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Hydrological data are lacking in arid regions for a variety of reasons, making emprical methods of flood estimation unsatisfactory. Physically based models which are calibrated in the field using measurements of soil hydrological properties offer a viable alternative modelling strategy, and this article reviews the main elements required in such an approach. These include coupled submodels of 1) infiltration and runoff production; 2) overland flow routing; 3) channel routing to propagate flood waves down wadis beyond runoff source areas; and 4) transmission 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 deposit) sediments in wadis in providing additional evidence of flood magnitudes is also discussed, and a methodology is suggested in which physical modelling and sedimentological analyses are combined.