Engineering Assessment of Umm al Khair Dam (Jeddah, Saudi Arabia)

Jeddah is the second-largest city in Saudi Arabia, with a population of 3 million. A large earthfill dam was constructed in 2012 to mitigate flash-flood hazards from Wadi Mthawab, following the catastrophic events of 2009 and 2011. An extensive evaluation was carried out to verify the capacity and stability of this dam. The study includes hydrology and geotechnical analyses. The flood for 300 and 500 years return periods was predicted from local IDF curves. The obtained peak discharge (Qp) and runoff volume (Vh) for T300 and T500 are 207 m3/s and 224 m3/s respectively; the equivalent Vh are 3.3 × 10 m3 and 3.5 × 10 m3. The dam’s static stability was assessed against overturning, dam-face sliding and foundation bearing. The obtained factors of safety (Fs) using limit-equilibrium methods are 1.94, 1.32 and 1.8 respectively. The reservoir capacity is 3.5 × 103 m3, and the dam outlet demonstrated its ability to discharge the reservoir water within a short time (36 hours). Wind-induced wave action was found to be negligible. Results confirm that the dam safely accommodates design floods up to the 500-year event without overtopping or stability compromise. It seems Umm al Khair Dam satisfies its design aim as flood mitigation and has proved that it is stable and can match a 500-year storm if continuous safety measures are reviewed. Continuous tracking of seepage, pore-pressure, and structural movement is advised to sustain long-term operation and safety.