INCLUDING SPATIALLY-VARIABLE EFFECTIVE SOIL DEPTHS IN TOPMODEL

TOPMODEL (Beven and Kirkby, 1979; Beven et al., 1995) was one of the f irst attempts to model distributed hydrological responses based on var iable contributing area concepts. It makes use of an index of hydrolog ical similarity based on an analysis of the topographic data. The inde x approach was later generalised to take account of spatial variabilit y of soil transmissivities, but no similar spatial analysis of the var iability in the rate of the decrease of the transmissivity with depth has yet been examined. This paper shows how the TOPMODEL theory can be extended to handle this spatial variability, using a 2D distribution function of a new soil depth-topographic index of hydrological similar ity, A first sensitivity analysis of the effect of variable soil depth s on the model predictions for the Maurets catchment, France, is prese nted, Predicted discharges and calibrated parameter values are not sen sitive to the patterns of effective soil depth investigated. Distribut ed predictions may be more sensitive but raise questions of how to obt ain the parameter data required. (C) 1997 Published by Elsevier Scienc e B.V.