Several different methods are available for predicting runoff rates. Some of the more productive methods are described in Chapter 4; however, more sophisticated hydrologic methods may be used. For TxDOT consideration, the peak runoff rate for the drainage area served by a reservoir should be associated with a flood event having a 2% AEP (a minimum recurrence interval of 50 years). The hydraulic designer may determine the magnitude of the 2% AEP event by procedures provided in Chapter 4, specifically the following:

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A comprehensive hydraulic analysis of a reservoir operation requires a valid or reliable flood hydrograph. The peak discharge alone does not suffice.