GIS MAPPING OF STREAM POWER DISTRIBUTION IN SOUTHERN ONTARIO STREAMS

The drainage basin of Highland Creek (Toronto) underwent rapid urbanization in the 1970s and 1980s which has led to radical changes in frequency and magnitude of peak flows. Like many streams in the region, Highland Creek incised and confined within a narrow valley which is a corridor for recreation and sewer lines. Channel instability has damaged the infrastructure and threatens several bridge crossings. Locally the channel has been engineered to attempt to prevent further erosion and incision. There is a need to prevent further damage to infrastructure while allowing the river channel to remain as natural as possible and adjust to the new flow regime within a confined valley. Highland Creek is an extreme case of problems that occur on many streams in the region.

In many cases, channel protection work and channel restoration projects have been done without a system-wide analysis of river stability. Highland Creek presents an opportunity to test a stream-power based, rapid assessment of river system stability against historical records of channel change, descriptive geomorphic assessment of stability and more detailed analyses of river hydraulics. The goal is to develop a relatively fast, standardized, physically-based and easily repeatable method for assessing locations of potential instability and incision along the river system.

The method is based on using DEMs to derive stream gradient and drainage areas along the river, in order to calculate total stream power. Results have provided an interesting comparison between values derived from GIS analysis of DEMs of two different scales, a HEC-RAS steady flow model, large scale topographic maps and ground survey. Challenges pertaining to the modelling of discharge along a watercourse in an urban environment will also be addressed.

As a final product, maps of total stream power distribution along Highland Creek have been created. This system-wide perspective of energy distribution will be presented as a first-step approach for assessing instability along a watercourse. The potential exists to further refine the analysis to create maps of specific stream power, as well as to calibrate the model using power-based erosion thresholds and recent results from erodibility testing of non-alluvial material.