Modelling the effects logging roads on the streamflow of a mountainous, snow dominated watershed

Logging roads have the ability to alter streamflow by converting subsurface flow paths to surface flow paths. The two primary mechanisms by which this occurs are the interception of subsurface flow at road cuts and production of infiltration excess overland flow on road surfaces. The impact of subsurface flow interception in a snow dominated regime, at basin and sub-basin scales, was explored in this study with the application of the hydrologic model, Distributed Hydrology-Soil-Vegetation Model (DHSVM). Sensitivities of the model to road cut depth, increased stream density and increased road density were also examined in addition to the comparison of modeled versus observed tributary flow. Redfish Creek and two of its sub-basins are the subject watersheds located in the Kootenay Mountains of the British Columbia interior. At the 26 km2 scale of Redfish Creek basin, no substantial alteration in annual yield or annual peak flow occurred resulting from the presence of 16 km of logging roads. There was also no appreciable change due to modeled minimal stream extension to culverts connected to the stream via surface flow or the addition of skid trails and an abandoned road both modeled in the form of increased road density. Greater changes occurred at the sub-basin scale. Redfish Upper Tributary, in a 1 km2 sub-basin, experienced decreases of less than 5% in annual yield and annual peak flow. The largest changes occurred for the South tributary, in a 0.8 km sub-basm. The annual yield increased by 19.6% and the annual peak flow increased by 11.3%. Redfish Creek model sensitivities to the refinements in representing logging roads and their effects are greater at smaller scales. As compared against a roadless model, the addition of logging roads to Redfish Upper tributary did not noticeably improve the fit of modeled flows with observed flows.Forestry, Faculty ofGraduat