pimpama river catchment hydrological study · 2019-06-23 · river catchment based on design...

1

Pimpama River Catchment

Hydrological Study December 2014

Version 1 – August 18 TRACKS-#43467383-v2-PIMPAMA_RIVER_HYDROLOGICAL_STUDY_REPORT_DECEMBER_2014

of 104

Title: Pimpama River Catchment Hydrological Study

Author:

Study for: City Planning Branch

Planning and Environment Directorate

The City of Gold Coast

File Reference: WF18/44/02-

TRACKS-#43467383

Version history

Version Comments/Change Changed by

& date Reviewed by &

date

1.0 Draft (Tracks#22941355)

2.0 Review (Tracks #22941355)

3.0 Review (Tracks #22941355)

4.0 Peer Review (Tracks #22941355)

5.0 Review

6.0 Grammar review

Distribution list

Name Title Directorate Branch


of 104

1. Executive Summary

Overview

In December 2007, City of Gold Coast (City) commissioned WRM Water & Environment Pty Ltd (WRM) to undertake a comprehensive study to review and update its ten hydrological models to a consistent standard. WRM assessed all aspects of the hydrological model development, calibration and estimation of design discharges in hydrological studies undertaken for the City, WRM (2008a) (Ref 1). Based on this assessment, WRM recommended a methodology for use in hydrological modelling for the catchments in the City area. In 2009, the Pimpama River catchment hydrological modelling (Ref 2) was undertaken on the basis of these recommendations. A comprehensive hydrological study of Pimpama River catchment, along with other catchments of City, has been undertaken in 2013 with some minor modifications of the WRM’s 2008 (Ref 16) methodologies.

The main objective of this study is to develop a hydrological model of the Pimpama River catchment using the URBS modelling software, calibrate and verify against available data and estimate design flood discharges for design events ranging from 2 year Average Recurrence Interval (ARI) to Probable Maximum Flood (PMF).

In this study, the hydrological modelling of the Pimpama River catchment was undertaken using a methodology consistent with the other catchments in the City area. The model configuration was kept as simple as possible and global model parameters were maintained for the whole catchment. The model was configured based on current catchment land uses and best available industry standard modelling approaches. Finally, the adopted methodology, tasks and results of the study have been documented to a consistent standard with other updated models.

Model Calibration and Verification

All rainfall and stream flow data used in this study were provided by Bureau of Meteorology (BOM). Rainfall data for a total of nine historical flood events between 1999 and 2013 were available. Stream flow data were available only for seven historical events since 2004. From the available data, three events (January 2008, January 2012 and January 2013) were selected for model calibration and four events (February 2004, March 2004, November 2004 and June 2005) were selected for model verification.

The URBS model was calibrated to achieve the best possible fit between recorded and predicted discharge hydrographs at the four gauging stations within the Pimpama River catchment for the selected calibration events. The calibration attempted to match the predicted and recorded flood peaks, timing, volumes and the shape of the flood hydrograph. The calibrated model was then verified by comparing the model predictions against the stage hydrographs recorded at the Kerkin Road Alert gauging station for the selected verification event. A joint calibration between the UBRS model and the Woongoolba Flood Mitigation Hydraulic Model (Ref 5) was also undertaken for all calibration events because of the limited availability of stream gauge data, uncertainties regarding the adopted rating curves and the impact of tidal influence on recorded water levels at two gauging stations in the lower reaches of the river. The calibrated model was then verified by comparing the recorded water levels against the Mike11 predicted water levels using URBS results as input.

A single set of model parameters were adopted and maintained for all calibration and verification events. The model parameters were adjusted to achieve the best calibration for all events. Rainfall


of 104

losses were adjusted to achieve the best possible hydrograph shapes and flood volumes. A uniform initial loss and continuing loss rate were adopted for the whole catchment. Where necessary, reach length factors (f) were changed in the model to represent differences in channel routing characteristics. The adopted model parameters are shown below.

Parameter Adopted Value

(Channel Lag Parameter) 0.3

(Catchment Lag Parameter) 3.0

m (Catchment non-linearity Parameter) 0.75

F (Forest Factor) F*0.5

Satisfactory calibration was achieved throughout the catchment, considering the uncertainties with the adopted rating curves and gauge datum at the calibration stations, the tidal impacts and two-dimensional nature of flows in the lower reaches, and that a single set of model parameters were adopted for all seven calibrations and verification events.

At Hotham Creek Alert gauging station, the hydrograph timing, shapes and volumes are good for the January 2008 event, January 2012 and January 2013 flood event but the predicted peak discharges are a slightly higher than the recorded peak discharges.

At Stewarts Road Alert gauging station, the agreement between predicted and recorded peak discharges, timing of the peak discharges and the hydrograph shapes and volumes are excellent for the January 2008 event, January 2012 and January 2013, but the predicted peak discharges are lower than the recorded peak discharge for the January 2012 and January 2013 events.

The URBS model did not produce good calibration results at Norwell Alert gauging station; this is attributed to uncertainties with the rating curve, the tidal impact and two-dimensional nature of flows near this station. The joint calibration of the URBS and Mike11 model produces excellent calibration results for the January 2012 and January 2013 flood event.

The URBS model did not reproduce discharges well at Kerkin Road Alert station. This is attributed to uncertainties in the rating curve and the tidal impacts at the gauging station. The model calibration was checked by comparing the recoded water levels against the Mike11 predicted water levels through joint calibration of the URBS and Mike11 models. An excellent calibration result was achieved at this gauging station for the most recent flood event January 2013 and a reasonable calibration and verification results were achieved for the February 2004, November 2004, June 2005 and January 2012 events. There is no recorded water level data available at this station for the January 2008 event.

It is noted that there are significant differences between gauge zero (datum) levels obtained from BOM and surveys undertaken by the City at the Norwell Alert and Kerkin Alert gauging stations. Mike 11 produces better results with BOM datum level at Kerkin Road Alert prior to January 2008 flood events and City datum level produces better results at Norwell and Kerkin Road Alert gauging stations for flood events January 2008 and after.


of 104

Design Flood Discharges

The calibrated URBS model was used to estimate design flood discharges throughout the Pimpama River catchment based on design rainfall intensity – frequency – duration (IFD) data from a number of sources. Design flood discharge hydrographs were estimated for a range of storm durations up to the 96 hour event for the 2, 5, 10, 20, 50, 100, 200, 500, 2000 year ARI events, and the Probable Maximum Precipitation Design Flood (PMPDF) and Probable Maximum Flood (PMF) events. The design rainfall data (including IFD data, temporal patterns, areal reduction factors, rainfall spatial distribution and design rainfall losses) adopted in the study are based on a comprehensive review of the latest available data (Ref 16). The table below shows URBS model design discharges at four gauging stations within the Pimpama River catchment for a range of return periods.

ARI

(Years)

Peak Design Discharge (m3/s)

Hotham

Creek Alert

Stewarts

Road Alert

Norwell

Alert

Kerkin

Road Alert

2 40 34 32 77

5 71 66 65 149

10 93 90 89 203

20 119 117 115 261

50 148 147 146 330

100 171 172 171 385

200 190 194 192 431

500 217 224 222 496

1000 238 235 251 566

2000 266 252 284 655

PMPDF 720 687 657 1473

PMF 675 694 723 1626

The table above shows that PMPDF design discharge is higher than PMF design discharge at the Hotham Creek Alert station. This is because critical storm duration at Hotham Creek Alert is 6 or 9 hours for different ARIs; however, temporal patterns for less than 24 hour durations are not available in the top ten individual storm temporal patterns to run PMF.

A comparison was made between the estimated design discharges from this study with those of the design discharges reported in WBM 2008 (Ref 9), GCCC 2007 (Ref 8), GCCC 2005 (Ref 7) and GCCC 2009 (Ref 2). The current study design discharge estimates are significantly lower than WBM (2008), GCCC (2007) and GCCC (2005a) and slightly higher than GCCC (2009) design discharges was undertaken. This is likely due to the following differences:


of 104

WBM (2008) and GCCC (2007) and GCCC (2005a) studies did not use calibrated URBS models for design discharge estimates (all three studies used parameter values of neighbouring catchments).

WBM (2008) and GCCC (2007) design discharge estimates are based on the old design rainfall temporal patterns (see Section 9.3 ).

WBM (2008) and GCCC (2007) studies did not apply ARF’s to the design rainfalls.

The current study calibrated the model to two additional recent flood events (January 2012 and January 2013) and used an additional model parameter (forest factor) than GCCC (2009) study along with some modification of methodologies.

Joint Probability Approach (JPA)

Joint Probability Approach (JPA) was undertaken using the Total Probability Theorem (TPT) and Cooperative Research Centre – Catchment Hydrology (CRC-CH) simulation. The design flood discharges throughout the Pimpama River catchment was estimated using TPT and CRC–CH simulations. A comparison of design discharge estimates from Design Event Approach (DEA) and Monte Carlo Simulation at Hotham Creek, Stewarts Road, Norwell and Kerkin Road Alert gauging stations are given in the following figures. The results of the Monte Carlo approach gave further support of the discharges obtained from the DEA with comparable discharges achieved up to ARIs 200.


of 104


of 104

Flood Frequency Analysis

A sufficient record of historical peak height or discharge data is not available to undertake a flood frequency analysis (FFA) at any of the four stream gauging stations located within the Pimpama River catchment.

Conclusion

An URBS model of the Pimpama River catchment has been reasonably well calibrated and verified against available data. The calibrated model has been used to estimate design flood discharges at key locations in the catchment for design events ranging from 2 year ARI to PMF. All analyses in this study have been undertaken using methodology consistent with the hydrologic modelling currently being undertaken for other catchments in the Gold Coast. The methodology, tasks and results of this study have been documented to a consistent standard.


of 104

Table of Contents

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

2. Introduction ................................................................................................................................. 12

2.1 Overview ............................................................................................................................ 12

2.2 Study Objectives and Scope .............................................................................................. 12

2.3 Limitation Statement .......................................................................................................... 13

2.4 Acknowledgement ............................................................................................................. 13

2.5 Previous Studies ................................................................................................................ 13

2.5.1 Woongoolba Drainage Study (1994) (Ref 4) ............................................................ 13

2.5.2 Woongoolba Flood Mitigation Hydraulic Study (2004) (Ref 5) ................................. 14

2.5.3 Woongoolba Flood Mitigation Scheme Supplementary Report (2004) (Ref 6) ........ 14

2.5.4 Pimpama River Catchment Investigation - Hydrological Study (2005) (Ref 7) ......... 14

2.5.5 Logan River Catchment Hydraulic Study (2007) (Ref 8) .......................................... 15

2.5.6 Pimpama River Catchment and Stormwater Management Plan (2008) (Ref 9) ....... 15

2.5.7 Pimpama River Catchment Hydrological Study (2009) (Ref 2) ................................ 15

3. Catchment Description ............................................................................................................... 16

3.1 Overview ............................................................................................................................ 16

3.2 Land Use ........................................................................................................................... 17

3.3 Stream Gauging Stations ................................................................................................... 19

4. Methodology ................................................................................................................................ 21

4.1 Comprehensive Review of Existing Models and Data ....................................................... 21

4.2 Model Construction ............................................................................................................ 21

4.3 Model Calibration and Verification ..................................................................................... 21

4.4 Design Discharge Estimation ............................................................................................. 22

4.5 Joint Probability Approach/Monte Carlo Simulation ........................................................... 22

4.6 Preparation of Study Report .............................................................................................. 22

5. Available Data .............................................................................................................................. 23

5.1 Topographic Data .............................................................................................................. 23

5.2 Land Use Data ................................................................................................................... 23

5.3 Rainfall Data ...................................................................................................................... 23

5.4 Streamflow Data ................................................................................................................ 26

5.5 Rating Curves .................................................................................................................... 28

5.5.1 Hotham Creek Alert (146922) ................................................................................... 28

5.5.2 Stewarts Road Alert (146923) .................................................................................. 29

5.5.3 Norwell Alert (146925) .............................................................................................. 29

5.5.4 Kerkin Road Alert (146809) ...................................................................................... 30

6. Model Development .................................................................................................................... 32

6.1 Model Description .............................................................................................................. 32

6.2 Model Configuration ........................................................................................................... 34


of 104

6.2.1 Land Use .................................................................................................................. 34

6.2.2 Catchment Subdivisions ........................................................................................... 35

7. Model Calibration and Verification ............................................................................................ 39

7.1 Selection of Calibration and Verification Events ................................................................ 39

7.2 Calibration Methodology .................................................................................................... 39

7.3 Joint Calibration with Hydraulic Model ............................................................................... 39

7.4 Assignment of Rainfall and Temporal Patterns ................................................................. 42

7.5 Adopted Model Parameters ............................................................................................... 43

7.6 Initial and Continuing Losses ............................................................................................. 45

7.7 Calibration Results ............................................................................................................. 45

7.7.1 Overview................................................................................................................... 45

7.7.2 January 2008 Event.................................................................................................. 46

7.7.3 January 2012 Event.................................................................................................. 46

7.7.4 January 2013 Event.................................................................................................. 46

7.8 Verification Results ............................................................................................................ 47

7.8.1 Overview................................................................................................................... 47

7.8.2 February 2004 Event ................................................................................................ 47

7.8.3 March 2004 Event .................................................................................................... 48

7.8.4 November 2004 Event .............................................................................................. 48

7.8.5 June 2005 Event....................................................................................................... 48

8. Flood Frequency Analysis .......................................................................................................... 49

9. Design Flood Estimation ............................................................................................................ 50

9.1 Methodology ...................................................................................................................... 50

9.2 Rainfall Depth Estimation .................................................................................................. 56

9.2.1 Frequent to Large Design Events (up to and including 100 years ARI) ................... 56

9.2.2 Rare to Extreme Design Events (200 to 2000 years ARI) ........................................ 56

9.2.3 Probable Maximum Precipitation Design Flood (PMPDF) ........................................ 56

9.2.4 Probable Maximum Flood (PMF) .............................................................................. 57

9.3 Temporal Patterns ............................................................................................................. 57





9.4 Areal Reduction Factors .................................................................................................... 58





9.5 Rainfall Losses .................................................................................................................. 59



of 104




9.6 Spatial Distribution ............................................................................................................. 60





9.7 Design Discharges ............................................................................................................. 61





9.7.5 Comparison with Previous Studies ........................................................................... 64

10. Joint Probability Approach (JPA) .............................................................................................. 66

11. Conclusion ................................................................................................................................... 69

12. Recommendations ...................................................................................................................... 70

13. Reference ..................................................................................................................................... 71

14. Appendices .................................................................................................................................. 74

Appendix A – URBS Catchment Definition File .......................................................................... 74

Appendix B – Calibration and Verification Hydrographs ............................................................. 80

Appendix B1 - January 2008 calibration ............................................................................ 80



Appendix B4 - February 2004 verification .......................................................................... 87

Appendix B5 - March 2004 verification .............................................................................. 88

Appendix B6 - November 2004 verification ....................................................................... 89

Appendix B7 - June 2005 verification ................................................................................ 90

Appendix C – Design Temporal Patterns .................................................................................... 91

Appendix D – Probable Maximum Precipitation (PMP) Calculation ............................................ 92

Appendix D1 - PMP Method Selection .............................................................................. 92

Appendix D2 - Generalised Short Duration Method (GSDM) ............................................ 93

Appendix D3 - Generalised Tropical Storm Method Revised (GTSMR) ............................ 96

Appendix E – Design Event Hydrographs ................................................................................... 98

Appendix F – Monte Carlo Results ........................................................................................... 102


of 104

2. Introduction

2.1 Overview

In recent years, City developed numerous hydrological models of its catchments and waterways. These models have been developed by City staff and/or consultants, using a range of approaches and assumptions. The standard of these models, with respect to their configuration, calibration, use for design discharge estimation and documentation, vary significantly.

To provide a consistent basis for floodplain management and local government planning, the City commissioned WRM Water & Environment (WRM) in December 2007 to undertake a major study to review and update its hydrological models to a consistent standard of methodology and documentation. Coomera, Nerang, Logan-Albert, Pimpama, Worongary, Mudgeeraba, Loders, Biggera, Tallebudgera and Currumbin catchment’s hydrological models were included in that study.

A comprehensive review of data, previous hydrological models and associated reports for the above mentioned 10 catchments covering the City were undertaken prior to the commencement of model updates. This review assessed all aspects of model development, calibration and use for the estimation of design discharges. Based on the review, a set of recommendations were provided to update the 10 models in a consistent manner across the city area using the latest data and modelling approaches. Details of the model review and its findings are given in WRM 2008a (Ref 1).

Based on WRM recommendations City upgraded the hydrological model for Pimpama River catchment using URBS modelling software in August 2009 (Ref 2). The upgraded model is again reviewed in this study as per Don Carroll’s (Ref 3) recommendations. The upgrade includes review of rating curves, model calibration, design rainfall, temporal patterns and undertaking Monte Carlo simulation.

This report describes the development of URBS hydrological model, calibration, Monte Carlo simulation and design events simulation for Pimpama River catchment.

2.2 Study Objectives and Scope

The main objective of the study was to develop a hydrological model for the Pimpama River catchment based on URBS hydrological modelling software (URBS), calibrated and verified against available data, and fully documented to a consistent standard. Once this objective is achieved, the calibrated model is to be used to estimate design flood discharges using a consistent methodology.

The scope of work was as follows:

Review existing models and data

Update the existing model to a standard consistent with other catchments

Review and update model calibration and verification

Undertake Monte Carlo simulation

Estimate design discharges and extreme event discharges at key locations throughout the catchment using current industry standard methodology; and


of 104

Document the adopted methodology, tasks and results to a standard consistent with other updated models.

2.3 Limitation Statement

The following limitations apply in the preparation of this report.

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

The analysis and approach by this study is specifically prepared for internal use. Use of contents of this report is prohibited unless a written approval is obtained from City.

The result of this study is accurate only for its intended purpose.

2.4 Acknowledgement

The assistance provided by the Bureau of Meteorology (BOM), and in particular, for this study is gratefully acknowledged. The Bureau provided the copies of their URBS hydrological models used for flood forecasting purposes and all the historical rainfall and stream flow data used in this study for model calibration and verification.

2.5 Previous Studies

There are many studies of relevance to the hydrological modelling of the Pimpama River catchment which are briefly described below.

2.5.1 Woongoolba Drainage Study (1994) (Ref 4)

In 1994, Albert Shire Council engaged Sinclair Knight Merz (SKM) to evaluate the Woongoolba Flood Mitigation Scheme (WFMS) condition and to determine the performance capacity of the WFMS. A RORB hydrologic model and a MIKE11 hydraulic model of the region were developed for the study.

The summary of the SKM study is as follows: WFMS layout was based on 1991 aerial photos with drains and structures based on 1994

ground surveys.

A hydrological model (RORB) was developed for Woongoolba with 33 sub-catchments using 1987 Australian Rainfall and Runoff’s (ARR) rainfall and temporal patterns (rainfall distribution). No calibration was undertaken.

An estimated rainfall Intensity- Frequency Duration (IFD) of 236mm for the 1 in 2-year ARI flood with 72-hour storm duration was used.

A 1D hydrodynamic model (MIKE 11) was developed using 1994 survey information, subdivided into various catchments (Old Sandy Creek, Wolfs Drain, Kerkins Drain and Sandy-Behms Creek). A total of 38 structures were included.

The flood storage for the model was estimated from the 0.5 metre contours and 1991 aerial photos.


of 104

As a model boundary, the study used an artificial tidal prediction at Jacobs Well, Cabbage Tree Point and the Logan/Albert River confluence using Brisbane Bar tidal constituents.

2.5.2 Woongoolba Flood Mitigation Hydraulic Study (2004) (Ref 5)

In 2004, the City’s Technical Service Branch undertook an internal review of the 1994 SKM study. The review included upgrading the MIKE11 model to the latest survey information and incorporating structures that were upgraded since 1994. The same RORB hydrologic model results from the 1994 study were used in this review.

A summary of the study is as follows: The WFMS layout was based on the 1991 aerial photos and drains and structures were based

on 2004 ground surveys

A hydrological model (RORB) was developed for Woongoolba with 33 sub-catchments using 1987 ARR rainfall and temporal patterns (rainfall distribution). No calibration was undertaken.

The 1 in-10 year ARI was estimated based on a factor of 1.6 to the 1 in 2-year ARI event.

An estimated rainfall IFD of 236mm for the 1 in 2-year ARI flood with 72-hour storm duration was used.

A single 1D hydrodynamic model (MIKE 11) was developed using 2004 survey information.

The flood storage for the model was estimated from the 0.5 metre contours and 1991 aerial photos.

As a model boundary, the study used an artificial tidal prediction at Jacobs Well, Cabbage Tree Point, the Logan/Albert River confluence and Pimpama using tidal constituents.

2.5.3 Woongoolba Flood Mitigation Scheme Supplementary Report (2004) (Ref 6)

Both the original 1994 SKM (Ref 4) and the 2004 (Ref 5) studies used the one dimensional (1D) model (MIKE 11) to simulate the complex flood flows. This supplementary study was initiated in 2004 in which a two dimensional (2D) model (MIKE FLOOD model) using a 30-metre grid bathymetry was developed to simulate the complex flood flow.

The summary of the study is the same as for the 2004 study except that: A 2D hydrodynamic model (MIKE Flood Model) was developed based on a 30-metre model

grid.

The grid was based on 2001 airborne laser survey data.

The flood storage was calculated using the 2D model grid.

2.5.4 Pimpama River Catchment Investigation - Hydrological Study (2005) (Ref 7)

In 2005, City undertook a catchment wide hydrological modelling study of the Pimpama River catchment using the URBS model. This model divided the Pimpama River (including Hotham Creek)


of 104

catchment into 17 sub catchments. Due to the unavailability of recorded data at the time of the study, the model was not calibrated against recorded data. The model was run using calibrated parameters of the adjoining Coomera River catchment to produce design flow hydrographs for 5, 10, 20, 50 and 100 year Average Recurrence Interval (ARI) storm events.

2.5.5 Logan River Catchment Hydraulic Study (2007) (Ref 8)

In 2007, City undertook a flood study for the Logan River catchment. The Pimpama River catchment 2005 URBS model was upgraded as part of the study. The study identified a significant interaction of flood flows between Logan River and Pimpama River floodplains. The 2007 model also included the McCoys Creek catchment. This URBS model was developed with a finer sub-catchment resolution than the 2005 study and had 42 sub catchments representing Pimpama River, Hotham Creek and McCoys Creek catchments. Again, the model was not calibrated, but this time the model was run using calibrated parameter values for the neighbouring Nerang River and Coomera River catchments. The more conservative design flow hydrographs obtained from the two sets of parameters were adopted for input to the Logan River MIKEFLOOD model.

2.5.6 Pimpama River Catchment and Stormwater Management Plan (2008) (Ref 9)

In 2008, WBM developed a URBS model of the Pimpama River catchment with an even finer sub-catchment resolution than the previous City studies to develop a catchment wide stormwater management plan (WBM, 2008). The model was based on a revision of the GCCC (2007) model and used the same model parameters. The revised model was used to estimate peak discharges at various locations within the catchment for 2, 5, 10, 20, 50 and 100 year ARI storm events for both existing and future development scenarios, and to assess the possible impacts of development on design discharges.

2.5.7 Pimpama River Catchment Hydrological Study (2009) (Ref 2)

City, in collaboration with WRM Water and Environment, developed a hydrological model in URBS of Pimpama River catchment as part of the study. The model was calibrated to November 2004, June 2005 and January 2008, and verified against February 2004 historical flood events. The calibrated model was used to estimate design flood discharges for 2 to 2000 year Average Recurrence Interval (ARI), PMPDF and PMF for up to 72 hour storm durations.


of 104

3. Catchment Description

3.1 Overview

Pimpama River catchment is bounded by the Logan River catchment to the north and west, Coomera River catchment to the south, and the South Moreton Bay to the east. The total area of the catchment is about 125.6 km2. The Pacific Highway and the Gold Coast railway line, which run almost parallel to each other and in an east-west direction almost divides the low lying floodplains on the eastern side of the catchment and higher land on the western side. There are no significant storages in the catchment. Figure 1 is a locality map of Pimpama River catchment.

Figure 1: Locality map, Pimpama River Catchment


of 104

Pimpama River has two main tributaries, namely Hotham Creek and McCoys Creek. The main stem length of Pimpama River is about 30.6 km. The Pimpama River channel is not well defined along the upper reaches but is well defined along the lower reaches. The channel width of the well-defined reaches varies from about 12.0m near the Pimpama Jacobs Well Road to about 55.0m near the river mouth. Three significant cane drains (Oppman, Norwell and Kerkin) located to the north of the river facilitate cross catchment flows between Pimpama River and Behms Creek in the adjoining Logan River catchment during significant flood events. The average slope of Pimpama River is approximately 0.15%.

Hotham Creek, which has a main stem length of approximately 14.6 km, flows into Pimpama River about 2.5 km downstream of railway line. The catchment area of Hotham Creek is about 35.6 km2. The average channel slope from the upstream extent of the catchment to the confluence of Pimpama River is approximately 0.35%.

McCoys Creek, which has a main stem length of approximately 8.2 km, joins Pimpama River at the Pimpama River catchment outlet. The catchment area of McCoys Creek is about 10.0 km2. The average channel slope from the upstream extent of the catchment to the confluence of Pimpama River is approximately 0.10%.

It is of note that the average slopes of Pimpama River, Hotham Creek and McCoys Creek mentioned above were calculated from City’s 5 m DTM using QUDM’s equal area slope method.

3.2 Land Use

Figure 2 shows land use in the Pimpama River catchment. The western side of the Pacific Highway is mainly forested, with few urban and rural development areas. This area has some potential for future urban developments. The eastern side of the highway mainly consists of low lying floodplain area and is dominated by sugar cane cultivation, some aquaculture, and some rural and urban developments. About 47% of the total catchment area is covered by rural residential developments, a further 34% by forested areas and the remaining 19% by urban developments of varying intensities. Land use data are discussed in section 5.2 and 6.2.1 .


of 104

Figure 2: Land use in the Pimpama River Catchment


of 104

3.3 Stream Gauging Stations

There are four stream gauging stations (Hotham Creek Alert, Stewarts Alert, Norwell Alert and Kerkin Road Alert) operating within the Pimpama River catchment. The following is of note:

Hotham Creek Alert station is located about 100 m downstream of the Pacific Highway.

Stewarts Road Alert station is located approximately 150 m downstream of the railway line.

Norwell Alert station is located just upstream of Pimpama Jacobs Well Road.

Kerkin Road Alert station is located about 40 m upstream of Kerkin Road.

There are no gauging stations along McCoys Creek.

There are significant differences of gauge zero levels obtained from BOM and survey conducted by City in April 2013 at Norwell and Kerkin Road Alert gauging stations (Table 1).

Figure 3 shows the location of the gauging stations and Table 1 shows the main stem length, gauge zero and catchment areas to the gauging stations and catchment outlet.

Table 1 - Stream gauge stations, Pimpama River Catchment

River Station Number

Station Name

/ Key Location

Stream Name Period of Operation

Gauge Zero (m AHD)

Catchment Area (km2)

Main Stem Length (km) Survey in

April 2013 ( City )

BOM

146922 Hotham

Creek Alert Hotham Creek

Unknown - present

2.95 NA 24.0 8.0

146923 Stewarts

Road Alert Pimpama

River Unknown -

present 0.84 NA 30.0 12.6

146925 Norwell Alert

Pimpama River

Unknown - present

0.08 -0.85 40.0 17.7

146809 Kerkin Road

Alert Pimpama

River 21/05/2002 -

present -0.03 -1.97 92.6 23.0

- Catchment

Outlet Pimpama

River - - - 125.6 30.6

Note: NA – not available


of 104

Figure 3: Pimpama River drainage network and stream gauging station location


of 104

4. Methodology

The hydrologic modelling of the Pimpama River catchment was undertaken using an approach and methodology consistent with the other catchments in the City area. The study adopted a systematic approach and consisted of the following steps:

4.1 Comprehensive Review of Existing Models and Data

The specific tasks included:

Review of previous studies.

Review of the existing URBS model and related files.

Review of catchment and sub-catchments boundaries using the latest DTM and drainage network data.

Review and update of rating curves at Hotham Creek Alert, Stewarts Road Alert, Norwell Alert and Kerkin Road Alert gauging.

Review of available rainfall and stream gauging data.

Review of existing land use data and update them based on current land uses identified from aerial photography and land use planning scheme maps.

4.2 Model Construction


Update the URBS model configuration

Generation of catchment (network) file and assigning appropriate output locations and calibration points.

Update model to reflect current land use in the catchment.

4.3 Model Calibration and Verification


Selection of calibration and verification events.

Process rainfall and stream flow data for the selected calibration and verification events.

Rainfall analysis of all selected events to create sub-catchment specific rainfall sequences to generate rainfall definition file for URBS model.

Calibration and verification of the URBS model against historic flood events using global model parameters, and jointly with the Woongoolba (Mike11) hydraulic (Ref 5) model.


of 104

4.4 Design Discharge Estimation


Estimation of design rainfalls and loss rates for storm events ranging from 2 year ARI to Probable Maximum Precipitation (PMP).

Undertaking of design event model runs for storm durations up to 72 hours and storm severities ranging from 2 year ARI to PMP design Flood and Probable Maximum Flood (PMF).

Estimation of design discharges at key locations throughout the catchment for flood events ranging from 2 year ARI to PMF.

Verify the design discharges against Monte Carlo simulation.

4.5 Joint Probability Approach/Monte Carlo Simulation


Simulate the model using Monte Carlo Total Probability Theorem (TPT).

Simulate the model using Monte Carlo Cooperative Research Centre for Catchment Hydrology (CRCCH) approach.

4.6 Preparation of Study Report


Documentation of the adopted methodology, tasks and results to a standard consistent with other updated models.


of 104

5. Available Data

5.1 Topographic Data

A 5m grid Digital Terrain Model (DTM), and 5m and 10m contour data sets, which cover most of the City area, were available for this study. In addition, a digital drainage network layer was available from the Department of Natural Resources and Mines (DERM) to better define the drainage paths within the catchment.

5.2 Land Use Data

The land use data used in this study was obtained from the latest GIS layers provided by City’s Infrastructure Planning Coordination Unit. The relevant data were available from the Land Use, Domain and Local Area Plan data layers for the City area. Aerial photos and cadastre data were also used to supplement the above GIS data. Adopted land use categories are discussed in section 6.2.1

5.3 Rainfall Data

Rainfall data used in this study were provided by the Bureau of Meteorology (BOM). Table 2 lists the rainfall stations of relevance to the Pimpama River catchment for which available data were supplied by BOM. Figure 4 shows the location of rainfall stations within and adjacent to the Pimpama River catchment. The rainfall data from these stations were used for the calibration and verification of different flood events. Appendix B shows location of rainfall stations (data) used for each individual calibration and verification event.

The following is of note with regards to the available rainfall data:

A total of thirteen stations have been used for this study.

Four of the stations (Luscombe, Hotham Creek, Stewarts Road, Norwell Road and Kerkin Road) are located within the Pimpama River catchment. The remaining ten stations are located outside, but in close proximity, to the catchment.

The Luscombe Alert is the only station shown in Table 2 that has data prior to 2004 and these are for the March 1999 and January 2001 flood events.

The availability of data at each of the stations for the selected model calibration and verification events is also shown in Table 2.

Three out of the thirteen stations do not have data prior to the January 2008 flood event.


of 104

Table 2 - Rainfall Data Availability for the Pimpama River Catchment

Station No Station Name Data Type

Operator

Data Available

Feb 2004

Mar 2004

Nov 2004

Jun 2005

Jan 2008

Jan 2012

Jan 2013

040761 Wolffdene Alert

P BOM √ √ √ √ √ √ √

040516 Coomera Foxwell Road

D BOM √ √ √ √ √ NA NA

540293 Coomera Shores Alert

P BOM √ √ √ √ √ √ √

540376 Hotham Creek Alert

P City NA NA NA N/A √ √ √

540294 Kerkin Road Alert

P City √ √ √ √ √ √ √

040345 Luscombe Alert

P BOM √ √ √ √ √ √ √

540269 Monterey Keys Alert

P BOM √ √ √ √ √ √ √

540408 Norwell Alert P City NA NA NA NA √ √ √

540292 Oxenford Weir Alert

P BOM √ √ √ √ √ √ √

540295 Steiglitz Wharf Alert

P BOM √ √ √ √ √ √ √

540377 Stewarts Road Alert

P City NA NA NA NA √ √ √

040341 Wongawallan Alert

P BOM √ √ √ √ √ NA NA

540236 Carbrook (Riedel Road)

P BOM/LCC NA NA NA NA NA NA √

√ - Data available P- Pluviograph; D- Daily, NA – Data not available, LCC – Logan City Council


of 104

Figure 4: Rainfall Station Location Map, Pimpama River Catchment


of 104

5.4 Streamflow Data

Currently there are four stream gauging stations operating within the Pimpama River catchment. Table 3 shows details of these stations, including the availability of recorded data for the selected calibration and verification events. Figure 3 shows the station locations. The following is of note with regard to the stream gauging stations:

There are differences of gauge zero levels obtained from BOM and City (Section 3.3 ).

There is no recorded data at any of the stations prior to 2004, and only Kerkin Road Alert station has data prior to January 2008.

Kerkin Road Alert and Norwell Alert stations are affected by tidal fluctuations.


of 104

Table 3 - Stream gauge data availability, Pimpama River Catchment

Station No

Station Name

Stream Name

Catchment Area (km2)

Station Operator

Max. Gauged Height (m)

Max. Gauged Flow (m3/s)

Streamflow Data Available

Feb 2004

Mar 2004

Nov 2004

Jun 2005

Jan 2008

Jan 2012

Jan 2013

146922 Hotham Creek Alert

Hotham Creek

N/A City Not

Gauged - NA NA NA NA √ √ √

146923 Stewarts Road Alert

Pimpama River

N/A City Not


146925 Norwell Alert Pimpama River

N/A City Not


146809 Kerkin Road Alert

Pimpama River

N/A City Not

Gauged - √ √ √ √ NA √ √

√ - Data available P- Pluviograph; D- Daily, NA – Data not available


of 104

5.5 Rating Curves

All four stream gauging stations in the catchment are operated by City. BOM used these stations for flood warning purposes and none of the stations have been gauged and/or rated. New rating curves were developed for these stations using the techniques outlined in Hydrologic Techniques for Checking River Ratings (Ref 10). The datum used for gauging stations to present rating curves in this section is sourced from City (Table 1). It is noted that

5.5.1 Hotham Creek Alert (146922)

Figure 5 shows the rating curve adopted for the Hotham Creek Alert station.

Figure 5: Adopted rating curve for Hotham Creek Alert station (gauge zero assumed at 2.94 m AHD)


of 104

5.5.2 Stewarts Road Alert (146923)

Figure 6 shows the rating curve adopted for the Stewarts Road Alert station.

Figure 6: Adopted rating curve for Stewarts Road Alert station (gauge zero assumed at 0.84 m AHD)

5.5.3 Norwell Alert (146925)

Figure 7 shows the rating curve adopted for the Norwell Alert station. Recorded water levels at the Norwell gauging station are influenced by tide levels. Therefore, a reasonable calibration of the model could not be achieved with the rating curve. It is of note that a set of dependant rating curves were developed for a range of tide levels for Norwell Alert in GCCC (2009) study (Ref 2). Those rating curves are not used for this study because it did not improve the calibrations at Norwell Alert.


of 104

Figure 7: Adopted rating curve for Norwell Alert station (Gauge zero assumed at 0.08 m AHD)

5.5.4 Kerkin Road Alert (146809)

Figure 8 shows the rating curve adopted for the Kerkin Road Alert station. Recorded water levels at the Kerkin Road gauging station are influenced by tide levels. Therefore, a reasonable calibration of the model could not be achieved with the rating curve. It is of note that like Norwell Alert a set of dependant rating curves were developed for a range of tide levels for Kerkin Road Alert in GCCC (2009) study (Ref 2). Those rating curves are not used for this study because it did not improve any calibration.


of 104

Figure 8: Adopted rating curve for Kerkin Road Alert station (gauge zero assumed at -0.03 m AHD)


of 104

6. Model Development

6.1 Model Description

URBS is a networked (i.e. sub-catchment based) runoff-routing model that estimates flood hydrographs by routing rainfall excess through a module representing the catchment storage. In URBS, the storages are arranged to represent the drainage network of the catchment. The distributed nature of storage within the catchment is represented by a separate series of concentrated storages for the main stream and for major tributaries to provide a degree of physical realism. The storages in the model are generally non-linear, but linear storages can be used.

The model provides a number of options for conceptualising the rainfall-runoff process. Rainfall excess is first estimated from rainfall data using one of several available techniques (i.e. loss models) before applied to the runoff-routing component of the model to compute the surface runoff hydrograph. Baseflow, if significant, is estimated separately and added to the surface runoff hydrograph to provide the total catchment hydrograph. The model can easily incorporate the effects of land use change, construction of reservoirs, changes to channel characteristics and other changes in the catchment.

The model provides different options for runoff routing. The user is given the option of lumping the catchment runoff and channel flow components into a single routing component or modelling them as separate routing components. The latter option (i.e. the ‘Split’ model) was adopted for the Pimpama River catchment.

In the Split model the rainfall excess for each sub-catchment is first determined by subtracting losses from the rainfall hyetograph. The rainfall excess is then routed through conceptual catchment storage to determine the local runoff hydrograph for the sub-catchment. The storage - discharge relationship for catchment routing is:

m2

2

catch Q)U1(

)F1(AS

Where Scatch is the catchment storage (m3 h/s);

is the catchment lag parameter;

A is the area of sub-catchment (km2);

U is the fraction urbanisation of sub-catchment;

F is the fraction of sub-catchment forested; and

m is the catchment non-linearity parameter.

In the above equation, β is determined during model calibration and is a global parameter.


of 104

The local runoff hydrograph is then combined with runoff from the upstream sub-catchment and routed through channel storage to obtain the outflow hydrograph for the sub-catchment. Channel routing is based on the non-linear Muskingum Model. The channel routing storage-discharge relationship is given by:

ndu

c

chnl ))1((*

QxQxS

LnfS

Where Schnl is the channel storage (m3 h/s);

α is the channel lag parameter

f is the reach length factor;

L is the length of reach (km);

Sc is the channel slope (m/m);

QU is the inflow at upstream end of reach (includes catchment inflow) (m3/s);

Qd is the outflow at downstream end of the channel reach (m3/s);

x is the Muskingum translation parameter;

n is the Muskingum non-linearity parameter (exponent); and

n* is the Manning's 'n' or channel roughness.

In the above equation, α and f are the principal calibration parameters. Note also that α is a global parameter, whereas f can be varied for each channel reach.

URBS allows the user to select one of several standard loss models. The available options are: initial and continuing loss model, proportional loss model, Manley-Phillips infiltration model and water balance model. The initial and continuing loss model was adopted for the Pimpama River catchment. This model assumes that there is an initial loss of ‘il’ mm before any rainfall becomes runoff. After this, a continuing loss rate of ‘cl’ mm per hour is applied to the rainfall, subject to the limit of the soil infiltration capacity (IFmax). The loss rates can be specified ‘globally’ to the entire catchment or ‘individually’ to each sub-catchment. Global loss values were adopted for the Pimpama River catchment.

Full details of the URBS model and its features are given in the URBS User Manual (Ref 11).


of 104

6.2 Model Configuration

6.2.1 Land Use

Table 4 shows the adopted five major land use categories for the purpose of URBS modelling, and how these land use categories correspond to the different land classifications in the City are also shown in the table.

Table 4 - Pimpama River land use categories

URBS Model Land Use Classification City Classification

UF (Forested) o Forest

o Forest/Grassland

UR (Rural Land) o Grassland _ Urban/Suburban

o Grazing

o Open _ Ground

o Recreation (Facilities & Sub/Urban Parks)

o Rural _ Residential

o Tourism _ Recreation Park

o Vacant _ Land

o Waste _ Disposal

UH (High Density Urban)a o Access _ Restriction Strip

o Commercial

o Constructed Waterway _ Lake

o Industrial

o Marina

o Residential Choice

o Tourism _ Accommodation

o Transport (Rail, Road & Paved Areas)

o Utilities _ Infrastructure

o Water

o Wetlands

UM (Medium Density Urban) o Detached Dwelling

UL (Low Density Urban) o Park Living

o Tourism _ Caravan Park

UL/UM/UHb o Highly Disturbed _ Under Development

o Urban Residential a - Roads are included in this category. b - Appropriate classification selected based on aerial photos and site inspections.

Of the five different land uses, four relate to the amount of urbanisation in the catchment, affecting both the per cent imperviousness (losses) and the routing characteristics. The forested land use only affects the routing characteristics.


of 104

In the Pimpama River catchment, 2.1%, 7.5%, 8.7%, 47% and 34% of the catchment can be currently categorised (based on the URBS definitions) as Low Density Urban (UL), Medium Density Urban (UM), High Density Urban (UH), Rural Land (UR) and Forest (UF) respectively.

6.2.2 Catchment Subdivisions

Figure 9 shows the configuration of the Pimpama River catchment URBS model. The model consists of 49 main sub-catchments. Within the overall catchment, Hotham Creek and McCoys Creek tributary catchments were divided into 15 and 5 sub-catchments respectively. The sub catchments boundaries were delineated based on City’s DTM (May 2011), Waterways Layer (2006), Air Photo (2009) and DNRM’s drainage layers (April 2008). Areas of each sub-catchment within the model are given in Table 5.


of 104

Figure 9: Pimpama River Catchment URBS model configuration


of 104

Table 5 - Pimpama River sub-catchment areas and land uses

Sub-Catchment

Area (km2) UL UM UH UR UF

1 4.15 0.121 0.000 0.045 0.260 0.573

2 1.15 0.032 0.000 0.006 0.564 0.398

3 1.01 0.000 0.000 0.055 0.284 0.662

4 1.49 0.076 0.000 0.001 0.373 0.550

5 1.63 0.025 0.000 0.001 0.425 0.550

6 2.08 0.000 0.000 0.031 0.388 0.581

7 2.23 0.000 0.000 0.012 0.099 0.889

8 2.20 0.000 0.000 0.016 0.492 0.492

9 3.04 0.000 0.000 0.055 0.801 0.144

10 1.72 0.000 0.039 0.006 0.508 0.447

11 3.36 0.003 0.201 0.171 0.545 0.080

12 3.52 0.122 0.145 0.024 0.509 0.200

13 1.68 0.000 0.242 0.264 0.266 0.227

14 1.97 0.000 0.171 0.051 0.378 0.400

15 4.35 0.013 0.000 0.062 0.868 0.057

16 3.58 0.000 0.000 0.000 0.200 0.800

17 3.25 0.000 0.000 0.266 0.119 0.615

18 2.26 0.050 0.000 0.016 0.035 0.900

19 0.78 0.000 0.000 0.012 0.000 0.988

20 2.17 0.000 0.000 0.072 0.464 0.464

21 3.62 0.000 0.000 0.015 0.098 0.886

22 3.02 0.000 0.000 0.029 0.437 0.534

23 1.66 0.000 0.000 0.020 0.539 0.441

24 1.02 0.000 0.122 0.000 0.658 0.220

25 0.57 0.000 0.177 0.021 0.802 0.000

26 3.24 0.023 0.176 0.049 0.382 0.370

27 4.76 0.056 0.259 0.115 0.490 0.080

28 4.24 0.177 0.018 0.056 0.554 0.196

29 5.86 0.000 0.000 0.040 0.883 0.077

30 2.86 0.046 0.001 0.000 0.953 0.000

31 4.38 0.000 0.234 0.076 0.450 0.241


of 104

Sub-Catchment

Area (km2) UL UM UH UR UF

32 1.12 0.000 0.277 0.001 0.673 0.050

33 4.29 0.000 0.170 0.066 0.705 0.059

34 2.76 0.000 0.146 0.000 0.104 0.750

35 1.57 0.000 0.419 0.000 0.081 0.500

36 3.92 0.000 0.173 0.071 0.569 0.187

37 3.99 0.000 0.003 0.064 0.934 0.000

38 2.10 0.000 0.000 0.448 0.542 0.010

39 2.85 0.011 0.000 0.216 0.728 0.045

40 0.77 0.000 0.000 0.185 0.815 0.000

41 4.19 0.000 0.000 0.296 0.342 0.362

42 1.95 0.000 0.000 0.242 0.316 0.442

43 2.23 0.000 0.012 0.113 0.636 0.239

44 2.03 0.000 0.426 0.027 0.166 0.380

45 1.65 0.057 0.208 0.055 0.229 0.450

46 3.30 0.000 0.091 0.112 0.344 0.453

47 1.53 0.000 0.021 0.411 0.338 0.230

48 1.91 0.000 0.000 0.141 0.313 0.546

49 0.63 0.000 0.000 0.370 0.388 0.242


of 104

7. Model Calibration and Verification

7.1 Selection of Calibration and Verification Events

Pimpama River catchment’s rainfall and streamflow data for seven historical flood events since 2004 were available from BOM (section 5.3 and 5.4 ). All of these seven events were selected for the model calibration and verification. Table 6 shows the selected calibration and verification events for Pimpama River catchment.

Table 6 - Selected calibration and verification events, Pimpama River catchment

Event Calibration Verification

January 2008

January 2012

January 2013

February 2004

March 2004

November 2004

June 2005

7.2 Calibration Methodology

The URBS model was calibrated to achieve the best possible fit between recorded and predicted discharge hydrographs at the various gauging stations within the Pimpama River catchment for the selected calibration events. At these stations, the calibration attempted to match the predicted and recorded flood peaks and volumes, and also the shape of the flood hydrograph. The calibrated model was then verified by comparing the model predictions against the stage hydrographs recorded at the Kerkin Road Alert station for the selected verification event.

A single set of global parameters (α, β, m and forest factor F) were adopted for all calibration events. In addition, uniform initial and continuing losses (IL and CL) were applied for the whole catchment. The model parameters were adjusted to achieve the best calibration (i.e. achieve best timing and hydrograph shape) across all events. Initial and continuing losses were adjusted to achieve the correct hydrograph starting point and hydrograph volume respectively. Where necessary, reach length factors (f) were changed in the model to represent differences in channel routing characteristics.

7.3 Joint Calibration with Hydraulic Model

A joint calibration between the UBRS model and City’s Woongoolba Hydraulic Model (Mike11)(GCCC 2004, Ref 5) was also undertaken because of the limited availability of stream gauge data specially at Norwell and Kerkin Road Alert, uncertainties regarding the adopted rating curves and the impact of tidal influence on recorded water levels at some of gauging stations. Some modifications were made to the Mike 11 model to make it better suit for the joint calibration. The model modifications and extents are as follows:


of 104

The model was further extended to the Broadwater along Pimpama River. Figure 10 shows the model layout.

Cross sections of Hotham and Pimpama branches were extended to flood plain using City’s 2m DTM (September 2012) to provide better representation surface storage.

Figure 10 shows Mike 11 model layout. The model extent does not cover up to the Hotham Creek and Stewarts Road Alert. It starts from about 2.2 km and 2.1 km downstream of Stewarts Road Alert and Hotham Creek Alert station respectively. The tailwater boundary along Pimpama River located about 2.4 km downstream from Kerkin Road Weir.


of 104

Figure 10: Mike 11 model layout


of 104

The hydrological input of the Mike 11 model outside Pimpama River catchment is sourced from Logan Hydrological Study 2014 (Ref 12). This input was required to take into account because there is interaction of flooding between Pimpama River and Logan River (Behms Creek, Sandy Creek, Oppman Drain etc) at high discharges. However, the hydrology of Logan River catchment for the verification events February 2004 and June 2005 were not available due to the unavailability of rainfall data. Therefore, Mike 11 model setup for these two events is based on Pimpama River catchment hydrology only (no hydrological input assigned outside Pimpama River catchment).

The tailwater boundaries of the Mike 11 model were sourced from Regional Broadwater Model (Ref 13) and recorded water levels at Steiglitz Wharf Alert and Coomera Shores Alert based on availability of data. However, the Broadwater Model was given priority as a tailwater because of availability f hydrograph at exact location of the Mike 11 boundaries. Table 7 shows source of tailwater boundaries for the Mike 11 model.

Table 7 – Source of tailwater and availability Logan River Catchment hydrology for Mike 11 model

Event Tailwater Source

February 2004 BOM (Coomera Shores Alert)

March 2004 BOM (Steiglitz Wharf Alert)

November 2004 BOM (Coomera Shores Alert)

June 2005 BOM (Coomera Shores Alert)

January 2008 Regional Broadwater Model (Ref 13)



7.4 Assignment of Rainfall and Temporal Patterns

Rainfall depths and temporal patterns for each sub-catchment in the model were generated from available pluviograph and daily rainfall data using an inverse distance squared method based on the nearest four rainfall stations to the sub-catchment centroid. This method ensures that all of the available data are used and that the most appropriate rainfall temporal pattern is assigned to each sub-catchment. Table 8 shows the total weighted average rainfalls of the catchment for the selected calibration and verification events.


of 104

Table 8 – Weighted average total rainfalls, Pimpama River Catchment

Event Average Rainfall (mm)

February 2004 209

March 2004 112

November 2004 335

June 2005 330

January 2008 110

January 2012 401

January 2013 237

7.5 Adopted Model Parameters

Table 9 shows the global catchment and channel parameters adopted for the Pimpama River catchment. The same parameter values were applied for all calibration and verification events.

Table 9 – Adopted catchment and channel parameters, Pimpama River catchment

Parameter Adopted Value

(Channel Lag Parameter) 0.3

(Catchment Lag Parameter) 3.0

m (Catchment non-linearity Parameter) 0.75

F (Forest Factor) F*0.5

It is noted that reach length factors were introduced within the URBS model to represent differences in channel routing characteristics between the upper and lower reaches of the drainage system. Figure 11 shows the reaches for which a reach length factor of 3.5 have been applied. The upper reaches have been assigned the default value of 1.0.


of 104

Figure 11: Channel reaches for which non-default reach length factors have been adopted


of 104

7.6 Initial and Continuing Losses

Table 10 shows the adopted initial loss and continuing loss rates for the Pimpama River URBS model for calibration and verification events. The losses of Pimpama River catchment were adjusted to produce the best calibration, and as such the amount and quality of available rainfall data for each event will have some effect on the adopted initial and continuing losses. It is of note that a uniform Initial and a continuing loss were adopted for calibration and verification events.

Table 10 - Adopted Initial and Continuing Losses for Calibration and Verification Event

Event Initial Loss

(mm)

Continuing Loss (mm/hr)

January 2008 40 0.25

January 2012 50 3.50

January 2013 50 4.00

February 2004 110 6.00

March 2004 30 3.00

November 2004 140 6.00

June 2005 140 6.00

7.7 Calibration Results

7.7.1 Overview

A good calibration was achieved for the Pimpama River catchment for all three calibration events, considering the uncertainties with the available rating curves at the calibration stations, the tidal impacts and two-dimensional nature of flows in the lower reaches, and that a single set of model parameters were adopted for all events. The model predicted better calibrated results using gauge zero levels sourced from City (Table 1) at Norwell Alert and Kerkin Road Alert. Table 11 shows the comparison of modelled and recorded peak discharges and Table 12 shows comparison of modelled (Mike 11) and recorded peak flood levels at Norwell and Kerkin Road gauging stations for calibration events. Calibration results for individual events are further discussed in sections 7.7.2 to 7.7.4 .

Table 11 - Modelled and recorded peak discharges at Hotham Creek and Stewarts Road Alert for calibration events

Event

Peak Discharge

Hotham Creek Alert Stewarts Road Alert

Modelled (m3/s) Recorded (m3/s) Modelled (m3/s) Recorded (m3/s)

January 2008 35.7 31.8 38.6 39.0

January 2012 81.0 73.2 60.0 69.0

January 2013 38.3 31.8 58.9 71.6


of 104

Table 12 - Modelled (Mike 11) and recorded peak flood level at Norwell and Kerkin Road Alert for calibration events

Event

Peak Flood Level

Norwell Alert Kerkin Road Alert

Modelled

(m AHD)

Recorded

(m AHD*)

Modelled

(m AHD)

Recorded

(m AHD*)

January 2008 - - - No data

January 2012 1.65 1.61 1.49 1.46

January 2013 1.17 1.15 1.16 1.2

Note: *based on gauge zero level sourced from City 2013 (Table 1)

7.7.2 January 2008 Event

A comparison of recorded and modelled peak discharges at the Hotham Creek and Stewarts Alert are shown in Table 11. Calibration hydrographs of these two locations for January 2008 event are shown in Figure B. 2 and Figure B. 3 (Appendix B). At the Hotham Creek station, the agreement between predicted and recorded peak discharges, timing of the peak discharges and the hydrograph shapes and volumes are excellent. At the Stewarts Road Alert, an excellent calibration is achieved for this event with respect to peak discharge, timing and shape of hydrograph.


A comparison of recorded and modelled peak discharges at the Hotham Creek Alert and Stewarts Road Alert stations are shown in Table 11. Calibration hydrographs of these two locations for January 2012 are given in Appendix B (Figure B. 5 and Figure B. 6). The calibration of this event is satisfactory with respect to timing and shape of hydrographs at Hotham Creek and Stewarts Road Alert; however the predicted peak discharge at Stewarts Road Alert is lower than recorded peak discharge.

It is recalled that the water levels at the Norwel and Kerkin Road Alert stations are influenced by tidal effects. Hence, the discharge estimates obtained using the rating curves adopted for these station cannot be used with confidence to calibrate the URBS model. The calibration was therefore checked by comparing the recorded water levels against the Mike11 predicted water levels. Table 12 shows a comparison between the recorded and Mike11 predicted peak water levels at the Norwell and Kerkin Road Alert stations based on a joint calibration of the URBS and MIKE 11 models, and Appendix B (Figure B. 7 and Figure B. 8) shows the calibration plot of these two stations. The results show that the recorded and predicted hydrographs match reasonably well. It is noted that the gauge zero levels at Norwell and Kerkin road Alert used for this event are based on survey undertaken in April 2013 by City (Table 1) and the tailwater of the Mike 11 model is sourced from Regional Broadwater Model (Ref 12).


A comparison of recorded and modelled peak discharges at the Hotham Creek Alert and Stewarts Road Alert stations are shown in Table 11. Calibration hydrographs of these two locations for January 2013 are given in Appendix B (Figure B. 10 and Figure B. 11). A good calibration is achieved for this


of 104

event at the Hotham Creek and Stewarts Road Alert with respect to shape of hydrographs, timing and volume of water. However the model over estimated and under estimated flood at the Hotham Creek and Stewarts Road Alert respectively. It is noted that there are uncertainties associated with gauge zero level and rating curve at Stewarts Road Alerts station.

Due to the reason stated in section 7.7.3 , the model calibration was checked by comparing the recorded water levels against the Mike 11 predicted water levels obtained via a joint calibration of URBS and Mike 11 models. Table 12 shows a comparison between the recorded and Mike11 predicted peak water levels at the Norwell and Kerkin Road Alert stations based on a joint calibration of the URBS and the MIKE 11 models, and Appendix B (Figure B. 12 and Figure B. 13) shows calibration plots at the Norwell and Kerkin Road Alert stations. The model results show that a good calibration is achieved at these two stations considering hydrograph shapes, timing and hydrograph peaks. The gauge zero levels at Norwell and Kerkin Road Alert used for this event are based on survey undertaken in April 2013 by City (Table 1) and the tailwater of the Mike 11 model is sourced from Regional Regional Model (Ref 12).

7.8 Verification Results

7.8.1 Overview

The calibrated URBS model was verified against the recorded data for the February 2004, March 2004, November 2004 and June 2005 flood events using the same global parameters as for the calibration events. Reasonable model results were achieved for the all verification events. The model predicted better verification results using gauge zero levels sourced from BOM (Table 1) at Kerkin Road Alert. Table 13 shows the modelled (Mike 11) and recorded peak flood levels at the Kerkin Road Alert for verification. Verification results for individual events are discussed in sections 7.8.2 to 7.8.5 .

Table 13 - Modelled (Mike 11) and recorded peak flood level at Kerkin Road Alert for verification events

Event

Peak Flood Level

Kerkin Road Alert

Modelled

(m AHD)

Recorded

(m AHD*)

February 2004 0.84 0.88

March 2004 0.99 1.03

November 2004 0.99 0.94

June 2005 1.23 1.06

Note: *based on gauge zero level sourced from BOM (Table 1)

7.8.2 February 2004 Event

For the February 2004 event, data is available only for the Kerkin Road Alert station. Like calibration events, the model verification was also checked by comparing the recorded water level against the Mike 11 predicted water level. Table 13 and Figure B. 15 (Appendix B) show the recorded and Mike 11 predicted water levels at the Kerkin Road Alert station based on input from the calibrated URBS model. The result show that the recorded and modelled hydrographs match well up to first peak and


of 104

the timing of subsequent peaks are also very good. However Mike 11 under estimated the second and subsequent flood peaks. It is of note that hydrology of Logan River catchment was not available for this event due to unavailability of rainfall data. The gauge zero levels at Kerkin Road Alert used for this event is sourced from BOM (Table 1) and the tailwater of the Mike 11 model is sourced from recorded water levels at the Coomera Shores Alert.

7.8.3 March 2004 Event

For the March 2004 event, data is available only for the Kerkin Road Alert station. Like calibration events, the model verification was also checked by comparing the recorded water level against the Mike 11 predicted water level. Table 13 and Figure B. 17 (Appendix B) show the recorded and Mike 11 predicted water levels at the Kerkin Road Alert station based on input from the calibrated URBS model. The Mike 11 produces good verification results for this event considering the timing and magnitude of some model predicted peaks. The gauge zero levels at Kerkin Road Alert used for this event is sourced from BOM (Table 1) and the tailwater of the Mike 11 model is sourced from recorded water levels at Steiglitz Wharf Alert.

7.8.4 November 2004 Event

For the November 2004 event, data is available only for the Kerkin Road Alert station. Table 13 and Figure B. 19 (Appendix B) show a comparison of recorded and Mike11 predicted water levels at Kerkin Road Alert based on input from the calibrated URBS model. An excellent verification result was achieved for this event at Kerkin Road Alert station. The recorded and Mike11 hydrographs timing and flood peaks matched very well at this station. The gauge zero levels at Kerkin road Alert used for this event is sourced from BOM (Table 1) and the tailwater of the Mike 11 model is sourced from recorded water levels at Coomera Shores Alert.

7.8.5 June 2005 Event

Similar to all other verification events, data is available only for the Kerkin Road Alert station for this event. Table 13 and Figure B. 21 (Appendix B) show the recorded and Mike 11 predicted water levels at the Kerkin Road Alert station based on input from the calibrated URBS model. The Mike 11 predicted higher flood than recorded water levels; however, the modelled hydrographs shapes and timing match very well. It is of note that hydrology of the Logan River catchment was not available for this event due to the unavailability of rainfall data. The gauge zero levels at Kerkin Road Alert used for this event is sourced from BOM (Table 1) and the tailwater of the Mike 11 model is sourced from recorded water levels at the Coomera Shores Alert.


of 104

8. Flood Frequency Analysis

Sufficient historical peak height or discharge data was not available to undertake a flood frequency analysis (FFA) for any of the four stream gauging stations located within Pimpama River catchment.


of 104

9. Design Flood Estimation

The calibrated URBS model was used to estimate design flood discharges throughout the Pimpama River catchment based on design rainfall intensity - frequency – duration (IFD) data from a number of sources. Design flood discharge hydrographs were estimated for a range of storm durations up to 120 hours for the 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000 year Average Recurrence Interval (ARI) events, and for the Probable Maximum Precipitation Design Flood (PMPDF) and Probable Maximum Flood (PMF) events.

9.1 Methodology

Based on a comprehensive review of available design rainfall data (IFD data, temporal patterns, areal reduction factors, rainfall spatial distribution and design rainfall losses), WRM (2008d) (Ref 16) recommended the methodology for use in design event hydrology modelling for catchments in the City area. A number of modifications were made to the WRM (2008d) recommended methodology (Ref 3) and these are summarised in Table 14. The methodology recommended in Table 14 has been adopted for this study.

Version 1 – August 18 TRACKS-#43467383-v2-PIMPAMA_RIVER_HYDROLOGICAL_STUDY_REPORT_DECEMBER_2014 of 104

Table 14 - Summary of Recommended Methodology for Design Event Analysis

Design Flood Parameter

ARI Range (Years) Available Sources/Methods Comment Recommendation

Rainfall depth

≤ 100

ARR 1987 (Ref 17) Industry standard approach. Not Recommended (Rainfall data till 1986)

AWE 1998 a (Ref 18) or

AWE 1992 (Ref 19)

Uses same methodology as ARR 1987 with additional data. AWE 1998 is recommended for Gold Coast catchments.

AWE 1992 is recommended for Logan River catchment.

Both methods use standard methodology with a longer period of recorded data.

Refer Table 15.

CRCFORGE (Ref 20) Based on analysis of daily data.

Adopted for Hinze Dam hydrology (HDA 2007) for events from 10 to 2000 year ARI (Ref 21).

Recommended for storm durations ≥ 96 hours

Refer Table 15.

BOM Pilot Study (Ref 22) Data was provided by BoM for investigation of Hinze Dam hydrology, but it is no longer available.

Not Recommended

BOM 2013 New draft IFD was released by BOM in July 2013. The final IFD is expected to be released in 2015.

Not Recommended (Not finalised)

> 100 to 500

ARR 1987 Industry standard approach. Not Recommended

AWE 1998 a (Ref 18) or

AWE 1992 (Ref 19)

Uses same methodology as ARR 1987 with additional data. AWE 1998 is recommended for Gold Coast catchments.

AWE 1992 is recommended for Logan River catchment.

Refer Table 15.

CRCFORGE(Ref 20) Based on analysis of daily data.

Adopted for Hinze Dam hydrology (HDA) for events from 10 to 2000 year ARI (Ref 21).

Recommended for storm durations ≥ 96 hours

Refer Table 15

> 500 to <2000 Interpolate between ARI 500 (AWE) and ARI 2000 (CRCFORGE)

Creates a smoother transition between rainfall sources. Recommended for all storm durations, excluding storm durations ≥ 96 hours.

Refer Table 15.

2000 CRCFORGE(Ref 20) Based on analysis of daily data.

Adopted for Hinze Dam hydrology (HDA 2007) for events from 10 to 2000 year ARI Ref 21).

Recommended.

Refer Table 15.

2,000 to < PMP Interpolate between CRCFORGE & PMP methods.

No explicit methodology is available to estimate rainfall depths for events of this magnitude.

Recommended.

Refer Table 15.




Section 3.6.3 of ARR 1999 provides a methodology for interpolation (Ref 23).

PMP GSDM (≤ 6 hours)

GTSMR (> 24 hours)

Industry standard approach.

Linearly Interpolated for durations between 6 and 24 hours.

Recommended.

Refer Table 15.

Areal Reduction Factors

< 2000

ARR 1987 Based on United States data. Not Recommended

CRC ARF (Ref 24 and Ref 25) Derived from regional data for durations ≥ 24 hours. Recommended.

Adopt 24 hour duration ARFs for durations less than 24 hours.

Verify using flood frequency analysis where possible.

2,000 to < PMP Interpolate between CRCFORGE & PMP methods (Ref 23 and Ref 24).

Interpolate as recommended by ARR 1999 Section 3.6 using CRCFORGE and PMP rainfalls which are already factored for catchment area.

Recommended.


GTSMR (> 24 hours)

Industry standard approach. Recommended.

Temporal Pattern

≤ 100

ARR 1987 Industry standard approach. Not Recommended.

AWE 2000 Uses same methodology as ARR 1987 with additional data. Alternative patterns derived for ARI > 30 years (but only recommended for sensitivity analysis).

Not Recommended.

UWS 2006 Uses same methodology as ARR 1987 & AWE 2000 with additional data.

Not Recommended.

WRM v7 (Ref 14) (≤ 72 hours)

GTSMR (≥ 96 hours)

AWE 2000 patterns have been filtered by WRM to eliminate sub-duration inconsistencies.

Industry standard approach.

Recommended

Use of filtered AWE 2000 patterns (≤ 72 hours) (Ref 14) and GTSMR (≥96 hours) recommended for Gold Coast and Logan Catchment.

Refer Table 16.

> 100 to < PMP GSDM (≤ 6 hours)

GTSMR (> 24 hours)

Interpolate between WRM7 and GSDM or GTSMR.

PMP temporal patterns are recommended by ARR 1999 for this range of event magnitudes (Ref 23).

Recommended.

Refer Table 16.


GTSMR (> 24 hours)

Industry standard approach. Recommended.

Refer Table 16.




Spatial Distribution

≤ 100 AWE 1998 a (Ref 18) Estimate design rainfall at the centroid of each model sub-catchment and apply ARF based on whole catchment, as recommended in ARR 1987 (Ref 17).

Recommended.

> 100 to 2000 CRCFORGE Estimate CRCFORGE rainfall at the centroid of each model sub-catchment.

Recommended.

> 2,000 to PMP GSDM (≤ 6 hours)

GTSMR (> 6 hours)

Adopt PMP spatial distribution for events greater than 2000 year ARI as recommended by ARR 1999 (Ref 23).

Recommended.

Rainfall Losses

≤ 100

ARR 1987 (Ref 17) Very little Queensland data used in recommended loss values for Queensland.

Suggests Initial losses in the range 15-35mm and a continuing loss rate of 2.5mm/hr.

Recommends adoption of median values from catchment-specific model calibration.

Not Recommended.

Ilahee 2005 (Ref 26) Comprehensive study based on data for 48 Queensland catchments.

Estimated the median initial and continuing loss rates for eastern Queensland catchment to be 38mm and 1.52mm/hr respectively.

Recommended.

Adopt 38mm for initial loss and median continuing loss values from catchment specific model calibration.

> 100 to < PMP ARR 1999 (Ref 23) Interpolate losses between 100 year ARI and PMP Design Flood using approach recommended by ARR 1999.

Recommended.

PMP ARR 1999 (Ref 23) Adopt minimum values from catchment-specific model calibration, as recommended by ARR 1999.

Recommended.

a Includes IEAust 1987 Skewness


Table 15- Adopted Rainfall Depth (IFD) for Gold Coast Catchments.

Storm Duration

(hour)

ARI (Years)

1 2 5 10 20 50 100 200 500 1000 2000 PMP

0.5 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC GSDM

1 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC GSDM

1.5 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT GSDM


4.5 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT GSDM


9 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT INT

12 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC INT

18 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC INT

24 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC GTSMR

36 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT GTSMR



96 INT INT CRC CRC CRC CRC CRC CRC CRC CRC CRC GTSMR

120 INT INT CRC CRC CRC CRC CRC CRC CRC CRC CRC GTSMR


Table 16 - Adopted Temporal Patterns for Gold Coast Catchments.

Storm Duration

(hour)

ARI (Years)

1 2 5 10 20 50 100 200 500 1000 2000 PMP

0.5 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT GSDM

1 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT GSDM





9 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT INT



24 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT GTSMR




96 GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR INT INT INT INT GTSMR

120 GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR INT INT INT INT GTSMR


of 104

9.2 Rainfall Depth Estimation

9.2.1 Frequent to Large Design Events (up to and including 100 years ARI)

Design rainfall intensities for storms of varying durations (30 minutes to 72 hours) for all ARI’s up to and including the 100 Year ARI event were determined at the centroid of each model sub-catchment using City’s Intensity-Frequency-Distribution (WRM 2008c, Ref 15) utility program. Note that the IFD calculation parameters in City’s IFD 2008 utility program were updated after a review of the original parameters used in City IFD 1998 utility (AWE 1998, Ref 18). The extracted average rainfall intensities for each duration and ARI were converted to total rainfall depths to use in the URBS model. Design rainfall depths for storm durations of 96 and 120 hours for all ARIs up to and including 100 year ARI events were estimated at the centroid of each model sub-catchment using the CRC-FORGE rainfall application (Hargraves c.2004, Ref 20). The adopted rainfall depth for the Pimpama River catchment is summarised in Table 15.

9.2.2 Rare to Extreme Design Events (200 to 2000 years ARI)

Design rainfall depths for the 200, 500, 1000 and 2000 Year ARI events were estimated as follows:

Design rainfall depths for durations of between 30 minutes and 72 hours for the 200 and 500 Year ARI events were estimated at the centroid of each model sub-catchment using City’s IFD 2008 utility program (WRM 2008c, Ref 15).

Design rainfall depths for storm durations 30 minutes, 1 hour, 3 hour, 6 hour, 12 to 24 hour and 48 to 120 for the 2000 year ARI were estimated at the centroid of each model sub-catchment using the CRC-FORGE rainfall application (Hargraves c.2004, Ref 20). The rainfall depths for the 1.5 hour, 4.5 hour, 9 hour and 36 hour for the 2000 year ARI were estimated by interpolating between the previous and next available storm duration’s rainfall.

Design rainfalls depths for durations of 30 minutes to 72 hour for the 1000 year ARI event were estimated by interpolating between the 500 and 2000 year ARI rainfall estimates.

Design rainfall depths for durations 96 to 120 hours for the 200, 500 and 1000 year ARI events were estimated at the centroid of each model sub-catchment using the CRC-FORGE rainfall application (Hargraves c.2004, Ref 20).

Table 15 shows details of rainfall used in this study.

9.2.3 Probable Maximum Precipitation Design Flood (PMPDF)

Probable Maximum Precipitation (PMP estimation) for the Pimpama River catchment is presented in Appendix E. PMP rainfall depths were estimated as follows:

PMP depths for durations of up to 6 hours were estimated using the methodology given in ‘Estimation of Probable Maximum Precipitation in Australia: Generalised Short Duration Method’ (BOM 2003a, Ref 27).

PMP depths for durations from 24 hours to 120 hours were estimated using the methodology given in ‘Generalised Tropical Storm Method (GTSMR) – Revised Edition’ (BOM 2003b, Ref 28). The total catchment area of the Pimpama River catchment and the topographic adjustment


of 104

factors (TAF) at the centroid of each model sub-catchment were used to obtain the individual sub-catchment PMP estimates from the overall catchment PMP estimate.

The PMP depths for 9 to 18 hour durations were obtained by interpolating the rainfall depths between the 6 hour GSDM and 24 hour GTSMR estimates.

9.2.4 Probable Maximum Flood (PMF)

PMP rainfalls were applied for estimation of PMF discharges and rainfall depths were obtained as described in Section 9.2.3 .

9.3 Temporal Patterns


A sub-duration inconsistency within the temporal patterns adopted by City (AWE 2000, Ref 29) was identified during GCCC 2009 (Ref 2) study. The AWE (2000) temporal patterns, which was adopted by City until 2008, produces design rainfalls for shorter durations within a particular pattern that are greater than the design rainfalls given by the patterns for durations equal to these shorter durations. For instance, at a number of locations the 72 hour storm temporal pattern has within it 6 hour, 12 hour, 24 hour and 48 hour design rainfalls that are larger than the equivalent design rainfalls given by the 6 hour, 12 hour, 24 hour and 48 hour storm temporal patterns. Further, this problem was present for the full range of rainfall ARI’s from 2 to 100 years. The inconsistencies within the AWE (2000) temporal patterns produce unrealistically long critical storm durations and large design discharges for Gold Coast catchments.

As part of the GCCC 2009 (Ref 2) study, the above sub-duration inconsistencies of the original AWE (2000) temporal patterns were filtered and smoothed by adjusting the longer duration patterns according to the methodology outlined in IEAust 1998 (Ref 30) and BOM 1991 (Ref 31) (refer WRM 2008b, Ref 14). The filtering and smoothing were undertaken until the inconsistencies were completely removed for all ARI’s up to 100 years, whilst maintaining the basic shape and integrity of the original patterns. The adopted temporal patterns are given in Table 16 and Appendix C.


The temporal patterns for the 200, 500, 1000 and 2000 ARIs and all durations from 1 to 120 hour storm durations were estimated by interpolation between 100 year ARI and PMP (Table 16 and Section 9.3.3 ).


Temporal patterns for PMPDF design storms were obtained as follows:

The temporal pattern for durations up to and including 6 hours were obtained from ‘The Estimation of Probable Maximum Precipitation in Australia: Generalised Short Duration Method’ (BOM 2003a, Ref 27).

Temporal patterns for durations from 24 hours to 72 hours were obtained for ‘The Coastal AVM storms from the Generalised Tropical Storm Method – Revised Edition’ (BOM 2003b, Ref 28).


of 104

The temporal pattern for 9 hours, 12 hours and 18 hours were obtained by interpolating between the 6 hours and 24 hours temporal patterns.

The adopted temporal patterns are given in Appendix C.


Temporal patterns for durations from 24 hours to 120 hours for the top ten individual storms were obtained from ‘The Coastal Storms from the Generalised Tropical Storm Method – Revised Edition’ (BOM 2003b, Ref 28). Table 17 shows historical temporal patterns used in this study.

Table 17 - Ten Historical Temporal Patterns used for PMF

24 hours 36 hours 48 hours 72 hours 96 hours 120 hours

PMF01 1893FEB03-1 1893FEB03-2 1893FEB03-2 1918JAN24-3 1918JAN25-5 1918JAN25-5

PMF02 1898APR03-2 1898APR03-2 1918JAN24-3 1972JAN12-5 1972JAN12-5 1972JAN12-5

PMF03 1916DEC29-2 1918JAN24-3 1972JAN12-5 1974JAN28-4 1974JAN23-6 1974JAN23-6

PMF04 1954FEB21-1 1954FEB21-2 1974JAN27-2 1974MAR13-4 1974JAN28-4 1975FEB25-6

PMF05 1955FEB25-2 1955FEB25-2 1975DEC10-2 1979JAN06-4 1974MAR13-4 1979JAN06-5

PMF06 1963APR16-4 1963APR16-4 1979JAN06-4 1981JAN13-7 1975FEB25-6 1981JAN13-7

PMF07 1970JAN19-1 1974JAN27-2 1982JAN22-2 1991JAN01-7 1979JAN06-5 1985MAR28-5

PMF08 1974JAN27-2 1979JAN06-4 1995FEB28-4 1995FEB28-4 1981JAN13-7 1991JAN01-7

PMF09 1979JAN06-4 1989MAR14-2 1998DEC10-2 1998JAN29-4 1991JAN01-7 1997MAR06-7

PMF10 1989MAR14-1 1998DEC10-2 1999FEB13-2 1998MAR05-7 1998MAR05-7 1998MAR05-7

9.4 Areal Reduction Factors


The Queensland Extreme Rainfall Estimation Project (EREP) (Hargraves c.2004, Ref 20) developed the following relationship between ARF, catchment area and storm duration for Queensland catchments:

ARF = 1 – 0.226 x (Area0.1685 – 0.8306 x log (Duration)) x Duration-0.3994

Where

ARF = Areal reduction factor

Area = Catchment area (km2)

Duration = Rainfall duration (hours)

The above relationship was used to estimate areal reduction factors for this study as recommended in WRM 2008b (Ref 14). Note that the derivation of the EREP ARF equation was based on daily rainfall data. Hence, the applicability of ARF’s derived from the above equation for durations shorter than 24 hours is uncertain. For consistency with the approach adopted in two recent major dam studies in the


of 104

Gold Coast area, namely the Hinze Dam upgrade study in the Nerang River catchment (HDA 2007, Ref 21) and the Wyaralong Dam design study in the Logan River catchment (Sunwater 2007, Ref 32), the 24 hour ARF was adopted in this study for all durations shorter than 24 hours. Table 18 shows the adopted ARF’s (based on total catchment area) for design rainfalls for different storm durations and ARI’s.

Table 18 - Adopted Areal Reduction Factors

Storm Duration

(Hours)

Areal Reduction Factor (ARF)

based on Total Catchment Area

24 and less 0.93

36 0.95

48 0.96

72 0.97

96 0.98

120 0.98


Areal reduction factors were applied to the 200, 500, 1000 and 2000 Year ARI design rainfalls as described in section 9.4.1 .


As aerial reduction factors are incorporated in the PMP rainfall estimation methodology (BoM 2003a, Ref 27 and BoM 2003b, Ref 28), so no additional ARFs were applied to the rainfalls estimated for the catchment using this method.


No additional ARF were applied as described in section 9.4.3 .

9.5 Rainfall Losses


The initial loss (IL) and continuing loss (CL) method of accounting for rainfall losses was adopted for this study. Due to lack of historical data, a reconciliation of URBS model design discharges and flood frequency analysis results could not be undertaken in this study. Therefore, the loss rates adopted for the adjoining Logan River catchment (Ref 12) were adopted for this study. Table 19 shows the adopted loss rates.


of 104

Table 19 - Adopted Initial Loss and Continuing Loss, 2 to 100 Year ARI Events

ARI (Years)

Adopted Loss

Initial Loss (mm) Continuing Loss (mm/hour)

2 20 3.0

5 15 2.0

10 10 1.2

20 0 0.8

50 0 0.4

100 0 0.1


An initial loss (IL) of 0.0 mm was adopted for 100 year ARI event (refer section 9.5.1 ). So it was considered appropriate to adopt the same IL for all events greater than 100 year ARI. For the same reason, a CL of 0.1 mm/hour (refer section 9.5.1 ) was adopted for all ARI’s greater than 100 years.


As recommended in Table 14 and as per the reason given in section 9.5.2 , an initial loss 0.0 mm and a 0.1 mm/hour continuing loss rate were adopted for the PMP design flood event.


The initial loss and continuing loss rate adopted for PMPDF (IL= 0.0 mm and CL= 0.5 mm/hr) were adopted for the PMF event.

9.6 Spatial Distribution


Spatial variation in design rainfalls was taken into account by using design rainfalls for durations from 30 minutes to 72 hours for all ARIs up to and including 100 years at the centroid of each model sub-catchment as described in section 9.2.1 . This is in accordance with the methodology described in Table 14.


Spatial variation in design rainfalls was taken into account by using design rainfalls for durations from 30 minutes to 120 hours for all ARIs between 200 and 2000 years (inclusive) at the centroid of each model sub-catchment as described in section 9.2.2 . This is in accordance with the methodology described in Table 14.


of 104


Spatial distribution of rainfall is accounted for in the PMP estimation methodology.


Spatial distribution of rainfall is accounted for in the PMP estimation methodology.

9.7 Design Discharges


Table 20 and Table 21 show the URBS model predicted design discharges and critical storm durations respectively for the 2, 5, 10, 20, 50 and 100 year ARI events at the four gauging stations in the Pimpama River catchment. Design event hydrographs (for the critical storm duration) at four gauging stations are shown in Figure E. 1 to Figure E. 4 (Appendix E). It is noted that all the design discharge estimates are based on the application of the ARF for the total Pimpama River catchment area.

Table 20 - URBS Model Predicted Design Discharges, 2 to 100 year ARI events

Gauging

Station Stream Name


2 Year

ARI

5 Year

ARI

10 Year

ARI

20 Year

ARI

50 Year

ARI

100 Year

ARI Hotham Creek Alert

Hotham Creek

40 71 93 119 148 171

Stewarts Road Alert

Pimpama River

34 66 90 117 147 172

Norwell Alert Pimpama River

32 65 89 115 146 171

Kerkin Road Alert

Pimpama River

77 149 203 261 330 385

Table 21 - URBS Model Predicted Critical Storm Durations, 2 to 100 year ARI events

Gauging

Station Stream Name

Critical Storm Duration (hours)

2 Year

ARI

5 Year

ARI

10 Year

ARI

20 Year

ARI

50 Year

ARI

100 Year

ARI

Hotham Creek Alert

Hotham Creek

9 9 9 9 9 9

Stewarts Road Alert

Pimpama River

12 12 12 12 12 12


18 24 24 24 24 24

Kerkin Road Alert

Pimpama River

18 24 24 24 24 24


of 104


Table 22 and Table 23 show the URBS model predicted design discharges and critical storm durations for the 200, 500, 1000 and 2000 year ARI events at the four gauging stations in the Pimpama River catchment. Design event hydrographs (for the critical storm duration) at the four gauging stations are given in Figure E. 5 to Figure E. 8 (Appendix F). The following is of note:

The design discharge estimates are based on the application of the ARF for the total Pimpama River catchment area.

The URBS model generated 9 hours and 36 hours storm durations as critical duration for the 1000 and 200 year ARI respectively at the Stewarts Road Alert. However, the model estimated close design discharges for 9 hours and 12 hours (235m3/s and 233m3/s respectively) for the 1000 year ARI and for 9 hours and 36 hours (250.4m3/s and 251.6m3/s respectively) for the 2000 year ARI at the station.

The critical storm duration for the 200 and 500 year ARI events at Norwell Alert and Kerkin Road Alert stations is the same (24 hours).

The critical storm duration for the 1000 year ARI events at Norwell Alert and Kerkin Road Alert stations is the same (36 hours).

The critical storm duration for the 2000 year ARI events at Stewarts Road Alert and Norwell Alert is the same (36 hours).

Table 22 - URBS Model Predicted Design Discharges, 200 to 2000 year ARI events

Gauging

Station Stream Name


200 Year

ARI

500 Year

ARI

1000 Year

ARI

2000 Year

ARI

Hotham Creek Alert

Hotham Creek

190 217 238 266

Stewarts Road Alert

Pimpama River

194 224 235 252


192 222 251 284

Kerkin Road Alert

Pimpama River

431 496 566 655

Table 23 - URBS Model Predicted Critical Storm Durations, 200 to 2000 year ARI events

Gauging

Station Stream Name

Critical Storm Duration (hours)

200 Year

ARI

500 Year

ARI

1000 Year

ARI

2000 Year

ARI

Hotham Creek Alert

Hotham Creek

9 9 6 6

Stewarts Road Alert

Pimpama River

12 12 9 36


24 24 36 36

Kerkin Road Alert

Pimpama River

24 24 36 48


of 104


Table 24 shows the URBS model predicted peak PMP Design Flood (PMPDF) discharges and critical durations at the four gauging stations in the Pimpama River catchment. PMPDF event hydrographs (for the critical storm duration) at the four gauging stations are given in Figure E. 5 to Figure E. 8 (Appendix F). To estimate PMPDF discharges, the URBS model was run for all storm durations from 30 minutes up to 120 hours.

Table 24 - URBS Model Predicted Design Discharges and critical storm duration, PMPDF event

Gauging

Station Stream Name PMPDF Discharge

(m3/s)

PMPDF Critical

Duration (hours)

Hotham Creek Alert

Hotham Creek

720 6

Stewarts Road Alert

Pimpama River

687 9


657 18

Kerkin Road Alert

Pimpama River

1473 36


Table 25 shows the URBS model predicted peak PMF discharges and critical durations at the four gauging stations in the Pimpama River catchment. PMF event hydrographs (for the critical storm duration) at the four gauging stations are given in Figure E. 5 to Figure E. 8 (Appendix F). To estimate PMF discharges, the URBS model was run for the storm durations from 24 hours to 72 hours for the top ten individual storm temporal patterns.

It is noted that the model produced less discharge for PMF than PMPDF at Hotham Creek Alert station. This is likely due to:

The model produces 6 and 9 hour storm durations as a critical duration for the different ARI from 2 to 2000 year and PMPDF at Hotham Creek Alert. However, the PMF was not run for the durations less than 24 hours due to unavailability of the top ten individual storm temporal patterns for the storm durations less than that.

Table 25 - URBS Model Predicted Design Discharges and critical storm duration, PMF events

Gauging

Station Stream Name PMF Discharge

(m3/s)

PMF Critical

Duration (hours)

Critical PMF

Temporal Patterns

Hotham Creek Alert

Hotham Creek

675 36 21 February 1954

Stewarts Road Alert

Pimpama River

694 36 21 February 1954


723 36 21 February 1954

Kerkin Road Alert

Pimpama River

1626 36 21 February 1954


of 104

9.7.5 Comparison with Previous Studies

Table 26, Table 27 and Table 28 compare the design discharges estimated in this study with the design discharges reported in WBM 2008 (Ref 9), GCCC 2007 (Ref 8), GCCC 2005 (Ref 7) and GCCC 2009 (Ref 2). The current study design discharge estimates are significantly lower than WBM (2008), GCCC (2007) and GCCC (2005a) and slightly higher than GCCC (2009) design discharges. This is likely due to the following differences:

WBM (2008) and GCCC (2007) and GCCC (2005a) studies did not use calibrated URBS models for design discharge estimates (all three studies used parameter values of neighbouring catchments).

WBM (2008) and GCCC (2007) design discharge estimates are based on the old design rainfall temporal patterns (see Section 9.3 ).

WBM (2008) and GCCC (2007) studies did not apply ARF’s to the design rainfalls.

The current study calibrated the model to two additional recent flood events (January 2012 and January 2013) and used an additional model parameter (forest factor) than GCCC (2009) study along with some modification of methodologies.

It is noted that model results presented for GCCC (2007) in tables below were extracted from WBM (2008).

Table 26 - Comparison of design discharges estimated by current and previous studies at Hotham Creek Alert station

ARI (years)

Estimated Design Discharge (m3/s)

GCCC (2007) WBM (2008) GCCC

(2009) Current

2 81 82 39 40

5 118 119 72 71

10 141 143 93 93

20 171 174 114 119

50 195 198 140 148

100 225 229 160 171


of 104

Table 27 - Comparison of design discharges estimated by current and previous studies at Stewarts Road, Norwell and Kerkin Road Alert station

ARI

(years)


Stewarts Road Alert Norwell Alert Kerkin Road Alert

GCCC

(2009) Current

GCCC

(2009) Current

GCCC

(2009) Current

2 31 34 30 32 74 77

5 63 66 60 65 140 149

10 86 90 83 89 191 203

20 107 117 105 115 241 261

50 132 147 130 146 296 330

100 153 172 150 171 339 385

Table 28 - Comparison of design discharges estimated by current and previous studies at catchment outlet

ARI (years)


GCCC (2005a) GCCC (2007) WBM (2008) GCCC

(2009) Current

2 NA 239 246 79 82

5 401 338 348 154 162

10 493 398 410 216 227

20 644 478 492 274 292

50 776 566 583 336 372

100 899 647 667 386 435


of 104

10. Joint Probability Approach (JPA)

The Joint Probability Approach (JPA), also referred to as Monte Carlo simulation technique, has been under development for the last few years. Currently there are two Monte Carlo techniques available: the Total Probability Theorem (TPT) (Ref 33) and Cooperative Research Centre – Catchment Hydrology (CRC-CH) (Ref 35). The TPT methodology is based on the current critical storm duration approach where the BOM burst IFD tables are used. The CRC-CH methodology is based on design storms of variable storm durations and the event based IFD tables are generally derived from the raw pluviographs.

Don Carroll 2013 (Ref 3) study has developed a relationship between the complete storm IFD table and the burst IFD table for Gold Coast region as part of City’s Hydrological Study Review in April 2013 (Ref 3). The following relationships are established based on raw pluvio data from the BOM.

Ie = p Dq Tr Ib

Where Where p, q and rare constants, D is the Duration (hours), T is the ARI in years, I is the intensity. b=burst, e = event.

For the Gold Coast region Don Carroll 2013 study has recommended the following values (Ref 3): p = 0.1 x 12D24 – 0.25 q = 0.6 x (1 – p) r = - 0.025 The mean duration is 0.9 x 12D241.56 where I2D24 is the 2 year 24 hour burst intensity. It is noted that both approaches have some limitations (Ref 3). The TPT has been developed for large to extreme floods and its applications for more frequent events are questionable. The CRC-CH is often applied in the derivation of design flow estimates up to large floods so this approach is not robust in the estimation of rare and extreme floods. In this study the TPT and CRC-CH Monte Carlo simulations are undertaken only to verify the results of the Design Event Approach. Other limitations (Ref 3) are (i) the assumption that the loss distribution applied is consistent across the entire frequency range – generally higher losses are experienced with the more frequent ARI events (ii) convective storms are typically front loaded whereas frontal storms are end loaded which is not accounted for, (iii) storm patterns are likely to be less variable with increasing ARI and (iv) how El Nino/La Nina cycles impact antecedent conditions. It is obvious that further research work is required to apply these technologies over the entire frequency spectrum, but as applied it is likely there will be over-estimation of peak flows for the more frequent design events. The Monte Carlo simulation has been undertaken in this study for comparative purpose only with the URBS Design Event Approach (DEA). Figure 12, Figure 13, Figure 14 and Figure 15 show comparisons of the design discharges at Hotham Creek Alert, Stewarts Road Alert, Norwell Alert and Kerkin Road Alert respectively for the DEA and JPA modelling approaches. For the more frequent ARIs the Monte Carlo approaches produced higher peak discharges, which could be attributed to the DEA approach using high loss values for more frequent flooding events whereas the Monte Carlo approach assumes that the loss distribution applied is consistent across the entire frequency range. The Monte Carlo approach supports the DEA estimates. URBS estimated discharges from DEA and Monte Carlo simulation are given in Appendix F (Table F. 1 to Table F. 4). The design discharges given in the Appendix F included an Areal Reduction Factor based on total catchment area.


of 104

Figure 12: Comparison of design discharge estimates from DEA and JPA modelling approach at Hotham Creek Alert Station

Figure 13: Comparison of design discharge estimates from DEA and JPA modelling approach at Stewarts Road Alert Station


of 104

Figure 14: Comparison of design discharge estimates from DEA and JPA modelling approach at Norwell Alert Station

Figure 15: Comparison of design discharge estimates from DEA and JPA modelling approach at Kerkin Road Alert Station


of 104

11. Conclusion

An URBS model of the Pimpama River catchment has been reasonably well calibrated and verified against available data using a single set of model parameter values for all calibration and verification events. The model has been calibrated against three historical flood events (January 2008, January 2012 and January 2013) and then verified against another four historical flood events (February 2004, March 2004, November 2004 and June 2005). The calibration attempted to match the predicted and recorded flood peaks, volumes, shape and timing of the hydrographs at four gauging stations within the catchment. The calibrated model was then verified by comparing the model predictions against the stage hydrographs recorded at the Kerkin Road Alert gauging station for the selected verification event. A joint calibration between the UBRS model and Woongoolba Flood Mitigation Hydraulic Model (Ref 5) was also undertaken for all calibration and verification events (where data was available).

The calibrated model has been used to estimate design flood discharges at key locations in the catchment for design events ranging from 2 year ARI to PMF. The design rainfall and other input data (including IFD data, temporal patterns, areal reduction factors, spatial distribution and design rainfall losses) adopted in the study are based on a number of sources. Monte Carlo Simulation (both TPT and CRCCH) was also undertaken to verify the results of the Design Event Approach. A comparison of the estimated design discharges from this study with the design discharges in previous studies (GCCC 2005, GCCC 2007, WBM 2008 and GCCC 2009) was undertaken. This study produced higher design discharges than GCCC (2009) study and lower design discharges than all other three previous studies due to use of different methodologies, land use data and temporal patterns. It is also noted that none of the previous studies, except GCCC (2009), calibrated their models.

All analyses in this study have been undertaken using methodology consistent with the hydrological modelling currently being undertaken for other catchments in the Gold Coast area. The methodology, tasks and results of this study have been documented to a consistent standard.


of 104

12. Recommendations

The following issues should be addressed in any future studies to improve the quality of design discharge estimates in the Pimpama River catchment:

None of the four gauging stations within the Pimpama River catchment have been gauged and/or rated. The rating curves developed in this study for Hotham Creek Alert and Stewarts Road Alert appear to be acceptable, but there are great uncertainties associated with the rating curves developed for Norwell Alert and Kerkin Road Alert stations. It is recommended that these stations be properly rated. Once the rating curves are upgraded, the model calibration should be reviewed and updated as necessary.

The URBS model design discharges are to be reviewed after release of new design rainfall and temporal patterns.

There are significant differences noticed between gauge zero levels obtained from BOM and the survey undertaken by City in 2013 (Section 3.3 ) at Norwell Alert and Kerkin Road Alert stations. The Mike 11 model produces better results with City surveyed gauge datum for recent flood events (January 2012 and January 2013) and BOM gauge datum for the February 2004, March 2004, November 2004 and June 2005 flood events. It is recommended to survey gauge zero level at these stations after any future flood events to verify gauge zero levels and calibrate the URBS model at these stations.


of 104

13. Reference

1. WRM (2008a). Summary Findings of the Review of Hydrological Models for the Gold Coast City Catchments, March 2008.

2. GCCC (2009). Pimpama River Catchment Hydrological Study, August 2009. TRACKS-#22941355-PIMPAMA RIVER CATCHMENT HYDROLOGICAL MODEL

3. Don Carroll (2013). Review and Update of GCCC’s Hydrological Models, report prepared by Don Carroll Project Management Pty Ltd, April 2013.

4. SKM (1994). Woongoolba Drainage Study, July 1994. TRACKS-#38074733-WOONGOOLBA DRAINAGE STUDY - ALBERT SHIRE COUNCIL 1994 (SINCLAIR KNIGHT MERZ)

5. GCCC (2004). Woongoolba Agricultural Flood Mitigation – Hydraulic Study, 2004. pcdocs://TRACKS/38074712/RTRACKS-#38074725-WOONGOOLBA AGRICULTURAL DRAIN - FLOOD MITIGATION - HYDRAULIC STUDY

6. GCCC (2004). Woongoolba Flood Mitigation Scheme Supplementary Report, 2004. TRACKS-#38074712-WOONGOOLBA FLOOR MITIGATION SCHEME SUPPLEMENTARY REPORT

7. GCCC (2005). Pimpama River Catchment Investigation – Hydrological Study, 2005 (FS 707)

8. GCCC (2007). Logan River Catchment Hydraulic Study, August 2007. TRACKS-#19746090-REPORT LOGAN RIVER CATCHMENT - HYDRAULIC STUDY AUGUST 2007

9. WBM (2008). Pimpama River Catchment and Stormwater Management Plan – Hydrology Modelling, 2008.

10. BOM (2008). Hydrologic Techniques for Checking River Flow Ratings, C. Wright and T. Melon, Bureau of Meteorology. Source: In, Proceedings of Water Down Under 2008; pages 271 – 282. Lambert, Martin (Editor); Daniell, TM (Editor); Leonard, Michael (Editor). Modbury, SA: Engineers Australia; 2008.

11. Don Carroll (2012). URBS - A Rainfall Runoff Routing Model for Flood Forecasting and Design, Version 5.00, Manual and Software 2012 by D.G Carroll, 2012.

12. City (2014). Logan River Catchment Hydrological Study, 2014. TRACKS-#45737331-LOGAN_RIVER_HYDROLOGICAL_STUDY_SEPTEMBER_2014

13. GCCC (2011). Regional Broadwater Model, January 2011.

14. WRM (2008b). Revision of Design Rainfall Temporal Patterns for Gold Coast Catchments, Report prepared by WRM Water and Environment Pty. Ltd., November 2008.

15. WRM (2008c). GCCC IFD Utility Modifications, Report prepared by WRM Water and Environment Pty. Ltd., July 2008.


of 104

16. WRM 2008d. Design Event Hydrology Review, Report prepared by WRM Water and Environment Pty. Ltd, August 2008.

17. IEAust (1987). Australian Rainfall and Runoff. A Guide to Flood Estimation. 1987.

18. AWE (1998). Review of Gold Coast Rainfall Data, Final Report, May 1998, Volume 1, Report prepared by Australian Water Engineering Pty Ltd for City of Gold Coast.

19. AWE (1992). Logan River Floodplain Filling Study. November 1992.

20. (Hargraves, c2004). Final Report, Extreme Rainfall Estimation Project, CRCFORGE and (CRC) ARF Techniques, Queensland and Border Locations, Development and Application, Report prepared by Gary Hargraves, Water Assessment Group, Water Assessment and Planning, Resource Sciences Centre, undated, circa 2004.

21. HDA (2007). Hinze Dam, Update of Flood Hydrology, Briefing note for 23 January 2007 meeting, prepared by Hinze Dam Alliance, January 2007, Draft for discussion.

22. BOM (2005). A Pilot Study to Explore Methods for Deriving Design Rainfalls for Australia. 2005.

23. IEAust (1999). Australian Rainfall and Runoff. A Guide to Flood Estimation. Revised Edition. 1999.

24. Hargraves, G. Extreme Rainfall Estimation Project, CRCFORGE and (CRC) ARF Techniques, Queensland and Border Locations, Development and Application. 2004.

25. IEAust. Spatial Patterns of Design Rainfall. Collation and Review of Areal Reduction Factors from Applications of the CRC-FORGE Method in Australia.

26. Mahbub Ilahee. Modelling losses in Flood Estimation. PhD Thesis. Queensland University of Technology. 2005

27. BOM (2003a). The Estimation of Probable Maximum Precipitation in Australia: Generalised Short-Duration Method, Prepared by the Hydrometeorological Advisory Service, Australian Government Bureau of Meteorology, June 2003. (http://www.bom.gov.au/hydro/has/pmp.shtml on 11 October 2007)

28. BOM (2003b). Guide to the Estimation of Probable Maximum Precipitation: Generalised Tropical Storm Method, Report and accompanying CD prepared by the Hydrometeorological Advisory Service, Australian Government Bureau of Meteorology, November 2003.

29. AWE (2000). Review of Gold Coast Rainfall Data, Volume 3, Temporal Patterns, Final Report, October 2000, Report prepared by Australian Water Engineering Pty Ltd for Gold Coast City Council.

30. IEAust (1998). Australian Rainfall and Runoff, Volume 1, Institution of Engineers Australia, 1998.


of 104

31. BOM (1991). Temporal Pattern Distributions within Rainfall Bursts, Hydrology report series, HRS Report No. 1, Kennedy, M.R., Turner, L.H,Canterford, R.P. and Pearce, H.J., Bureau Of Meteorology, September 1991.

32. Sunwater (2007). Wyaralong Dam, Design Flood Hydrology Report, Report Prepared by SunWater, September 2007.

33. Weinman, PE et al. Use of a Monte-Carlo Framework to Characterise Hydrologic Risk. ANCOLD conference on dams. Adelaide. 2002

34. Carroll D.G. Investigation of sub-tropical rainfall characteristics for use in the joint probability approach to Design Flood Estimation. HIC, Koyoto. 2004.

35. Carroll D.G & Rahman A (2004), “Investigation of sub-tropical rainfall characteristics for use in the joint probability approach to Design Flood Estimation” HIC, Kyoto, 2004.


of 104

14. Appendices

Appendix A – URBS Catchment Definition File

Pimpama URBS model (Hydrology review update 2013, prepared by ) MODEL: SPLIT USES: L,F*0.5,U DEFAULT PARAMETERS: alpha=0.3 m=0.75 beta=3.0 n=1.0 CATCHMENT DATA FILE = Pimpama.csv Factor = 1.0 {*********************} RAIN #1 L=0 {Print. LH_SC1} {X=526,186.51, Y=6,917,566.48} Route Thru #1 L=2.57 Store. RAIN #2 L=0 {Print. LH_SC2} {X=527,221.64, Y=6,919,159.61} Route Thru #2 L=0.68 Get. Store. RAIN #3 L=0 {Print. LH_SC3} {X=526,052.64, Y=6,919,193.02} Route Thru #3 L=1.04 Get. Route Thru #4 L=0.77 Store. RAIN #4 L=0 {Print. LH_SC4} {X=527,104.11, Y=6,920,287.11} Get. Route Thru #4 L=0.92 Store. RAIN #5 L=0 {Print. LH_SC5} {X=528,154.42, Y=6,920,792.78} Route Thru #5 L=1.33 Get. Route Thru #4 L=0.45 Store. RAIN #6 L=0 {Print. LH_SC6} {X=525,811.25, Y=6,919,862.46} Route Thru #6 L=1.99 Get. Route Thru #4 L=0.16 Store. RAIN #7 L=0 {Print. LH_SC7} {X=524,517.45, Y=6,919,219.61} Route Thru #7 L=1.41 Store. RAIN #8 L=0 {Print. LH_SC8} {X=523,635.26, Y=6,920,488.06} Route Thru #8 L=1.3 Get. Route Thru #9 L=1.32 Store. RAIN #9 L=0 {Print. LH_SC9} {X=525,469.05, Y=6,920,803.14} Get. Route Thru #9 L=2.96 Get. Route Thru #10 L=0.46 Store. RAIN #10 L=0 {Print. LH_SC10} {X=526,071.82, Y=6,921,935.34} Route Thru #10 L=1.03 Get. Route Thru #11 L=2.75 Store. RAIN #11 L=0 {Print. LH_SC11} {X=527,833.13, Y=6,922,693.76} Get. Print. HothamCk {Pacific Motorway - Hotham Creek Alert X=527833.13 Y=6922,693.76} Factor = 3.5 {********************************} Route Thru #11 L=1.33 Store. RAIN #12 L=0 {Print. LH_SC12} {X=526,660.62, Y=6,922,957.59} Route Thru #12 L=2.03 Print. LH_SC12 {} Get. Route Thru #11 L=0.9 Route Thru #15 L=0.93 Store. RAIN #13 L=0 Print. LH_SC13 {X=528,930.87, Y=6,922,794.16} Route Thru #13 L=1.34 Get.


of 104

Route Thru #15 L=0.80 Store. RAIN #14 L=0 Print. LH_SC14 {X=529,663.63, Y=6,922,441.33} Route Thru #14 L=1.41 Get. Route Thru #15 L=0.77 Store. RAIN #15 L=0 Print. LH_SC15 {X=529,854.58, Y=6,924,427.39} Get. Route Thru #15 L=1.85 Store. Factor = 1.0 {********************************} RAIN #16 L=0 {Print. LH_SC16} {X=522,180.70, Y=6,920,235.22} Route Thru #16 L=1.09 Route Thru #17 L=1.22 Store. RAIN #17 L=0 {Print. LH_SC17} {X=522,158.77, Y=6,922,229.45} Get. Route Thru #17 L=1.13 Route Thru #18 L=0.93 Store. RAIN #18 L=0 {Print. LH_SC18} {X=521,608.10, Y=6,923,744.64} Route Thru #18 L=0.63 Get. Route Thru #18 L=0.72 Store. RAIN #19 L=0 {Print. LH_SC19} {X=522,779.42, Y=6,922,732.12} Route Thru #19 L=0.92 Get. Route Thru #20 L=1.36 Store. RAIN #20 L=0 {Print. LH_SC20} {X=523,215.70, Y=6,923,926.19} Get. Route Thru #20 L=0.68 Store. RAIN #21 L=0 {Print. LH_SC21} {X=522,402.91, Y=6,925,231.38} Route Thru #21 L=1.80 Get. Route Thru #20 L=1.37 Store. RAIN #22 L=0 {Print. LH_SC22} {X=524,091.63, Y=6,922,244.09} Route Thru #22 L=1.02 Route Thru #23 L=0.54 Store. RAIN #23 L=0 {Print. LH_SC23} {X=523,797.56, Y=6,923,246.56} Get. Route Thru #23 L=2.62 Get. Route Thru #24 L=0.35 Store. RAIN #24 L=0 {Print. LH_SC24} {X=524,695.37, Y=6,923,710.12} Route Thru #24 L=0.23 Get. Route Thru #24 L=1.08 Store. RAIN #25 L=0 {Print. LH_SC25} {X=525,381.24, Y=6,923,980.67} Route Thru #25 L=0.87 Get. Route Thru #27 L=0.61 Store. RAIN #26 L=0 {Print. LH_SC26} {X=523,814.07, Y=6,925,339.72} Route Thru #26 L=1.97 Get. Print. TH_SC27 {Pacific Motorway - Pimpama River}{X=525,408.06, Y=6,925,105.50} Factor = 3.5 {********************************} Route Thru #27 L=2.06 Store. RAIN #27 L=0 Print. LH_SC27 {X=526,575.32, Y=6,925,794.20} Get. Print.Stewarts Route Thru #27 L=2.10 Route Thru #29 L=2.47 Store.


of 104

RAIN #28 L=0 Print. LH_SC28 {X=527,754.79, Y=6,925,785.20} Route Thru #28 L=1.67 Get. Route Thru #29 L=1.94 Store. RAIN #29 L=0 Print. LH_SC29 {X=529,572.77, Y=6,927,353.89} Route Thru #29 L=1.33 Get. Route Thru #29 L=0.52 Print.Norwell Route Thru #30 L=1.24 Store. Rain #30 L=0 Print. LH_SC30 {X=531,020.77, Y=6,925,261.01} Get. Get. Route Thru #30 L=0.79 Store. RAIN #31 L=0 Print. LH_SC31 {X=530,855.40, Y=6,922,551.56} Route Thru #31 L=1.8 Store. RAIN #32 L=0 Print. LH_SC32 {X=530,485.61, Y=6,923,077.06} Route Thru #32 L=1.15 Get. Route Thru #31 L=0.58 Get. Route Thru #30 L=0.59 Route Thru #33 L=1.39 Store. RAIN #33 L=0 Print. LH_SC33 {X=532,817.12, Y=6,924,415.72} Get. Store. RAIN #34 L=0 Print. LH_SC34 {X=532,018.36, Y=6,921,112.48} Route Thru #34 L=2.38 Store. RAIN #35 L=0 Print. LH_SC35 {X=531,335.19, Y=6,921,463.14} Route Thru #35 L=1.95 Get. Route Thru #34 L=0.44 Route Thru #33 L=2.35 Get. Print.KerkinRd Route Thru #33 L=1.20 Store. RAIN #36 L=0 Print. LH_SC36 {X=533,663.22, Y=6,922,807.54} Route Thru #36 L=1.67 Get. Route Thru #41 L=0.88 Store. RAIN #41 L=0 Print. LH_SC41 {X=534,561.05, Y=6,924,705.40} Get. Store. RAIN #37 L=0 Print. LH_SC37 {X=532,283.59, Y=6,926,645.97} Route Thru #37 L=1.78 Store. RAIN #38 L=0 Print. LH_SC38 {X=533,847.59, Y=6,927,094.44} Route Thru #38 L=1.18 Get. Route Thru #41 L=1.76 Get. Route Thru #41 L=1.51 Store. RAIN #39 L=0 Print. LH_SC39 {X=535,076.49, Y=6,926,412.84} Route Thru #39 L=1.90 Get. Store. RAIN #40 L=0 Print. LH_SC40 {X=536,044.83, Y=6,925,629.50} Route Thru #40 L=0.50 Get. Route Thru #41 L=0.55 Route Thru #43 L=1.14 Store. RAIN #43 L=0 Print. LH_SC43 {X=536,612.55, Y=6,923,758.55}


of 104

Get. Store. RAIN #42 L=0 Print. LH_SC42 {X=535,552.33, Y=6,922,939.24} Route Thru #42 L=1.54 Get. Route Thru #43 L=1.67 Store. RAIN #44 L=0 {Print. LH_SC44} {X=532,669.67, Y=6,919,956.05} Route Thru #44 L=0.68 Route Thru #45 L=0.88 Store. RAIN #45 L=0 {Print. LH_SC45} {X=533,255.18, Y=6,920,966.34} Get. Print. TH_SC45 {Sc4-45} {X=533,255.18, Y=6,920,966.34} Route Thru #45 L=0.78 Route Thru #46 L=1.06 Store. RAIN #46 L=0 Print. LH_SC46 {X=534,192.02, Y=6,921,314.88} Get. Route Thru #46 L=1.34 Route Thru #47 L=0.6 Store. RAIN #47 L=0 Print. LH_SC47 {X=535,722.39, Y=6,921,529.95} Get. Route Thru #47 L=0.61 Route Thru #48 L=1.06 Store. RAIN #48 L=0 Print. LH_SC48 {X=536,657.59, Y=6,922,213.31} Get. Route Thru #48 L=1.17 Get. Store. RAIN #49 L=0 Print. LH_SC49 {X=537,557.07, Y=6,921,840.09} Route Thru #49 L=0.77 Get. Print. Catch_out{X=537,516.78, Y=6,922,600.25} END OF CATCHMENT DATA. 4 RATING CURVES: LOCATION.HothamCk {Station NO.540376 (HothamCk Creek Alert)} LOCATION.Norwell{Station NO.540408 (Norwell Alert)} LOCATION.Stewarts {Station NO.540377 (Stewarts Road Alert)} LOCATION.kerkinrd{Station NO.540294 (Kerkin Road Alert)} END OF RATING CURVE DATA. 49 PLUVIOGRAPHS: LOCATION.PimpaP01 1 SUBAREAS: 1 LOCATION.PimpaP02 1 SUBAREAS: 2 LOCATION.PimpaP03 1 SUBAREAS: 3 LOCATION.PimpaP04 1 SUBAREAS: 4 LOCATION.PimpaP05 1 SUBAREAS: 5 LOCATION.PimpaP06 1 SUBAREAS: 6 LOCATION.PimpaP07 1 SUBAREAS: 7 LOCATION.PimpaP08 1 SUBAREAS: 8 LOCATION.PimpaP09 1 SUBAREAS: 9 LOCATION.PimpaP10 1 SUBAREAS: 10 LOCATION.PimpaP11 1 SUBAREAS: 11 LOCATION.PimpaP12


of 104

1 SUBAREAS: 12 LOCATION.PimpaP13 1 SUBAREAS: 13 LOCATION.PimpaP14 1 SUBAREAS: 14 LOCATION.PimpaP15 1 SUBAREAS: 15 LOCATION.PimpaP16 1 SUBAREAS: 16 LOCATION.PimpaP17 1 SUBAREAS: 17 LOCATION.PimpaP18 1 SUBAREAS: 18 LOCATION.PimpaP19 1 SUBAREAS: 19 LOCATION.PimpaP20 1 SUBAREAS: 20 LOCATION.PimpaP21 1 SUBAREAS: 21 LOCATION.PimpaP22 1 SUBAREAS: 22 LOCATION.PimpaP23 1 SUBAREAS: 23 LOCATION.PimpaP24 1 SUBAREAS: 24 LOCATION.PimpaP25 1 SUBAREAS: 25 LOCATION.PimpaP26 1 SUBAREAS: 26 LOCATION.PimpaP27 1 SUBAREAS: 27 LOCATION.PimpaP28 1 SUBAREAS: 28 LOCATION.PimpaP29 1 SUBAREAS: 29 LOCATION.PimpaP30 1 SUBAREAS: 30 LOCATION.PimpaP31 1 SUBAREAS: 31 LOCATION.PimpaP32 1 SUBAREAS: 32 LOCATION.PimpaP33 1 SUBAREAS: 33 LOCATION.PimpaP34 1 SUBAREAS: 34 LOCATION.PimpaP35 1 SUBAREAS: 35 LOCATION.PimpaP36 1 SUBAREAS: 36 LOCATION.PimpaP37 1 SUBAREAS: 37 LOCATION.PimpaP38 1 SUBAREAS: 38 LOCATION.PimpaP39 1 SUBAREAS: 39 LOCATION.PimpaP40 1 SUBAREAS: 40 LOCATION.PimpaP41


of 104

1 SUBAREAS: 41 LOCATION.PimpaP42 1 SUBAREAS: 42 LOCATION.PimpaP43 1 SUBARES: 43 LOCATION.PimpaP44 1 SUBAREAS: 44 LOCATION.PimpaP45 1 SUBAREAS: 45 LOCATION.PimpaP46 1 SUBAREAS: 46 LOCATION.PimpaP47 1 SUBAREAS: 47 LOCATION.PimpaP48 1 SUBAREAS: 48 LOCATION.PimpaP49 1 SUBAREAS: 49 END OF PLUVIOGRAPH DATA. 4 GAUGING STATIONS: LOCATION.HothamCk {Station NO.540376 (HothamCrk Creek Alert)} LOCATION.Norwell {Station NO. 540408(Norwell Alert)} LOCATION.Stewarts {Station NO.540377 (Stewarts Road Alert)} LOCATION.KerkinRd {Station NO.540408 (Kerkin Road Alert)} END OF GAUGING STATION DATA.


of 104

Appendix B – Calibration and Verification Hydrographs

Appendix B1 - January 2008 calibration

Figure B. 1: Pluviograph and Daily Rainfall Stations data used (January 2008)

Figure B. 2: Modelled and recorded discharge hydrographs at the Hotham Creek Alert station, January 2008 event


of 104

Figure B. 3: Modelled and recorded discharge hydrographs at the Stewarts Road Alert station, January 2008 event


of 104





of 104


Figure B. 7: Comparison of Mike 11 predicted and recorded stage hydrographs at the Norwell Alert station, January 2012 event


of 104

Figure B. 8: Comparison of Mike 11 predicted and recorded stage hydrographs at the Kerkin Road Alert station, January 2012 event




of 104




of 104

Figure B. 12: Comparison of Mike 11 predicted and recorded stage hydrographs at the Norwell Alert station, January 2013 event

Figure B. 13: Comparison of Mike 11 predicted and recorded stage hydrographs at the Kerkin Road Alert station, January 2013 event


of 104

Appendix B4 - February 2004 verification

Figure B. 14: Pluviograph and Daily Rainfall Stations data used (February 2004)

Figure B. 15: Comparison of Mike 11 predicted and recorded stage hydrographs at the Kerkin Road Alert station, February 2004 event


of 104

Appendix B5 - March 2004 verification

Figure B. 16: Pluviograph and Daily Rainfall Stations data used (March 2004)

Figure B. 17: Comparison of Mike 11 predicted and recorded stage hydrographs at the Kerkin Road Alert station, March 2004 event


of 104

Appendix B6 - November 2004 verification

Figure B. 18: Pluviograph and Daily Rainfall Stations data used (November 2004)

Figure B. 19: Comparison of Mike 11 predicted and recorded stage hydrographs at the Kerkin Road Alert station, November 2004 event


of 104

Appendix B7 - June 2005 verification

Figure B. 20: Pluviograph and Daily Rainfall Stations data used (June 2005)

Figure B. 21: Comparison of Mike 11 predicted and recorded stage hydrographs at the Kerkin Road Alert station, June 2005 event


Appendix C – Design Temporal Patterns

PERIOD 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

30 MINUTE DURATION in 6 PERIODS OF 5 MINUTES

ARI<=30, WRMv7 13.9 26.6 20.2 15.6 12.4 11.3

ARI>30≤100, WRMv7 13.9 25.6 19.5 17.0 12.0 12.0

ARI>100, GSDM 20.4 23.65 20.45 17.2 12.4 5.9 1 HOUR DURATION in 12 PERIODS OF 5 MINUTES

ARI<=30, WRMv7 5.5 8.2 9.5 11 10.4 17.8 8.0 7.3 6.2 5.7 5.5 4.9

ARI>30≤100, WRMv7 5.9 7.5 8.4 11.3 11.0 17.7 7.9 6.6 6.2 6.0 5.8 5.7

ARI>100, GSDM 8.1 12.3 12.1 11.55 10.75 9.7 8.8 8.4 7.3 5.1 3.8 2.1 1.5 HOUR DURATION in 18 PERIODS OF 5 MINUTES

ARI<=30, WRMv7 3.4 4.8 6.7 7.3 12.1 8.2 6.1 6 5.7 5.3 4.3 5.2 4.4 4.4 4.2 4.1 4.0 3.8

ARI>30≤100, WRMv7 4.4 4.7 6.4 6.8 11.0 8.8 5.6 6.1 6.0 5.3 4.8 5.3 4.4 4.3 4.2 4.1 4.0 3.8

ARI>100, GSDM 5.1 6.8 8.5 8.3 7.7 7.6 7.2 6.8 6.5 6.1 5.6 5.5 5.0 4.2 3.2 2.7 1.9 1.3 3 HOUR DURATION in 12 PERIODS OF 15 MINUTES

ARI<=30, WRMv7 6.6 12.1 15.8 9.7 7.3 6.8 5.9 7.8 11.1 6.2 5.5 5.2

ARI>30≤100, WRMv7 7.2 11.7 15.8 9.1 7.5 7.1 6.4 7.4 10.5 6.1 5.9 5.3

ARI>100, GSDM 8.1 12.3 12.1 11.55 10.75 9.7 8.8 8.4 7.3 5.1 3.8 2.1 4.5 HOUR DURATION in 18 PERIODS OF 15 MINUTES

ARI<=30, WRMv7 8.8 6.1 4.5 7.1 4.8 5.5 3.5 7.5 11.7 8.6 4.6 3.2 4 3.7 3.0 4.6 5.2 3.6

ARI>30, WRMv7 7.7 6.6 4.7 7 4.9 5.6 4 6.5 10.9 7.9 4.8 4.0 3.9 3.7 3.4 4.9 5.6 3.9

ARI>100, GSDM 5.1 6.8 8.5 8.3 7.7 7.6 7.2 6.8 6.5 6.1 5.6 5.5 5.0 4.2 3.2 2.7 1.9 1.3 6 HOUR DURATION in 12 PERIODS OF 30 MINUTES

ARI<=30, WRMv7 5.8 6.1 7.3 9.6 17.2 6.6 13.5 7.7 6.4 4.5 9.9 5.4

ARI>30≤100, WRMv7 6.1 6.9 7.4 10.2 15.3 7.2 12.2 8.2 6.8 4.8 9.8 5.1

ARI>100, GSDM 8.1 12.3 12.1 11.55 10.75 9.7 8.8 8.4 7.3 5.1 3.8 2.1

9 HOUR DURATION in 18 PERIODS OF 30 MINUTES

ARI<=30, WRMv7 3.8 4.3 2.6 3.4 4.9 4.5 6.1 7.1 8.5 7.4 11.7 6.7 5.8 5.2 3.7 2.9 6.9 4.5

ARI>30≤100, WRMv7 3.7 4.4 3.0 3.8 5.6 4.5 5.8 6.9 8.2 7.2 11.2 6.7 5.7 5.4 4.1 2.9 6.9 4.0

ARI>100, GSDM GTSMR 5.83 5.83 8.0 8.0 7.58 7.58 7.28 7.28 6.5 6.5 5.5 5.5 4.43 4.43 3.13 3.13 1.77 1.77

12 HOUR DURATION in 24 PERIODS OF 30 MINUTES

ARI<=30, WRMv7 3.2 2.5 2.6 2.8 3.1 3.2 3.5 4.4 5.1 4.0 4.6 7.4 4.7 9.7 5.8 5.3 4.4 3.3 3.7 2.5 3.0 4.5 3.6 3.1

ARI>30, WRMv7 3.3 2.5 2.8 3.3 3.9 3.5 3.8 4.2 4.7 3.8 4.7 7.2 4.4 9.5 5.5 4.9 4.4 3.8 3.8 2.5 3.1 4.2 3.3 2.9

ARI>100, GSDM GTSMR 4.0 4.0 5.6 5.6 5.65 5.65 5.6 5.6 5.7 5.7 5.8 5.8 4.3 4.3 3.83 3.83 3.35 3.35 2.68 2.67 2.18 2.17 1.33 1.33

18 HOUR DURATION in 18 PERIODS OF 1 HOUR

ARI<=30, WRMv7 3.5 2.7 2.3 4.7 4.9 7.1 9.0 14.4 5.0 7.8 7.0 5.7 6.3 5.2 4.2 3.4 3.9 2.9

ARI>30≤100, WRMv7 3.6 2.7 2.2 4.8 5.2 6.8 9.5 14 5.0 7.6 6.7 4.8 6.5 5.2 4.4 3.7 4.2 3.1

ARI>100, GSDM GTSMR 4.93 5.93 6.93 6.97 7.23 7.5 8.07 8.45 8.83 5.57 5.17 4.78 3.99 3.88 3.77 3.27 2.67 2.07

24 HOUR DURATION in 24 PERIODS OF 1 HOUR

ARI<=30, WRMv7 3.3 2.0 2.5 2.0 2.4 3.8 4.9 5.4 3.8 5.1 6.1 6.8 11.5 3.1 6.5 7.9 4.2 3.6 2.6 3.0 2.4 3.4 2.0 1.7

ARI>30≤100, WRMv7 3.4 1.7 2.5 1.9 2.5 3.6 5.1 5.5 3.4 5.3 6.2 6.9 12.2 3.0 6.4 7.8 3.7 3.4 2.4 2.9 2.2 3.3 2.5 2.2

ARI>100, GTSMR 3.95 3.95 3.95 4.69 4.69 4.69 5.6 5.6 5.6 7.43 7.43 7.43 4.17 4.17 4.17 2.47 2.47 2.47 3.24 3.24 3.24 1.78 1.78 1.78

36 HOUR DURATION in 18 PERIODS OF 2 HOURS

ARI<=30, WRMv7 3.5 2.5 2.8 3.4 3.6 6.9 4.0 4.7 5.8 3.4 15.2 8.9 7.7 11.8 5.9 3.7 3.4 2.8

ARI>30, WRMv7 3.9 3.1 2.8 3.6 3.2 6.5 3.6 4.3 5.9 3.6 14.3 9.9 8.3 10.9 6.5 3.7 3.2 2.7

ARI>100, GTSMR 3.53 2.9 2.27 4.68 5.3 5.93 3.64 3.88 4.12 7.15 6.72 6.3 12.33 10.56 8.8 5.07 3.96 2.86


ARI<=30, WRMv7 2.4 2.2 2.3 2.3 3.2 3.4 2.5 3.6 2.7 3.7 3.5 5.5 13.5 8.9 6.2 3.4 5.3 8.7 3.5 4.1 2.8 2.3 2.0 2.0

ARI>30≤100, WRMv7 2.8 2.5 2.4 2.1 3.0 3.2 2.1 3.6 2.7 3.5 3.5 5.8 11.8 9.3 6.7 4.1 5.9 8.6 3.3 4.1 2.5 2.3 2.1 2.1

ARI>100, GTSMR 4.16 3.37 2.57 1.3 1.97 2.64 3.88 3.75 3.61 4.36 5.99 7.62 9.84 7.47 5.1 3.32 4.64 5.95 5.39 3.77 2.16 1.9 3.83 1.44


ARI<=30, WRMv7 6.3 2.9 4.2 7.3 4.7 3.4 9.2 11.7 16.8 6.1 4.2 3.9 3.9 3.4 3.2 3.1 2.9 2.8

ARI>30≤100, WRMv7 6.5 3.4 4.2 6.7 4.5 3.3 8.0 11.1 16.9 6.8 4.8 3.9 3.8 3.5 3.4 3.3 3.0 2.9

ARI>100, GTSMR 6.19 8.69 15.11 6.71 2.91 8.25 9.6 4.25 1.64 1.13 2.64 3.53 3.46 10.23 7.95 3.94 2.07 1.69


ARI<=30, GTSMR 1.96 1.61 2.81 0.82 2.22 1.8 2.24 3.12 2.79 1.57 0.28 5.07 6.83 10.1 6.19 7.77 2.1 0.76 2.95 5.67 3.85 3.24 4.49 4.33 0.62 2.15 1.65 0.91 2.77 1.21 4.24 1.88

ARI>30≤100, GTSMR 1.96 1.61 2.81 0.82 2.22 1.8 2.24 3.12 2.79 1.57 0.28 5.07 6.83 10.1 6.19 7.77 2.1 0.76 2.95 5.67 3.85 3.24 4.49 4.33 0.62 2.15 1.65 0.91 2.77 1.21 4.24 1.88

ARI>100, GTSMR 1.96 1.61 2.81 0.82 2.22 1.8 2.24 3.12 2.79 1.57 0.28 5.07 6.83 10.1 6.19 7.77 2.1 0.76 2.95 5.67 3.85 3.24 4.49 4.33 0.62 2.15 1.65 0.91 2.77 1.21 4.24 1.88


ARI<=30, GTSMR 0.46 0.13 0.39 0.98 0.9 1.57 4.0 1.89 1.02 3.3 3.04 1.26 0.83 1.46 2.34 6.29 10.3 5.53 3.74 2.55 2.76 3.43 1.41 0.7 0.73 2.22 1.78 2.12 7.97 4.98 6.97 4.36 2.9 1.64 1.13 0.3 0.57 0.24 1.2 0.61

ARI>30≤100, GTSMR 0.46 0.13 0.39 0.98 0.9 1.57 4.0 1.89 1.02 3.3 3.04 1.26 0.83 1.46 2.34 6.29 10.3 5.53 3.74 2.55 2.76 3.43 1.41 0.7 0.73 2.22 1.78 2.12 7.97 4.98 6.97 4.36 2.9 1.64 1.13 0.3 0.57 0.24 1.2 0.61

ARI>100, GTSMR 0.46 0.13 0.39 0.98 0.9 1.57 4.0 1.89 1.02 3.3 3.04 1.26 0.83 1.46 2.34 6.29 10.3 5.53 3.74 2.55 2.76 3.43 1.41 0.7 0.73 2.22 1.78 2.12 7.97 4.98 6.97 4.36 2.9 1.64 1.13 0.3 0.57 0.24 1.2 0.61

PERIOD 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40


of 104

Appendix D – Probable Maximum Precipitation (PMP) Calculation

Appendix D1 - PMP Method Selection

Worksheet D.1: PMP method selection, Pimpama River Creek catchment

Catchment Name: Pimpama Catchment Area: 125.6 km2

Long Duration PMP

HIGHLIGHT THE ZONE IN WHICH THE CATCH MENT IS LOCATED

GTSMR (Coastal)

GTSMR (Inland)

GTSMR (Coastal

& SWWA)

Coastal Transition - GTSMR Coastal - GSAM Coastal

GSAM (Coastal)

WA Transition - GTSMR Coastal

-GSAM Inland

GSAM (Inland)

WCTas

Short Duration PMP (GSDM)

Short duration PMP estimates can not be calculated for the catchment

PMP estimates for up to 6 hours can be calculated using the GSDM for this catchment

PMP estimates for up to 6 hours can be calculated using the GSDM for this catchment and can include winter estimates

PMP Method Summary

Method Zone Season Duration

GSDM 6 hours Monthly 0.5 – 6 hours

GTSMR Coastal Summer 24 – 72 hours

What Next?

GTSMR: Calculate the PMP estimates for the catchment following the procedures in the guidebook

GSDM: Calculate the PMP estimates for up to 6 hours following the GSDM (Bureau of Meteorology, 2003) guidebook (http://www.bom.gov.au/hydro/has/gsdm_document.shtml)

GSAM: Contact the Hydrometeorological Advisory Service, Bureau of Meteorology

WCTas: Contact the Hydrometeorological Advisory Service, Bureau of Meteorology

West Coast Tasmania Method Zone

Inland Zone

Inland Zone

HOBART

DARWIN

PERTH

Port Hedland

Townsville

BRISBANE

CANBERRACANBERRA

SYDNEYSYDNEYSW WAWinter Zone

Coastal Transition Zone

Coastal Zone

Coastal Zone

ADELAIDE

GTSMR

GSAM

GTSMR

GTSMR

GSAM

GSAM-GTSMR

GSAM-GTSMRWA Transition Zone

Is the catchment less than 1000km2?

Is the catchment less than 500km2 and south of 300 S?

YES

NO

YES

NO


of 104

Appendix D2 - Generalised Short Duration Method (GSDM)

Worksheet D.2: GSDM PMP calculation sheet, Pimpama River catchment

Location Information

Catchment: Pimpama Area: 125.6 km2

State: QLD Duration Limit: 6 hrs

Latitude (dd.dd): 27.820 S Longitude (dd.dd): 153.270 E

Proportion of Area Considered

Smooth, S (0.0 - 1.00): 0.0 Rough, R (0.0 - 1.0): 1.0

Elevation Adjustment Factor (EAF)

Mean Elevation: 43.5 mAHD

Adjustment for Elevation (-0.05 per 300m above 1500m)

EAF = 1 (0.85 - 1.00)

Moisture Adjustment Factor (MAF)

MAF = 0.84 (0.40 - 1.00)

PMP Values (mm)

Durations Initial Depth Initial Depth PMP Estimates = Rounded

(hours) - Smooth - Rough (DSxS + DRxR) PMP Estimate

(DS) (DR) x MAF x EAF (nearest 10 mm)

0.25 160 160 134.4 130

0.50 235 235 197.4 200

0.75 300 300 252 250

1.0 365 365 306.6 310

1.5 415 470 394.8 390

2.0 470 540 453.6 450

2.5 505 610 512.4 510

3.0 540 660 554.4 550

4.0 600 745 625.8 630

4.5 625 780 655.2 660

5.0 650 815 684.6 680

6.0 695 870 730.8 730

Note: Value of 4.5 hours duration obtained from interpolation between 4 & 5 hour values


of 104

Figure D. 1: GSDM design spatial distribution of PMP, Pimpama River catchment

Table D. 1 - GSDM, mean rainfall depth between ellipses, Pimpama River catchment

Ellipse

Mean Rainfall Depth between Ellipses (mm)

Storm Duration (hours)

0.5 1 1.5 3 4 4.5 5 6

A 282 414 534 757 865 909 953 1008

B-A 247 370 473 666 761 798 836 892

C-B 208 321 415 578 652 683 715 764

D-C 180 282 369 514 585 614 643 676

E-D 155 264 310 469 498 507 515 603

a Value obtained from Interpolation between 4 and 5 hours value

A

C

D

E

B


of 104

Table D. 2 - Average rainfall intensity between ellipses, Pimpama River catchment

Ellipse

Mean Rainfall Intensity (mm/hr)

Storm Duration (hours)

0.5 1 1.5 3 4 4.5 5 6

A 564 414 356 252 216 202 191 168

B-A 494 370 315 222 190 177 167 149

C-B 416 321 277 193 163 152 143 127

D-C 360 282 246 171 146 136 129 113

E-D 310 264 207 156 125 113 103 101

a Value obtained from Interpolation between 4 and 5 hours value

Figure D. 2: GSDM average rainfall intensity distribution, Pimpama River catchment


of 104

Appendix D3 - Generalised Tropical Storm Method Revised (GTSMR)

Worksheet D.3 – GTSMR PMP calculation sheet, Pimpama River catchment

Location Information

Catchment Name: Pimpama State: QLD

GTSMR zone (s): Coastal

Catchment Factor

Topographic Adjustment Factor TAF = 1.3899 (1.0 -2.0)

Decay Amplitude Factor DAF = 0.9783 (0.7 -1.0)

Annual Moisture Adjustment Factor MAFa = EPWcatchment/120

Extreme Precipitable Water (EPWcatchment): 86.8047 MAFa = 0.73373 (0.4 - 1.1)

Winter Moisture Adjustment Factor (where applicable) MAFw = EPWcatchment_winter/82.30

Winter EPW (EPWcatchment_winter) = n/a MAFw = n/a (0.4 - 1.1)

PMP Values (mm) - Annual Coastal

Duration (hours) Initial Depth

(Da) PMP Estimate

=DaxTAFxDAFxMAFa

Preliminary PMP Estimate (nearest

10mm)

Final PMP Estimate

0.5

Calculate GSDM (Bureau of Meteorology, 2003) depths

200 1 310

1.5 390 2 450 3 550 4 630

4.5 660 5 680 6 730 9 No preliminary estimates available 870

12 No preliminary estimates available 990 18 No preliminary estimates available 1150 24 1322 1300 1300 1300 36 1614 1588 1590 1590 48 1886 1856 1860 1860 72 2367 2329 2330 2330 96 2658 2614 2610 2610 120 2785 2740 2740 2740

PMP VALUES (mm) - Winter (where applicable)

Duration (hours) Initial Depth

(Dw) PMP Estimate

=DwxTAFxDAFxMAFw

Preliminary PMP Estimate (nearest

10mm)

Final PMP Estimate

1

Calculate GSDM (Bureau of Meteorology, 2003) depths

2 3 4 5 6

12 No preliminary estimates available

18 No preliminary estimates available

24

36

48

72

96

120


of 104

Worksheet D.4 – GTSMR design spatial distribution, Pimpama River catchment

PMPi = PMPc x Average Ratioi (TAFi) / Average Ratioc (TAFc)

i = individual sub catchment

c = catchment

PMPi = average PMP depth for individual sub catchment

PMPc = average PMP depth over the whole catchment

TAFc = 1.8339

Sub Catchment

ID

TAFi of Subcatchment

(1.0-2.0)

PMP Rainfall Depth (mm)

Duration (hours)

9 12 18 24 36 48 72

1 1.42675 890 1020 1180 1330 1630 1910 2390 2 1.42037 890 1010 1180 1330 1620 1900 2380 3 1.42314 890 1010 1180 1330 1630 1900 2390 4 1.4178 890 1010 1170 1330 1620 1900 2380 5 1.41114 880 1010 1170 1320 1610 1890 2370 6 1.42308 890 1010 1180 1330 1630 1900 2390 7 1.4249 890 1010 1180 1330 1630 1910 2390 8 1.42131 890 1010 1180 1330 1630 1900 2380 9 1.42291 890 1010 1180 1330 1630 1900 2390

10 1.42105 890 1010 1180 1330 1630 1900 2380 11 1.41128 880 1010 1170 1320 1610 1890 2370 12 1.41498 890 1010 1170 1320 1620 1890 2370 13 1.40135 880 1000 1160 1310 1600 1880 2350 14 1.3968 870 990 1160 1310 1600 1870 2340 15 1.38951 870 990 1150 1300 1590 1860 2330 16 1.41483 890 1010 1170 1320 1620 1890 2370 17 1.41012 880 1000 1170 1320 1610 1890 2360 18 1.40151 880 1000 1160 1310 1600 1880 2350 19 1.41485 890 1010 1170 1320 1620 1890 2370 20 1.4144 890 1010 1170 1320 1620 1890 2370 21 1.40566 880 1000 1160 1310 1610 1880 2360 22 1.42094 890 1010 1180 1330 1630 1900 2380 23 1.4175 890 1010 1170 1330 1620 1900 2380 24 1.41863 890 1010 1170 1330 1620 1900 2380 25 1.41654 890 1010 1170 1320 1620 1900 2370 26 1.41336 880 1010 1170 1320 1620 1890 2370 27 1.4111 880 1010 1170 1320 1610 1890 2370 28 1.40213 880 1000 1160 1310 1600 1880 2350 29 1.38288 870 980 1140 1290 1580 1850 2320 30 1.37066 860 980 1130 1280 1570 1830 2300 31 1.39009 870 990 1150 1300 1590 1860 2330 32 1.38596 870 990 1150 1300 1590 1850 2320 33 1.36485 850 970 1130 1280 1560 1830 2290 34 1.38063 860 980 1140 1290 1580 1850 2310 35 1.38558 870 990 1150 1300 1590 1850 2320 36 1.35939 850 970 1120 1270 1560 1820 2280 37 1.35847 850 970 1120 1270 1550 1820 2280 38 1.34302 840 960 1110 1260 1540 1800 2250 39 1.33631 840 950 1110 1250 1530 1790 2240 40 1.33028 830 950 1100 1240 1520 1780 2230 41 1.34312 840 960 1110 1260 1540 1800 2250 42 1.3408 840 960 1110 1250 1530 1790 2250 43 1.33024 830 950 1100 1240 1520 1780 2230 44 1.37818 860 980 1140 1290 1580 1840 2310 45 1.36699 860 970 1130 1280 1560 1830 2290 46 1.35534 850 970 1120 1270 1550 1810 2270 47 1.34218 840 960 1110 1260 1540 1800 2250 48 1.33789 840 950 1110 1250 1530 1790 2240 49 1.32703 830 950 1100 1240 1520 1780 2220


of 104

Appendix E – Design Event Hydrographs

Figure E. 1: Frequent to large event hydrographs at Hotham Creek Alert Station

Figure E. 2: Frequent to large design event hydrographs at Stewarts Road Alert Station


of 104

Figure E. 3: Frequent to large design event hydrographs at Norwell Alert Station

Figure E. 4: Frequent to large design event hydrographs at Kerkin Road Alert Station


of 104

Figure E. 5: Rare to extreme design event hydrographs at Hotham Creek Alert Station

Figure E. 6: Rare to extreme design event hydrographs at Stewarts Road Alert Station


of 104

Figure E. 7: Rare to extreme design event hydrographs at Norwell Alert Station

Figure E. 8: Rare to extreme design event hydrographs at Kerkin Road Alert Station


of 104

Appendix F – Monte Carlo Results

The design discharge estimates in the Table F. 1 to Table F. 4 include an Areal Reduction

Factors (ARF) based on total catchment area.

Table F. 1 - URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Hotham Creek Alert

ARI (Years)

Peak Flow (mᶟ/s) @ Hotham Creek Alert

Design TPT CRC-CH

2 40 51 39

5 71 74 72

10 93 91 93

20 119 109 114

50 148 135 140

100 171 156 160

200 190 179 172

500 217 205 200

1000 238 235 222

2000 266 280 247

Table F. 2 - URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Stewarts Road Alert

ARI (Years)

Peak Flow (mᶟ/s) @ Stewarts Road Alert

Design TPT CRC-CH

2 34 45 31

5 66 72 63

10 90 88 86

20 117 110 107

50 147 133 132

100 172 154 153

200 194 170 168

500 224 201 196

1000 235 224 206

2000 252 269 232


of 104

Table F. 3 - URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Norwell Alert

ARI (Years)

Peak Flow (mᶟ/s) @ Norwell Alert

Design TPT CRC-CH

2 32 46 30

5 65 68 60

10 89 86 83

20 115 104 105

50 146 128 130

100 171 147 150

200 192 169 164

500 222 196 195

1000 251 228 221

2000 284 270 253

Table F. 4 - URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Kerkin Road Alert

ARI (Years)

Peak Flow (mᶟ/s) @ Kerkin Road Alert

Design TPT CRC-CH

2 77 107 74

5 149 154 140

10 203 193 191

20 261 233 241

50 330 286 296

100 385 328 339

200 431 376 381

500 496 438 451

1000 566 512 517

2000 655 609 589


of 104

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

pimpama river catchment hydrological study · 2019-06-23 · river catchment based on design...

Documents