EVALUATING CHANNEL-FORMING DISCHARGES: A STUDY OF LARGE RIVERS IN OHIO

摘要

Measured data were used to evaluate whether bankfull discharges were related to effective discharges for large rivers in Ohio. The frequency and sediment transport associated with these channel-forming discharges was also examined. Rural watersheds in the Midwest region of the U.S. are dominated by agricultural land uses that incorporate subsurface drainage improvements. Bankfull discharges were determined by measuring fluvial features at each USGS gage and then relating these features to the rating curve and historic daily discharge data for each gage. Effective discharges were determined by using suspended sediment data obtained at the gages, the Wolman-Miller method for calculating geomorphic work, and bin sizes based on stage intervals to group sediment and discharge data. There was good agreement between the effective discharge and bankfull discharge estimates. Bankfull and effective discharges were primarily related to flows that transported the middle 50% of the total sediment load. Recurrence intervals of the bankfull and effective discharges ranged from 0.3 to 1.4 years. These recurrence intervals are more frequent than generally reported in the literature. The duration of daily discharges that equaled or exceeded the channel-forming discharge ranged from 1 to 24 days annually, with mean values of 9 and 11 days for the bankfull discharge and effective discharge, respectively. Common methods for determining the recurrence interval are inadequate for frequent channel-forming discharges, and better insight is obtained by determining the number of days on which these flows are exceeded annually