Floodwater harvesting within Wadi Billi, Egypt

Abstract

ABSTRACT Water scarcity is a major feature in Egypt. However, events of heavy rain occur increasingly, leading to repetitive flash floods. Wadi Billi is a poorly gauged drainage basin in the Eastern Desert of Egypt and hosts El-Gouna town in the delta, which depends on the desalination of brackish groundwater as the main source of freshwater. On 9 March 2014, the wadi was exposed to a flash flood event that extended to the Red Sea causing damages to humans and infrastructure. In this paper, a system of infiltration trenches supported with a series of simple surface and subsurface dams has been designed to protect the downstream urban area and recharge the flooded water into shallow aquifers. The rainfall-runoff and sediment transport processes have been modeled using a 1D lumped hydrological model. The susceptible areas for groundwater recharge have been determined using geospatial analysis. The results show that the storm event produced 1,78 million m3 of flooded water carrying 5523 t of sediments. The streams and valleys that penetrate the downstream mountain formation have the highest potentiality for groundwater recharge. Four longitudinal infiltration trenches are needed with an average dimensions of 3,000 m × 25 m × 15 cm. In addition to 37 simple surface dams and 10 sub-surface dams with a total length of 2.7 km and 0.94 km, respectively. The spatial analysis showed almost 27.63 km is potentially suitable to extend the infiltration trenches with a width range of 25–250 m, which have a minimum capacity to recharge more than 4 million m3 for one event. By considering El-Gouna’s water demands, harvesting the flooded water for one flash flood event provides a new source of cheap and high-quality freshwater for 162–261 days. In addition to avoiding the potential damages for infrastructure and human lives.