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.