The use of sediment budget concepts to assess the impact on watersheds of forestry operations in the southern interior of British Columbia

Sediment budget concepts can be applied to the assessment of the impacts of forest resource development on the sediment regime of streams. In British Columbia, these impacts are of concern because of the extent of commercially valuable forests. Increases in sediment yield from forestry operations can affect water quality, fish habitat, and channel stability. To address these concerns, the BC Ministry of Forests conducted several sediment budget studies from about 1992 to 2002. This paper reports the results of two studies, focusing on the water quality of streams used for community water supply. The studies address several questions: How sensitive are the streams to an increase in sediment supply? Are development-related sediment sources significant compared to natural sources? What forest practices are responsible for increasing or minimizing sediment impacts? How can the impact of forestry operations on water quality be monitored? The studies used a paired watershed approach, with discharge, turbidity, sediment yield, and solute yield measured on watersheds undergoing logging and road building, and on similar undeveloped watersheds. The studies concluded that erosion from forest roads can be a significant source of suspended sediment, but sediment from logging operations is usually negligible. The risk of landslides is an important factor in the sediment budgets, but is difficult to quantify. Differences in geology and groundwater regime can influence the sensitivity of watersheds to sediment impacts.