DISCHARGE AND WATER-TABLE PREDICTIONS USING A GENERALIZED TOPMODEL FORMULATION

A simple, generalized saturated zone formulation is presented in this paper to relax the assumption of an exponential function originally ma de in TOPMODEL. This saturated zone model is based on the concept of a 'discharge : relative storage' (Q Delta S) function which is derived empirically, using recession curve analysis, and may be of arbitrary f orm. The generalized formulation is applied to the Seternbekken MINIFE LT catchment in Norway, where detailed distributed water table data ha ve been measured. These water table data are used to suggest an empiri cal, power law modification of the topographic a/tan beta index. Resul ts for the simulation through time of discharges and water table depth s at a few locations show that the generalized saturated zone formulat ion is as efficient a simulator of the observed data as a conventional TOPMODEL, but requires one parameter less to be calibrated. The simul ation of detailed water table distributions is only approximate in bot h cases. The modified power law index shows only a small improvement b ut provides a basis for a discussion of possible sources of error in t he TOPMODEL assumptions for this site. (C) 1997 by John Wiley & Sons, Ltd.