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Rapport Année : 2018

Review of good practice in managing riverbank instability and erosion

Résumé

1. Rivers are dynamic elements of the landscape that, almost by definition, erode. They exist in a state that is often termed a ‘dynamic equilibrium’; i.e. they are not stable, but range within certain bounds. These natural bounds form the starting point for recognising when erosion is excessive and, consequently, when intervention may be needed. Intervention can be at the catchment, corridor or river reach scale. 2. Before specific measures are implemented, it is important to understand the causes of any unexpected erosion. This understanding should be developed as part of a formalised project management framework that starts with the definition of project objectives, followed by agreement on how project success is defined. Appropriate interventions can then be identified based on monitoring and diagnosis that is focussed on identifying the causes of the erosion. The framework also provides the mechanism for post-project appraisal and adaptive management, whereby new objectives can be defined and, if necessary, new or modified interventions developed. 3. Very often the problems of localised erosion can be attributed to activities upstream or within the catchment; often they are a response to cumulative activities of changes. Consequently, interventions that can be considered as being sustainable frequently involve better catchment management, especially related to land use activities and associated runoff. The need to allow rivers to erode within their natural bounds is recognised in corridor-scale approaches to management, exemplified by the ‘freedom space’ concept of Piégay et al. (1997). This involves, for example, better spatial zonation of floodplain activities, retaining some areas for agriculture or development but ‘giving other areas back to the river’. Even when localised intervention is deemed necessary, the long-term success of such measures will be facilitated by complementary actions at the catchment and/or corridor scales. 4. Historically, localised interventions have involved ‘hard engineering’. These are expensive, unsightly and frequently only partially successful. Badly conceived engineering may simply displace the problem (e.g. cause erosion downstream) or even exacerbate it. As a result, the last 2 decades have seen the emergence of so-called ‘soft’ or ‘bio-engineering’ approaches. These involve the use of a variety of plant materials, inserted or planted in ways that add cohesive strength to the banks and help dissipate the river’s energy. 5. Bio-engineering approaches that have been shown to be successful include the use of live fences, live palisades and root wads. All of these involve large woody species. Work in the tropics, including research in Malaysia, has provided lists of recommended native tree and shrubs species to use for these structures. In addition, the grass Vetiver (Chrysopogon zizaniodes L.) has been used widely in tropical regions to control erosion on steep slopes, both along roads and rivers. 6. Key to the success of bio-engineering approaches is ensuring that plants have time to establish and set down roots. This may involve constructing barriers to protect them from flow forces during the interim phase. Once established, these plants contribute to riparian biodiversity and can play important functional roles within this ecotone.
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Dates et versions

hal-04648840 , version 1 (15-07-2024)

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  • HAL Id : hal-04648840 , version 1

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Baptiste Marteau, Chris Gibbins, Ramon J. Batalla, Damià Vericat. Review of good practice in managing riverbank instability and erosion. WWF Malaisie. 2018. ⟨hal-04648840⟩
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