Distributed Hydrologic Modelling of Floods in Mountainous Regions Using the TOPMODEL

It is has long been suspected that macropore flow at shallow subsurface depths combined with surface runoff may be the primary source of runoff in the hilly catchments of eastern Kentucky. A distributed model that may be adapted to such hydrologic environments is TOPMODEL, which is a topography based hydrologic model. To demonstrate this, runoff associated with extreme floods from the Tygarts Creek catchment (drainage area of 156 sq. km.) located in eastern Kentucky is modelled using TOPMODEL. This is carried out using both a lumped (single catchment) and a distributed (subcatchment) representation of the Tygarts Creek catchment. Delineation of the catchment and subcatchments is accomplished using the Watershed Modeling System (WMS) together with a digital elevation map (DEM). The topographic index curve, which forms the fundamental basis of the TOPMODEL, is then derived using a Digital Terrain Analysis (DTA) system called GRIDATB. This DTA system is provided within the TOPMODEL framework. Based on the topographic index curve, several observed flood events, measured at the Tygarts Creek catchment outlet, are simulated using TOPMODEL. Results show reasonably good correlation between simulated and observed flows in spite of using point rainfall inputs as recorded by a nearby National Weather Service (NWS) gauge. Future efforts will attempt to incorporate spatial rainfall data from radar (NEXRAD) for refining the modelling efforts.