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  1. Abstract

    The distinction between a “stream” and “river” is imprecise and vague despite the popular usage of the terms across disciplines for describing flowing waterbodies. Based on an analysis of named flowing waterbodies in the continental United States, we suggest a bank‐to‐bank channel width of 15 m as a working threshold in defining smaller “streams” from larger “rivers.”

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  3. Abstract

    Mountain rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes. Once emplaced in the river, the movement of this sediment depends on flow, grain size distribution, and channel and network geometry. Here, we simulate downstream bed elevation changes that result from discrete inputs of sediment (∼10,000 m3), differing in volume and grain size distribution, under medium and high flow conditions. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. This work builds on a Lagrangian, bed‐material sediment transport model and applies it to a 27 km reach of the mainstem Nisqually River, Washington, USA. We compare observed bed elevation change and accumulation rates in a downstream lake to simulation results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of synthetic sediment pulses by comparing the results against a baseline condition (without pulse). Our findings suggest that bed response is primarily influenced by the sediment‐pulse grain size and distribution. Intermediate mixed‐size pulses (∼50% of the median bed gravel size) are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed‐size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform‐size pulse. This work has important implications for river management, as it allows us to better understand fluvial geomorphic responses to variations in sediment supply.

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  4. Despite decades of policy that strives to reduce nutrient and sediment export from agricultural fields, surface water quality in intensively managed agricultural landscapes remains highly degraded. Recent analyses show that current conservation efforts are not sufficient to reverse widespread water degradation in Midwestern agricultural systems. Intensifying row crop agriculture and increasing climate pressure require a more integrated approach to water quality management that addresses diverse sources of nutrients and sediment and off-field mitigation actions. We used multiobjective optimization analysis and integrated three biophysical models to evaluate the cost-effectiveness of alternative portfolios of watershed management practices at achieving nitrate and suspended sediment reduction goals in an agricultural basin of the Upper Midwestern United States. Integrating watershed-scale models enabled the inclusion of near-channel management alongside more typical field management and thus directly the comparison of cost-effectiveness across portfolios. The optimization analysis revealed that fluvial wetlands (i.e., wide, slow-flowing, vegetated water bodies within the riverine corridor) are the single-most cost-effective management action to reduce both nitrate and sediment loads and will be essential for meeting moderate to aggressive water quality targets. Although highly cost-effective, wetland construction was costly compared to other practices, and it was not selected in portfolios at low investment levels. Wetland performance was sensitive to placement, emphasizing the importance of watershed scale planning to realize potential benefits of wetland restorations. We conclude that extensive interagency cooperation and coordination at a watershed scale is required to achieve substantial, economically viable improvements in water quality under intensive row crop agricultural production.

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  5. Abstract

    Meandering river floodplains often contain intermittently flooded complex channel networks. Many questions remain as to the pervasiveness, function, and evolution of these floodplain channels. In this present work, we analyzed size‐specific sediment transport potential and assessed whether the channelized floodplain of the meandering East Fork White River near Seymour, Indiana is on a net erosional or depositional trajectory. We applied a two‐dimensional hydrodynamic model and used simulated model results to estimate the largest sediment size that can be moved in suspension and as bedload at various flows for grain size classes between 4 µm and 64 mm. We developed a probabilistic method that integrates the largest sediment size that can be moved at various flows to compute an effective grain size, which we compared to measured field data. Results show that the river is capable of supplying sand to the floodplain and these floodplain channels can transport sand in suspension and gravel as bedload. This suggests that sediment supplied from the river could be transported as bedload in floodplain channels. These floodplain channels are supply limited under the current hydrologic regime and the grain size distribution of the bed surface is set by the flow conditions; thus, these floodplain channels are net erosional. Finally, our proposed method of probabilistically integrating the largest sediment size that can be moved at various flows can be used to predict the upper end of the grain size distribution in suspension and in bed material, which is applicable to floodplains as well as coastal areas.

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