Development of a Coupled Model for Surface and Groundwater Flows and Application to the Barcés River Basin, Spain

Abstract:

The Finite Element Method was used to develop a code that solves both the shallow water equation, governing the free surface flow, and the depth-averaged equation that governs the motion of water through saturated unconfined porous media. The coupled model is based on solving these equations jointly by using a newly developed moving boundary conservative interface. The model, called MHICO, is able to solve the hydrodynamics of water in natural basins. The current numerical coupled surface-groundwater flow models are usually only based upon oversimplified equations for the assessment of the surface flow such as the diffusion wave approximation or the kinematic wave approximation to the Saint Venant equation, or the continuity equation. The present work introduces some improvements in this analysis by using the justified governing equations.

An efficient 2D model solves the shallow water equation. The moving boundary interface provides a way to achieve positive depths. A 2D model solves the other equation using a minimum thickness condition, since negative thicknesses cannot either be considered. The coupled model solves the interaction between both flows by setting two different domains with moving boundaries. The solution is iteratively achieved by solving both models one at a time in their respective domain using their associated boundary conditions. Other conditions such as rainfall conditions can be used. The model has been successfully applied on the Barcés River basin located in the province of A Coruña, Spain. Based on data collected during field campaigns, the model produces adequate results in the joint resolution of the flow. Proper surface water levels are obtained in the river and in a downstream reservoir. With respect to the reservoir, small groundwater isolated areas show up as occurs in reality. According to the interaction, the solution shows infiltration of surface water in the upper part and discharge in the lower part.