33-Impacts of Urbanization on Streamflow.

Abstract

This study has concentrated on the temporal and spatial changes in streamflow patterns due to urbanization and/or rainfall trends within the watershed. The analyses were conducted by using the rainfall data from two stations, and streamflow data from three gauging stations. The results of the streamflow analysis showed that there is relative change in the mean and standard deviation of the stream flow with the reference distribution for all three stations. Also, analysis of location, scale and, shape parameters indicated that streamflow data show a non linear trend and statistically significant change for most of the location and scale parameters. A comparison of the earlier and later years of streamflow showed that Erindale, which has been significantly urbanized, has the maximum number of parameters with greater than 2% significance followed by Cataract; which shows a clear indication of effect of urbanization on streamflow. In addition, the pattern of high flow and low fl ow has changed, and the summer flows in all the gauging stations have become closer to the spring flow. The Frequency Duration Curve analysis showed that except for Orangeville, the order of high flow and low flow curves changed positions with time. The effect of urbanization was tested by taking the relative changes in flow during summer and spring season which showed a reduction of 0.07 m3 s-1 yr-1. The results from rainfall analysis showed that the rainfall intensities have slightly decreased in recent years for Pearson and Fergus stations. It also supports that higher streamflow in recent years is due to urbanization not increase in rainfall amount for the watershed.