PART A - Answer in a separate booklet QUESTION A1 (16 marks) Your company has been asked to undertake a flood study for

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Part A Answer In A Separate Booklet Question A1 16 Marks Your Company Has Been Asked To Undertake A Flood Study For 1 (93.31 KiB) Viewed 22 times

Part A Answer In A Separate Booklet Question A1 16 Marks Your Company Has Been Asked To Undertake A Flood Study For 2 (113.66 KiB) Viewed 22 times

PART A - Answer in a separate booklet QUESTION A1 (16 marks) Your company has been asked to undertake a flood study for a 10 km² catchment. You have undertaken the hydrologic analysis so that your colleagues can use a hydraulic model to estimate the flood extents. Given the inputs and outputs from your hydrologic analysis (Table 1 and Figure 1), answer the following questions. 350 300 250 H 200 150 100 50 60 120 180 270 1080 1440 360 540 720 Max Burst Duration (min) Figure 1: Box plots of peak flows at the catchment outlet for the 1% AEP flood event. Ensemble average flow is shown as a star in each box plot. Table 1. Design Intensity-Frequency-Duration Rainfall Data (depth in mm) Annual Exceedance Probability (AEP) Duration 63.2% 50% 20% 10% 5% 2% 1% 1 hour 43.4 51.0 58.5 2 hours 55.0 64.8 74.6 3 hours 63.7 75.2 88.0 4.5 hours 71.8 86.9 102 6 hours 83.8 99.5 116 9 hours 100 119 135 12 hours 114 136 159 18 hours 129 164 185 24 hours 155 187 220 2 LE ▬▬▬▬▬ 28.8 36.7 42.5 49.0 55.5 64.1 73.9 85.4 98.6 HD+ +++ 32.3 41.1 47.5 55.5 62.1 71.8 83.0 101 112 68.7 88.0 103 121 138 160 191 234 265 76.7 98.6 116 134 156 181 216 263 300
a) Given the ensemble of peak flows shown in Figure 1, what is the critical storm duration? Explain why you selected this duration as the critical storm duration [2 marks] b) Based on Table 1, what is the rainfall intensity for a 1% AEP event for the critical storm duration? [1 mark] c) Given that an ensemble of 10 temporal patterns is available for each storm duration, describe how do you would select which single temporal pattern to give to your colleagues for the hydraulic analyses for the critical storm? [1 mark] d) Given the temporal patterns shown in Table 2 and IFD data in Table 1, an initial loss of 0 mm and a continuing loss of 1 mm/hr, what is the effective rainfall hyetograph for the 10% AEP 180 minute storm? [4 marks] Table 2: 180 minute storm temporal patterns (% of total depth in each increment) Time Increment Rare Storms Frequent Storms Intermediate Storms 0-30 minutes 5% 5% 5% 30-60 minutes 10% 15% 25% 60-90 minutes 25% 40% 55% 90-120 minutes 20% 25% 10% 120-150 minutes 30% 10% 5% 150-180 minutes 10% 5% 0% e) Your client asks you about the impacts of climate change on your peak flow estimate. Assume that the catchment behaviour is linear, and temperature is expected to increase by 2.5 degrees by the end of the design life, what is your estimate of the future design peak flow if the current climate design peak flow is 280 m³/s? [4 marks] f) Your colleagues need to estimate the PMF flow as well. Given that the MAF is 0.6 and the elevation of the catchment is 200 m above sea level, what is the 2.5 hour PMP rainfall estimate? Assume that the catchment is located 10 km from topography that has elevation changes of more than 50 m in 400 m. Rainfall depths are provided in Table 3 [4 marks] Table Generalised Short Duration Method Rainfall Depths (mm) Duration Point Rainfall 1 km² 10 km² 100 km² 2 hour smooth 710 645 590 490 2 hour rough 880 770 690 560 2.5 hour smooth 760 690 625 525 2.5 hour rough 990 850 760 635 3 hour smooth 810 725 660 555 3 hour rough 1090 940 835 685 4 hour smooth 900 790 730 620 4 hour rough 1250 1065 955 770 3