Quantification of Shallow Water Table Effects on Vegetative Filter Strips Runoff Sediment and Pesticide Trapping Efficiency
Évaluation d'un algorithme mécaniste pour représenter l'influence d'une nappe phréatique peu profonde sur l'hydrologie et le transport des sédiments et pesticides au sein d'une bande enherbée
Résumé
Natural or introduced areas of vegetation, also known as vegetative filter strips (VFS), are a common environmental control practice to protect surface water bodies from human influence. In Europe, VFS are placed along the water network to protect from agrochemical drift during applications in addition to runoff control. Their bottomland placement next to the streams often implies the presence of a seasonal shallow water table which can have a profound impact on the efficiency of the buffer zone. In a companion paper a physically-based algorithm describing ponded infiltration into soils bounded by a water table proposed by Salvucci and Enthekabi (1995), was further developed to simulate VFS dynamics by making it explicit in time, account for unsteady rainfall conditions, and by coupling to a numerical overland flow and transport model (VFSMOD). In this paper, we evaluate the importance of the presence of a shallow water table on filter efficiency (reductions in runoff, sediment and pesticide mass), in the context of all other input factors used to describe the system. Global sensitivity analysis (GSA) was used to rank the important input factors and the presence of interactions, as well as the contribution of the important factors to the output variance. GSA allowed us to interpret the results from the multivariate Monte-Carlo uncertainty analysis and gain insights on the management and placement of the buffer systems. In addition, the impact of selecting alternative soil hydraulic functions (Brooks and Corey, van Genuchten or Gardner) on the model sensitivity is discussed.