Case study:Arnos Park - Pymmes Brook

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Location: 51° 37' 16.08" N, 0° 8' 8.59" W

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Project overview

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Status	Planned
Project web site
Themes	Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology, Social benefits, Urban
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	River Restoration Centre, London Borough of Enfield, London Wildlife Trust, Environment Agency, Greater London Authority
Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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To re-establish natural geomorphological features within the Pymmes Brook, including the creation of natural instream features, natural banks, wet berms, potentially wetland scrapes and wet grassland i.e. reconnecting the river with the surrounding habitats, its floodplain.

Potential work: The first step would be to carry out a feasibility study of the Pymmes though Arnos Park, including the surrounding landscape, defining the potential habitats which could be create and where. This would also give an idea of the cost and time scales involved. Depending on the outcomes of the feasibility study, a topography study of the area maybe needed if the its decide that wet scrapes and marshy areas should be created, thereby defining the works that would be needed to create these areas.

The North East Thames River restoration document highlights this area as having potential for full river restoration. The works should include the removal of all impounding structures and artificial embankments. Once this has been completed there should be a low flow channel created which meanders its way along the natural course of the Pymmes (may not be the current course, decided by a topographical study). Outside, the low flow channel a peak flow course should be created, this should include wet berms and setback flood defences to allow the river to naturally flood. These areas should contain back waters, wet berms, natural erosional cliff faces and wetland scrapes, which would significantly improve the biodiversity value of the area and the amenity value to local residents.

The Pymmes Brook is a clay-based river in a high-energy river catchment. Sections of the Pymmes Brook that resemble naturalised river forms exhibit characteristic features of a high-energy system, meanders, small meander cliffs, gravel bars and pool. The river through Arnos Park has been resectioned, constricted, has a concreted lining (in places) and contains a number of weirs which impound and stagnate the water, resulting in extremely poor water quality (GQA class E) as well as a lose of natural morphological features. Arnos Park has been designated as SINC Borough level 2 for it ancient woodland and damp grassland, the pymmes runs through the middle of the park and currently provides little ecological value, while the potential of the river remains huge. A Flood Risk Management project is being investigated for wider benefits and includes potential significant enhancements to this section of river.

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Catchment and subcatchment Select a catchment/subcatchment Site Edit site Name WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body National/international site designation Local/regional site designations Protected species present Invasive species present 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) 1000 m1 km <br />100,000 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 Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Other 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