Regional curves to support stream restoration initiatives in Southern Ontario

Abstract

An important first step in channel restoration design is determining appropriate bankfull dimensions. However, bankfull indicators are often absent or unreliable in creeks needing restoration. To help solve this problem, this study developed a series of regional curves for selected hydrophysiographic regions of southern Ontario where the principal controls on channel form, such as surface geology and precipitation, are uniform. The curves relate bankfull dimensions at riffles to watershed drainage area. Riffles were measured since these features tend to have consistent cross-sectional areas whereas pool cross-sectional areas may vary greatly. This study focused on creeks in smaller watersheds (<100 km2) because restoration projects tend to be located in these areas. A total of 31 creeks were measured in three different hydrophysiographic regions of southern Ontario, with at least nine creeks measured in each region. Bankfull geometry equations, as related to drainage area, were developed for the regions of Waterloo, Peel and York-Durham. Bankfull cross-sectional area and drainage area were strongly related (R2 ≥ 0.95) in all three regions. The relation between drainage area and other bankfull dimensions, such as width and mean depth, was not as strong but was statistically significant. The results supported combining data from all regions into a single set of composite curves, and it is recommended that these composite curves be applied in practice. The composite regional curves may be used to provide an indication of appropriate bankfull dimensions for an impaired watercourse that lacks reliable bankfull features. The curves may be referenced by stream designers to assist with the design process, and by regulators who are tasked with reviewing channel designs. This paper describes how sites were selected, outlines the process used to collect and analyze data and provides examples of how the curves may be applied to design.