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Levee setbacks can create space for side channels, reduce flood impacts, and provide environmental benefits. Guidance is needed on how side channel design affects geomorphic changes over time. This paper explores application of existing research on natural and forced side channels to a levee setback with side channel on the White River (Washington). The side channel maintained a high bifurcation angle into the setback for 2 years. High flows then reset the bifurcation to a lower angle. Flow and sediment volumes and deposition patterns from each 2-year period matched results from existing studies for either a high or low angle. Application of existing research insight into expected flows and sediment patterns was dependent on a static bifurcation angle. In this case study, because the entrance area did not restrict the bifurcation angle and the flow regime included high flows, the bifurcation angle could adjust to maintain the side channel. Designing a large setback entrance enabled the channel to self-adjust to maintain flow and sediment transport into the side channel without the need for engineering intervention. [ABSTRACT FROM AUTHOR]

The Integrated, Section Surface Difference Over Time, version 2 (ISSDOTv2) method provides a means of quantifying bedload in large sandbed rivers. Like all measurements, it is important to understand the uncertainty associated with the method before making management decisions based on its results. A methodology is presented for quantifying and combining the uncertainty for each component of the ISSDOTv2 method including particle density, bed porosity, acoustically measured bed topography, the timing of measurements, sand wave identification, and regression analysis used for geometric correction of bedload measurements. The approach provides an indication of the relative magnitude of each source of uncertainty in addition to the uncertainty in the final resultant transport rate. Laboratory flume measurements were used to evaluate the uncertainty limits and verify the approach. The greatest contributor to uncertainty was found to be the bathymetric uncertainty, and, at the highest transport rates, cumulative relative uncertainty was found to be approximately 10%. Cumulative relative uncertainties grew rapidly with decreasing flow rates, driven primarily by the higher relative contribution of the effect of bathymetric uncertainty on the smaller bedforms that are typically present at lower transport rates. The approach documented here will be transferrable to real-world systems to determine the uncertainty in measured bedload sediment transport rates using the ISSDOTv2 method. [ABSTRACT FROM AUTHOR]

Quantification of sediment transport rates is necessary for river management but remains difficult due to large volumes of sediment in motion, spatiotemporal heterogeneity in discharge, depth, and morphology, the need for expensive equipment, and personnel costs. During efforts to quantify sediment bed load in the Mississippi (MS) River near Vicksburg, MS, US, the US Army Corps of Engineers-Engineer Research and Development Center (USACE-ERDC) collected acoustic multibeam topographic data during the 2011 MS River flood. Bed topography data were analyzed to quantify the effect of changing flow rates on bed topography. Bedforms were much higher and longer in the center section than near either bank, and superimposed bedforms were found during the falling limb of the 2011 flood hydrograph. Bedform amplitudes and lengths were positively correlated with flow depths, but amplitudes were typically higher and lengths shorter than predicted in previous research. Topography data from three lower flows are included to illustrate the morphometric variation induced by a wide range of discharges. [ABSTRACT FROM AUTHOR]

Bed-load transport is an important process impacting riverine morphology, but until recently it has proven difficult to measure in large sand-bed rivers. Integrated Section, Surface Difference Over Time, version 2 (ISSDOTv2) method provides a means of quantifying the bed load in large sand-bed rivers. A series of flume experiments, which included frequent measurements of bed topography and an independent measurement of bed load across a range of flows, was used to provide validation for the ISSDOTv2 method. The mean difference between the ISSDOTv2 calculations and the estimated bed load was 5.6% (high flow), 12.9% (medium flow), and 56% (low flow), indicating improved accuracy for higher flow and transport conditions. It was also found that the ISSDOTv2 method responded appropriately to rapid step-downs in flow, as indicated by agreement between ISSDOTv2 load results and accompanying independent measurements of bed load. [ABSTRACT FROM AUTHOR]