Unit hydrographs to model quick and slow runoff components of streamflow

This article derives the unit pulse response functions (unit hydrographs (U Hs)) for the quick and slow runoff components of streamflow (quick runoff: direct or surface runoff; slow runoff: the sum of rapid subsurface, delayed subsurface, and groundwater runoffs) using the model of three serial tanks with a parallel tank. The interdependence between the tanks is described b y exponential functions of the model's parameters. The parameters are ident ified using the Simplex method. Ln comparison to traditional unit hydrograp h (TUH) methods, the proposed UH method has the following advantages: (1) i t can be used to separate quick and slow streamflow components; (2) it is a ppropriate for forecasting streamflow hydrographs produced by various storm s such as single-peak storms and multi-peak storms without resorting to cha nging model's parameters; and (3) it does not require either an a priori ca lculation of rainfall excess or baseflow separation for deriving the UH. Th e TUH models such as the Sherman model and the Nash model with three cascad e reservoirs are particular cases of the proposed model. The applicability and validity of the proposed model are verified using observed rainfall-str eamflow data from an actual basin. The resulting computed streamflows show a good correspondence with observed ones. (C) 2000 Elsevier Science B.V. Al l rights reserved.