Determination of Imperviousness in the Highland Creek Watershed

Abstract

The Highland Creek watershed, an area of about 100 square kilometres in the region of Toronto, was selected for this study. As a highly urbanized area, construction of roads and buildings has increased the region’s imperviousness to watershed, which can cause severe impairment to both the quality and quantity of water. The imperviousness of this region therefore needed to be assessed to manage the watershed area effectively, and to improve future development projects. The task of assessing the watershed area was accomplished using digitized aerial photographs and Geographical Information Systems (GIS). Because GIS does not give detail total road area of land use, the difference between total area and impervious area was calculated and assigned as a total road area. The ratio between the impervious area and the total area was calculated to assess the impervious ratio of the watershed area, and was assigned a value of 0.533. Using this method, more than 120 subcategories can be selected within this watershed area, and the imperviousness can be calculated using land use subcategory ratios and averages ratios.