Hydraulic Design Evaluation of the Culvert of Wadi AL- Hamam That Feeds Wadi Mjeneen Dam

Abstract

Wadi AL-Hamam is one of the main tributaries feeding Wadi Mjeneen Dam such that the catchment area of Wadi AL-Hamam accounts for approximately 30% of the total watershed of the dam. Generally, the surface runoff of water flowing into valleys depends on three main factors: the watershed area, rainfall intensity, and rate of infiltration of watershed surface. The watershed area is a primary element in the determination of the rate of surface runoff resulting from rainfall that reaches its peak flow in case of raining over the whole watershed area. Due to the intersection of the main road connecting Aurban and Awata regions with Wadi AL-hamam, a multi-cell concrete box culvert was constructed to carry the water flowing through the Wadi based on hydrologic and hydraulic study prepared for this purpose. In September 2024, Wadi AL- Hamam was subject to an extreme rainstorm that has not been recorded before with an estimated rainfall quantity of  about 3.8 million cubic meters and rainfall depth of 63 mm. The storm resulted in flooding, overtopping, erosion of abutments on both sides of the culvert in addition to sediment and debris accumulation that exceeded half of the culvert height. In this study, an assessment for hydraulic design of the culvert was carried out to determine the causes behind the culvert inability to accommodate and carry the quantity of flowing water in the Wadi that resulted in culvert flooding. The study results showed that the culvert capacity was not sufficient to carry the flowing water in the Wadi even in the case of neglecting the deviation of culvert direction with respect to the stream direction in addition to the reduction in capacity due to the large deviation of culvert direction and the multiplicity of culvert cells.