SIMILARITY IN CATCHMENT RESPONSE .1. STATIONARY RAINSTORMS

The variability in Hortonian surface runoff discharge and volume produ ced by stationary rainstorms on watersheds with spatially distributed soil saturated hydraulic conductivity is examined using a two-dimensio nal runoff model and a Monte Carlo methodology. Results indicate that rainfall duration t(r), rainfall intensity i, representative variation C-v play major roles in the variability of surface runoff. Similarity in surface runoff generated on heterogeneous soils is governed by the following dimensionless parameters: T = t(r)/t(re), K* = K-m/i, and C-v. The variability in both discharge and runoff volume for randomly distributed systems increases with K and C-v, compared to the runoff generated from uniformly distributed systems. Runoff variability decre ases when T increases unless the mean value of hydraulic conductivity approaches the rainfall intensity (K --> 1). In highly pervious wate rsheds the steady state discharge depends on the spatial distribution of hydraulic conductivity. Lumped values of saturated hydraulic conduc tivity are found to typically underestimate the peak discharge and run off volume.