PROGRESS IN ARID-LANDS RAINFALL-RUNOFF MODELING

Hydrological data are lacking in arid regions for a variety of reasons , making emprical methods of flood estimation unsatisfactory. Physical ly based models which are calibrated in the field using measurements o f soil hydrological properties offer a viable alternative modelling st rategy, and this article reviews the main elements required in such an approach. These include coupled submodels of 1) infiltration and runo ff production; 2) overland flow routing; 3) channel routing to propaga te flood waves down wadis beyond runoff source areas; and 4) transmiss ion losses into wadi beds. Examples are presented of flood simulations using a new physically-based model with such a structure. The role of both coarse-grained (bed material) and fine-grained (slackwater depos it) sediments in wadis in providing additional evidence of flood magni tudes is also discussed, and a methodology is suggested in which physi cal modelling and sedimentological analyses are combined.