A distributed, physically-based, rainfall-runoff model incorporating topography for real time flood forecasting

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Ralph M. Parsons Laboratory for Hydrology and Water Resource Systems, Department of Civil Engineering, Massachusetts Institute of Technology

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This report presents a distributed, physically-based model of runoff generation in a catchment, for operation use in flood forecasting. The model accounts for both the infiltration excess and saturation excess mechanisms of runoff production from watersheds, and for lateral subsurface flows. The effect of local terrain slope and topography on subsurface flows and the development of areas of saturated soil is accounted for. The model uses spatial discretization into rectangular elements which correspond to the grid of a digital elevation map. Each basin element consists of a soil column in which hydraulic conductivity decreases with depth, in the form of an exponential function. Spatial discretization allows for distributed terrain slope, soil parameters, moisture conditions, and rainfall inputs. Time discretization allows for consideration of time-variable rainfall rates. The mathematical models uses the kinematic approximation of infiltration and subsurface water flow which is assumed to occur only within the porous soil matrix. The kinematic model of infiltration is used to show how decreasing conductivity with depth may result in the development of a zone of perched saturation during a rainstorm, and that the water flow in the perched saturated zone is diverted laterally if the terrain is inclined.


Report no 332

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