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Half-Yield Discharge: Process-Based Predictor of Bankfull Discharge
AbstractThe river management and restoration community has devoted much effort to predicting the bankfull discharge, Qbf, and associated channel geometry at Qbf for the purposes of channel study, classification, and design. Four types Qbf prediction methods predominate: (1) direct estimation based on field indicators of bankfull stage, (2) downstream hydraulic geometry equations, (3) a flood peak discharge with a specified return interval based on the annual maximum flood series (e.g., the 1.5- to 2-year flood) or regional flood peak statistical relations, and (4) process-based approaches that incorporate the magnitude and frequency of sediment transport such as the most effective discharge Qeff. Process-based Qbf predictors are calculated using sediment transport data from 95 gauged sites across the United States including coarse, bed load–dominated channels and fine, suspended load–dominated channels with drainage areas ranging from 6 to 1.4×105 km2. These values are compared with observations of Qbf made from field measurements of bankfull indicators. It was found that the discharge associated with 50% of cumulative sediment yield based on the flow record—Qh, the half-yield discharge—predicts Qbf well. When compared with Qeff and the 1.5- and 2-year floods (Q1.5 and Q2), Qh has the lowest relative error in predicting Qbf for coarse and fine bed sites. Log-log regression models of observed–predicted data pairs indicate that Qh and Q1.5 calculated for fine bed sites are the only Qbf predictor models whose slopes are not significantly different from unity and whose intercepts are not significantly different from zero. The most effective discharge, Qeff, and Qh both perform well in predicting Qbf in coarse bed sites, followed by Q1.5, whereas Qeff uniformly underpredicts Qbf in fine bed sites. The behavior of Qh, a process-based predictor of Qbf, is characterized to highlight circumstances in which sediment yield analysis may be important in estimating the bankfull discharge. The half-yield discharge represents a novel estimator of Qbf in rivers not previously discussed in this context.
Half-Yield Discharge: Process-Based Predictor of Bankfull Discharge
AbstractThe river management and restoration community has devoted much effort to predicting the bankfull discharge, Qbf, and associated channel geometry at Qbf for the purposes of channel study, classification, and design. Four types Qbf prediction methods predominate: (1) direct estimation based on field indicators of bankfull stage, (2) downstream hydraulic geometry equations, (3) a flood peak discharge with a specified return interval based on the annual maximum flood series (e.g., the 1.5- to 2-year flood) or regional flood peak statistical relations, and (4) process-based approaches that incorporate the magnitude and frequency of sediment transport such as the most effective discharge Qeff. Process-based Qbf predictors are calculated using sediment transport data from 95 gauged sites across the United States including coarse, bed load–dominated channels and fine, suspended load–dominated channels with drainage areas ranging from 6 to 1.4×105 km2. These values are compared with observations of Qbf made from field measurements of bankfull indicators. It was found that the discharge associated with 50% of cumulative sediment yield based on the flow record—Qh, the half-yield discharge—predicts Qbf well. When compared with Qeff and the 1.5- and 2-year floods (Q1.5 and Q2), Qh has the lowest relative error in predicting Qbf for coarse and fine bed sites. Log-log regression models of observed–predicted data pairs indicate that Qh and Q1.5 calculated for fine bed sites are the only Qbf predictor models whose slopes are not significantly different from unity and whose intercepts are not significantly different from zero. The most effective discharge, Qeff, and Qh both perform well in predicting Qbf in coarse bed sites, followed by Q1.5, whereas Qeff uniformly underpredicts Qbf in fine bed sites. The behavior of Qh, a process-based predictor of Qbf, is characterized to highlight circumstances in which sediment yield analysis may be important in estimating the bankfull discharge. The half-yield discharge represents a novel estimator of Qbf in rivers not previously discussed in this context.
Half-Yield Discharge: Process-Based Predictor of Bankfull Discharge
Bledsoe, Brian P (author) / Sholtes, Joel S
2016
Article (Journal)
English
Half-Yield Discharge: Process-Based Predictor of Bankfull Discharge
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