A 2-D, diffusion-based, wetland flow model

Surface water flow in wetlands occurs typically in a low gradient environment where topographic and flow resistance variations control the discharge distribution. It is within this fluid mechanical regime that the biochemical processes constituting wetland ecology take place. Presented herein are the basics of a mathematical model that takes advantage of the hydraulics typical of wetlands. The resulting model, in the form of a 2-D, non-linear diffusion equation, allows incorporation of spatial variations in flow resistance and topography. The applicability of the model to one- and two-dimensional wetland type flow is demonstrated using two cases: a laboratory experiment and a wetland pond. Results illustrate the versatility of the formulation and the important influence of topography variations on flow depth and velocity variations. The use of a fixed rectangular calculation domain to simulate the flow pattern in wetlands with irregular wet boundaries is the most significant practical aspect of the WETFLOW model. Future research will concentrate on dealing with extreme heterogeneity in the elevation and flow resistance distributions, through a combination of measurements and use of stochastic fractals to represent property distributions (Molz and Boman, 1993, Water Resour. Res., 29: 3769–3774). Experimental studies are needed to quantify the relationship of flow resistance to different combinations of slope, water depth, and a suitable measure of vegetation density for a wetland ecosystem.