Flash Flood Modelling of Ungagged Watershed based on Geomorphology and Kinematic Wave: Case Study of Billi Drainage Basin, Egypt
Abstract
Billi is one of the ungagged drainage basins in the Eastern desert of Egypt and characterized by drought and rare precipitation. However, events of heavy rain are occuring increasingly leading to repetitive flash flood events that extend to Red sea coast casing damages for human and infrastructures. El-Gouna is a touristic urban area locates in the valley’s delta, which is not prepared with protection structures and depends on desalination of salt groundwater as the main source for fresh water. Due to the lack of historical data and the availability of non reliable data for the flash flood event of 09th March 2014, this paper adapts the KW-GIUH model to investigate the hydrological response of Billi drainage basin and to model the rainfall-runoff process based on the basin’s geomorphological characteristics and kinematic-wave equations. The sensitivity analysis showed a significant effect of rainfall intensity, the overland and channel roughness coefficients, and the sub catchment contributing area over the peak discharge and time to peak. The simulated hydrograph looks more reasonable and within the acceptable limits with the analytical solution comparing with the field measurement, where the peaks occurred almost in the same time and an error of peak discharge by -19% and runoff volume error of -7.69%. The differences attributed to the limited difference in the estimated effective precipitation with -1%, which is responsible for an error of -10.29% in the peak value, and -8.71% in water volume. The results of KW-GIUH model are promising and could be used as a reliable input to another robust shallow water model to examine the effects of flash flood events over urban areas located in the deltas of ungagged watersheds. This will reduce the amount of required data, computational efforts, and provide reliable results that could be used for protection and rain water harvesting applications.