Physics-based simulations of the impacts forest management practices have on hydrologic response
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The impacts of logging on near-surface hydrologic response at the catchment and watershed scales were examined quantitatively using numerical simulation. The simulations were conducted with the Integrated Hydrology Model (InHM) for the North Fork of Caspar Creek Experimental Watershed, located near Fort Bragg, California. InHM is a comprehensive physics-based hydrologic-response model. The North Fork watershed (including 11 tributary catchments) is the site of an ongoing study monitoring the impacts of forest practices. InHM was parameterized and calibrated using existing data and new field measurements of soilhydraulic properties. Continuous long-term simulations were conducted for three wet seasons: before logging, after logging, and after a period of regrowth. Simulated increases in flow and peak discharges were considerably higher after clearcut harvesting. Concept-development simulations of cumulative watershed effects (CWEs) examined potential impacts of alternative timber harvest levels and methods relative to those that occurred in the North Fork watershed. Results from these simulations show that the increases in the simulated discharge after clearcutting were significant for the catchment and watershed scales and that relatively small changes in soil-hydraulic properties produced substantial changes in hydrologic response. The simulations in this study illustrate that timber harvesting can alter the streamflow generation mechanisms and patterns within a catchment.