UNIT-HYDROGRAPH REVISITED - AN ALTERNATE ITERATIVE APPROACH TO UH ANDEFFECTIVE PRECIPITATION IDENTIFICATION

A new approach in lumped rainfall-runoff modelling, called FDTF - ERUD HIT, has been developed over the last 10 years. Although still based o n the concept of the unit hydrography (UH), it tries to cope with the drawbacks encountered with most of the identification techniques alrea dy proposed, which are briefly reviewed. The specific points retained are the simultaneous identification of the excess precipitation series and the first differenced transfer function or UH. Differencing the d ischarge series to avoid any arbitary technique of baseflow removal, a s well as the absence of any assumption on the structure of the loss m odel, is also stressed. The algorithmic set-up as an alternate iterati ve converging process is described in detail, with the various options available. A worked example is provided on the Gardon d'Anduze waters hed (550 km2), in the Mediterranean region of South-East France. The f inal discussion comments on the delicate problem of baseflow separatio n, common to many UH identification techniques. The paper stresses the improvements yielded by the new approach, although the limitations co nnected with the UH framework remain.