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distributed multi-process model system

1. 2D single layer

PIHM has incorporated channel routing, surface overland flow, and subsurface flow together with interception, snow melt and evapotranspiration using the semi-discrete approach with FVM. Table 1 shows all these processes along with the original and reduced governing equations. For channel routing and overland flow which is governed by St. Venant equations, both kinematic wave and diffusion wave approximation are included. For saturated groundwater flow, the 2-D Dupuit approximation is applied. For unsaturated flow, either shallow groundwater assumption in which unsaturated soil moisture is dependent on groundwater level or 1-D vertical integrated form of Richards’s equation can be applied. From physical arguments, it is necessary to fully couple channel routing, overland flow and subsurface flow in the ODE solver. Snowmelt, vegetation and evapotranspiration are assumed to be weakly coupled. That is, these processes are calculated at end of each time step, which is automatically selected within a user specified range in the ODE solver.