Pimpama River
Catchment
Hydrological Study Addendum Report
July 2015
Title: Pimpama River Catchment Hydrological Study
- Addendum Report 2015
Author:
Study for: City Planning Branch
Planning and Environment Directorate
File Reference: WF18/44/02 (P3)
TRACKS #50622520
Version history
Changed by Reviewed by & Version Comments/Change & date date
1.0 Adoption of BOM’s new IFD 2013
2.0 Grammar Review
Distribution list
Name Title Directorate Branch NH Team PE City Planning
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1. Executive Summary The City of Gold Coast (City) undertook a hydrological study for Pimpama River catchment in December 2014 (City 2014, Ref 1). In the study, the Pimpama River catchment hydrological model was developed using the URBS modelling software. The model was calibrated to three historical flood events and verified against another four flood events. The design rainfalls from 2 to 2000 year annual recurrence intervals (ARIs) of the study were based on study undertaken by Australian Water Engineering (AWE) in 1998 and CRC-FORGE. In early 2015, the Bureau of Meteorology (BOM) released new IFD (2013) design rainfalls as part of the revision of Engineers Australia’s design handbook ‘Australian Rainfall and Runoff: A Guide to Flood Estimation’. In July 2015, the 2014 calibrated Pimpama hydrological model was used to run the design events using rainfall data obtained from the BOM’s new 2013 IFD tables. This report documents the review of City 2014 model and should be read in conjunction with the City 2014 hydrological study report.
The original forest factor, catchment and channel parameters obtained from the 2014 calibrated Pimpama hydrological model were used for this study update. The table below shows these parameter values:
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
The BOM’s new (IFD 2013) rainfalls were adopted for all durations and ARIs less than and equal to 100 years. For the ARIs greater than 100 year to 2000 year:
The extrapolated BOM rainfalls are used for durations less than 24 hours.
The maximum intensity of BOM’s new IFD 2013 and CRC-FORGE is adopted for durations greater than and equal to 24 hours.
The URBS model was used to estimate design discharges for:
A range of design events from 2 to 2000 year ARIs.
The Probable Maximum Precipitation Flood (PMPDF).
The Probable Maximum Flood (PMF) with the adopted rainfalls and rainfall losses.
The table below shows the URBS estimated design discharges obtained in the current study at the four gauging stations for a range of return periods including PMPDF and PMF. All the design discharges given in the table include an Areal Reduction Factor (ARF) based on total catchment area.
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Peak Design Discharge (m3/s) ARI (years) Hotham Stewarts Norwell Kerkin Creek Alert Road Alert Alert Road Alert 2 40 39 40 94
5 68 66 68 158
10 92 90 94 216
20 121 118 122 281
50 154 150 156 359
100 184 179 186 427
200 212 207 213 490
500 253 247 253 581
1000 289 282 285 656
2000 328 319 322 736
PMPDF 717 684 652 1459
PMF 671 689 717 1612
A comparison of design discharges obtained from the current and City 2014 studies was undertaken at four gauging stations. Table below shows design discharges obtained from current and City 2014 studies at Hotham Creek and Kerkin Road Alert stations.
Estimated Design Discharge (m3/s)
ARI (years) Hotham Creek Alert Kerkin Road Alert
City 2014 Current City 2014 Current Study Study 2 40 40 77 94
5 71 68 149 158
10 93 92 203 216
20 119 121 261 281
50 148 154 330 359
100 171 184 385 427
As can be seen from this table the differences of URBS’s discharge estimates at Hotham Creek gauging station are minor, though URBS discharge estimates at the Kerkin Road gauging station are approximately 5 to 10% higher than the City 2014 study.
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In addition, Monte Carlo simulations were undertaken in this study for comparative purposes only. Both the Total Probability Theorem (TPT) and the Cooperative Research Centre – Catchment Hydrology (CRC-CH) Monte Carlo techniques were applied in this study. These techniques are collectively known as the Joint Probability Approach (JPA). The figures below show the comparison of design discharges at the Hotham Creek and Kerkin Road Alert stations for the Design Event Approach (DEA) and the JPA modelling approach.
The updated URBS model design discharges were compared with the previous study’s results and verified with Monte Carlo Simulation. It is concluded that the Joint Probability Approach (Monte Carlo) supports the URBS model design discharge estimates.
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Table of Contents
1. Executive Summary ...... 3 2. Introduction ...... 7 3. Project Details ...... 7 3.1 Adopted Model parameters ...... 7 3.2 Rainfall Intensity ...... 7 3.3 Rainfall Losses ...... 8 3.4 Flood Frequency Analysis (FFA) ...... 8 3.5 Design Flood Estimation ...... 9 3.5.1 Frequent to Large Design Events (up to including 100 years ARI) ...... 9 3.5.2 Rare to Extreme Design Events (200 to 2000 years ARI) ...... 10 3.5.3 Probable Maximum Precipitation Design Flood (PMPDF) ...... 11 3.5.4 Probable Maximum Flood (PMF) ...... 11 3.5.5 Comparison with the City of Gold Coast 2014 Study (Ref 1) ...... 12 4. Joint Probability Approach (Monte Carlo Simulation) ...... 14 5. Conclusion ...... 16 6. References ...... 17 7. Appendices ...... 18 Appendix A - Intensity-Frequency-Duration Curves (IFD) ...... 18 Appendix B – Design Event Hydrographs ...... 20 Appendix B1 - Frequent to Large Design Events ...... 20 Appendix B2 - Rare to Extreme Design Events ...... 22 Appendix C – Monte Carlo Results ...... 24
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2. Introduction City developed an URBS hydrological model for Pimpama River catchment in December 2014 (Ref 1). The model was calibrated against January 2008, January 2012 and January 2013 historical flood events and was verified against February 2004, March 2004, November 2004 and June 2005 flood event. The design rainfalls from 2 to 500 year ARIs of the study were based on study undertaken by Australian Water Engineering (AWE) in 1998 (Ref 4) and CRC-FORGE (Ref 6). In early 2015 the Bureau of Meteorology (BOM) released a new IFD (2013) design rainfalls as part of the revision of Engineers Australia’s design handbook ‘Australian Rainfall and Runoff: A Guide to Flood Estimation’. The revision of temporal patterns, areal reduction factors and losses are yet to be released.
In June 2015, the 2014 calibrated Pimpama hydrological model was used to run all the design events using rainfalls obtained from the BOM’s new IFD 2013 tables.
This addendum needs to be read in-conjunction with the original report of Pimpama River Catchment Hydrological Study, December 2014.
3. Project Details
3.1 Adopted Model parameters
As mentioned, the 2014 calibrated Pimpama River Hydrological is used for this study. Table 1 shows adopted global catchment and channel parameters.
Table 1: Adopted catchment and channel parameters (source: City 2014a – Ref 1)
Parameter Adopted Value
(Channel Lag Parameter) 03.
(Catchment Lag Parameter) 3.0 m (Catchment non-linearity Parameter) 0.75 F (Forest Factor) F*0.5
3.2 Rainfall Intensity
The methodologies used in this study to use the new IFD 2013 are: The new BOM IFD tables are transformed to ARI’s and extrapolated to ARI 2000 using a fitted GEV distribution as used by BOM. The new rainfalls are adopted for all ARIs less than and equal to 100 years for all durations For ARIs greater than 100 and up to 2000 years: o The extrapolated BOM rainfalls are used for durations less 24 hours o The maximum intensity of BOM’s new IFD 2013 and CRC-FORGE is adopted for durations greater than and equal to 24 hours The above approach was adopted based on an internal review and peer reviewer recommendations. Appendix - A (Figure A. 1 to Figure A. 3) shows examples of adopted intensity-frequency-duration curves at upper and lower regions of the Pimpama River Catchment.
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3.3 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 (see Section 3.4 ). Therefore, the loss rates adopted for the adjoining Logan River catchment (Ref 3) were adopted for this study. Table 2 shows the final ILs and CLs for the Pimpama River catchment for all ARIs up to and including the 100 year ARI event.
Table 2: Adopted initial and continuing loss values
Adopted Losses
Current Study (July 2015) ARI (Years) December 2014 Study (Ref 1) Source: City (2015) – Ref 3
Initial Loss Continuing Loss Initial Loss Continuing Loss (mm) (mm/hour) (mm) (mm/hour) 2 20 3.0 20 2.25
5 15 2.0 15 1.9
10 10 1.2 10 1.5
20 0 0.8 0 1.1
50 0 0.4 0 0.9
100 0 0.1 0 0.6 Note: Same initial losses are adopted for both December 2014 and current studies
An initial loss of 0.0 mm and continuing loss of 0.6 mm/hour are adopted for ARIs greater than 100 year as per the 2014 study (refer Section 9.5.2 of City 2014a study, Ref 1).
3.4 Flood Frequency Analysis (FFA)
There was insufficient historical peak height and discharge data to undertake a flood frequency analysis (FFA) for any of the four stream gauging stations located within the Pimpama River catchment (Ref 1).
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3.5 Design Flood Estimation
3.5.1 Frequent to Large Design Events (up to including 100 years ARI) The URBS model was simulated for the storm durations 0.5, 1, 1.5, 3, 6, 9, 12, 18, 24, 36, 48, 72, 96 and 120 hours for a range of ARIs from 2 to 100 year with the BOM’s new 2013 IFD tables together with design losses as per Table 2. The Aerial Reduction Factor (ARF) for these simulations was calculated based on total catchment area (125.6 km2). Table 3 and Table 4 show URBS estimated design discharges and critical storm durations for up to and including the 100 years ARIs. Design event hydrographs at four gauging stations are shown in Appendix B1 (Figure B. 1 to Figure B. 4).
Table 3 - URBS model predicted design discharges, 2 to 100 year ARI events
Peak Design Discharge (m3/s) Gauging Stream Name Station 2 Year 5 Year 10 Year 20 Year 50 Year 100 Year ARI ARI ARI ARI ARI ARI Hotham Creek Hotham Creek 40 68 92 121 154 184 Alert Stewarts Road Pimpama 39 66 90 118 150 179 Alert River Pimpama Norwell Alert 40 68 94 122 156 186 River Kerkin Road Pimpama 94 158 216 281 359 427 Alert River
Table 4 - URBS model predicted critical storm durations, 2 to 100 year ARI events
Critical Storm Duration (hours) Gauging Stream Name Station 2 Year 5 Year 10 Year 20 Year 50 Year 100 Year ARI ARI ARI ARI ARI ARI Hotham Creek Hotham Creek 9 9 9 9 9 9 Alert Stewarts Road Pimpama 24 12 12 12 12 12 Alert River Pimpama Norwell Alert 24 24 24 24 24 24 River Kerkin Road Pimpama 24 24 24 24 24 24 Alert River
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3.5.2 Rare to Extreme Design Events (200 to 2000 years ARI) The URBS model was simulated for the storm durations 0.5, 1, 1.5, 3, 6, 9, 12, 18, 24, 36, 48, 72, 96 and 120 hours for a range of ARIs from 200 to 2000 year with the blended BOM’s new IFD 2013 and CRC-FORGE (section 3.2 ) curves and adopted new losses (Table 2). The Areal Reduction Factor (ARF) for these simulations was calculated based on total catchment area. Table 5 and Table 6 show URBS estimated design discharges and critical storm durations obtained from this study. Design event hydrographs at four gauging stations are sown in Appendix B2 (Figure B. 5 to Figure B. 8).
Table 5 - URBS model predicted design discharges, 200 to 2000 year ARI events
Peak Design Discharge (m3/s) Gauging Stream Name Station 200 Year 500 Year 1000 Year 2000 Year ARI ARI ARI ARI Hotham Creek Hotham Creek 212 253 289 328 Alert Stewarts Road Pimpama 207 247 282 319 Alert River Pimpama Norwell Alert 213 253 285 322 River Kerkin Road Pimpama 490 581 656 736 Alert River
Table 6 - URBS model predicted critical storm durations, 200 to 2000 year ARI events
Critical Storm Duration (hours) Gauging Stream Name Station 200 Year 500 Year 1000 Year 2000 Year ARI ARI ARI ARI Hotham Creek Hotham Creek 9 9 9 9 Alert Stewarts Road Pimpama 12 12 9 9 Alert River Pimpama Norwell Alert 24 24 18 18 River Kerkin Road Pimpama 24 24 24 24 Alert River
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3.5.3 Probable Maximum Precipitation Design Flood (PMPDF) The calibrated model obtained from City 2014a study (Ref 1) was simulated for PMPDF with the rainfall losses adopted for this study. Table 7 shows the URBS model predicted peak PMPDF discharges and critical durations at four gauging stations location in the Pimpama River catchment. To estimate PMPDF discharges, the URBS model was run for all storm durations from 0.5 to 120 hours. Design event hydrographs at four gauging stations are sown Appendix B2 (Figure B. 5 to Figure B. 8).
Table 7 - URBS model predicted design discharges and critical storm duration, PMPDF event
Gauging Stream Name PMPDF Discharge PMPDF Critical Station (m3/s) Duration (hours) Hotham Creek Hotham Creek 717 6 Alert Stewarts Road Pimpama 684 9 Alert River Pimpama Norwell Alert 652 18 River Kerkin Road Pimpama 1459 36 Alert River
3.5.4 Probable Maximum Flood (PMF) The calibrated model obtained from the City 2014a study (Ref 1) was simulated for PMF with the rainfall losses adopted for this study. Table 8 shows the URBS model predicted peak PMF discharges and critical durations at four gauging stations in the Pimpama River catchment. To estimate PMF discharges, the URBS model was run for the storm durations from 24 hours to 120 hours for the top ten individual storm temporal patterns. Design event hydrographs at four gauging stations are sown in Appendix B2 (Figure B. 5 to Figure B. 8).
Table 8 - URBS model Predicted design discharges and critical storm duration, PMF events (Comparable to Table 25 of City 2014a study report)
Gauging Stream Name PMF Discharge PMF Critical Critical PMF Station (m3/s) Duration (hours) Temporal Patterns Hotham Creek Hotham Creek 671 36 21 February 1954 Alert Stewarts Road Pimpama 689 36 21 February 1954 Alert River Pimpama Norwell Alert 717 36 21 February 1954 River Kerkin Road Pimpama 1612 36 21 February 1954 Alert River
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3.5.5 Comparison with the City of Gold Coast 2014 Study (Ref 1) Table 9 and Table 10 compare the design discharges estimated in this study with the design discharges obtained from the City 2014a (Ref 1) study. The model results show a close match of design discharges at Hotham Creek, Stewarts Road and Norwell gauging stations up to and including 100 year ARI, PMPDF and PMF design flood events. However the URBS model estimated higher discharges than City 2014a study because of rainfall differences.
Table 9 - Comparison of design discharges estimated by current and City 2014a studies at Hotham Creek and Stewarts Road Alert stations
Estimated Design Discharge (m3/s)
ARI (years) Hotham Creek Alert Stewarts Road Alert
City (2014a) Current City (2014a) Current
2 40 40 34 39
5 71 68 66 66
10 93 92 90 90
20 119 121 117 118
50 148 154 147 150
100 171 184 172 179
Q200 190 212 194 207
Q500 217 253 224 247
Q1000 238 289 235 282
Q2000 266 328 252 319
PMPDF 720 717 687 684
PMF 675 671 694 689
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Table 10 - Comparison of design discharges estimated by current and City 2014a studies at Norwell and Kerkin Road Alert stations
Estimated Design Discharge (m3/s)
ARI (years) Norwell Alert Kerkin Road Alert
City (2014a) Current City (2014a) Current
2 32 40 77 94
5 65 68 149 158
10 89 94 203 216
20 115 122 261 281
50 146 156 330 359
100 171 186 385 427
Q200 192 213 431 490
Q500 222 253 496 581
Q1000 251 285 566 656
Q2000 284 322 655 736
PMPDF 657 652 1473 1459
PMF 723 717 1626 1612
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4. Joint Probability Approach (Monte Carlo Simulation) The Monte Carlo simulation has been undertaken for comparative purposes only with that of the Design Event Approach (DEA). Both the Total Probability Theorem (TPT) and Cooperative Research Centre – Catchment Hydrology (CRC-CH) Monte Carlo techniques have been applied in this study. Figure 1 to Figure 4 show comparison of design discharges at different locations from DEA and Joint Probability Approach (JPA) modelling approach. Overall the Monte Carlo approach supports the DEA estimates. URBS estimated design discharges from DEA and Monte Carlo simulations are given in Appendix C (Table C. 1 to Table C. 4).
Figure 1: Comparison of design discharge estimates from DEA and JPA, Hotham Creek Alert
Figure 2: Comparison of design discharge estimates from DEA and JPA approach, Stewarts Road Alert
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Figure 3: Comparison of design discharge estimates from DEA and JPA approach, Norwell Alert
Figure 4: Comparison of design discharge estimates from DEA and JPA approach, Kerkin Road Alert
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5. Conclusion The 2014 calibrated Pimpama River catchment hydrological (City 2014a) model was used to re-estimate design discharges using the BOM’s new 2013 IFD tables. Due to lack of sufficient historical data to reconciliation of URBS model design discharges and flood frequency analysis results, the initial and continuing losses obtained from the adjoining Logan River Catchment was adopted for this study. The Monte Carlo simulations (TPT and CRC-CH) were undertaken to verify the results of the Design Event Approach. A comparison of design discharges with City 2014a study was undertaken.
This addendum needs to be read in-conjunction with the original report of Pimpama River Catchment Hydrological study (City 2014a – Ref 1).
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6. References 1. City (2014a). Pimpama River Catchment Hydrological Study, December 2014. Report prepared by the City of Gold Coast. TRACKS-#43467383-REPORT PIMPAMA RIVER HYDROLOGICAL MODELLING REPORT DECEMBER 2014
2. City (2014b). Logan River Catchment Hydrological Study, December 2014. Report prepared by the City of Gold Coast. TRACKS-#45737331-LOGAN_RIVER_HYDROLOGICAL_STUDY_DECEMBER_2014
3. City (2015). Logan River Catchment Hydrological Study Addendum, July 2015. Report prepared by the City of Gold Coast, July 2015. TRACKS-#50056335-LOGAN RIVER HYDROLOGICAL STUDY ADDENDUM REPORT JULY 2015
4. 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.
5. IEAust. Australian Rainfall and Runoff: A Guide to Flood Estimation.
6. (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.
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7. Appendices
Appendix A - Intensity-Frequency-Duration Curves (IFD)
Figure A. 1: Intensity-Frequency-Duration curves at sub catchment 01, Pimpama River catchment
Figure A. 2: Intensity-Frequency-Duration curves at sub catchment 21, Pimpama River catchment
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Figure A. 3: Intensity-Frequency-Duration curves at sub catchment 36, Pimpama River catchment
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Appendix B – Design Event Hydrographs
Appendix B1 - Frequent to Large Design Events
Figure B. 1: Frequent to large event hydrographs at Hotham Creek Alert
Figure B. 2: Frequent to large event hydrographs at Stewarts Road Alert
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Figure B. 3: Frequent to large event hydrographs at Norwell Alert
Figure B. 4: Frequent to large event hydrographs at Kerkin Road Alert
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Appendix B2 - Rare to Extreme Design Events
Figure B. 5: Rare to extreme event hydrographs at Hotham Creek Alert
Figure B. 6: Rare to extreme event hydrographs at Stewarts Road Alert
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Figure B. 7: Rare to extreme event hydrographs at Norwell Alert
Figure B. 8: Rare to extreme event hydrographs at Kerkin Road Alert
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Appendix C – Monte Carlo Results
Table C. 1: URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Hotham Creek Alert (comparable to Table 31 of City 2014a study)
ARI Peak Flow (mᶟ/s) @ Hotham Creek Alert (Years) Design TPT CRC-CH 2 40 47 54 5 68 73 81 10 92 90 104 20 121 112 125 50 154 145 170 100 184 175 220 200 212 206 264 500 253 248 316 1000 289 293 367 2000 328 358 374 Note: All values the table above are calculated using an Areal Reduction Factor (ARF) based on total catchment area.
Table C. 2: URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Stewarts Road Alert (comparable to Table 32 of City 2014a study)
ARI Peak Flow (mᶟ/s) @ Stewarts Road Alert (Years) Design TPT CRC-CH 2 39 45 50 5 66 70 76 10 90 90 96 20 118 112 120 50 150 138 160 100 179 168 205 200 207 191 244 500 247 237 335 1000 282 272 354 2000 319 328 359 Note: All values in the table above are calculated using an Areal Reduction Factor (ARF) based on total catchment area.
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Table C. 3: URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Norwell Alert (comparable to Table 33 of City 2014a study)
ARI Peak Flow (mᶟ/s) @ Norwell Alert (Years) Design TPT CRC-CH 2 40 48 50 5 68 70 74 10 94 90 97 20 122 112 119 50 156 142 156 100 186 166 193 200 213 194 260 500 253 233 308 1000 285 266 322 2000 322 324 345 Note: All values the table above are calculated using an Areal Reduction Factor (ARF) based on total catchment area.
Table C. 4: URBS model estimated peak design discharges from DEA, TPT and CRC-CH approach, Kerkin Road Alert (comparable to Table 34 of City 2014a study)
ARI Peak Flow (mᶟ/s) @ Kerkin Road Alert (Years) Design TPT CRC-CH 2 94 110 119 5 158 161 176 10 216 204 225 20 281 255 283 50 359 323 364 100 427 380 437 200 490 441 597 500 581 532 703 1000 656 606 736 2000 736 727 800 Note: All values in the table above are calculated using an Areal Reduction Factor (ARF) based on total catchment area.
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For more information P 1300 GOLDCOAST (1300 465 326) W cityofgoldcoast.com.au
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