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We present a new GRASS GIS module r.terradyn that evolves a given terrain using sediment flux information provided by the SIMWE (SImulated Water Erosion) GRASS GIS modules r.sim.water and r.sim.sediment originally developed by Mitas and Mitasova (1998). SIMWE is a distributed, bivariate, steady-state watershed scale sediment erosion, transport, and deposition model that employs a path sampling Monte Carlo method in which erosion, transport, and deposition conditions are treated as a continuous field, resulting in fully distributed erosion/deposition patterns.. Module r.terradyn modifies the original digital elevation model (DEM) over time steps, each corresponding to a single rainfall event, which is then used as the input DEM for subsequent SIMWE and r.terradyn iterations. New techniques were derived that include the application of a gravitational diffusion term, an approximate Neumann boundary condition routine for use with GRASS GIS module r.slope.aspect, a comparative band-pass filter for numerical stability of the iterative feedback system, and a simple rainfall excess calculation methodology derived from accumulated runoff curve number tables that enables spatially distributed infiltration. Application of r.terradyn to a sample watershed demonstrates results for distributed land cover and infiltration and for various soil types. Terrain change impact from disturbed areas is also presented. Preliminary comparisons to field observations and total discharge data are currently being used to calibrate model parameters. Verification of the model is still ongoing as data becomes available. The influence of grain size dependent transport mechanisms on short-term and long-term topological changes induced by human impact, such as mining and construction, may lead to the determination of the optimum location, size, and frequency of control measures to more cost effectively meet emerging TMDL requirements.