Case study:Arnos Park - Pymmes Brook

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Location: 51° 37' 16", -0° 8' 9"
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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. The first step would be to carry out a feasibility study of the Pymmes Brook 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. An application has been made to the London Mayors Parks Programme (need to see if this project gets funding from this). Get partners together discuss desires for the park and constraints, design and estimate costs and estimate the finances available to the project.

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

Catchment

River basin district Thames
River basin London

Subcatchment

River name Pymmes Brook (upper channel with Muswell St & Bounds Grn Brk)
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 131
131 m
0.131 km
13,100 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Suburban
Waterbody ID GB106038027940



Other case studies in this subcatchment: Friary Park, Friern Barnet Former Sewage Works, Merdian Water development site, Parks between A10 and Melville Gardens, Pymmes Brook and new river crossing point, Weir removal at Tile Kiln Park, Wilmer Way School Playing Field


Site

Name
WFD water body codes GB106038027940
WFD (national) typology
WFD water body name Pymmes Brook (upper channel with Muswell St & Bounds Grn Brk)
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

Reach length directly affected (m) 1000 m
1 km
100,000 cm
Project started 2008/01/01
Works started
Works completed
Project completed
Total cost category
Total cost (k€)
Benefit to cost ratio
Funding sources Environment Agency Grant in Aid, Local Authorities, Greater London Authority

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

Mitigation of a pressure
Hydromorphology Channel pattern/planform
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications Creation of berms, Barrier removal, Embankment renaturalization, Creation of low flow channel, Creation of backwaters
Floodplain / River corridor River naturalisation, Scrapes, Floodplain reconnection, Remeandering
Planform / Channel pattern
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
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Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



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Additional links and references

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Supplementary Information

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