hr 37.6 48.1 60.6 67.8 77.6 90.4 100

2Hrs 31.7 40.7 52.0 58.6 67.4 79.1 88.0

3Hrs 24.6 31.9 41.7 47.5 55.2 65.5 73.5

4.5Hr 19.0 24.9 33.3 38.5 45.3 54.4 61.5

6Hrs 15.9 20.9 28.5 33.2 39.3 47.6 54.2

9HR 12.5 16.6 23.0 27.0 32.3 39.4 45.1

12Hrs 10.7 14.2 19.8 23.4 28.0 34.3 39.4

18HR 8.7 11.6 16.2 19.1 22.9 28.0 32.1

24Hrs 7.65 10.1 14.1 16.5 19.7 24.1 27.6

36HR 6.4 8.5 11.5 13.4 15.9 19.3 21.9



Figure A-2 Etty Bay Intensity Frequency Duration Data

Design rainfall totals, derived from ARR IFD estimates, are only directly applicable to small catchments and rainfall depths should be adjusted to take into consideration spatial variability over a wider area. Since the local catchment draining across Mourilyan (approximately 4km²) and Etty Bay Road is small, no Areal Reduction Factors have been applied.

Design rainfall temporal patterns were derived using the AR&R method (Institution of Engineers, Australia 1987). Temporal patterns for design storm events ranging in duration from 10 minutes to 72 hours have been statistically derived for broad geographical regions across Australia. Temporal patterns represent the hyetograph shape and are specific to each design storm duration. Based on the AR&R (1987) temporal pattern delineation, the Mourilyan and Etty Bay Road area falls within Zone 3. An example of the Zone 3, 24 hour storm duration, 1% AEP temporal pattern is shown Figure A-3.

3

30

300

0.5 5 50

Rai

nfal

l Int

ensi

ty (m

m/h

r)

Storm Duration (minutes)

63% AEP (1 Year ARI)









Figure A-3 Design Rainfall Temporal Patterns

A.3 Hydrological Modelling No hydrological modelling was undertaken. The hydraulic model extents covered the full external local catchments for Mourilyan and Etty Bay, and the direct rainfall approach was used. The direct rainfall approach is outlined in the hydraulic modelling section of this report (Section A.4.6.1). The rainfall volume falling over the 1D domain in Mourilyan was distributed across 1D channels.

A.4 Hydraulic Modelling The 2D/1D hydrodynamic modelling software package TUFLOW was used for the flood modelling in this study. TUFLOW solves the full 2D shallow water equations based on the calculation scheme developed by Stelling (1984) and subsequently improved by Syme (1991) and Syme et al (1999). The solution is based on the alternating direction implicit finite difference method. A square grid is used to define the discretisation of the computational domain.

This section is presented in the following sub-section:

2D model domain schematisation;

1D model domain schematisation; and

Boundary Conditions.

A.4.1 2D Model Domain Schematisation For Mourilyan, the 2D hydraulic model domain covers an area of 616 hectares. A finer resolution domain over the urban development area (comprised of a 3m grid) was embedded into the main 2D domain, which comprised of a 6m grid. The 2D domain regular grid was aligned to match the road grid alignment in Central Mourilyan.

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12Rainfall 3.8% 9.1% 20.3 3.7% 6.6% 13.7 1.8% 1.7% 2.2% 4.3% 3.0% 6.6% 4.9% 2.7% 2.5% 1.5% 1.5% 3.4% 2.0% 1.2% 1.0% 1.1% 0.8% 0.6%

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

22%R

ainf

all P

erce

ntag

e (%

)

Time (hours)



For Etty Bay Road three 2D domains were utilised:

A course grid of 18m was used over the shallow grade low lying wetland areas;

A finer grid of 6m was used generally across the residential development areas; and

A fine grid of 3m was used in the Bulguru Rd area to capture better detail of the open channel drains.

Each square grid element contains information on ground topography (sampled from the DEM, see Section A.2.1), surface resistance to flow (Manning’s ‘n’ value, see Section A.4.1.2) and initial water level. The grid cell size is considered to be sufficiently fine to appropriately represent the variations in floodplain topography and land use.

Linear features that potentially influence the flow behaviour, such as gullies, levees and embankments or large buildings, were incorporated into the topography using 3D ‘breaklines’ to ensure that these were contained within the model grids and accurately represented in the model. It is noted that although brick walls and fences could also significantly affect local overland flood flowpaths, these have not explicitly been incorporated into the model, and were instead considered in the setting of appropriate Manning’s ‘n’ values for urban areas.

A.4.1.1 Open Stormwater Channels and Watercourses Open channel drains along the roads in Mourilyan have generally been modelled in 1D and dynamically linked to the 2D domain. This approach was adopted as the 2D grid cell size of 3m (for the embedded finer 2D domain) was considered too course to represent the flow capacity of these drains.

Beyond the urban centre of Mourilyan, the cane drains and Ninds Creek have been modelled in the 2D domain using 3D breaklines to ensure that a contiguous string of grid cells along the drain thalwegs were captured in the 2D domain terrain.

In Etty Bay, the open channel drains were modelled in the 2D domain utilising breaklines to capture the drain invert levels.

A.4.1.2 Hydraulic Roughness Roughness coefficients represent the resistance to flood flows in channels and floodplains. The land use delineation of the baseline model is based on aerial photography and on-site photographs. The land use delineation used in the TUFLOW model is presented in Figure 2-5 for Mourilyan and Figure 2-6 for Etty Bay.

The hydraulic roughness of the ground surface is represented in the flood model using the Manning’s ’n’ roughness coefficients. Values of the roughness coefficients have been based on industry standards (e.g. Chow 1959) and adopted values of previous TUFLOW models.

In order to accurately represent the hydraulic characteristics of the study area, a variable depth-dependent hydraulic roughness value was applied in the TUFLOW model for sugar cane and buildings in Mourilyan. The adopted Manning’s ‘n’ roughness coefficients for the land uses within the Mourilyan are listed in Table A-5.



Table A-3 Mourilyan Manning’s ‘n’ Roughness Coefficients in TUFLOW Model

Description Depth 1 (m) Mannings 'n' 1 Depth 2 (m) Mannings 'n'

2

2D Domains:

Waterway 0.060

Waterway Maintained 0.030

Sugar Cane 0.200

Roads 0.020

Tree Canopy 0.100

Buildings (in floodway) 0.03 0.015 0.05 1.00

Low Density Residential 0.03 0.100 0.10 0.045

1D Domains:

Bitumen 0.020

Ballast 0.018

Concrete 0.013

Grass 0.060

Gravel 0.018

Note: The Manning’s ‘n’ values between depth 1 and depth 2 are interpolated linearly

The adopted Manning’s ‘n’ roughness coefficients for the land uses within the Etty Bay Road are listed in Table A-4.

Table A-4 Etty Bay Manning’s ‘n’ Roughness Coefficients in TUFLOW Model

Description Manning’s n

Waterways 0.030

Buildings 1.000

Roads 0.015

Trees / Dense Vegetation 0.100

Reeds / Weedy Pools 0.080

Pasture / High Grass 0.045

Sugar Cane 0.200

Rural Residential 0.045

Hard Stand Areas 0.020

Concrete Drain 0.013



A.4.2 1D Model Domain Schematisation

A.4.2.1 Representation of Stormwater Drainage Network Much of the open channels along road sides in the urbanised parts of Mourilyan were modelled in 1D. In addition, the underground stormwater drainage system and hydraulic structures (such as culverts) were modelled in the 1D domain. TUFLOW has the ability to represent a pipe network of underground drainage systems that are linked to either / both a 1D open channel network and / or 2D overland flowpaths. The 1D and 2D components of the hydraulic model were dynamically linked, allowing water to flow from the 2D floodplain into the open channel drains and underground pipe network (1D model), and vice versa (surcharging).

The underground pipe network is linked to the 2D model via a pit inlet, allowing flow in both directions. A schematic diagram of this linkage is presented in Table A-3. The linkage is explained in greater detail in Application of 2D Flood Models with 1D Drainage Elements (Benham and Rogencamp, 2003). A schematic representation of the pit and pipe modelling setup is shown in Figure A-3.

All known stormwater pits and pipes within the Mourilyan area are included in the flood model. This required substantial data collection to define the dimensions and capacity of the pipe drainage network (Section 2.1.2).

For Etty Bay, cross drainage across roads has been included, as well as open channel drains. However, no underground piped drainage has been included in the model.

It is noted that no private drainage systems or detention basins on private properties have been incorporated in the TUFLOW model. Stormwater on private land is therefore modelled as overland flow to Council’s stormwater drainage system. This may have some implications for the definition of flooding. Model results that show ponded stormwater may not flood in reality because private drainage systems may have the capacity to drain some or all of the runoff. Furthermore, private drainage systems may alter the apparent flooding. As such, model results in these areas should be interpreted with caution.



Figure A-4 Linking Underground 1D Stormwater Drainage Network to the Overland 2D Domain

A.4.3 Pit Inlets In Mourilyan, pits have been modelled in the TUFLOW model as pit channels, which are represented by zero length channels that convey water to/from a 2D overland domain to a 1D pipe network. Within the study area, pits occur as grates or lintels, or a combination of grates and lintels.

The discharge of water through a gully pit is determined by the depth to discharge relationship that has been derived from experimental work undertaken by Sunderland Shire Council. An example pit inlet curve is presented in Figure A-4.

Pits are categorised as either:

‘On-grade’ – water bypassing the pit will likely continue to flow down grade, away of the pit.

‘Sag’ pits – pits located within a depression, if the inlet capacity is exceeded, water will pond over the pit.



Figure A-5 Example Pit Inlet Curve

A.4.4 Underground Stormwater Drainage Pipes As discussed previously, underground conduits were included in the Mourilyan hydraulic model as 1D elements. Details required for accurate representation include size, shape, inverts and number of barrels. The underground 1D pipe network was dynamically connected to the 2D overland surface via pits, as described in Section A.4.2.

No Underground stormwater drains have been included in the Etty Bay Road model.

A.4.5 Bridges and Culverts Hydraulic structures were modelled as 1D culvert channels in the Mourilyan and Etty Bay Road models. In TUFLOW, culvert channels can be either rectangular, circular (pipe) or irregular in shape. A range of different flow regimes is simulated with flow in either direction. The model can accommodate all inlet and outlet controlled flow regimes. Adverse slopes are accounted for and flow may be subcritical or supercritical. Flow over the structure was modelled within the 2D domain using a 3D breakline to define the level of the road crest.

The adopted exit and entry loss coefficients applied to the hydraulic structures have been based on recommended loss coefficients in the TUFLOW user manual. The adjusted energy loss feature has been used in the modelling to automatically adjust the energy losses at structures, according to the approach and departure velocities in the upstream and downstream channels of the structure.

A.4.6 Boundary Conditions The TUFLOW model includes three boundary conditions types:

(1) Direct rainfall inflow boundaries over the 2D domain extents;

(2) Flow versus time 1D boundaries over the 1D domain to represent the rainfall volume falling over the 1D domain (Mourilyan only); and

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.5 1 1.5 2

Dep

th a

t G

ully

Pit

(m

)

Discharge Flow Rate (m3/s)



(3) Water level boundaries at the downstream edge of the model.

These boundary conditions were updated to consider two climate scenarios:

(1) Current climate ; and

(2) Climate Change (2100 planning horizon).

A.4.6.1 Rainfall Inflow Boundaries A direct rainfall approach was adopted for the Mourilyan and Etty Bay Road models. In the direct rainfall approach, rainfall is directly applied to every cell in the 2D model domain and the rainfall-runoff processes that generate stormwater runoff flows throughout the catchment are simulated by the shallow water equations. Derivation of design rainfall inputs is described in Section A.1.

A.4.6.2 Downstream Boundary Condition For the modelling of the downstream boundary of the TUFLOW model, a constant water level boundary condition was adopted representing minor flooding (2 year ARI) water surface levels in the Johnstone River floodplain. The location of the downstream boundary is shown on Figure 2-5 for Mourilyan and Figure 2-6 for Etty Bay.The downstream boundary level was 1.4mAHD for both the Mourilyan and Etty Bay Road models.

A.4.6.3 Climate Change Boundary Conditions To take into consideration variation in the flood regime due to climate change, changes in the boundary conditions of the hydraulic model were applied. Rainfall intensities were increased by 20% for the direct rainfall and 1D rainfall flow boundaries of the hydraulic model.

The downstream boundaries for Mourilyan and Etty Bay Road were increased by 0.94m to 2.34mAHD. This corresponds with the increase in flood level due to climate change in the Ninds Creek floodplain for a minor flood (18% AEP) – determined from results from the regional flood modelling (BMT WBM, 2014).

A.4.7 Kerb Inlet and Structure Blockage Factors Kerb inlet blockage factors have been applied in the hydraulic model based on those outlined in FNQROC. Blockage factors applied in this regard are presented in Table A-5.

Table A-5 Kerb Inlet Blockage Factors

Inlet Type Blockage Factor

On Grade – Side Entry (no Grate) 20%

On Grade – Side Entry (with Grate) 10%

On Grade – Grate only 50%

Sag - Side Entry (no Grate) 20%

Sag - Side Entry (with Grate) Nil

Sag – Grate only 50%



A.4.8 Representation of Buildings Building outlines were digitised where overland flow paths exist and used to define a high hydraulic roughness (as outlined in Table A-5) to minimise flow though the buildings. Fences are not directly representing in the hydraulic model.



A.5 Upgrade Assessment The upgrade methodology tasks were divided into the following sub tasks;

(1) Determine elements where surface water flooding interferes with road trafficability in the 10% AEP flood event.

(2) Determine the cause of the problem (i.e. pipe element undersized, downstream network undersized).

(3) Address the problem area by increasing pipe dimensions until flooding on the road is alleviated.

Each element of the drainage network was allocated an ‘immunity standard’ which has been adopted from the FNQROC development guidelines as outlined in the Phase 1 report. Pit and pipe infrastructure within the urban areas of Mourilyan were allocated an 18% AEP immunity requirement. Cross drainage features in urban areas were allocated a 10% AEP requirement. Kerb and channel draining the Bruce Highway were allocated a 18% AEP immunity requirement and cross drainage structures crossing the Bruce Highway were allocated a 2% AEP requirement.

The hydraulic capacity elements within the network were determined using the hydraulic model as outlined above. Where the water surface level exceeded the ground surface level at the upstream end of a pipe the pipe capacity was categorized as ‘exceeding’ its capacity. For cross road drainage, the capacity has been manually assigned based on overtopping of the road.

When determining the upgrade requirements a qualitative assessment of the pipe network was undertaken to determine constraining aspects of the network that caused the capacity exceedance. The cross-sectional area of the constraining parts of the network was increased to ensure the upstream pipes conformed to the design guidelines.

Cassowary Coast Regional Council Master Drainage Study: Mourilyan B-1 Infrastructure Tables


Appendix B Infrastructure Tables

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94

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79

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87

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91

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54

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28

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92

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59

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45

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99

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00

398,

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96

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Cas

sow

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3 In

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Pipe

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04

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05

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06

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L09

14

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44

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53

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61

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L09

62

398,

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62

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94

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95

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96

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m

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-10%

*6

3%-1

8%

18%

0.

19

0.30

0.

30

0.30

0.

30

0.26

0.

28

0.28

0.

28

0.28

1x

ᶿ0.9

m

1xᶿ0

.9m

L08

22

398,

559.

78

8055

749.

38

1xᶿ0

.525

m

63%

-18%

18%

0.

29

0.34

0.

36

0.37

0.

37

0.31

0.

36

0.37

0.

37

0.37

1x

ᶿ0.9

m

1xᶿ0

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L08

23

398,

559.

24

8055

749.

05

1xᶿ0

.45m

>6

3%

18

%

0.17

0.

18

0.19

0.

19

0.19

0.

18

0.19

0.

19

0.19

0.

19

L08

24

398,

562.

48

8055

750.

74

1xᶿ0

.525

m

63%

-18%

18%

0.

30

0.35

0.

36

0.36

0.

36

0.33

0.

36

0.36

0.

36

0.36

1x

ᶿ0.9

m

1xᶿ0

.9m

L08

25

398,

562.

41

8055

749.

94

1xᶿ0

.375

m

>63%

18%

0.

17

0.20

0.

21

0.21

0.

21

0.15

0.

20

0.20

0.

20

0.20

L08

50

398,

597.

18

8055

821.

54

3xᶿ0

.6m

63

%-1

8%

18

%

1.01

1.

26

1.30

1.

34

1.35

1.

16

1.33

1.

34

1.35

1.

35

3xᶿ0

.9m

3x

ᶿ0.9

m

L08

53

398,

616.

24

8055

841.

75

1xᶿ0

.45m

10

%-2

%

18%

-10%

18

%

0.06

0.

08

0.09

0.

11

0.12

0.

07

0.10

0.

11

0.14

0.

15

L08

56

398,

610.

72

8055

851.

39

3xᶿ0

.6m

*2

%-1

%

*10%

-2%

18

%

1.08

1.

40

1.99

2.

07

2.12

1.

26

2.01

2.

06

2.23

2.

32

3xᶿ0

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3x

ᶿ0.9

m

L08

57

398,

587.

77

8055

796.

74

1xᶿ0

.3m

63

%-1

8%

18

%

0.09

0.

15

0.15

0.

15

0.16

0.

12

0.15

0.

15

0.16

0.

16

L08

71

398,

457.

21

8055

519

3xᶿ0

.3m

63

%-1

8%

18

%

0.12

0.

16

0.16

0.

16

0.16

0.

14

0.16

0.

16

0.16

0.

16

L08

74

398,

466.

41

8055

517.

91

3xᶿ0

.3m

10

%-2

%

18%

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18

%

0.12

0.

16

0.16

0.

16

0.16

0.

14

0.16

0.

16

0.16

0.

16

L08

77

398,

485.

69

8055

535.

27

3xᶿ0

.3m

<1

%

18

%

0.12

0.

16

0.16

0.

16

0.16

0.

13

0.16

0.

16

0.16

0.

16

L09

64

398,

529.

44

8055

573.

31

3xᶿ0

.375

m

<1%

18%

0.

12

0.16

0.

16

0.16

0.

16

0.12

0.

16

0.16

0.

16

0.16

L09

68

398,

507.

59

8055

554.

27

3xᶿ0

.3m

10

%-2

%

18%

-10%

18

%

0.13

0.

16

0.16

0.

16

0.16

0.

13

0.16

0.

16

0.16

0.

16

Up

str

eam

of

ou

tlet

L075

2

L07

49

398,

483.

56

8055

913.

42

1xᶿ0

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63

%-1

8%

18

%

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0.

12

0.16

0.

30

0.30

0.

08

0.17

0.

25

0.26

0.

27

L07

50

398,

483.

21

8055

912.

68

1xᶿ0

.45m

63

%-1

8%

18

%

0.07

0.

13

0.16

0.

30

0.30

0.

09

0.17

0.

22

0.26

0.

27

L07

52

398,

489.

94

8055

916.

68

4xᶿ0

.525

m

*2%

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0%-2

%

18%

0.

87

1.14

1.

18

1.75

1.

75

0.97

1.

23

1.47

1.

52

1.55

L07

56

398,

461.

46

8055

863.

12

2xᶿ0

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2%

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10

%-2

%

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0.

86

0.88

0.

89

0.97

0.

97

0.89

0.

89

0.98

0.

98

0.98

L07

60

398,

475.

10

8055

888.

69

1xᶿ0

.125

m

10%

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63

%-1

8%

18%

0.

00

0.00

0.

00

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00

0.00

0.

00

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0.

00

0.00

L07

61

398,

385.

51

8055

842.

64

1xᶿ0

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63

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8%

18

%

0.30

0.

32

0.34

0.

34

0.34

0.

33

0.34

0.

38

0.38

0.

44

L07

62

398,

434.

88

8055

815.

83

1xᶿ0

.6m

>6

3%

18

%

0.33

0.

37

0.38

0.

43

0.43

0.

37

0.39

0.

42

0.42

0.

42

L07

63

398,

431.

10

8055

806.

5 1x

ᶿ0.4

5m

*<1%

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%

18%

0.

14

0.18

0.

18

0.18

0.

18

0.17

0.

18

0.18

0.

18

0.18

L07

64

398,

432.

30

8055

795.

77

1xᶿ0

.3m

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1%

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-2%

18

%

0.10

0.

14

0.14

0.

14

0.14

0.

14

0.14

0.

14

0.14

0.

14

Cas

sow

ary

Coa

st R

egio

nal C

ounc

il M

aste

r Dra

inag

e St

udy:

Mou

rilya

n B-

5 In

fras

truc

ture

Tab

les

G

:\Adm

in\B

1892

1.g.

cdh\

R.B

1892

1.01

7.02

.Mou

rilya

n.do

cx

ID

Pipe

Cen

troid

C

urre

nt S

ize

Cur

rent

C

apac

ity

(AE

P)

Futu

re C

limat

e C

apac

ity (w

here

di

ffere

nt)

(AE

P)

Des

ign

Cap

acity

Cur

rent

Clim

ate

AEP

Flo

w (m

³/s)

Futu

re C

limat

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EP F

low

(m³/s

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pgra

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equi

red

East

ing

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thin

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%

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%

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63%

18

%

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1%

C

urre

nt

Clim

ate

Futu

re

Clim

ate

L08

35

398,

343.

18

8055

866.

54

1xᶿ0

.6m

63

%-1

8%

18

%

0.23

0.

23

0.24

0.

24

0.24

0.

24

0.25

0.

27

0.27

0.

27

L08

36

398,

363.

79

8055

846.

83

1xᶿ0

.375

m

*18%

-10%

18%

0.

13

0.13

0.

13

0.13

0.

13

0.13

0.

13

0.13

0.

13

0.13

L08

38

398,

299.

26

8055

889.

59

2xᶿ0

.6m

10

%-2

%

18

%

0.44

0.

46

0.46

0.

46

0.46

0.

45

0.45

0.

45

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0.

45

L08

39

398,

331.

01

8055

864.

2 2x

ᶿ0.3

75m

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%

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%

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0.

20

0.20

0.

24

0.25

0.

20

0.21

0.

24

0.28

0.

30

L08

42

398,

314.

49

8055

864.

75

2xᶿ0

.375

m

63%

-18%

18%

0.

13

0.16

0.

16

0.19

0.

20

0.14

0.

17

0.19

0.

21

0.23

L08

44

398,

296.

19

8055

860.

11

2xᶿ0

.375

m

10%

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63

%-1

8%

18%

0.

10

0.15

0.

17

0.18

0.

18

0.11

0.

18

0.18

0.

18

0.20

L08

45

398,

275.

68

8055

852.

89

1xᶿ0

.3m

<1

%

18

%

0.02

0.

03

0.03

0.

03

0.03

0.

03

0.03

0.

03

0.03

0.

03

L08

46

398,

277.

13

8055

945.

48

1xᶿ0

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m

>63%

18%

0.

06

0.07

0.

08

0.09

0.

10

0.06

0.

08

0.09

0.

11

0.11

P

ipeU

pda0

1

398,

260.

73

8055

898.

17

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11

8%

0.41

0.

44

0.44

0.

44

0.44

0.

41

0.42

0.

42

0.42

0.

42

Pip

eUpd

a02

398,

249.

85

8055

867.

96

1xᶿ0

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63

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8%

21

8%

0.39

0.

44

0.44

0.

44

0.44

0.

40

0.42

0.

42

0.42

0.

42

Pip

eUpd

a03

398,

239.

41

8055

842.

7 1x

ᶿ0.6

m

18%

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63

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8%

618%

0.

19

0.26

0.

27

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0.

30

0.23

0.

28

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0.

30

0.30

P

ipeU

pda0

4

398,

240.

66

8055

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79

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m

10%

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0.

00

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0.03

P

ipeU

pda0

5

398,

232.

58

8055

824.

62

1xᶿ0

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10

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%

63%

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51

8%

0.19

0.

26

0.27

0.

29

0.30

0.

23

0.28

0.

29

0.30

0.

30

Pip

eUpd

a06

398,

226.

05

8055

807.

95

1xᶿ0

.6m

10

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%

18%

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41

8%

0.19

0.

24

0.24

0.

25

0.25

0.

22

0.25

0.

25

0.25

0.

25

Pip

eUpd

a07

398,

219.

00

8055

789.

88

1xᶿ0

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10

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%

18%

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10

18%

0.

15

0.18

0.

18

0.19

0.

19

0.18

0.

19

0.19

0.

19

0.19

P

ipeU

pda0

8

398,

232.

91

8055

782.

5 1x

ᶿ0.6

m

10%

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0.

15

0.17

0.

18

0.18

0.

18

0.17

0.

17

0.17

0.

17

0.17

P

ipeU

pda0

9

398,

232.

12

8055

774.

09

1xᶿ0

.225

m

*2%

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%

318%

0.

05

0.06

0.

06

0.06

0.

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0.06

0.

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0.06

P

ipeU

pda1

0

398,

246.

08

8055

775.

71

1xᶿ0

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10

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%

11

18%

0.

10

0.12

0.

12

0.12

0.

12

0.12

0.

12

0.12

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12

0.12

P

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pda1

1

398,

260.

93

8055

768.

13

1xᶿ0

.225

m

63%

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%

0.05

0.

06

0.06

0.

06

0.06

0.

06

0.06

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0.06

0.

06

Pip

eUpd

a12

398,

261.

67

8055

757.

94

1xᶿ0

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m

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%

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%

0.06

0.

06

0.06

0.

06

0.06

0.

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0.06

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0.06

0.

06

Pip

eUpd

a13

398,

254.

27

8055

844.

95

1xᶿ0

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m

10%

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818%

0.

01

0.01

0.

01

0.03

0.

03

0.01

0.

01

0.01

0.

03

0.03

H

igh

way C

ross D

rain

ag

e

L00

18

398,

127.

74

8055

693.

63

1x3.

35m

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8m

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%

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3.32

6.

23

7.25

8.

64

8.97

4.

00

7.38

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20

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9.

22

L00

19

398,

130.

67

8055

696.

58

1x3.

25m

x2.

1m

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3.80

7.

14

8.31

9.

90

10.2

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58

8.45

9.

39

10.3

9 10

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L00

20

398,

134.

11

8055

697.

34

1x3.

35m

x1.

8m

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%

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3.32

6.

23

7.26

8.

64

8.97

4.

00

7.38

8.

20

9.07

9.

22

L00

23

397,

487.

95

8055

031.

44

1x2.

4m x

1.5m

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1%

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2.

60

4.81

5.

38

6.82

8.

41

3.51

5.

59

6.27

8.

78

8.78

L00

24

397,

489.

40

8055

033.

75

1x2.

4m x

1.5m

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1%

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2.

74

4.76

5.

50

6.85

8.

41

3.55

5.

60

6.35

8.

79

8.79

L09

02

397,

441.

26

8054

942.

87

1xᶿ1

.2m

*<

1%

2%

0.

77

1.74

1.

94

2.59

2.

98

0.93

1.

99

2.28

3.

07

3.25

Cas

sow

ary

Coa

st R

egio

nal C

ounc

il M

aste

r Dra

inag

e St

udy:

Mou

rilya

n B-

6 In

fras

truc

ture

Tab

les

G

:\Adm

in\B

1892

1.g.

cdh\

R.B

1892

1.01

7.02

.Mou

rilya

n.do

cx

ID

Pipe

Cen

troid

C

urre

nt S

ize

Cur

rent

C

apac

ity

(AE

P)

Futu

re C

limat

e C

apac

ity (w

here

di

ffere

nt)

(AE

P)

Des

ign

Cap

acity

Cur

rent

Clim

ate

AEP

Flo

w (m

³/s)

Futu

re C

limat

e A

EP F

low

(m³/s

) U

pgra

de R

equi

red

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ing

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thin

g 63

%

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%

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%

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urre

nt

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ate

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re

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ate

L09

03

397,

441.

86

8054

944.

29

1xᶿ1

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*<

1%

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0.

78

1.73

1.

95

2.59

2.

97

0.93

2.

01

2.28

3.

07

3.25

L09

12

397,

874.

52

8055

449.

99

1xᶿ1

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*<

1%

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0.

20

1.75

2.

47

2.81

2.

85

0.41

2.

53

2.75

2.

86

2.88

L09

13

398,

034.

50

8055

608.

42

1xᶿ1

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1%

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0.

48

1.99

2.

52

2.70

2.

70

1.32

2.

49

2.70

2.

70

2.70

L09

55

398,

088.

33

8055

652.

07

1xᶿ1

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0%-2

%

2%

0.

15

0.27

0.

29

0.40

0.

40

0.20

0.

30

0.39

0.

40

0.40

L09

57

398,

231.

21

8055

852.

74

1xᶿ0

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*<

1%

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2%

0.

31

0.38

0.

45

0.47

0.

47

0.32

0.

46

0.47

0.

47

0.48

(* c

ap

acit

y i

den

tifi

ed

by i

nsp

ecti

ng

ro

ad

im

mu

nit

y n

ear

the d

rain

ag

e in

fra

str

uctu

re)

Cas

sow

ary

Coa

st R

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nal C

ounc

il M

aste

r Dra

inag

e St

udy:

Mou

rilya

n B-

7 In

fras

truc

ture

Tab

les

G

:\Adm

in\B

1892

1.g.

cdh\

R.B

1892

1.01

7.02

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rilya

n.do

cx

B.2

Et

ty B

ay

ID

Pipe

Cen

troid

C

urre

nt S

ize

Cur

rent

Cap

acity

(AE

P)

Futu

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limat

e C

apac

ity (w

here

diff

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t) (A

EP)

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esig

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cassowary coast regional council master drainage …...2016/08/11 · cassowary coast regional...

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