R655-11-4E. Flood Routing

A. In routing the IDF through the reservoir, the initial water surface should reflect conservative estimates which would exist at the time of the flood event. Unless documentation can be provided to the contrary, it should be assumed that all low level outlets are closed during routing of the IDF. For dams receiving inflow from pipelines and supply canals, it should be assumed these additional sources are operating at capacity during the flood event. In the event the spillway is gated or has "stop logs", which are only allowed on existing dams, documentation must be provided to show the gates are automated or operational procedures are in place to insure that the gates can be opened or the stop logs removed in a timely manner.

B. The SEF can be routed so the maximum water surface is at an elevation equal to the lowest point on the crest of the dam with no residual freeboard.

C. In generating the IDF, the basin characteristics used and the parameters used to generate the unit hydrograph should be based on the best information available. Unit hydrographs generated from historical records or calibrated watersheds should be used, where data is available, rather than using synthetic procedures.