Integrated Modeling System for Flash Flood Routing in Ephemeral Rivers under the Influence of Groundwater Recharge Dams

Abstract

Flash floods in ephemeral rivers are characterized by pronounced runoff dynamics, rapidly rising hydrographs, and infiltration through permeable river beds. In numerous countries, this infiltration—which is commonly referred to as transmission loss—is artificially increased by means of dams to promote groundwater recharge of local aquifers. However, flow dynamics are significantly altered by dam operation, i.e., initially pronounced process dynamics are reduced and standing/receding wave effects may occur in downstream river sections. For the adequate portrayal of such flow processes, this paper develops an integrated modeling system for flow routing in ephemeral rivers with groundwater recharge dams. The proposed system is based on a process-oriented description of flow, infiltration, and reservoir evaporation and allows for a robust application under a limited data situation, as usually encountered in arid and semiarid regions. Particularly, the proposed framework accounts for (1) the considerable loss of mass and momentum from the weakly dynamic flow downstream of a dam, attributable to transmission losses; (2) the transient character of transmission losses, which are nonlinearly depending on time and changing channel flow conditions; and (3) circumvents any numerical inconveniences associated with the modeling of dam release flow over initially dry beds by employing an analytical solution procedure of the governing flow equations. Following a comprehensive sensitivity analysis, relevant process parameters are estimated and the modeling system is applied for Wadi Ma’awil, Northern Oman. The application demonstrates both the system’s accurateness and robustness for flash flood routing under transmission losses along the wadi, where a recharge dam causes strong flow retention. Therefore, the proposed modeling system can aid in deriving potential groundwater recharge rates, which is of high importance for a sound water resources assessment in the study area.