A Mechanistic Model to Simulate Rill Erosion

The key objective of this paper is to develop a mechanistic, 1-D hydrodynamic and sediment transport model namely, RILL 1D, that handles transcritical flows over abrupt changes and predicts changes in rill bed elevation, without violating the flow continuity equation. Replication of rill conditions necessitated the use of an enhanced TVD-MacCormack scheme with implementation of Tseng's surface gradient method, to provide an oscillation free solution over formed pool crests. The performance of the model is evaluated by comparing its results with rill observations from a flume study with fixed bed geometry and two field investigations with mobile beds. It is shown that the enhanced TVD-MacCormack scheme approximates, satisfactorily, depth and velocity for a fixed bed rill with steps and pools, except near the pool headwalls where a backroller forms with negative velocities. With field data the code is tested for its ability to reproduce measured values of sediment transport rates. RILL 1D performs reasonably well in these simulations in terms of sediment prediction rates and faired adequately in terms of replicating rill bed morphology. A sensitivity analysis is performed to assess the effects of cell size and critical erosional strength in the predictive ability of the model.