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Abstract Relatively little is known about the geomorphological characteristics of floodplain secondary channels and the potential for floodplain flows to mobilize bed material within these channels. This study examines the geomorphological characteristics (channel form, material properties, wood jams) and bed‐material mobilization potential of secondary channels on the floodplain of a meandering river in Illinois, USA. It also compares these attributes to those of the main channel. Results show that secondary channels are at most about one‐third the size of the main channel but also vary in size over distance. Channel dimensions tend to be greatest near the proximal connection of secondary channels to the main channel, suggesting that flow from the main channel is effective in producing scour where it enters secondary channels. The beds of secondary channels consist mainly of mud in contrast to sand and gravel on the bed of the main channel, implying that secondary channels do not convey bed material from the main channel onto the floodplain. Secondary channels connected to the main channel at both ends have more abundant active wood jams than those connected only at the proximal end. Flow from the main channel enters secondary channels at sub‐bankfull stages, but maximum mobilization of cohesive bed material in secondary channels only occurs during flows that exceed the average bankfull stage in the main channel. Overall, secondary channels are active conduits of flow, sediment, and large wood on floodplains and can contribute to floodplain sediment fluxes through entrainment of bed material.
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Sediment Transport Potential in a Hydraulically Connected River and Floodplain‐Channel System
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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- Award ID(s):
- 1911321
- PAR ID:
- 10442529
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 57
- Issue:
- 5
- ISSN:
- 0043-1397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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