Flash flood simulations for an Egyptian city - mitigation measures and impact of infiltration

Abstract

Flash flood simulations for an Egyptian city-mitigation measures and impact of infiltration Within this work, the impact of mitigation measures and infiltration on flash floods is investigated by using a 2D robust shallow water model including infiltration with the Green-Ampt model. The results show the combined effects of infiltration and mitigation measures as well as the effectiveness of bypass channels in addition to retention basins. Retention basins at appropriate locations could reduce the maximum water depth at critical locations by 23 %, while the additional implementation of drainage channels lead to a reduction of 75 %, considering also infiltration lead to a further reduction of 97 %. If infiltration was considered without mitigation measures, the peak water depth was reduced by 67 %. For an exceptional extreme event the measures lead to a reduction of 73 % at some locations, while at other locations the overflow from retention basins due to overstraining generated even higher inundations with an increase of 58 %.

Applicability of literature values for Green-Ampt parameters to account for infiltration in hydrodynamic rainfall-runoff simulations in ungauged basins

“…It is a Java-based flexible and extendable modeling framework, which has been developed at the Chair of Water Resources Management and Modeling of Hydrosystems of the Technische Universität Berlin, Germany. Previous studies using hms have been carried out for example by Hassan et al [23], Özgen et al [49], Simons [62], and Tügel et al [69]. In hms, the depth-averaged 2D shallow water equations are solved with an explicit cell-centered finite volume method, and incorporates robust numerical methods such as the HLLC Riemann solver and a sophisticated total variation diminishing method (TVD) to deal with the numerical challenges, which are associated for example with the simulation of very small water depths over complex topography or the propagating wet-dry fronts [63].…”

“…[54] leads to a strong overestimation of infiltration, as the entire rainfall inside the domain and almost the whole incoming flood wave from the large wadi catchment completely infiltrated before reaching the city of El Gouna [69]. As there have been large flooding areas observed by the population -reported in personal conversations with shop owners and staff members of the desalination plant as well as reported through photographs of inundation areas and resulting damages -it is obvious, that the infiltration is not represented realistically.…”

“…Hydrodynamic models are more and more used to simulate not only the flow and flooding areas of surface waters but also rainfall-induced overland flow in small catchments [6,34,43,63,75], the propagation of flash floods [1,5,26,69], and flood inundation in urban areas [9,32,59,80]. Due to the enhanced accuracy and resolution of topographic data, the interest in using 2D hydrodynamic models is continuously increasing, and since different techniques of high-performance computing are developed to accelerate numerical computations, the powerful potential of shallow water models can be realized more and more and be used also in practical applications [33,48].…”

Influence of Calibration Parameter Selection on Flash Flood Simulation for Small to Medium Catchments with MISDc-2L Model

“…In hydrological operation, infiltration is the most important water loss during flash floods, and a good understanding of infiltration is crucial for an appropriate representation of runoff generation and losses [53]. Attempts to improve the infiltration process were made by previous studies [26,30,53,54]. Liu et al [26] modified the Green-Ampt equation in the MISDc model to improve flood simulation with fixed values of the maximum water capacity parameter (W_max) but the improvement was minuscule, where the evaluation index (NSE) increased from 0.71 to 0.73.…”

Validation of Flash Flood Simulations Using Satellite Images and Community-Based Observations—Impact of Infiltration and Small-Scale Topographical Features

“…In previous work, a sensitivity analysis on a simplified catchment was carried out, and the results showed that in addition to other parameters, such as friction and rain intensity, infiltration has a strong influence on runoff at the outlet of the catchment (Tügel et al 2018). In Tügel et al (2020a), the impacts of infiltration under different parameter sets as well as under different mitigation measure scenarios for the city of El Gouna were studied, and infiltration was represented for different extreme rainfall events. As Hou et al (2020) showed that the temporal storm resolution plays an important role in obtaining reliable simulation results of inundated areas, a temporal rainfall distribution was incorporated in the model used to study flash floods in El Gouna instead of a simplified approach consisting of a constant average rain intensity, as used in earlier studies, e.g., Tügel et al (2020a).…”