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Re-introduction of structurally complex wood jams promotes channel and habitat recovery from overwidening: Implications for river conservation

Henshaw, Alexander J.; Harvey, Gemma L.; Sayer, Carl D.; Parker, Chris

Authors

Alexander J. Henshaw

Gemma L. Harvey

Carl D. Sayer

Chris Parker Chris2.Parker@uwe.ac.uk
Senior Lecturer in Physical Geography



Abstract

Copyright © 2017 John Wiley & Sons, Ltd. Large wood is a powerful geomorphic agent in rivers, providing important habitat functions for a range of aquatic organisms, but has been subject to a long history of removal. Internationally, approaches to river restoration are increasingly incorporating large wood features, but generally favour simple flow deflectors (e.g. single logs, stripped of branches and anchored in place) over more complex structures that more accurately mimic natural wood jams. This paper explores channel response to wood-based restoration of an overwidened lowland chalk stream that incorporated whole felled trees. Hydraulics, sediment, topography and vegetation data were assessed for a 3year period for two restored reaches: an upstream reach where pre-restoration baseline data were obtained, and a downstream reach restored before data collection. Where pre-restoration data were available, the introduction of wood jams generated sediment deposition within jams leading to the development of vegetated marginal ‘benches’ and bed scour in adjacent areas of flow convergence. Patterns were less clear in the downstream reach, where restoration design was less ambitious and outcomes may have been affected by subsequent restoration work upstream. The results indicate that reintroduction of large wood (whole trees), can promote channel and habitat recovery from overwidening in lowland rivers, creating important ecological benefits through the provision of structurally complex marginal habitat and associated food resources. Longer-term assessments are required to establish whether the trajectories of change are persistent. The work emphasizes the effectiveness of restoration approaches that aim to ‘work with nature’. The ambitious design, incorporating structurally complex wood jams, was also low-cost, using materials available from the river corridor (existing riparian trees). Furthermore, ecosystem engineering effects were amplified by the colonization of wood jams by aquatic vegetation. The approach should, therefore, be transferable to other lowland rivers, subject to wider catchment constraints.

Citation

Sayer, C. D., Henshaw, A. J., Harvey, G. L., Harvey, G., Henshaw, A., Parker, C., & Sayer, C. (2018). Re-introduction of structurally complex wood jams promotes channel and habitat recovery from overwidening: Implications for river conservation. Aquatic Conservation: Marine and Freshwater Ecosystems, 28(2), 395-407. https://doi.org/10.1002/aqc.2824

Journal Article Type Article
Acceptance Date Jul 5, 2017
Publication Date Apr 1, 2018
Journal Aquatic Conservation: Marine and Freshwater Ecosystems
Print ISSN 1052-7613
Electronic ISSN 1099-0755
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 28
Issue 2
Pages 395-407
DOI https://doi.org/10.1002/aqc.2824
Keywords river, stream, restoration, catchment management, vegetation
Public URL https://uwe-repository.worktribe.com/output/883442
Publisher URL http://dx.doi.org/10.1002/aqc.2824
Additional Information Additional Information : This is the peer reviewed version of the following article: [Harvey, G., Henshaw, A., Parker, C. and Sayer, C. (2017) Re-introduction of structurally complex wood jams promotes channel and habitat recovery from overwidening: Implications for river conservation. Aquatic Conservation: Marine and Freshwater Ecosystems, 28 (2). pp. 395-407. ISSN 1052-7613], which has been published in final form at http://dx.doi.org/10.1002/aqc.2824. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

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