Flood energy dissipation in anabranching channels

Entwistle, NS; Heritage, G; Milan, DJ

Abstract

This study examines the character of developing anabranched channel networks on the River Wear, north England using metre-scale aerial LiDAR. DSM-DTM interpretation reveals a well-developed vegetation structure and a locally diverse terrain, dominated by an interlinked channel network split by low elevation depositional areas with the gross morphology of the reach resembling that of a strongly active meandering / wandering channel suggesting that an anabranching network may develop within systems that were initially active meandering and wandering, evolving in line with floodplain vegetative succession. Utilisation of the LiDAR DEM in the hydrological component of the CAESAR-Lisflood (version 1.4) morpho-dynamic model has generated local hydraulic variable estimates through the anabranched reaches for a range of flows. These data clearly demonstrate how elevated flows are transferred out of the primary channel and distributed along the interconnected secondary channel network, creating a diverse set of hydraulic environments. Areas between the channels rapidly become inundated as flows increase, dissipating flow energy. Shear stress estimates throughout the study site reveal a generally reduced ability to mobilise sediments and erode channel margins, in comparison to a single-thread reach immediately downstream. Anabranched secondary channels appear to operate in disequilibrium and act predominantly as aggradational zones, although with some evidence of scour at channel bifurcation and confluence points. It would appear that the topographic character of anabranching sites efficiently manages flood flow energy, activating secondary channels and low elevation areas to distribute flood flows. These findings contrast with the hydraulic data from an adjacent single-thread reach, characterised by flood flows concentrated in-channel creating a high erosive potential. We propose that anabranching rivers could play an important role in natural flood and sediment management in many UK river systems.

Citation

Entwistle, N., Heritage, G., & Milan, D. (2018). Flood energy dissipation in anabranching channels. River Research and Applications, 34(7), 709-720. https://doi.org/10.1002/rra.3299

• Journal Article Type: Article
• Acceptance Date: Apr 6, 2018
• Online Publication Date: Jul 20, 2018
• Publication Date: Jul 20, 2018
• Deposit Date: May 15, 2018
• Publicly Available Date: Jul 20, 2019
• Journal: River Research and Applications
• Print ISSN: 1535-1459
• Publisher: Wiley
• Volume: 34
• Issue: 7
• Pages: 709-720
• DOI: https://doi.org/10.1002/rra.3299
• Publisher URL: https://doi.org/10.1002/rra.3299
• Related Public URLs: https://onlinelibrary.wiley.com/journal/15351467