Modified hydrograph method for arid regions

There is a real need for more research on regionalization of flood estimation methods in and zones. Such estimations are important because reliable long-term storm rainfall and corresponding runoff measurements are commonly unavailable. This is the situation in many parts of the Kingdom of Saudi Arabia. Hence, it is necessary to develop a new approach, one that suits the conditions found in the Kingdom, which depend on available, but incomplete measurements and catchment morphological features. In this paper, a modified methodology based on the classical Snyder approach is proposed and it is referred to as the Saudi Geological Survey (SGS) approach in order to reflect works of this kind within the Survey. The basis of the methodology has two phases, namely, logical and empirical. The former phase is valid for any part of the world whether humid or arid, but the latter phase is location specific, which in the case of this paper, is the Arabian Peninsula. The application of the methodology is presented for Wadi Baysh, a major wadi in the south-western part of the Kingdom. Furthermore, a synthetic unit hydrograph (UH) methodology based on a Gamma distribution function is also presented with applications to some of the Wadi Baysh sub-basins. For this purpose, a dimensionless UH has been obtained, which is special for the area. Copyright (c) 2007 John Wiley & Sons. Ltd.