Biggera Creek Catchment Hydraulic Study · Biggera Hydraulic Study 2015 Natural Hazards Planning &...

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Biggera Creek Catchment

Hydraulic Study August 2016

Version 4 – August 18 TRACKS-#45330069-v4-BIGGERA_CREEK_HYDRAULIC_STUDY_2015 Page 2 of 71

Title: Biggera Creek Catchment Hydraulic Study

Author: Ryan van Doorn

Senior Hydraulic Engineer

Study for: City Planning Branch

Planning and Environment Directorate

The City of Gold Coast

File Reference: WF27/44/01(P9)

TRACKS #45330069

Version history

Version Comments/Change Changed by

& date Reviewed by &

date

1.0 Draft RVD 2014 HM 2014

2.0 DTM update RVD 2015 EC 2015

3.0 Edited Terry Mitchell

July, 2016 Ryan van Doorn August, 2016

4.0 Edited Elton Chong August 2016

Distribution list

Name Title Directorate Branch

35468

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Executive Summary

The Natural Hazards (NH) team has developed a hydraulic model for the Biggera Creek catchment to generate a designated flood level (DFL) for the upcoming Gold Coast Planning Scheme or City Plan. The DFL (or flood planning level) is the statistical 1 in 100 year rainfall (or 1% Annual Exceedance Probability (AEP)) with adopted climate change factors and a coinciding storm surge event.

The Biggera hydraulic model was built using a 5m grid cell size to balance topographical representation with model stability and simulation run times. The hydraulic model is calibrated to tidal conditions and to historic rainfalls/flood events. An ALERT station located near the entrance of the low flow pipe at Biggera Dam’s embankment, was used to calibrate the model to historical flood events. Tidal information recorded by the Griffith Centre for Coastal Management in 2004-2005 was utilized for tidal calibration. This tidal information was used to compare the model's performance when simulating the same 2004-2005 tide. Good calibration was achieved by the Biggera Creek hydraulic model for both tidal and flooding interaction.

The Biggera hydraulic model has been used to simulate design event floods commonly known as average return intervals (ARI). Design events ranging from the 1 in 2 year ARI to the 1 in 2000 year ARI were simulated and for a variety of scenarios. The scenarios varied initial conditions, storm surge interactions and climatic conditions.

The model described in this report has been used to develop the DFL for the Biggera Creek Catchment. Its results will be adopted in the 2015 City Plan Major Update 2 (Resolution G16.0726.020) as the new flood planning map.


Table of Contents

Executive Summary ............................................................................................................................. 3

1. Introduction ................................................................................................................................... 7

1.1 Overview .............................................................................................................................. 7

1.2 2003 Flood Planning Level .................................................................................................. 7

1.3 Assumptions and Limitations ............................................................................................... 8

1.3.1 Information Use .......................................................................................................... 8

1.3.2 Model Grid (DEM) ....................................................................................................... 8

1.3.3 Hydraulic Model .......................................................................................................... 8

1.3.4 Hydrologic Model ........................................................................................................ 8

1.4 Acknowledgement ............................................................................................................... 8

2. Background ................................................................................................................................... 9

2.1 Catchment Description ........................................................................................................ 9

2.2 Previous Studies ................................................................................................................ 10

2.2.1 Biggera Creek Catchment Drainage Study (Ref. 3) ................................................. 10

2.2.2 Preliminary Design of Biggera Creek Flood Mitigation Dam (Ref. 4) ....................... 10

2.2.3 Biggera Creek Flood Mitigation Scheme (Ref. 5) ..................................................... 10

2.2.4 Flood Levels in Lower Biggera Creek (Ref. 6) .......................................................... 10

2.2.5 Biggera Creek Hydraulic Report (Ref. 7) .................................................................. 11

2.2.6 Biggera Creek Dam Break Analysis (Ref. 8) ............................................................ 11

2.2.7 Biggera Creek Dam Maintenance Plan and Manual (Ref. 9) ................................... 11

3. Hydraulic Model Development ................................................................................................... 12

3.1 Overview ............................................................................................................................ 12

3.2 Software Modelling Choice ................................................................................................ 12

3.3 Software Version ............................................................................................................... 12

3.4 Hydrology ........................................................................................................................... 12

3.5 Hydraulic Modelling Approach ........................................................................................... 13

3.6 Datum ................................................................................................................................ 13

3.6.1 Horizontal Datum ...................................................................................................... 13

3.6.2 Vertical Datum .......................................................................................................... 13

3.7 Hydraulic Model Extent ...................................................................................................... 14

3.8 Input Locations .................................................................................................................. 15

3.9 Tailwater Conditions .......................................................................................................... 16

3.10 Storm Surge Conditions ..................................................................................................... 16

3.11 Digital Elevation Model ...................................................................................................... 17

3.12 Bathymetric Surveys .......................................................................................................... 18

3.12.1 Field Reconnaissance Survey .............................................................................. 18

3.13 Model Parameters ............................................................................................................. 19

3.13.1 Floodplain Roughness ......................................................................................... 19


3.13.2 Eddy Viscosity ...................................................................................................... 21

3.13.3 Flooding and Drying ............................................................................................. 21

3.14 Structures .......................................................................................................................... 22

3.14.1 Hydraulic Structures Not in Model ........................................................................ 23

3.14.2 Culvert Data ......................................................................................................... 25

3.14.3 Bridge Data .......................................................................................................... 27

3.15 Biggera Creek Dam ........................................................................................................... 29

4. Model Calibration and Verification ............................................................................................ 30

4.1 ALERT Stations ................................................................................................................. 30

4.2 Maximum Height Gauges and Historical Debris Mark ....................................................... 31

4.3 Tide Table .......................................................................................................................... 33

4.4 Tidal Calibration ................................................................................................................. 33

4.4.1 Tide Calibration Results ........................................................................................... 34

4.4.2 Discharge Calibration Results .................................................................................. 34

4.5 June 2005 Calibration ........................................................................................................ 35

4.5.1 Calibration Discussion .............................................................................................. 35

4.6 January 2008 Calibration ................................................................................................... 36

4.6.1 Calibration Discussion .............................................................................................. 36

5. Design Floods .............................................................................................................................. 37

5.1 Introduction ........................................................................................................................ 37

6.2 Initial Water Level .............................................................................................................. 38

6.3 Sensitivity Tests ................................................................................................................. 38

6. Conclusion ................................................................................................................................... 39

7. Recommendations ...................................................................................................................... 40

8. References ................................................................................................................................... 41

Appendix A. Figures illustrating Tidal and Discharge Calibrations, 2004-2005. .......................... 42

Figure A-1 December 2004 Tidal Calibration (B9) ................................................................... 42

Figure A-2 December 2004 Tidal Calibration (Seaway) ........................................................... 42

Figure A-3 January 2005 Tidal Calibration ............................................................................... 43

Figure A-4 January 2005 Tidal Calibration (Seaway Discharge) .............................................. 43

Figure A-5 January 2005 Tidal Calibration (North Channel Discharge) ................................... 44

Figure A-4 January 2005 Tidal Calibration (Southern Channel Discharge) ............................. 44

Appendix B ......................................................................................................................................... 45

Tidal Planes (Source: Marine Safety Queensland) ..................................................................... 45

Appendix C: Hydraulic Structures .................................................................................................... 46


LIST OF ABBREVIATIONS

AEP Annual Exceedance Probability

AFC Acceptable Flood Capacity

AHD Australian Height Datum

ALS Aerial Laser Survey

ARI Annual Recurrence Interval (similar to Return Period - years)

ARR Australian Rainfall and Runoff Guidelines Engineers Australia

Assets City Assets Branch (City Infrastructure Directorate)

BOM Bureau of Meteorology

DTM Digital Terrain Model

CoGC City of Gold Coast

GIS Geographic Information System

IFD Intensity Frequency Duration (design rainfall data)

LDG Land Development Guidelines (2005 edition)

MHG Maximum Height Gauge

MHWS Mean High Water Spring

NH Natural Hazards Team (Planning and Environment Directorate)

PAR Population at Risk

P&E Planning and Environment Directorate

PMF Probable Maximum Flood

PMPDF Probable Maximum Precipitation Design Flood

QUDM Queensland Urban Drainage Manual (2007 edition)

RL Reduced Level (m) (in this report in AHD unless stated otherwise)

TWL Tail-water Level (the downstream boundary for backwater analysis)

Biggera Hydraulic Study 2015 Natural Hazards Planning & Environment Directorate


1. Introduction

1.1 Overview

The Natural Hazards team (NH) has undertaken a hydraulic model development for the Biggera Creek catchment for the purpose of updating the Council of City of Gold Coast’s (City) designated flood level (or flood planning level). This new 1% AEP flood level (taking into account climate change scenarios) will be incorporate into the new Gold Coast Planning Scheme or City Plan.

The Biggera Creek hydraulic model has been based on MIKE FLOOD software which is capable of simulating complex flows in the floodplain and in the numerous river/canal systems. The selection of the MIKE FLOOD model was based on its capability to couple, hydro-dynamically, the two dimensional topographic grid with the one dimensional hydraulic structures. The model has more than 25 structures incorporated (i.e. weirs, culverts and bridges). The 5m topographic grid used in the model was the combination of the most recent airborne laser survey data and bathymetric information. The model uses hydrologic inputs which are sourced from City of Gold Coast City’s hydrology review project undertaken in 2009 and completed in 2014 (Ref. 1).

This report documents the hydraulic modelling methodology, its data sources and the model calibration results. It also provides details of the design run setups.

1.2 2003 Flood Planning Level

Previously, the Danish Hydraulic Institute’s software platform MIKE 11 was used to model the Biggera Creek catchment to establish flood planning levels in 2003. MIKE 11 is a one-dimensional model with the ability to simulate riverine flooding by using hydrologic inputs, interpolated cross-sections and set boundary conditions. It is also excellent at simulating design runs and historical rainfall events very quickly whilst producing reasonably accurate results.

In 2003, MIKE 11 simulated the then DFL scenario (which was a 1 in 100 year flood with a 1 in 100 year triangulated storm surge) and produced elevation points (water levels) along Biggera Creek. These water levels, produced by MIKE 11, were compared to the Digital Elevation Model of the Biggera catchment using a GIS program called MapInfo. Any topographic values along the creek which were below the MIKE 11 water levels were considered flooded. The end result from this GIS interpretation produced the flood map which was contained within the 2003 Planning Scheme for the Biggera catchment area.



1.3 Assumptions and Limitations

The development of this Biggera Creek Hydraulic Study had the following assumptions and limitations:

1.3.1 Information Use

The hydraulic report was prepared based on information available at the time of writing.

The analysis and overall approach adopted by this study is specifically prepared for internal use. For this reason, any third parties are not to use any of the contents contained in this report unless written approval from City of Gold Coast City is obtained.

City of Gold Coast City believes that the assessments in this report are accurate for their intended purpose and disclaims any responsibility for any loss or damage suffered as a result of placing reliance upon information provided in this report.

1.3.2 Model Grid (DEM)

The model grid is based on airborne laser surveys conducted between July 2010 and July 2012.

The airborne laser survey data acquisition and post-processing has been controlled to achieve a vertical accuracy of about 0.15 m and horizontal accuracy of about 0.45 m.

The topographical data is supplemented by hydrographical surveys conducted from various years which may influence flood conveyance and storage.

1.3.3 Hydraulic Model

Bridges have used the Energy Equation for loss calculations in the model engine.

Biggera Dam’s Crest is modelled in MIKE 21 by the DEM and its low flow pipe in MIKE11.

Cross-sections are modelled by Total Hydraulic Radius and Distributed flow coefficients.

The hydraulic model does not include a storm-water drainage system (e.g. pipe, inlet pits, etc.) which may influence local flooding paths and inundation extents. A separate model is required to simulate this type of pressurised flow through three-way coupling using specialised software (e.g. MIKE URBAN, TUFLOW or MOUSE).

1.3.4 Hydrologic Model

The calibrated URBS model outputs are from the 2009 Biggera Hydrology Study (Ref 1).

Catchments are routed specifically for hydraulic model input.

Local Hydrographs were printed at the centroid of individual catchments.

1.4 Acknowledgement

The City of Gold Coast would like to acknowledge the Bureau of Meteorology and Marine Safety Queensland for providing invaluable calibration data for this project.



2. Background

2.1 Catchment Description

The Biggera Creek catchment is a small catchment located within the larger Broadwater Catchment (Figure 1). It is approximately 9.4 km in length with a catchment area of about 21 km2 (Ref. 2).

Biggera Creek originates in the foothills of Parkwood and meanders through the suburbs of Arundel and Labrador where it gathers stormwater inflows, and then travels through the numerous canal estates of Runaway Bay, Biggera Waters before discharging into the Broadwater. It is a heavily urbanised catchment that receives a lot of stormwater runoff from the surrounding urban and industrial areas.

An important flood mitigation feature in the catchment is the Biggera Creek retardation basin, which was constructed in the 1980’s. The dam is located west of Olsen Avenue, Labrador (Gold Coast UBD Map 28, Ref. L3). It serves as a retardation dam that attenuates the flood peak and provides flood storage to reduce flood impacts downstream.

Figure 1 Biggera Creek Catchment

Note: Biggera Creek (Red) is part of the larger Broadwater Catchment and consists of a number of suburbs



2.2 Previous Studies

A number of flood studies have been previously undertaken on Biggera Creek. The following studies are of relevance.

2.2.1 Biggera Creek Catchment Drainage Study (Ref. 3)

In 1976, Cameron McNamara & Partners investigated the effectiveness of a retardation basin to the overall drainage system of the Biggera Creek catchment. The option ‘Basin C’, located near Olsen Avenue, was selected as the preferred location. In summary, the report detailed:

3 historical storms (Jan 1974, Mar 1974 and Mar 1976),

50 year ARI design storm and PMF hydrographs.

The critical storm duration at ‘Basin C’ was 6 hours (50 year ARI).

2.2.2 Preliminary Design of Biggera Creek Flood Mitigation Dam (Ref. 4)

Based on the June 1976 report, Cameron McNamara & Partners prepared a preliminary design of Biggera Creek’s retardation dam (Ref. 3). The report also contains a geotechnical investigation report by Coffey & Partners. This report recommended that the basin have an emergency spillway (30 m wide at invert of 12.5 m AHD), a 1.2 m outlet pipe and embankment crest level of about 15 m. This configuration was designed to enable spilling over the spillway for events greater than the March 1974 event, yet still prevents the dam overtopping the embankment due to a PMPDF event.

2.2.3 Biggera Creek Flood Mitigation Scheme (Ref. 5)

Cameron, McNamara & Partners investigated a number of flood mitigation options and evaluated the cost benefit of each option in 1980 (Ref. 5). This report documents the two options which were considered effective: a retention basin and unlined Biggera Creek channel.

2.2.4 Flood Levels in Lower Biggera Creek (Ref. 6)

Following the completion of the retention basin, Cameron McNamara prepared a report to determine the flood levels downstream of Brisbane Road using a direct step method (“DS BWC6”).

This investigation used the 1967 flood (which is about 1 in 50 year flood) to simulate post dam in the 1986 condition. The results derived consist of flood levels from Marine Parade to Olsen Avenue.



2.2.5 Biggera Creek Hydraulic Report (Ref. 7)

WFM prepared an internal report for Engineering Services to undertake a Dam Break Assessment for the Biggera Creek Dam in Labrador. The study developed a URBS hydrological model and a MIKE 11 model in 2004.

2.2.6 Biggera Creek Dam Break Analysis (Ref. 8)

An addendum to the 2004 hydraulic report assessed the dam break scenarios to local properties. The scenarios coincided with a Probable Maximum Flood (PMF) and a sunny dam break scenario for erosion and time dependent failures.

2.2.7 Biggera Creek Dam Maintenance Plan and Manual (Ref. 9)

GHD prepared a maintenance report to resolve current Biggera Creek Dam maintenance issues and to conduct routine maintenance inspections. In summary, the report states that:

The Director of Engineering Services is responsible to maintain this dam in accordance to the Queensland Dam Safety Management Guidelines.

The dam provides attenuation of floods and gradually releases flood water through a 1.2 Dia. outlet pipe.

The emergency spillway channel is about 30m wide at the dam crest.

Modification to the intake structure was undertaken in 2002 to increase the discharge capacity (reducing vortexes) and to reduce the noise induced by the vortex.



3. Hydraulic Model Development

3.1 Overview

A MIKE flood model requires hydrologic, structural and topographic information to enable simulations of water movement. The following section describes in detail the inputs and constraints within the Biggera Creek MIKE Flood hydraulic model. It also describes briefly the methodologies.

3.2 Software Modelling Choice

Due to the numerous concrete lined channels, culverts and intricate bridges incorporated within the Biggera Creek catchment, a sophisticated software platform was required to model riverine flooding of Biggera Creek. DHI’s MIKE Flood was chosen to model Biggera Creek due to its ability to simulate complex floodplains and canal systems using hydro-dynamically coupled two-dimensional topography grids with one-dimensional hydraulic structures. Simply speaking, MIKE Flood was able to represent hydraulic structures of bridges and culverts one dimensionally in MIKE 11 whilst simulating the hydrodynamics of overland flow in MIKE 21. Once the structures and topography are specified, the two software platforms can be dynamically coupled.

3.3 Software Version

At the time of development of the Biggera Creek hydraulic model, MIKE FLOOD 2014 with Service Pack 3 was the software package used.

Upgrading the model to newer versions of MIKE Flood requires the MIKE 11 network file be opened and resaved.

3.4 Hydrology

The hydraulic model hydrologic inputs are based on a hydrology review project undertaken by Natural Hazards in 2014 (Ref 1). The following are of note to this 2014 study:

Rating curves developed during this study are yet to be verified with BOM. A sufficient record of historical peak height or discharge data was not available to

undertake a flood frequency analysis (FFA) at the stream gauging station within the Biggera Creek catchment.

The 2014 URBS hydrological model is acceptable to use for hydraulic model simulation due to its calibration to the January 2008, January 2013 and June 2005 flood events.

The URBS model produces inflow hydrographs from Q2 to PMP. AWE2000 Temporal Patterns α (Channel Lag Parameter) = 0.2 β (Catchment Lag Parameter) = 2.0 m (catchment non-linearity parameter) = 0.8 Urbs32.exe version last edited 9/08/2009 3:31pm.

More information on the hydrology can be found in the hydrologic report (Ref 1).



3.5 Hydraulic Modelling Approach

The approach undertaken was to calibrate a hydraulic model to real flood events for the Biggera Creek system using a reputable software platform, i.e. the MIKE Flood software (2014, Service Pack 3) and to simulate a combination of design flood events to attain the DFL.

MIKE Flood is capable of simulating complex flows and floodplain storage in the 2D topographical terrain (using MIKE 21 grid) and is able to provide flow constriction of hydraulic structures (using MIKE 11 structures). This combination is very useful, as the Biggera floodplain consists of numerous structures (weirs, culverts and bridges) as well as the numerous river and canal systems.

The local stormwater drainage systems (i.e. the culvert pipes, inlet pits, grates etc.) are not included in this model as they have a relatively small impact on the regional flooding behaviour.

3.6 Datum

Figure 2 Map Grid of Australia

3.6.1 Horizontal Datum

The horizontal coordinates use Map Grid of Australia (MGA) Zone 56 projection.

3.6.2 Vertical Datum

The vertical coordinates is referenced to Australian Height Datum (AHD) 1992.



3.7 Hydraulic Model Extent

The hydraulic model covers the whole of the Biggera Creek catchment and includes Madang Canal and the Bayview Harbour area (Figure 3). Another model grid was developed so that it can be calibrated to tide. This extended version is shown in Figure 4. Further details of the tidal calibrations are discussed in Section 4.4 . The Biggera MIKE Flood model has one tidal boundary, which is sourced from the recorded data at the Gold Coast Seaway TM station. This one-boundary model is used for flood calibration and design runs (Figure 5). On the other hand, the tide model boundary is sourced from a calibrated Broadwater model (Ref 14).

Figure 3 Biggera Creek’s MIKE FLOOD model extent.

Figure 4 Biggera Creek’s MIKE FLOOD model extent for tide calibration.



3.8 Input Locations

There are 45 local inflow locations sourced from the hydrological model. The location of the inflow locations are shown in Figure 5. These 45 inflows are added into the hydraulic model via the source and sinks option in the MIKE 21 setup. A set of 4 cells are used as a reference point to distribute the flow into the system.

Figure 5 Model boundaries and inflow locations for the flood model.

Figure 6 Model boundaries for the Tide model



3.9 Tailwater Conditions

For all design runs, a constant boundary condition of Mean High Water Springs (0.66mAHD) was set (refer Appendix B for tidal planes). A constant boundary was set to ensure that high water level occur simultaneously with the flood peak and produced a positively estimated flood surface.

Table 1 Static Water Level Boundaries

In some instances, it was necessary to increase linearly the boundary condition to the MHWS mark. This was apparent in the future scenarios of 2050, 2070 and 2100 of Biggera Creek Design Event Simulations. It was necessary to increase the boundary to these levels, as initial conditions could not be determined for the future. As such, the boundary file was changed as per below.

Table 2 Time varying Boundary Conditions

For Historical Event simulations, the Biggera Creek MIKE Flood model used the tidal elevations recorded at the Gold Coast Seaway for the corresponding event.

For the Designated Flood level, two boundary conditions were set to create a flood surface envelope. The envelope was to contain two surfaces: a 1 in 100 Flood with a 1 in 20 year storm surge and a 1 in 20 year flood with a 1 in 100 year storm surge. The two surfaces produced by these scenarios were combined together in a GIS environment. Only the maximum value from each grid cell was obtained. The final values and grid surface was that of the Designated Flood Level.

The condition of MLWS was used to generate the maximum possible velocity. With a low tail-water condition, this allowed maximum flow out to the Broadwater.

3.10 Storm Surge Conditions

Storm surge conditions were received from an external consultant for three locations. The locations of storm surge conditions were at Logan, The Seaway and The Tweed.

Values of MHWS peak water levels are to reach 1.46mAHD by 2100 (at the Seaway). See the GHD Storm Tidy Study, Final Addendum Report. February 2013 #39733283 (Ref. 27) for more information of values and climate conditions.



3.11 Digital Elevation Model

Bathymetric data obtained in 2013 was combined with LiDAR information to create the DEM for the Biggera Creek MIKE Flood model. The following data sources were used to produce the DEM:

Aerial Laser Survey 2009/2011/2012 (GCCC_2m_DTM_Dec_2014)

Bathymetric Data from 2013

2003 Cross-section Survey Data (Bridge Decks).

The following figure depicts the DEM that is used in the Biggera MIKE Flood Model.

Figure 7 DEM Grid

There are limitations when using LiDAR for DEM modelling. See ‘limitations’ Department of Environment and Resource Management - LiDAR and Orthophoto Acquisition 2009 for more details.



3.12 Bathymetric Surveys

The 5m topographical grid used in the hydraulic model was developed from the 2011/12 Airborne Laser survey (conducted between July 2010 and July 2012). The data was supplemented by various bathymetric surveys as shown in Figure 8.

Figure 8 Data sources for model grid

3.12.1 Field Reconnaissance Survey

To ensure data quality, site inspections were also conducted to identify and verify ALERT gauging station locations and key hydraulic structures for this study (refer to Appendix C).



3.13 Model Parameters

The following are the MIKE 21 model calibration parameters:

3.13.1 Floodplain Roughness

The key calibration parameter for the hydraulic model is the floodplain roughness or Manning’s ‘M’ roughness coefficient. Based on literature review and past studies, the following roughness values were adopted as shown in the following table.

Table 3 Typical Manning’s roughness values

Description Manning’s ‘M’ Manning’s ‘n’

Road 50 0.020

Waterways 40 0.025

Open Space/Short Grass (No Trees) 30 0.033

Forest/Dense Brush 8.33 0.120

Mangroves 16.67 0.060

Sea grass 28.5 0.035

Low Density (>2000m2 block/Acreage/Golf Course) 25 0.040

Medium Density (1000-2000m2 block) 22.22 0.045

High Density (<1000m2 block/high rise) 13.33 0.075

The above values represent the floodplain roughness and are based on the recommended values from:

Chapter 7 of the ARR 1998 (Ref. 15)

Chapter 9 of the QUDM 2008 (Ref 16)

Chapter 4 of Main Road’s Road Drainage Manual (Ref. 17)

Appendix C of BCC’s Natural Channel Design Guidelines (Ref. 18)

An Australian Handbook of Stream Roughness Coefficients (Ref. 19)

Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Flood Plains (Ref. 20)

Verified Roughness Characteristics of Natural Channels (Ref. 21).

A roughness map was developed from aerial photography and Council’s GIS layers. The distribution of the Manning’s ‘n’ roughness coefficient is illustrated in Figure 9.



Figure 9 Manning’s roughness map.



3.13.2 Eddy Viscosity

Another MIKE 21 parameter is the velocity based eddy viscosity which is estimated by using the following formula:

Depthe 1.0

The values of 0.5 was selected in the floodplain and 10 around hydraulic structures (for stability)

3.13.3 Flooding and Drying

The minimum water depth allowed in a point before it is taken out of calculation (drying depth), and also the water depth at which the point will be re-entered into the calculation (flooding depth) will affect the extent of inundation on a floodplain, but not the maximum flood surface level.

To ensure proper mapping extent, taking into account floodplain shape and slope, the following drying and flooding values were adopted:

Drying = 0.02

Flooding =0.05.



3.14 Structures

About 24 key hydraulic structures, crucial for calibration, are incorporated in the hydraulic model. A summary of the hydraulic structure characteristic is shown in Figure 10 and listed in Section 3.14.2 and Section 3.14.3 .

More structure information is provided in the Appendix

Figure 10 Hydraulic structure locations



3.14.1 Hydraulic Structures Not in Model

A number of hydraulic structures are not in the current model as they are not important for flood mapping. Generally, pipes with diameters less than 900mm were not included in the modelling as it was assumed that they would have a relatively small impact on the flooding behaviour.

The structures that are not in the model are as follows:

Cross-drainage culverts along Olsen Avenue, Parkwood Drive and Smith Street

Subsurface culverts and pits around Captain Cook Drive and Kendor Street as well as MIKE Hatcher Racetrack stormwater pipes and basin (Figure 11)

The Middle, North and East Quay Bridges are not included in the current model setup due to the arch design (Figure 12).

Bayview Harbour was excluded from the MIKE21 component of the MIKE Flood Model.

Figure 11 Structures not in Model

Most hydraulic structures around Mike Hatcher Park and Kendor Street Drainage Corridor are not in the model.



Figure 12 Bridges in Harbour Quays are not in the model.

Figure 13 Bayview Harbour is not modelled

Bayview Harbour produced model instability and was sectioned off from the Broadwater. The harbour wall was continued around the harbour entrance to close the harbour into a lake. A level of 2.1mAHD was set for the extended wall height and this was set as consistent with the level surveyed for the harbour seawall.



3.14.2 Culvert Data

No x y U/s Invert

D/s Invert Description MIKE 11 Survey Remarks ID Description

CU1B 538125.2 6907771.7 2.81 2.59 Musgrave Ave Culverts Y

2.4Wx1.4H and 1.8Wx1.2H (3 box

culverts)

SWDP1112465,

66, 67

2.7Wx0.9Hx22.1L

(2)

CU2B 537166.9 6908387.3 5.59 5.52 Napper Rd Culverts Y 2.7m Dia (4 circular culverts)

SWDP1080202,

3, 4, 5 2.1 Dia x 50L (4)

CU3B 537927.2 6908448.3 2.54 2.27 Olsen Ave Culverts Y

2.4Wx1.6H (1 box culvert), Deck is

0.46 m thick SWDP1135308

2.4Wx1.5Hx37.6L

(1)

CU4B 538216.9 6908243.2 0.76 0.65 Govt Rd Culverts 1 Y

3.0Wx2.4H (1 box culvert), Deck is

0.76 m thick SWDP1112464

3.0Wx2.4Hx21.8L

(1)

CU5B 538887.0 6908289.8 ‐0.43 ‐0.42 Govt Rd Culverts 2 Y

3.0Wx2.4H (2 box culverts),

3.0Wx2.6H(1 box culvert)

SWDP1112461,

62, 63

3.3Wx2.4Hx26.3L

(3)

CU6B 538926.0 6908545.0 ‐0.34 ‐0.36 Central St Culverts Y 3.0Wx2.4H (5 box culverts)

SWDP1112613,

14, 15, 16

3.0Wx2.4Hx20.0L

(4)

CU7B 539119.4 6908944.7 ‐0.44 ‐0.43 Whiting St Culverts Y 3.0Wx2.4H (3 box culverts)

SWDP1116473,

74, 75, 76

3.0Wx2.4Hx20.1L

(5)

CU8B 537481.7 6910783.9 ‐2.01 ‐2.65 Compass Drive Culverts 3.6m Dia (3 circular culverts)

SWDP1241616,

17, 18

3.6 Dia x 56.6L

(3)

CU9B 537147.6 6910290.0 1.49 1.67 Brisbane Road Culverts Y 1.2Wx0.9H (12 box culverts)

SWDP1144220‐

31

1.2Wx0.9Hx30.3L

(12)

CU10B 537104.8 6910048.8 2.1 2.0 Kendor Street Culverts Y 2.7Wx1.5H (2 box culverts)

SWDP1112628,

29

2.7Wx1.5Hx26.1L

(2)

CU11B 536957.3 6910048.6 ‐ ‐

Kendor Street Drainage

Corridor N 0.9 Dia (3 circular culverts)

SWDP1074474,

75, 76

0.9 Dia x 307.3L

(3)

CU12B 536789.3 6910061.2 ‐ ‐ Captain Cook Dr Culverts N 2.1Wx0.9Hx18.6L (6 box culverts)

SWDP1112633‐

37

2.1Wx0.9Hx18.6L

(6)

CU11B 537674.5 6908427.5 3.25 2.75 Biggera Dam Pipe

1.2 Dia (1 circular culvert), 55 m

long (Source: Drawing No 31217) ‐ ‐

CU14B 537464.6 6908094.3 4.60 4.51 Napper Road Culverts 2 Y 2.1m Dia (4 circular culverts)

SWDP1080224,

25, 26, 27

2.1 Dia. x 56.4L

(4)



No x y U/s Invert

D/s Invert Description MIKE 11 Survey Remarks ID Description

CU15B 536640.0 6906693.0 12.6 12.4 Smith Street Culverts Y ‐

SWDP1113509‐

16

3.6Wx1.2Hx26L

(8)

CU16B 537060.7 6907365.7 9.75 9.77

Parkwood Boulevard

Culverts Y ‐

SWDP1113517‐

19

3.0Wx1.2Hx20.4L

(3)

CU17B 538034.2 6907322.8 7.3 4.9

Trotting Track Pipe

Culvert Y 0.9m Dia (1 circular culvert) SWDP1072074

0.9 Dia. x 19.7L

(1)

CU1X 535287.3 6905742.9 ‐ ‐ Ashmore Road Culvert N ‐ ‐ ‐

CU2X 535421.8 6905746.7 ‐ ‐

Cathedral Avenue

Culverts N ‐ ‐ ‐



3.14.3 Bridge Data

The culverts and bridges are represented in the model as MIKE 11 structures. Culverts are generally explicitly coupled to the model grid. Bridges are generally implicitly coupled to the model grid and use the basic energy equation to determine the discharge and the back water profile through the bridge (Ref 20). It takes into account the friction loss and contraction/expansion losses and it requires four cross sections (refer Figure 14).

Figure 14 Location of up- and downstream cross section (Source: DHI).

1: Upstream river cross section. Defined in the cross section editor.

2: Upstream bridge cross section. Defined in the network editor, bridge geometry.

3: Downstream bridge cross section. Defined in the network editor, bridge geometry.

4: Downstream river cross section. Defined in the cross section editor.

Figure 15 Definition of the bridge cross section markers (Source: DHI).

The bridge loss factors include Channel Resistance, Contraction and Expansion Losses. The values for resistance on the bridge structure between markers 1 and 4 and between 5 and 3. Manning’s ‘n’ of value 0.033 was used (Table 3). For other bed resistance, between markers 4 and 5, the value in the HD editor was used.

As for the contraction and expansion losses, the following values were applied universally:

Contraction Loss = 0.3 Expansion Loss = 0.5



No x y U/s Invert

D/s Invert Description

MIKE 11 2004 Survey Remarks ID Description

BR1B 538324.8 6908037.5 ‐ ‐ Keith Park Pedestrian Bridge N ‐ BRID35 1.25Wx11L

BR3B 538960.7 6909431.5 ‐0.51 ‐0.48 Kenny Dr Pedestrian Bridge Y 3 span BRID30 2.6Wx27L

BR4B 538884.3 6909722.9 ‐0.51 ‐0.58 Ashton St Pedestrian Bridge Y 2 span BRID21 2.2Wx26L

BR5B 538893.8 6909874.3

‐

0.993 ‐1.198 Brisbane Rd Bridge 1 Y 3 span BRID21 26.5Wx32L

BR6B 539150.3 6910510.5 Hollywell Rd Pedestrian Bridge N 3 span ‐ ‐

BR7B 539175.1 6910525.6 ‐2.61 ‐2.62 Hollywell Rd Bridge Y 3 span ‐ ‐

BR8B 539861.4 6910951.7 ‐2.37 ‐2.66 Marine Parade Bridge Y 3 span ‐ ‐

BR9B 538230.9 6910760.0 ‐0.95 ‐0.95 Oxley Drive Bridge Northbound Y 3 span ‐ ‐

BR10B 538243.0 6910770.8 ‐0.95 ‐0.95 Oxley Drive Bridge Northbound Y 3 span ‐ ‐

BR11B 538056.1 6910872.2 East Quay Drive Bridge N ‐ ‐ ‐

BR12B 537794.6 6910907.3 Middle Quay Drive Bridge N ‐ ‐ ‐

BR13B 537834.4 6911157.8 ‐ ‐ North Quay Bridge N ‐ ‐ ‐

BR14B 538379.1 6911359.8 ‐2.23 ‐2.26 Limetree Pde Bridge Y 3 span ‐ ‐

BR15B 538998.0 6911464.9 ‐1.38 ‐2.58 TheDraw Bridge Y 3 span ‐ ‐

BR16B 539196.0 6912064.4 ‐2.74 ‐2.34 Morala Ave Bridge Y 3 span ‐ ‐

BR17B 538995.6 6912326.2 ‐2.5 ‐2.37 The Runaway Bridge Y 3 span ‐ ‐

BR18B 539707.7 6912212.3 ‐2.83 ‐2.94 Bayview Street Bridge Y 3 span ‐ ‐

BR19B 539546.4 6912999.0 ‐ ‐ Bayview Street Bridge 2 N ‐ ‐ ‐

BR20B 538698.4 6912310.9 ‐ ‐ Pebble Beach Drive Bridge Y

3 span deck (WxHxL), Deck

is 0.5m thick (Assumed) ‐ ‐

BR21B 538652.0 6911470.7 ‐0.49 ‐0.68 Sundance Way Bridge Y

3 span deck (WxHxL), Deck

is 0.5m thick (Assumed) ‐ ‐

BR22B 538551.9 6909592.0 ‐ ‐

Cos Zantiotis Park Pedestrian

Bridge N ‐ BRID33 Wx1.4Hx10L

BR23B 538548.5 6909475.4 ‐ ‐

Cos Zantiotis Park Pedestrian

Bridge N ‐ BRID34 Wx1.8Hx6.5L

BR1X 537760.0 6905890.0 ‐ ‐ Gemini Circuit Bridge N ‐ ‐ ‐

BR2X 539840.0 6911290.0 ‐ ‐ Oatland Esplanade Bridge N ‐ ‐ ‐

BR3X 538970.3 6909760.0 ‐ ‐ Ashton St Bridge 2 N ‐ ‐ ‐



3.15 Biggera Creek Dam

Biggera Dam was surveyed in 2004. The crest height of the earth embankment is approximately 15.0 m AHD as shown in Figure 16 (Ref 7). The crest width is roughly 3.5 m wide. The height of the spillway is approximately 12.5 m AHD. There is a low flow pipe at the base of the embankment wall with an upstream invert of 3.22 m AHD and downstream invert of 2.75 m AHD. The pipe is 55 m in length. This information was sourced from GHD’s maintenance report (Ref 9).

The pipe has a peak discharge approximately 13 cubic metres per second. The volume of the dam, at the spillway, is approximately 3 million cubic metres. It will, therefore, take (approximately) just over 2.5 days for the dam to drain.

Figure 16 Biggera Creek Dam’s crest level (Source: 2004 survey)



4. Model Calibration and Verification

The following section details the processes undertaken to calibrate the hydraulic model to tide and two historical flood events. The process occurred in that order with the model first being calibrated to tide then to a historical rainfall event.

4.1 ALERT Stations

The Bureau of Meteorology (BOM) operates a number of flood telemetry systems, known as ALERT stations, on the Gold Coast and Logan region for flood prediction and climate data collection. These ALERT stations record water level, discharge and other meteorological data. Other telemetry stations, known as TM stations, are operated by The Marine Safety Queensland (MSQ) and Department of Environment and Resource Management (DERM). These stations generally record stream flow, water quality and tide data. Around the Biggera catchment area, both ALERT and TM stations data are available for flood and tide calibration (Figure 17). They are:

Biggera Dam AL (540360) – 3.25 m AHD (assumed gauge zero) (refer Figure 18)

Air Sea Rescue\Marine Operation Base AL (040881)

Gold Coast Seaway TM (540001)

Figure 17 Location of ALERT and TM stations in the Biggera Creek region.



For more information on these ALERT and TM stations, please refer to their respective websites (Ref. 11, Ref. 12 and Ref. 13).

Figure 18 Biggera Dam ALERT Station.

4.2 Maximum Height Gauges and Historical Debris Mark

City of Gold Coast maintains a number of maximum height gauges (MHG) (Table 4) and a database of historical debris marks. Four MHG’s are within the hydraulic model, but no data is available with the exception of the surveyed debris mark for the June 2005 event.

Table 4 Summary of Maximum Height Gauge Location and Surveyed Details.

ID Easting Northing Top of Gauge (m AHD)

413 538900.2 6909729.7 4.08

414 539092.3 6908843.8 4.37

417 538603.8 6907895.8 3.8

419 537868.8 6908465.4 6.21



Figure 19 Location of Maximum height gauges in the Biggera region.



4.3 Tide Table

Biggera Creek’s river mouth is situated in a minor, but influential, distance away from the Gold Coast Seaway ALERT station. As such, this distance creates a lag time and a reduction in the peak water level experienced at the river mouth compared to that seen at the Gold Coast Seaway. The Department of Maritime Safety Queensland (MSQ) has documented these tidal affects and has quantified the adaptations in water levels and lag times at various tidal locations across the City (Appendix A). The closest tidal locations for Biggera Creek are the Grand Hotel and Runaway Bay (refer Appendix B for tidal planes). The Grand Hotel has a water level tidal variance of 98% compared to that at the Gold Coast Seaway and a lag time of 16 minutes; meanwhile, Runaway Bay has a water level tidal variance of 86% and a high tide lag time of 32 minutes. Both tidal variances would be acceptable tail water conditions; however, it would not be entirely accurate to choose one location over the other.

4.4 Tidal Calibration

Griffith University undertook a comprehensive tidal water level and current measurement between late 2004 and early 2005. There were 1 tide station and 3 current transects available for calibration as shown in Figure 20. The recorded tide level at the Gold Coast Tide TM station is also available.

Tidal Stations:

Gold Coast Tide TM (Source: Marine Safety Queensland) B8 Runaway Bay (Allisee Harbour)

Current Measurement Transects (Discharge):

Gold Coast Seaway North Channel South Channel

A Broadwater model was developed and tide calibrated for the GEMS project in 2008 which was used for the boundaries for this model (Ref 14). The Biggera model grid was extracted to cover the Broadwater area for this tide calibration (Figure 6).

The simulated one week result was then compared to the surveyed hydrodynamic data from the period November 2004 to September 2005. Discharge comparison was made to measured current data (converted to discharge) and also recorded water level at the three ALERT stations and surveyed tide stations.

This tidal calibration process not only tries to simulate the complex tidal dynamics in the Broadwater but also ensures right conveyance through the river and canal systems. It is particularly effective as there are zero upstream flow/flows within the channel that provide scenarios to calibrate hydraulic model parameters (roughness and eddy viscosity).



Figure 20 Location of tide stations (red) and current measurement transects (cyan).

4.4.1 Tide Calibration Results

The tide calibration shows that the simulated water level is consistent with the surveyed water level in December 2004 and January2005 (about 10 cm). The tide water level plots are provided in the appendixes.

4.4.2 Discharge Calibration Results

The discharge across all transects is good it between the recorded and modelled data at most of the Seaway.

The discharge plots are provided in Appendix B.



4.5 June 2005 Calibration

A major flood occurred in South East Queensland on 30 June 2005 when heavy rainfall caused flash flooding in some parts of the Gold Coast area. This flood event is a good calibration as there was good recorded data at one ALERT station and surveyed flood heights at one MHG location.

BOM has prepared a report for this flood event, which is provided in Ref 23.

4.5.1 Calibration Discussion

The model calibration results show that there is quite a reasonable match for the simulated water level from the Biggera Dam ALERT station (Figure 21). It is important to note that the dam spillway level is about 12.5 m AHD and the dam has a low flow outlet pipe. For this study, the rating curve has not been verified for both structures (dam and outlet pipe) (Ref. 1). This in turn may affect the flood calibration.

Furthermore, it is assumed that the ALERT gauge zero is at 3.25 m AHD, which is reflected in the model’s initial water level condition. There might be some antecedent rainfall that was captured by the dam and recorded by the ALERT station but it is not replicated in the hydrological model. The other slight discrepancy is flood water receding, as shown in the following figure. Although there are some discrepancies, the hydraulic model simulated the flood levels consistently with the surveyed debris mark.

Figure 21 Comparison of modelled June 2005 to recorded water level at Biggera Dam AL



4.6 January 2008 Calibration

A flood calibration event occurred on 4 January 2008 whereby water level data from the Biggera Dam ALERT station was recorded.

BOM has also prepared a report of this flood event detailing its severity (Ref 24).

4.6.1 Calibration Discussion

As June 2005 is a more significant event than January 2008, the hydrology emphasized adjusting calibrations to fit more so on the June 2005 data. Hence, there is a slight discrepancy between the simulated water and the recorded water level for this event (Figure 22).

It is worthwhile to note that this station only records the water level behind the dam and the BoM does not have a rating curve for this station. The rating curve for Biggera Dam is particularly sensitive to low flows and thus achieving a good calibration is difficult.

Figure 22 Comparison of modelled January 2008 to recorded water level at Biggera Dam AL



5. Design Floods

5.1 Introduction

Design floods are hypothetical statistical floods used for flood planning and for designing of structures. They are based on a probability of occurrence, either as

AEP – Annual Exceedance Probability, or ARI – Average Recurrence Interval

For example, a 100 year ARI or 0.1 AEP flood has an average recurrence interval of 100 years, or, the flood has a 1% probability of being equalled or exceeded in any one year.

With ARI expressed in years, the relationship is:

The table below summarises the definition of the design floods used in this report.

Table 5 Design Floods Definition

ARI (in Years) AEP (as Percentage) Remarks 2 39.3 A hypothetical flood with 39.3%

chance of occurrence in any year

5 18.1

10 9.5

20 4.9

50 2.0

Large Event 100 1.0

200 0.5

Rare to Extreme 500 0.2

1000 0.1

2000 0.05

The calibrated Biggera Creek MIKE Flood hydrodynamic model was used to simulate design flood events ranging from 2 year ARI to PMF. The design runs include storm durations of 0.5, 1.0, 1.5, 3.0, 4.5, 6.0, 9.0, 12.0, 18.0, 24.0, 36.0, 48.0, 72.0, 96 and 120 hours. The hydrology of this study for both calibration and design events are sourced from the Biggera Creek Hydrological Study (Ref 1)

The tailwater boundary for all design events are based on the City of Gold Coast’s - Storm Tide Study May 2012, undertaken by GHD (Ref 27).



6.2 Initial Water Level

For the design events, the following initial water level was applied to all model setups:

Creeks and canal system = 0 m AHD

It is important to note that the initial water level in the floodplain is set at 0 m AHD to ensure the storage in the system is partly full. The dam may contribute additional flow as the dam level is considered full during simulation (a low flow pipe drains the dam storage out at the start of simulation). Furthermore, the Biggera Creek is small and its critical duration is short. If a very high tailwater is used, there would be large inundation from the adopted boundary conditions above. On the onset of a design flood, the followings dam water levels were devised (Ref 26)

Table 6 - Initial Water Levels Inside Biggera Dam

ARI Water Level

2 3.6

5 4.46

10 5.26

20 6.19

50 7.69

100 9.05

200 10.66

500 FULL

1000 FULL

2000 FULL

6.3 Sensitivity Tests

A sensitivity analysis has been carried out to assess the overall effect of a gross change in roughness on flood levels throughout the study area. This analysis is considered to be important as the behaviour of overland flow is primarily affected by the relative friction (roughness) throughout the Creek River floodplain. To analyse the sensitivity of this parameter, roughness values across the whole model were increased by 20%. The 1 in 100 year ARI flood event was then simulated and resulting flood levels were compared with those obtained using roughness values set out above. Flood levels were found to change in the order of 20 – 100mm. As such, it could be clearly seen that a shift in Manning’s n roughness values would not significantly affect flood levels throughout the study area.



1. Conclusion

Good calibration was achieved to the 2005, 2008 and 2013 events with the calibration point (Biggera Dam ALERT) demonstrating replicable curves to that of the real event.

The calibrated model has been set up and simulated for the 2, 5, 10, 20, 50, 100, 200, 500, 1000 and 2000 year ARI design flood events. The model has also been setup and simulated for PMP flood events. These results are stored on external hard drives within the Natural Hazards team area.

The City of Gold Coast’s Designated Flood Level for the City Plan 2015, for the Biggera Creek catchment, has been determined using this model. The City Plan 2015 map is the coincidental flood event of the Q100 flood with Q20 storm surge enveloped with the Q20 flood with Q100 storm surge and combined with sea level rise.

This model is the result of years of development and information accrual. This hydraulic model is representative of the environment in which the information was gathered but will require constant review and updating to take into account any changes in its floodplain in the future.



1. Recommendations

In the event that further information for calibration purposes becomes available, the

model is to be recalibrated.

Simulation times are quite significant for this model. Should technology permit faster simulation times using alternative methods of modelling, then consideration should be made to change modelling platforms.

Significant changes are planned to be made through the catchment due to the development of the Commonwealth Games Village and surrounding infrastructure. This model is to be updated with the as constructed information to allow better representation of the catchment.



2. References

1. Gold Coast City Council. Biggera Creek Hydrological Modelling. August 2014. TRACKS-#24796864-BIGGERA CREEK CATCHMENT HYDROLIGCAL MODELLING

2. Gold Coast City Council. Corporate GIS Layers (Catchment, Pipe Culverts, Bridge and Weirs).

3. Cameron McNamara & Partners. Report on Biggera Creek Catchment Drainage Study. June 1976.

4. Cameron McNamara & Partners. Preliminary Design of Biggera Creek Flood Mitigation Dam. Preliminary Report. February 1978.

5. Cameron McNamara & Partners. Biggera Creek Flood Mitigation Scheme. January 1980. TRACKS-#26782962-BIGGERA CK FLOOD MITIGATION SCHEME

6. Cameron McNamara & Partners. Report on Flood Levels in Lower Biggera Creek, Following Completion of the Retardation Basin Above Olsen Avenue. February 1986.

7. Gold Coast City Council. Biggera Creek Catchment Study. Hydraulic Report. FS688. January 2004. TRACKS-#20623958-BIGGERA CREEK HYDRAULIC REPORT

8. Gold Coast City Council. Biggera Creek Dam Break Analysis. FS695. January 2004. TRACKS-#20623951-BIGGERA CREEK DAM BREAK ANALYSIS

9. GHD. Biggera Creek Dam Maintenance Plan and Manual. November 2003. TRACKS-#26493473-BIGGERA CREEK DAM MAINTENANCE PLAN AND MANUAL

10. Department of Environment and Resource Management - LiDAR and Orthophoto Acquisition 2009.

11. Bureau of Meteorology website. http://www.bom.gov.au/hydro/flood/qld/ 12. Marine Safety Queensland website. http://www.msq.qld.gov.au/Home/Tides/ 13. Department of Environment and Resource Management website.

http://www.derm.qld.gov.au/water/monitoring/current_data/index.php 14. Gold Coast City Council. Regional Broadwater Model Calibration. January 2011.

TRACKS-#29264395-REPORT REGIONAL BROADWATER MODEL CALIBRATION REPORT 6 JANUARY 2011

15. The Institution of Engineers Australia. Australian Rainfall and Runoff – A Guide to Flood Estimation. 1998.

16. Queensland Department of Natural Resource and Water. Queensland Urban Drainage Manual. June 2008.

17. Queensland Department of Transport and Main Roads. Road Drainage Manual. March 2010.

18. Brisbane City Council. Natural Channel Design Guidelines. November 2003. 19. Land & Water Australia. An Australian Handbook of Stream Roughness Coefficients.

May 2009. 20. US FHWA. Guide for Selecting Manning's Roughness Coefficients for Natural

Channels and Flood Plains. WSP 2339. 21. USGS. Surface-Water Field Techniques: Verified Roughness Characteristics of

Natural Channels. 22. DHI MIKE 11 User’s Manual 2009. 23. Bureau of Meteorology. Heavy Rainfall Gold Coast. June 2005. 24. Bureau of Meteorology. South East Queensland Floods. January 2008. 25. Mirfenderesk H., Tomlinson R., Hughes. L., (2005a), “Field Data Collection and

analysis at the Broadwater, Gold Coast”, 17th Australasian Conference on Coastal and Ocean Engineering, Adelaide, Australia. P477-482.

26. Don Carroll. Loders and Biggera Retention Basin Studies. June 2014 #43295870 27. GHD Storm Tidy Study, Final Addendum Report. February 2013 #39733283



Appendix A. Figures illustrating Tidal and Discharge Calibrations,

2004-2005.

Water Level @ B9 Grand Hotel

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

10/1

2/04

11/1

2/04

12/1

2/04

13/1

2/04

14/1

2/04

15/1

2/04

Date

Wat

er L

evel

(m

AH

D)

Recorded

Modelled

Figure A-1 December 2004 Tidal Calibration (B9)

Water Level @ Gold Coast Tide TM

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

07/0

1/05

08/0

1/05

09/0

1/05

10/0

1/05

11/0

1/05

12/0

1/05

13/0

1/05

Date

Wat

er L

evel

(m

AH

D)

Recorded

Modelled

Figure A-2 December 2004 Tidal Calibration (Seaway)



Water Level @ B10 Seaway

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

07/0

1/05

08/0

1/05

09/0

1/05

10/0

1/05

11/0

1/05

12/0

1/05

13/0

1/05

Date

Wat

er L

evel

(m

AH

D)

Recorded

Modelled

Figure A-3 January 2005 Tidal Calibration

Discharge @ Gold Coast Seaway

-5000

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

12/01/200508:00

12/01/200510:24

12/01/200512:48

12/01/200515:12

12/01/200517:36

12/01/200520:00

12/01/200522:24

Time

Dis

char

ge

(cu

mec

s)

Recorded Discharge

Modelled Discharge

Figure A-4 January 2005 Tidal Calibration (Seaway Discharge)



Discharge @ Northern Channel

-4000

-3000

-2000

-1000

0

1000

2000

3000

12/01/200508:00

12/01/200510:24

12/01/200512:48

12/01/200515:12

12/01/200517:36

12/01/200520:00

12/01/200522:24

Time

Dis

char

ge

(cu

mec

s)

Recorded Discharge

Modelled Discharge

Figure A-5 January 2005 Tidal Calibration (North Channel Discharge)

Discharge @ Southern Channel

-1500

-1000

-500

0

500

1000

1500

12/01/200508:00

12/01/200510:24

12/01/200512:48

12/01/200515:12

12/01/200517:36

12/01/200520:00

12/01/200522:24

Time

Dis

char

ge

(cu

mec

s)

Recorded Discharge

Modelled Discharge

Figure A-4 January 2005 Tidal Calibration (Southern Channel Discharge)



Appendix B

Tidal Planes (Source: Marine Safety Queensland)



Appendix C: Hydraulic Structures

Musgrave Avenue Culverts (CU1B)

Figure C-1 Musgrave Avenue Culverts (Source: Ref 1)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Musgrave Ave Dimensions 2.7 m x 0.9 m (3 box culverts) (Pipe Culvert) Width (Waterway Length) 22.1 m (Pipe Culvert) Culvert Invert U/S 2.81 m AHD Surveyed (Ref. 7) Culvert Invert D/S 2.59 m AHD Surveyed (Ref. 7)

Keith Hunt Park Pedestrian Bridge – Roy Neil Reserve (BR1B)

Figure C-2 Keith Hunt Park Pedestrian Bridge (Source: Ref 1)



The small pedestrian bridge near Keith Hunt Park (Roy Neil Reserve) is not included in this model build (due to the lack of information).

Napper Road Culverts (CU2B)

Figure C-3 Napper Road Culverts (Source: Ref 7)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Napper Rd Dimensions 2.1 m Dia. (4 circular culverts) (Pipe Culvert) Width (Waterway Length) 50 m (Pipe Culvert) Culvert Invert U/S 5.59 m AHD Surveyed (Ref. 7) Culvert Invert D/S 5.52 m AHD Surveyed (Ref. 7)

Olsen Avenue Culverts (CU3B)

Figure C-4 Olsen Avenue Culverts (Source: Ref 7)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Olsen Ave Dimensions 2.4 m x 1.5 m (1 box culvert) (Pipe Culvert) Width (Waterway Length) 37.6 m (Pipe Culvert)



Culvert Invert U/S 2.54 m AHD Surveyed (Ref. 7) Culvert Invert D/S 2.27 m AHD Surveyed (Ref. 7)

Government Road Culvert 1 (CU4B)

Figure C-5 Government Road Culvert 1 (Source: Ref 7)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch GovtRd1 Dimensions 3.0 m x 2.4 m (1 box culvert) (Pipe Culvert) Width (Waterway Length) 21.8 m (Pipe Culvert) Culvert Invert U/S 0.76 m AHD Surveyed (Ref. 7) Culvert Invert D/S 0.65 m AHD Surveyed (Ref. 7)

Morinda Way Pedestrian Bridge – Roy Neil Reserve (BR2B)

Figure C-6 Morinda Way Pedestrian Bridge (Source: Ref 7)

Description MIKE 11 Culvert Details Remarks



MIKE 11 Branch Morinda Way Dimensions 3.6 m x 1.8 m (3 box culvert) Surveyed (Ref. 7) Width (Waterway Length) 1.4 m Surveyed (Ref. 7) Culvert Invert U/S 0.42 m AHD Surveyed (Ref. 7) Culvert Invert D/S 0.43 m AHD Surveyed (Ref. 7)

Government Road Culvert 2 (CU5B)

Figure C-7 Government Road Culvert 2 (Source: Ref 7)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch GovtRd2 Dimensions 3.0 m x 2.4 m (3 box culverts) (Pipe Culvert) Width (Waterway Length) 26.3 m (Pipe Culvert) Culvert Invert U/S -0.43 m AHD Surveyed (Ref. 7) Culvert Invert D/S -0.42 m AHD Surveyed (Ref. 7)

Central Street Culverts (CU6B)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Central St Dimensions 3.0 m x 2.4 m (5 box culverts) Surveyed (Ref. 7) Width (Waterway Length) 20.0 m (Pipe Culvert) Culvert Invert U/S -0.34 m AHD Surveyed (Ref. 7) Culvert Invert D/S -0.36 m AHD Surveyed (Ref. 7)



Whiting Street Culverts (CU7B)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Whitting St Dimensions 3.0 m x 2.4 m (5 box culverts) Surveyed (Ref. 7) Width (Waterway Length) 20.1 m (Pipe Culvert) Culvert Invert U/S -0.44 m AHD Surveyed (Ref. 7) Culvert Invert D/S -0.43 m AHD Surveyed (Ref. 7)

Kenny Drive Pedestrian Bridge (BR3B)

Figure C-8 Kenny Drive Pedestrian Bridge (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Kenny Drive Length 27 m (Bridge) Width (Waterway Length) 2.6 m (Bridge) Bridge Top Level 2.78m AHD Surveyed (Ref. 7) Bridge Bottom Level 2.28m AHD Assumed Deck is 0.5 m Thick



Ashton Street Pedestrian Bridge (BR4B)

Figure C-9 Ashton Street Pedestrian Bridge (Source: Ref 7)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Ashton St Bridge Length 26 m (Bridge) Width (Waterway Length) 2.2 m (Bridge) Bridge Top Level 2.89 m AHD Surveyed (Ref. 7) Bridge Bottom Level 2.39 m AHD Assumed Deck is 0.5 m Thick

Brisbane Road Bridge 1 (BR5B)

Figure C-10 Brisbane Road Bridge 1 (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Brisbane Rd Bridge Length 32 m (Bridge) Width (Waterway Length) 26.5 m (Bridge) Bridge Top Level 2.80 m AHD Surveyed (Ref. 7)



Bridge Bottom Level 2.0 m AHD Assumed Deck is 0.8 m Thick Hollywell Road Pedestrian Bridge (BR6B)

Figure C-11 Hollywell Road Pedestrian Bridge (Source: Ref 1)

The pedestrian bridge near Hollywell Road is not included in this model build (due to the lack of information).

Hollywell Road Bridge (BR7B)

Figure C-12 Hollywell Road Bridge (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Hollywell Rd Bridge Length 40 m Estimated Width (Waterway Length) 11.5 m Estimated Bridge Top Level 4.22m AHD Surveyed (Ref. 7) Bridge Bottom Level 3.72 m AHD Assumed Deck is 0.8 m Thick



Marine Parade Road Bridge (BR8B)

Figure C-13 Gold Coast Highway Road Bridge (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Marine Pde Bridge Modelled as culvert/weir combination Length 29 m Estimated Width (Waterway Length) 12.7 m (Bridge) Bridge Top Level 4.11 m AHD Surveyed (Ref. 7) Bridge Bottom Level 3.31 m AHD Assumed Deck is 0.8 m Thick

Oxley Drive Road Bridge Northbound (BR9B)

Figure C-14 Oxley Drive Road Bridge Northbound (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Oxley Dr Bridge North and South Bound Bridges Length 56.5 m Estimated Width (Waterway Length) 14.5 m Estimated (incl. ped. bridge) ~28 m Road (Left Bank/Right Bank) 5.57 m AHD Surveyed (Ref. 7) Bridge Top Level 5.07 m AHD Assumed deck is 0.5 m thick



Bridge Bottom Level Oxley Dr Bridge North and South Bound Bridges Oxley Drive Road Bridge Southbound (BR10B)

Figure C-15 Oxley Drive Road Bridge Southbound (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Oxley Dr Bridge North and South Bound Bridges Length 56.5 m Estimated Width (Waterway Length) 11.5 m Estimated (incl. ped bridge), ~28 m Bridge Top Level 5.57 m AHD Surveyed (Ref. 7) Bridge Bottom Level 5.07 m AHD Assumed deck is 0.5 m thick

East Quay Drive Bridge (BR11B)

The arch bridge at East Quay Drive, Harbour Quays, is not included in this model build

Middle Quay Drive Bridge (BR12B)

The arch bridge at Middle Quay Drive, Harbour Quays, is not included in this model build.

North Quay Bridge (BR13B)

The arch bridge at North Quay Drive, Harbour Quays, is not included in this model build



Compass Drive Culverts (CU8B)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Compass Dr Dimensions 3..6 m Dia. (3 circular culverts) (Pipe Culvert) Width (Waterway Length) 56.6 m (Pipe Culvert) Culvert Invert U/S -2.01 m AHD 2003 Bathymetric Survey Data Culvert Invert D/S -2.65 m AHD Estimated

Pine Ridge Road Weir (WE1B)

A walkway near Pine Road, between Compass Drive and Brisbane Road, is represented in the MIKE 21 model grid with level of about 1 m AHD.

Figure C-16 Pine Ridge Road Weir (Source: Ref 1)

Brisbane Road Weir (Gross Pollutant Trap) (WE2B)

Two gross pollutant traps with level of about 1 m AHD is located downstream of Brisbane Road. It is represented in the MIKE 21 model grid.



Figure C-17 Brisbane Road Weir (Source: Ref 1)

Brisbane Road Open Drain 1

An open channel, trapezoidal channel with 10m bottom width, is located downstream of the Brisbane Road culverts. It is represented in the MIKE 21 model grid.

Figure C-18 Brisbane Road Open Drain 1 (Source: Ref 1)

Brisbane Road Culverts (CU9B)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch BrisbaneRd2 Dimensions 1.2 m x 0.9 m (12 box culverts) (Pipe Culvert) Width (Waterway Length) 30.3 m (Pipe Culvert) Culvert Invert U/S 1.49 m AHD ALS (Ref. 10) Culvert Invert D/S 1.67 m AHD ALS (Ref. 10)

Brisbane Road Open Drain 2

An open channel, trapezoidal channel with 10m bottom width, is located upstream of the Brisbane Road culverts. It is represented in the MIKE 21 model grid (Error! Reference source not found.).



Figure C-19 Brisbane Road Open Drain 1 (Source: Ref 1)

Kendor Street Culverts (CU10B)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Kendor St Dimensions 2.7 m x 1.5 m (2 box culverts) (Pipe Culvert) Width (Waterway Length) 26.1m (Pipe Culvert) Culvert Invert U/S 2.1 m AHD ALS (Ref. 10) Culvert Invert D/S 2.0 m AHD ALS (Ref. 10)

Biggera Dam Pipe Culverts (CU11B)

Figure C-20 Biggera Dam Inlet Pipe (Source: Ref. 7)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch Biggera Pipe Dimensions 1.2 m Diameter (1 circular Drawing No. 31217 (Ref. 9)



culverts) Width (Waterway Length) 55m Drawing No. 31217 (Ref. 9) Culvert Invert U/S 3.25m AHD ALS (Ref. 10) Culvert Invert D/S 2.75m AHD ALS (Ref. 10)

Kendor Street Drainage Corridor (CU12B)

The Kendor Street Drainage Corridor culverts (0.9 m diameter circular culverts) are not included this model build (due to the lack of information).

Captain Cook Drive Culverts (CU13B)

The six Captain Cook Drive culverts (2.1 m x 0.9 m box culverts) are not included this model build (due to the lack of information).



Limetree Parade Bridge (BR14B)

Figure C-21 Limetree Parade Bridge (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch Limetree Pde Bridge Length 55.5 m Estimated Width (Waterway Length) 12 m Estimated Bridge Top Level 4.98m AHD Surveyed (Ref. 7) Bridge Bottom Level 4.48m AHD Assumed deck is 0.5 m thick.

The Drawbridge Bridge (BR15B)

Figure C-22 The Drawbridge Bridge (Source: Ref 1)

MIKE 11 Bridge Details Description Remarks MIKE 11 Branch TheDrawBridge Length 67.3 m Estimated Width (Waterway Length) 14 m Estimated Bridge Top Level 5.13 m AHD Surveyed (Ref. 7) Bridge Bottom Level 4.63 m AHD Assumed deck is 0.5 m thick.



Morala Avenue Bridge (BR16B)

Figure C-23 Morala Avenue Road Bridge (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch MoralaAveBridge Length 55.5 m Estimated Width (Waterway Length) 14 m Estimated Bridge Top Level 5.28 m AHD Surveyed (Ref. 7) Bridge Bottom Level 4.78 m AHD Assumed deck is 0.5 m thick.

The Runaway Bridge (BR17B)

Figure C-24 The Runaway Bridge (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch RunawayBayBridge Length 56 m Estimated Width (Waterway Length) 13 m Estimated Bridge Top Level 4.99 m AHD Surveyed (Ref. 7)



Bridge Bottom Level 4.49 m AHD Assumed deck is 0.5 m thick.

Bayview Street Bridge (BR18B)

Figure C-25 Bayview Street Bridge (Source: Ref 1)

Description MIKE 11 Bridge Details Remarks MIKE 11 Branch BayviewStBridge Length 62 m Estimated Width (Waterway Length) 12 m Estimated Bridge Top Level 5.18 m AHD Surveyed (Ref. 7) Bridge Bottom Level 4.68 m AHD Assumed deck is 0.5 m thick.

Bayview Street Bridge 2 (BR19B)

The Bayview Street Bridge, near Tari Court, is not included in this model build (due to a lack of information and outside Biggera catchment).

Pebble Beach Drive Bridge (BR20B)



Figure C-26 Pebble Beach Drive Bridge (Source: Ref 1)

From site inspection, there is no conveyance through Pebble Beach Bridge (MIKE 21 grid blocked).



Sundance Way Bridge (BR21B)

Figure C-27 Sundance Way Bridge (No Source)

From site inspection, there is no conveyance through Sundance Way Bridge (MIKE 21 grid blocked).

Napper Road Culverts 2 (CU14B)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch NapperRd2 Dimensions 2.1 m Dia. (4 circular culverts) (Ref. 1) Width (Waterway Length) 56.4 m (Pipe Culvert) Culvert Invert U/S 4.60 m AHD Surveyed (Ref. 7) Culvert Invert D/S 4.51 m AHD Surveyed (Ref. 7)

Smith Street Culverts (CU15B)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch SmithSt Dimensions 3.6 m x 1.2 m (8 box culverts) (Ref. 1) Width (Waterway Length) 26 m (Pipe Culvert) Culvert Invert U/S 12.6 m AHD ALS (Ref. 10) Culvert Invert D/S 12.4 m AHD ALS (Ref. 10)



Parkwood Boulevard Culverts (CU16B)

Figure C-28 Parkwood Boulevard Culverts (Ref. 2)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch ParkwoodBlv Dimensions 3.0 m x 1.2 m (1 box culvert) (Ref. 1) Width (Waterway Length) 20.4 m (Pipe Culvert) Culvert Invert U/S 9.75 m AHD ALS (Ref. 10) Culvert Invert D/S 9.77 m AHD ALS (Ref. 10)

Trotting Track Outlet Culverts (CU17B)

Figure C-29 Trotting Track Culvert (Ref. 2)

Description MIKE 11 Culvert Details Remarks MIKE 11 Branch TrottingPipe Dimensions 0.9 m Dia. (1 circular culverts) (Ref. 1) Width (Waterway Length) 19.7 m (Pipe Culvert) Culvert Invert U/S 7.3 m AHD ALS (Ref. 10)



Culvert Invert D/S 4.90 m AHD ALS (Ref. 10) Ashmore Road Culverts (CU1XB)

Figure C-30 Ashmore Road Culvert

The one Ashmore Road culvert (2.4m x 0.75m box culverts) near Macquarie Avenue is not included in this model build (due to the lack of information).

Cathedral Avenue Culverts (CU2XB)

Figure C-31 Cathedral Avenue Culverts

The two Cathedral Avenue culverts (2.1m x 2.1m box culverts) near Manse Court are not included in this model build (due to a lack of information).



Cos Zantiotis Pedestrian Bridge 1 (BR22B)

Figure C-32 Cos Zantiotis Pedestrian Bridge (Source: Ref 1)

The bridge at Cos Zantiotis Park, near Freeman Street is not included in this model build (due to lack of information).

Cos Zantiotis Pedestrian Bridge 2 (BR23B)

Figure C-33 Cos Zantiotis Foot Bridge (Source: Ref 1)

The bridge at Cos Zantiotis Park, near Freeman Street, is not included in this model build (due to a lack of information).

Gemini Court Bridge (BR1X)



Figure C-34 Gemini Circuit Bridge

The bridge near Gemini Circuit is not included in this model build (due to a lack of information).

Oatland Esplanade Bridge (BR2X)

Figure C-35 Oatland Esplanade Bridge (Source: Ref 1)

The bridge near Oatland Esplanade (in Madang Canal) is not included in this model build (due to a lack of information).

Ashton Street Bridge 2 (BR3X)



The bridge at Ashton Street is not included in this model build (due to a lack of information).


Figure C-36 East Quay Bridge Drawing


Figure C-38 Biggera Dam Pipe Culvert Drawing


Council of the City of Gold Coast PO Box 5042 GCMC Qld 9729 P 1300 GOLDCOAST E [email protected] W cityofgoldcoast.com.au

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