Utah Admin. Code R655-11-4A - Inflow Design Hydrograph Determination
A) In Utah, the IDF for all High and Moderate
Hazard Dams will be the more critical SEF. It will be necessary to calculate
both the 72 hour, general SEF using HMR49 with USUL as well as the 6 hour local
SEF using HMR49 with USUS. These precipitation values need not exceed values
calculated using HMR49 exclusively. Both of these hydrographs must be routed
through the reservoir to determine which one represents the most extreme
event.
B) Once the critical SEF has
been determined, it must be compared to a flood generated by the 100 year, 6
hour (for local storms), or 100 yr, 24 hour (for general storms) precipitation
applied on a saturated watershed. If the routed 100 year event, including
appropriate allowances for freeboard, is more critical than the SEF it must be
used as the minimum IDF. This 100 year flood should also be used as the IDF for
all Low Hazard Dams.
Notes
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