Flow Loss in Deltaic Distributaries: Impacts on Channel Hydraulics, Morphology, and Stability

• Published in: Water resources research 2020-05, Vol.56 (5), p.n/a
• Main Authors: Esposito, C. R., Georgiou, I. Y., Straub, K. M.
• Format: Article
• Language: English
• Subjects: Alluvial rivers; Channel morphology; Channels; Computational fluid dynamics; Data; Datasets; deltas; Distributaries; Flood control; floodplains; Flow; flow loss; Flow stability; Fluid flow; Hydraulic models; Hydraulics; hydrology; River channels; Rivers; Sediment; Sediment transport; Stable channels; Velocity; Water discharge
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2019WR026463

The most comprehensive data sets documenting hydraulic and sediment transport regimes in the lower reaches of alluvial rivers come from systems that are managed to prevent flow loss from the channel into the overbank environment. Even moderate losses can have significant impacts on in‐channel velocity and sediment transport; therefore, a full understanding of flow loss and its effects is an important prerequisite to insights into channel function and to designing effective management strategies. We use the term flow loss for losses of water that are locally small relative to the main channel discharge. We present a unique data set documenting discharge, channel geometry, and water surface elevation from three distributary channel networks in the Mississippi River Delta where flow loss is widespread. We apply our data to validate a 1‐D hydraulic model, which then drives a previously validated model of sediment transport. Results from the modeling effort demonstrate that velocity and sediment transport trends are substantially modulated by flow loss in the ranges observed in distributary networks. The effect of flow loss on distributary channels established, we then examine how flood control infrastructure may have impacted the morphological evolution of the lowermost reaches of a large alluvial river like the Mississippi. The expected outcome of preventing flow loss is erosion in the channel's lowermost reach, in agreement with observational data. Finally, we develop a theoretical metric for a stable channel, and show that flow loss is a potentially important and understudied contributor to the long‐term behavior of distributary channels. Key Points Velocity and sediment transport trends in the lowermost reaches of rivers are substantially modulated by flow loss from the channel The impacts of flow loss are strongest at locations close to the river's mouth Our results suggest that the lowermost Mississippi River is deeper because flow loss from the channel is restricted