Remove or modify in-channel hydraulic structures

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Remove or modify in-channel hydraulic structures

Remove or modify in-channel hydraulic structures06. In-channel structure and substrate improvement

General description

In few words: Remove in-stream hard structures to allow natural processes to re-establish

Groynes or wing deflectors are commonly employed at rehabilitation projects as structures for modifying the dynamics and directing the flow, increase the complexity of the substrate and the water level. There are many kinds of wing deflectors, but rock and rock-filled log crib deflector structures are the most common. When they are placed in sand bed streams it might be needed to put a filter layer or geotextile underneath the deflector for a correct settlement.

Since they redirect the flow and narrow the width of the channel, microturbulences are created even at low flows. Sometimes these microturbulences alternate the sediments size distribution, diversifying the substrate structure and enhancing habitat diversity.

On the other hand, these structures might be degradation source, since the turbulences created and a higher flow velocity can cause streambanks and channel bed erosion (figure 1). The backwater effects would damage riffle areas if they are placed too near to upstream riffles. Flooding frequency and periods of inundation might be intensified by increasing channel roughness.

Applicability

Expected effect of measure on (including literature citations):

  • HYMO (general and specified per HYMO element)
  • physico � chemical parameters
  • Biota (general and specified per Biological quality elements)

Temporal and spatial response

Pressures that can be addressed by this measure

Cost-efficiency

Case studies where this measure has been applied

Useful references

Adam, P, N. Debiais and J. R. Malavois. 2007. Manuel de restauration hydromorphologique des cours d´eau. Fiche 3. Épis. Direction de l´eau, des milieux aquatiques et de l´agriculture (DEMAA) Service Eaux de Surface. L´Agence de l´eau Seine-Normandie.

Stream corridor Restoration: Principles, Processes and Practices. 2001. Federal Interagency Stream Restoration Working Group. USDA- Natural Resources Conservation Service

Other relevant information

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