Drainage area and flow frequency distribution pattern of small Ontario streams

In the stream restoration process the hydraulic and the morphometric design of a stable channel is based on the effective discharge (Qe). The accuracy of the analytical solution for estimating Qe depends on the goodness of fit between the streamflow series and the assumed probability distribution function (pdf); and also the sediment transport rate of the stream. Most analytical investigations for estimating Qe assume that the daily streamflow data can be best approximated by a lognormal distribution. However, the frequency analysis of different Ontario streams indicate that below a certain drainage area the assumed lognormal pdf does not provide a good fit with the actual streamflow series. In this study a modified exponential fitting model has been introduced for analytically estimating Qe for those streams, whose size is below the critical drainage area. The analytical solutions for Qe from the modified exponential fitting model, lognormal and standard exponential pdf have been compared with the direct computational approach (DCA). The DCA can be considered as the most accurate method for estimating Qe as it incorporates the entire flow series from the stream.