A unified approach for hydrological modeling of arid catchments for flood hazards assessment: case study of wadi Itwad,
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ORIGINAL PAPER
A unified approach for hydrological modeling of arid catchments for flood hazards assessment: case study of wadi Itwad, southwest of Saudi Arabia Amro Elfeki 1
&
Milad Masoud 2 & Jalal Basahi 1 & Syed Zaidi 2
Received: 3 May 2019 / Accepted: 15 May 2020 # Saudi Society for Geosciences 2020
Abstract A unified and systematic approach for hydrological modeling is presented for assessing flood hazards in arid and semi-arid regions with wadi Itwad as a case study. The approach consists of the following steps: (1) estimation of the design storm duration, (2) estimation of the design rainfall depth, (3) development of the design storm hyetograph, (4) setup of the watershed hydrological system, (5) infiltration tests for estimate of soil characteristics, (6) land use and land cover analysis for curve number estimation, (7) how to incorporate dams (if any) and their reservoir characteristics for reservoir routing analysis, and (8) performing hydrological modeling under different scenarios, namely: lumped with and without the effect of dams and routed scenarios. An emphasis is made on the comparison between the SCS unit hydrograph and the unit hydrograph (UH) estimated for stream flow data. The UH method produces hydrographs that are typical of arid regions. It is characterized by a steep rising limb with a short time to peak, a rapid recession to zero base flow, and less flood volume due to transmission losses. The scenarios show that the lumped case overdesigns the protection schemes, while the lumped central basin with detention dams storing the flood water completely leads to underdesign in the downstream area. The routed scenario is more realistic, since it considers the detention dams with an overflow. The runoff volume (66.6 MCM) of the 10-year return period of the routed scenario is in the order of magnitude within the observed historical data (50 to 100 MCM) reported in the literature. The study concludes that the proposed approach is robust and takes into account the Saudi arid environment while performing flood risk assessment in KSA. Keywords Arid region . Rainfall–runoff modeling . Unit hydrograph theory . Flash floods . Detention dams . Wadi Itwad . Saudi Arabia
Introduction Since the flash floods that attacked Jeddah City in 2009 and 2011 (Elfeki and Bahrawi 2017; Elfeki et al. 2018; Azeez et al. 2019), the Saudi Arabian authorities have decided to make flood protection schemes to cities and new communities that are vulnerable to flood hazards. Therefore, for any urban Responsible Editor: Amjad Kallel * Amro Elfeki [email protected] 1
Department of Hydrology and Water Resources Management, Faculty of Meteorology, Environment & Arid Land Agriculture, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
2
Water Research Center, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia
development in the Kingdom of Saudi Arabia (KSA), a hydrological study is a must to check whether any urban development is subjected to flash floods or not, and if so, the designer has to put th
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