TOWARD A GENERALIZATION OF THE TOPMODEL CONCEPTS - TOPOGRAPHIC INDEXES OF HYDROLOGICAL SIMILARITY

Preliminary studies of the application of TOPMODEL to the 36-ha Ringel bach catchment suggested that the original form of exponential transmi ssivity function leading to the In (a/tan beta) topographic index and first-order hyperbolic base flow recession curve is not appropriate to this catchment. Two alternative forms of topographic index and soil-t opographic index are developed based on parabolic and linear transmiss ivity functions, leading to the more frequently observed second-order hyperbolic and exponential recession curves, respectively. It is shown how these can be used in the same way as the original to relate catch ment average water table depths to local water table depths so that pa tterns of saturation can be evaluated. Two companion [Ambroise et al., this issue; Freer et al., this issue] papers show how the new parabol ic index is used in the prediction of Ringelbach discharges, and how t he limitations of the model are reflected in the estimated predictive uncertainties using the Generalised Likelihood Uncertainty Estimation (GLUE) approach.