Author(s): Ivan Muzik
Linked Author(s):
Keywords: Dimensionless unit hydrograph; Lag-time; Regional analysis; Peak flow predictions
Abstract: The majority of hydrologic engineering applications deal with ungaged watersheds. Various empirical methods are available for synthesizing unit hydrographs for ungaged watersheds from information obtained from maps or field inspection of the watershed. An alternative to the employment of generalized synthetic unit hydrographs is to develop a regional dimensionless hydrograph to better characterize the local rainfall-runoff processes. The paper describes the derivation of such dimensionless hydrograph for Alberta foothills, based on the analysis of 31basins and 61 rainfall-runoff events. The analysis shows that it is possible to derive a representative dimensionless hydrograph for the region with reasonable accuracy by averaging the observed direct runoff hydrographs converted into a dimensionless form. However, considerable uncertainty is associated with the estimation of the excess rainfall duration and the lag time of the analysed events. The lag time is the key parameter needed to convert the regional dimensionless hydrograph into an ungaged watershed unit hydrograph. Possible reasons for unexplained lag time variations are discussed. The developed regional dimensionless hydrograph and lag time curve were used to regenerate the original 61 hydrographs. Results were compared with the generalized SCS dimensionless unit hydrograph which tended to produce larger errors in predicted peak flows. Error analysis indicates the limits of accuracy which may be expected from the method.
Year: 2002