Potential Flood Hazard in Wadi Qanunah and Wadi Alahsabah, Southwest Saudi Arabia

SGS-TR-2005-3 Mohammed I. Al-Zahrani, Saad G. Al Harthi, Hashim M. Hawsawi, Faisal A. Al-Ammawi, Mohammed S. Theban, Hussam A. Khiyami, and Zekai Șen
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Wadi Qanunah and Wadi al Ahsabah are located in the western part of the Kingdom of Saudi Arabia; they drain from the Western Escarpment, southwestward towards the Red Sea coast.  They are included in the Al Qunfudhah 250,000-scale quadrangle area, between lat. 19oN. and 20oN. and long 40o 30´E. and 42o00´E., in the Tihamat Asir region.  These wadis flood at various locations in the coastal regions.  In this report two different approaches are suggested to estimate possible flood magnitudes for Wadi Qanunah and Wadi al Ahsabah.  The first method is the construction of a synthetic-unit hydrograph from known characteristics and measurements of a number of physiographic parameters in each catchment area.  The second approach is the control-section calculation method, which predicts flood discharge peaks and the future frequency of flood-event occurrences.  Arid and semi-arid regions, such as the west-central part of Saudi Arabia, are most susceptible to flash floods, and the ability to predict or control such events is limited because of an absence of technological methods that forewarn us of the imminence of flood events.  Therefore, one logical alternative is the preparation of flood risk maps.  The availability of such maps is a key requirement in any program of urban or infrastructural development that entails construction of dams, tunnels, highways, and bridges in the catchment area.  Completion of these maps would permit the setting of safety protocols for construction according to sound scientific methods, and to begin long-term study of hazardous hydrological events.  One of the main objectives of flood calculations in a particular wadi catchment is an ability to demonstrate expected inundation boundaries following a flood event.  However, given the absence of digital elevation models (DEM) for each wadi catchment, classical topographic contour maps around representative cross-sections are presented as inundation boundaries.



Al Zahrani, M.I.,Al-Harthi, S.G., Hawsawi, H.M., Al-Ammawi, F.A., Theban, M.S., Khiyami, H.A., and Sen, Z.,  2007, Potential flood hazard in Wadi Qanunah and Wadi Alahsabah southwest Saudi Arabia: Saudi Geological Survey Technical Report SGS-TR-2005-3, 48 p., 41 figs. 14 tables, 10 apps