City of Morgan Hill Sewer System Master Plan 2017

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City of Morgan Hill
Sanitary Sewer Flow Monitoring and Inflow/Infiltration Study
12-0248 AEG CofMorganHill FM Rpt.docx Page 44 of 46
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. ummarizes 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 0.010
2 0.026
3 0.259
4 0.156
5 0.052
6 0.016
7 0.223
8 0.127
9 0.178
10 0.064
11 0.032
12 0.013
13 0.131
14 0.368
15 0.044
16 0.213
17 0.213
18 0.471
19 0.875
20 0.425
21 0.213
22 0.105
23 0.175
24 0.053
Total: 4.44
Figure 32. 10-Year, 24-Hour Design Storm Values and Profile (MORGA30)