ABSTRACT: The potential impacts of harvesting on the hydrologic dynamics of boreal watersheds.

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Forest harvesting activities can affect peak and base flows, water yield, and water quality. Forest companies are interested in methods to evaluate these hydrologic impacts, as a basis to modify forest harvesting plans, if necessary, to ensure the safety of the environment and downstream values. The objective of this project was to assess the potential impacts of forest harvesting on the Marten River watershed, a representative watershed that flows into the Lesser Slave Lake in northern Alberta, Canada. By 2050, almost 25\% of the watershed area will be harvested under existing harvest plans. The potential impacts on hydrologic dynamics of this harvesting were explored using two complementary models, a distributed hydrologic model, Regional HydroEcological Simulation System (RHESSys), and a lumped hydrologic model, Water Resource Evaluation of Non-Point Silvicultural Sources (WRENSS). RHESSys was used to predict the potential impacts of a single year harvest (up to 7.5\% of the watershed area) on the peak and base flows among years representing the range in climatic conditions within the Slave Lake Region. Scenarios ran in RHESSys included 1980, an average precipitation year preceded by 10 years of average precipitation; 1983, a wet year; 1987, a dry year; and 1990, an average precipitation year preceded by 10 years of variable precipitation. WRENSS was used to predict the potential impacts of the proposed harvests on the annual water yields and the time required for hydrologic recovery to occur following the completed and proposed harvests. Scenarios ran in WRENNS were (a) a best case scenario, where the area was logged and regenerated fully to a deciduous stand; (b) a worst case scenario, where the area was logged and regenerated fully to a coniferous stand; and (c) a probable case scenario, where the are was logged and regenerated to what existed before cutting, i.e. a mix of deciduous and coniferous. For each of the harvest scenarios, the potential impacts on the hydrologic dynamics were to increase the peak and base flows and to increase the annual yields. These increases, however, were generally within the Alberta Environmental Protection's criterion of a maximum of 15\% increase in the average annual water yield. To compare the potential impacts of this anthropogenic disturbance with a natural disturbance, a realistic wildfire scenario was conducted. While the potential increase in the annual water yield resulting from a single harvest ranged from 6 to 21\%,

Bibliography of Canadian Geomorphology