City of Morgan Hill Sewer System Master Plan 2017

City of Morgan Hill Sanitary Sewer Flow Monitoring and Inflow/Infiltration Study

Design Storm Development With the I/I response modeled by a synthetic hydrograph, design storms can be applied. This serves two functions: (a) predicted flows are based on the same storm event and are therefore normalized to each other, making for easier and better comparisons, and (b) the resulting I/I flows can be predicted for a design storm event. This helps to calibrate modeling efforts that will determine if the collection system has adequate capacity to handle very large storm events. V&A used a 10-year, 24-hour design storm for this analysis. Storm events were taken from the NOAA Precipitation-Frequency Atlas of the Western United States. Figure 32 summarizes the design storm magnitude and profile. This particular profile distribution also fits the NOAA criterion for 2-hour and 6-hour durations, in addition to the 24-hour duration.

10-Year, 24-hour Design Storm Hour Inches of Rain

1 2 3 4 5 6 7 8 9

0.010 0.026 0.259 0.156 0.052 0.016 0.223 0.127 0.178 0.064 0.032 0.013 0.131 0.368 0.044 0.213 0.213 0.471 0.875 0.425 0.213 0.105 0.175 0.053

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Total:

4.44

Figure 32. 10-Year, 24-Hour Design Storm Values and Profile (MORGA30)

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