FLOOD PLAIN MITIGATION IN ARID REGIONS CASE STUDY: SOUTH OF AL-KHARJ CITY, SAUDI ARABIA

Abstract

Most of Saudi Arabia can be considered a typically arid region where the annual average amount of rainfall varies between 50 and 100 mm. Higher amounts of rainfall are restricted to the Red Sea escarpment and to the north of Riyadh where annual average values reach 600 mm and 200 mm respectively. The current study aims at presenting the characteristics of the watersheds affecting the southern urban area of AlKharj, south of Riyadh, almost completely located inside the flood plain of wadiAlkharj and evaluating the flood hazards associated with higher rainfall events. Detailed field studies were conducted for the study area to inspect the existing drainage works, the conditions of neighboring areas, and the characteristics of the effective wadis. The hydrological study has been carried out utilizing the available data and the flow from wadis affecting the study area were routed through the main paths using the Muskingum approach to evaluate the hydrograph flowing through of study area and the effect of existing dams were also investigated to test their effect on the flood flow hydrograph. In this work, the flood risks were studied and the results are considered the baseline data required to designate the required protection system against these risks.