Potential Flood Hazards in Wadi Baish, Southwest Saudi Arabia

SGS-OF-2003-2 Hussam A. Khiyami, Ali B. Al Balkhi, Saad G. Al Harthi, Mohammed I. Al Zahrani, and Amro M. Dahlawi
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ABSTRACT
Surface water resources in southwestern Saudi Arabia are restricted to intermittent flows in the wadis, which discharge their waters, usually in the form of flash floods, into the coastal area between Jeddah and Jizan.  These wadis are namely Wadi Baish, Wadi Hali, Wadi al-Ahsibah, Wadi Yiba, Wadi Dawgah and Wadi al-Lith.  Estimations of the runoff in these wadis will give an idea of flood hazard risk in the downstream sections and also the amount of surface water resources that are lost each year in the coastal areas.  These floods commonly cause damage to property and may result in loss of lives. The accumulation of floodwater can later be a source of disease, affecting human health.  Clearly, surface water needs to be conserved and floods need to be controlled; dam sites selected by the former Ministry of Agriculture and Water should be reevaluated.  This document reports on surface water investigations performed in the Wadi Baish basin as a part of regional investigations that will be performed in the southwestern region of Saudi Arabia. The Wadi Baish basin is one of the largest in southwest Saudi Arabia, and covers an area of approximately 5,970 km2.  The wadi had only one flood gauging station in its downstream section in operation from 1959 starting date of recording to 1983 last date of recording.  The station was operative for 25 years under monitoring of former Ministry of Agriculture and Water, but only 14 years’ records were used for analysis.  Therefore, the amount of runoff was estimated using different techniques including the morphometric analysis.  The results indicate that around 85 mm of the rainwater will infiltrate into the ground per hour.  Any excess rain will be discharged at a maximum rate ranging between 6.51 and 9.90 m3/sec for every millimeter of rain. Corrective measures are recommended in order to conserve the water and to mitigate the flood hazards. A numerical analysis technique using WMS software to better estimate the amount of runoff is planned in the future.

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Khiyami, H.A., Al Balkhi, A.B., Al Harthi, S.G., Al Zahrani, M.I., Dahlawi, A.M., 2003, Potential flood hazards in Wadi Baish, southwest Saudi Arabia: Kingdom of Saudi Arabia: Saudi Geological Survey Open-File Report SGS-OF-2003-2, 28 p., 14 figs. 10 tables, 2 apps.