QUESTION A1 (16 marks) Your company has been asked to undertake a flood study for a 10 km catchment. You have undertaken

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Question A1 16 Marks Your Company Has Been Asked To Undertake A Flood Study For A 10 Km Catchment You Have Undertaken 1 (56.48 KiB) Viewed 18 times

QUESTION A1 (16 marks) Your company has been asked to undertake a flood study for a 10 km 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 -- Flow 3/5 200 1501 100 S3 60 120 180 270 720 1080 1440 360 540 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 28.8 32.3 43.4 51.0 58.5 68.7 76.7 2 hours 36.7 41.1 55.0 64.8 74.6 88.0 98.6 3 hours 42.5 47.5 63.7 75.2 88.0 103 116 4.5 hours 49.0 55.5 71.8 86.9 102 121 134 6 hours 55.5 62.1 83.8 99.5 116 138 156 9 hours 64.1 71.8 100 119 135 160 181 12 hours 73.9 83.0 114 136 159 191 216 18 hours 85.4 101 129 164 185 234 263 24 hours 98.6 112 155 187 220 265 300
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 5% 0-30 minutes 30-60 minutes 60-90 minutes 90-120 minutes 120-150 minutes 150-180 minutes Frequent Storms 5% 10% 25% 20% 30% 10% Intermediate Storms 5% 15% 40% 25% 10% 5% 25% 55% 10% 5% 0%