A Model for predicting flood hazards due to specific land-use practices

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Water Resources Research Center, Virginia Polytechnic Institute and State University

This investigation developed a finite element model for mathematically routing overland and channel flow when rainfall excess is known. To determine rainfall excess, a procedure was developed to subdivide a drainage area into similarly responding units, defined as hydrologic response units. These units were functions of soil texture, soil depth, land use, and hydrology group classification. A computer model, based on the Mein and Larson and Holtan infiltration equations, was developed to generate excess precipitation for each hydrologic response unit. A finite element grid, devised for both the watershed and the main streams, allowed use of the hydrologic response units within an element to obtain weighted rainfall excess values for each element.

A one-dimensional finite element scheme, in conjunction with Galerkin's residual method, simulated overland and open channel flow. Hurricane Camille (August, 1969) provided an event by which the model was tested and calibrated on the South River watershed in Augusta County, Virginia. Having the ability to report changes in land use, the finite element procedure allowed several arbitrary land-use changes to be incorporated into the model in order to observe the river's response under flood conditions. The effects of changes in the number and size of the elements in the watershed and in the streams also were observed, along with changes in the size of the time increment.