Simulating the impact of road construction and forest harvesting on hydrologic response

This paper incorporates a conceptual model of the effect of roads and fores t harvesting on hillslope soil moisture and runoff production into a hydroe cological modelling system and discusses model results for a range of scena rios for a small catchment in the Western Oregon Cascades, USA. The model i s used to explore the implications of road cut depth and road drainage patt erns on seasonal hydrologic responses including runoff production, soil moi sture and ecological processes such as evapotranspiration. By examining hyd rologic response within a seasonal and hillslope context, we illustrate the complex role played by roads in terms of both the spatial and temporal per sistence of the effects of an increase in local drainage efficiency associa ted with particular road segments. Model results are compared with observed outflow responses For a paired catchment study using the test case watersh ed. (catchment area in UK terminology). Results show the potential for an e cologically significant change in soil moisture in the area downslope from the road. These changes are mediated by the drainage patterns associated wi th roads, specifically whether road culverts serve to concentrate or to dif fuse flow. Field verification of these findings presents an avenue for furt her research. The modelled effects on seasonal outflow response are less si gnificant but do show clear temporal patterns associated with climate patte rn, hillslope drainage organization and road construction. Comparison betwe en modelled and observed outflow response suggests that the model does not yet capture all of the processes involved in assessing the effects of fores t road construction. Copyright (C) 2001 John Wiley & Sons, Ltd.