Case study:Pymmes Park Wetlands

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Location: 51° 37' 5", -0° 4' 16"
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Project overview

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Status Complete
Project web site
Themes Environmental flows and water resources, Flood risk management, Habitat and biodiversity, Monitoring, Social benefits, Water quality, Urban
Country England
Main contact forename Ian
Main contact surname Russell
Main contact user ID
Contact organisation London Borough of Enfield
Contact organisation web site
Partner organisations London Borough of Enfield, Friends of Pymmes Park, Thames21
Parent multi-site project

Case_study:Rewilding Enfield's Urban Rivers

This is a parent project
encompassing the following
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Project summary

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The Moore Brook, is a lost river, which drains a catchment area of roughly 350 hectares and flows from Winchmore Hill to Edmonton (Pymmes Park Lake) passing through Firs Farm Recreation Ground. As it drains a large catchment, the Moore Brook picks up a large amount of urban runoff contaminated with phosphates, nitrates, heavy metals, hydrocarbons and oils from footpaths and roads. It has been culverted since the 1950’s, and as a result has been prone to plumbing misconnections. This pollution accumulates throughout the catchment causing problems further downstream when it enters Pymmes Park Lake, and is particularly prominent during periods of dry weather. The London Borough of Enfield highlighted that the ongoing complaints from the smell and pollution of the lake required a holistic approach in managing. This lake directly outfalls into Pymmes Brook, one of the most polluted tributaries of the River Lea.

The London Borough of Enfield and Thames Water took on large scale project to resolve possible misconnections in the catchment. 800 misconnections were resolved, but to manage residual pollution from road runoff and additional misconnections a series of cascading wetland cells to capture dry weather flows, immobilise and filter pollutants from the stream before it entered the lake were introduced.

A total catchment of 294Ha is treated by the four cascading wetland cells. 216Ha of this catchment passes through the Firs Farm Wetlands, which introduces a “first treatment phases” upstream of the Lake. A total of 0.6Ha of wetlands has been constructed across the Moore Brook Catchment, in Pymmes Park and Firs Farm. As a result, Pymmes Park Wetlands filters around 85% of all dry weather flows entering the lake.

Monitoring surveys and results

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London Borough of Enfield has compiled pollution records and water quality data from the past, and has been collecting water quality data on Biological Oxygen Demand, Suspended Soilds and Nutrients for three years.

A Water Quality monitoring programme is now in place with Thames21, measuring parameters such as:

- Dissolved Oxygen and Biological Oxygen Demand

-Nutrients (nitrates, phosphates and ammonia)

- Faecal Coliforms

Lessons learnt

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Image gallery

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PP Construction 2.JPG
PP Before Planting.JPG
PP Planting Event.JPG
PP Planting.JPG
PP Lake cell.jpg
PP Planted wetlands.JPG
PP Looking north.JPG

Catchment and subcatchment


River basin district Thames
River basin London


River name Pymmes Brook (Salmons Brook to Lee, includes Part of Lee Navigation B)
Area category 10 - 100 km²
Area (km2)
Maximum altitude category Less than 100 m
Maximum altitude (m) 26
26 m
0.026 km
2,600 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Urban
Waterbody ID GB106038027910

Other case studies in this subcatchment: Firs Farm Wetlands


Name Pymmes Park Wetlands
WFD water body codes UKGB106038027910
WFD (national) typology
WFD water body name Pymmes Brook (Salmons Brook to Lee, includes Part of Lee Navigation B)
Pre-project morphology Closed culvert
Reference morphology
Desired post project morphology
Heavily modified water body Yes
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present No
Species of interest
Dominant hydrology Surface Water Runoff
Dominant substrate Clay, Gravel
River corridor land use Urban - Culverted, Parklands, Grassland
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)
Project started 2012/08/06
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

Reasons for river restoration

Mitigation of a pressure Poor Water Quality of Lake
Hydromorphology Quantity & dynamics of flow
Physico-chemical Oxygen balance, Nutrient concentrations, PH, Biological Oxygen Demand, Total Suspended Solids, Heavy Metals, Hydrocarbons
Other reasons for the project Improving Health and Wellbeing of local park users


Structural measures
Bank/bed modifications Deculverting, Ponds and pools inside the wetland
Floodplain / River corridor Reedbed creation, Creation of wetland, Deculverting, Extensive planting, Sustainable urban drainage ponds (SUDs), Floodplain creation
Planform / Channel pattern
Non-structural measures
Management interventions Reduced pollution
Social measures (incl. engagement) Community involvement, Community Education, Public amenity and perception


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
Before measures After measures Qualitative Quantitative

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

Additional documents and videos

Additional links and references

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Supplementary Information

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