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

A new approach in lumped rainfall-runoff modelling, called FDTF - ERUDHIT, has been developed over the last 10 years. Although still based on the concept of the unit hydrography (UH), it tries to cope with the drawbacks encountered with most of the identification techniques already 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 discharge series to avoid any arbitary technique of baseflow removal, as well as the absence of any assumption on the structure of the loss model, is also stressed. The algorithmic set-up as an alternate iterative converging process is described in detail, with the various options available. A worked example is provided on the Gardon d'Anduze watershed (550 km2), in the Mediterranean region of South-East France. The final discussion comments on the delicate problem of baseflow separation, common to many UH identification techniques. The paper stresses the improvements yielded by the new approach, although the limitations connected with the UH framework remain.