Urbanization, Channel Adjustment, and Restoration of a Suburban Semi-Alluvial Creek: the Case Study of Wilket Creek in Toronto

English Abstract:

Land use changes related to urbanization are known to have a profound impact on stream hydrology, sediment transport, ecology, and aesthetic value. Wilket Creek in Toronto is an excellent example of urban development in the 1960’s and 70’s because it is largely suburban, stormwater conveyance was massively increased, and a portion of the creek was preserved as a part of linear park. It is also semi-alluvial, which means that classic models of channel evolution may not be applicable. The objectives of the current study were to 1) assess the character and degree of channel change that has occurred since development, 2) determine whether channel enlargement is still ongoing, and 3) assess the likelihood of success for recent in-stream restoration efforts. Historic analysis was completed using aerial photographs, measurements from a relic channel, and a 15 year monitoring program of channel dimensions. Assessment of in-stream restoration efforts was completed using channel surveys, water-level gauges, and sediment tracking using RFID tracers. Results show that the stream network has been effectively ‘pruned’ as a result of development and channel enlargement is widespread. Flood hydrology is extremely flashy, with water level increases of over 1 m in less than an hour during floods. Nevertheless, a coarse layer of glacial till continues to exert an important influence on the channel gradient. Downstream of the incision of the channel through this layer, the channel is steeper and has enlarged approximately 3x from its historic dimensions, which is close to what is predicted from an analysis of the cumulative imperviousness. Continued instability has been found over the last 15 years as the channel adjusts its planform and develops a new wandering-type morphology. RFID tracking results show that the constructed pool-riffle morphology may succeed in reducing particle mobility despite the extreme hydrology.