HR: 10:45h
AN: NB22G-02    [Abstracts]
TI: Effective Suspended Sediment Discharges of Illinois Streams
AU: * Crowder, D W
EM: crowderd@sws.uiuc.edu
AF: Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820 United States
AU: Knapp, H V
EM: vknapp@uiuc.edu
AF: Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820 United States
AB: Dominant discharge theory is often utilized in stream restoration design. Dominant discharge theory assumes that there exists a single discharge that, if constantly maintained within a channel, will create the same average channel dimensions as those produced by a stable channel's entire hydrologic regime. If such a discharge exists, one can theoretically use this discharge as a basis for designing stable channel configurations in stream restoration projects. A stream's bankfull discharge, 1.5 year flow event, and effective discharge are often used as dominant discharge estimates. However, estimating such values within ungaged and incised streams, where stream restoration projects typically occur, is problematic. Moreover, prior research has shown that the recurrence intervals of bankfull and effective discharges are not always equal to the 1.5 year recurrence interval (as commonly assumed), but vary with watershed properties (e.g. size, hydrologic regime, and geology). Subsequently, there exists a desire to develop regionalized dominant discharge values which can be applied at ungaged locations. Two effective discharge values were computed at 20 sediment-discharge monitoring stations throughout Illinois. The first effective discharge value at each location was computed using a power curve to derive that station's sediment-discharge relationship. The second effective discharge value was computed using a "class-interval mean" approach to derive the monitoring station's sediment-discharge relationship. Recurrence intervals for both sets of effective discharge estimates were generally greater than a stream's mean discharge, but less than the 1.1 year recurrence interval. However, effective discharge estimates computed with the power curve were, on average, smaller than those estimated using the class-interval mean approach. Effective discharge results are difficult to validate and are sensitive to sediment-discharge relationships, the amount and quality of sediment data, and class-interval size. Consequently, channel design, based on effective discharge estimates, remains problematic. Suggestions for improving effective discharge estimates and regional dominant discharge studies are provided.
DE: 1800 HYDROLOGY
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly