Relative Importance of Hydrological and Sediment-Transport Characteristics Affecting Effective Discharge of Small Urban Streams in Southern Ontario

Effective discharge ( Qe ) is an important design variable used in stream restoration design. Qe of a stream reach is affected by both the hydrological characteristics of the upstream watershed and the sediment-transport characteristics of the stream reach. This study identified the most critical hydrological and sediment-transport characteristics affecting Qe of small urban streams in southern Ontario. Continuous simulation of hypothetical watersheds was conducted to generate hourly streamflow data. Qe and other related variables of interest were determined based on simulated streamflow series and randomly generated sediment-transport rating curve parameters. Global sensitivity analysis using samples of input and output data indicated that Qe is highly sensitive to, first, the exponent of the sediment rating curve (β) ; second, the watershed storage coefficient reflecting the storage characteristics of a watershed; and third, the time of concentration of a watershed. Further, this study showed that only when β values are within a specific range, Qe and the discharge corresponding to a particular return period are close to each other.