Case study:Salmons Brook River Restoration at Laymer Road

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Location: 51° 37' 45.55" N, 0° 4' 0.80" W

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Project overview

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Status	Planned
Project web site
Themes	Fisheries, Flood risk management, Habitat and biodiversity, Social benefits
Country	England
Main contact forename	John
Main contact surname	Bryden
Main contact user ID
Contact organisation	Environment Agency
Contact organisation web site	http://www.gov.uk/government/organisations/environment-agency
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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This stretch of river has been subject to a previous project undertaken by the Environment Agency’s predecessors the National Rivers Authority in 1994. This installed 5 small weirs and a toe boarding along a significant length of the river. These structures would now be seen as inappropriate due to the their impact on the morphology of the stream and the requirements of the Thames River Basin Management Plan. The proposal therefore is to removal the silt traps, regrade banks, meander river and remove the check weirs and toe boarding.

The Salmons Brook is an urban river running through Enfield, London. The river has large number of issues including water quality due to urban diffused pollution and physical modifications including weirs and hard banks. For this reason the catchment (water body) has been designated as Heavily Modified for urbanisation and flood protection in the Thames River Basin Management Plan with a target of getting the river into Good Ecological Potential by 2027. The section of river from the A10 (TQ3342994308) to Latymer Rd (TQ3389694053), has been identified as section which could be improved relatively significantly through relatively minor interventions. Once the river exists the A10 culvert it passes between 2 allotments with a small footpath running on top of the left bank. At the end of the allotments there’s a footbridge across the river where the left bank opens into a small recreation ground, with the right bank being a housing estate. The informal footpath follows the top of the left bank to Latymer Rd dividing the river from the a junior school.

The investigation needed to be completed and costed by April 2011. The consultants (whoever wins the work) will be required to undertake a detailed level survey of this stretch of river and develop options to remove these structures and restore the river to a natural morphology. The consultants should look to develop only in channel options as its not feasible to meander the channel – although regrading might be viable in some areas. Its believed that there should be two options produced 1) Complete removal or notching of the weirs, 2) replacement of the weir’s by a series of fixed gravel riffles. However if the consultants believe that there would be another viable option then they should fully investigate and present this. The consultants will also be required to investigate if the toe boarding can be removed as well.

Aspects to consider with the investigation include the reason for the installation (erosion control) of the structures and the future consequence of there removal on the surrounding areas. The consultants also need to consider cost of instillation as there is a limited budget available for installation and therefore a cost efficient solutions needs to be developed.

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Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Thames River basin London Subcatchment River name Salmons Brook Area category 10 - 100 km² Area (km2) Maximum altitude category 100 - 200 m Maximum altitude (m) 136136 m <br />0.136 km <br />13,600 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Suburban Waterbody ID GB106038027960 Other case studies in this subcatchment: Alma Road Rain Gardens, Bury Lodge Wetlands, Enfield Town Park Wetlands, Glenbrook Wetlands, Grovelands Park Wetlands, Houndsden Road Rain Gardens, Laymer Road Silt Trap and Recreational Ground, Rewilding Enfield's Urban Rivers, Salmons Brook Flood Alleviation Scheme, Montagu Recreation Ground site, Salmons Brook at Grange Park Site Edit site Name WFD water body codes GB106038027960 WFD (national) typology WFD water body name Salmons Brook Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Protected species present No Invasive species present No Species of interest Dominant hydrology Dominant substrate River corridor land use Average bankfull channel width category Average bankfull channel width (m) Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 500 m0.5 km <br />50,000 cm <br /> Project started 2008/01/01 Works started Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Flood risk management, Pollution incident, Urbanisation Hydromorphology Continuity for sediments, Channel pattern/planform, Substrate conditions Biology Physico-chemical Specific non-synthetic pollutants, Specific synthetic pollutants Other reasons for the project Recreation Measures Edit Measures Structural measures Bank/bed modifications Toeboard removal, Weir removal Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Improved public access Other Economic benefits Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information