Development of VFDM: a riparian vegetated filter dimensioning model for agricultural watersheds

Dimensioning and positioning structural beneficial management practices (BMPs) represent a "real life" challenge for soil conservation engineers, managers, planners and policy-makers. Different factors, such as trapping efficiency; implementation, management, and opportunity costs (resulting from cropland loss), and government policies and guidelines need to be weighed to meet this challenge. The trapping efficiency of structural BMPs may depend on many parameters, including: (1) characteristics of vegetated filters (VF) such as width and slope, vegetation height, vegetation density and species composition, (2) flow characteristics such as runoff velocity, discharge volume and water height, and (3) sediment characteristics such as particle size, aggregation and concentration. Government policies and guidelines may include dimension and location of VFs and/or a cropland percentage that needs to be converted into VF areas. The main objectives of this paper are to: (1) describe the development of the Vegetated Filter Dimensioning Model (VFDM), a mathematical model to determine the optimal dimensions of riparian vegetated filter strips (RVFSs) in agricultural watersheds, and (2) illustrate the potential use of the model on a pilot watershed, the Beaurivage watershed, in Quebec, Canada. The latter was done for the sole purpose of model testing with readily available input parameters and data. The model calculates the optimal width with respect to vegetation, topographical, hydrological and sedimentological characteristics. The results of this case study showed that the average recommended RVFS for the Beaurivage River watershed is about 3 m wide.