MOD_FreeSurf2D is a generally applicable computer model to simulate water movement and depth in rivers, streams, and shallow estuaries. It uses MATLAB to implement well established semi-Lagrangian and semi-implicit numerical algorithms that solve the depth-averaged, shallow water equations. MOD_FreeSurf2D has been validated against a dam-break flume experiment and three-dimensional river velocity and depth observations at the reach scale. An advantage of MOD_FreeSurf2D is that it can explicitly find and simulate the moving land/water boundary during flooding and tidal surge from topography and bathymetry.

Abstract: MOD_FreeSurf2D is an open-source MATLAB code that simulates fluid velocities and depths in rivers and streams. Although this model was designed for a specific purpose, MOD_FreeSurf2D can be employed in general scenarios when the depth-averaged, shallow water equations apply. The model approximates the depth-averaged, shallow water equations with a finite volume, semi-implicit, semi-Lagrangian representation. This numerical solution method provides accuracy and stability when using model time steps that exceed the Courant–Friedrichs–Lewy (CFL) restriction. An additional benefit of the numerical representation is the ability to simulate moving land/water boundaries. Model results were shown to be accurate when compared to published data from a dam-break experiment in a 21m flume and from velocity and depth measurements along a 400m river reach in Idaho. Results from the dam-break experiment simulations demonstrate the model’s ability to simulate wetting and drying. Additionally, sensitivity analyses conducted on the two scenarios show model convergence and demonstrate that the model can employ time steps that exceed the CFL restriction.