This project began the initial work to derive a procedure for deriving synthetic unit hydrographs for headwater basins. Standard procedures for deriving unit hydrographs are usually not applicable for mountain headwater basins where runoff is not gaged, because of the lack of an identifiable runoff pulse to associate with the flow response recorded at the basin outlet. In such cases, a suitable approximation of the headwater unit hydrograph can often be obtained using the physical characteristics of the basin to derive a synthetic unit hydrograph.
Existing synthetic unit hydrograph procedures were evaluated and the one which most nearly satisfied the criteria established by the project partners was tested using data from a headwater basin for which both rainfall floods and snowmelt floods had been recorded. A unit hydrograph derived from the rainfall-generated flood data using standard procedures provided the model with which the synthetic unit hydrograph could be compared. The approach utilized low-cost geographic information system (GIS) techniques to provide watershed hydrologic response characteristics.
The procedure developed appeared to be promising enough that a follow-on Partners award (S9316) was made to continue the evaluation.