Case study:Alma Road Rain Gardens

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Location: 51° 38' 48", -0° 2' 4"
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Project overview

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Status In progress
Project web site
Themes Environmental flows and water resources, Flood risk management, Habitat and biodiversity, Social benefits, Water quality, Urban
Country England
Main contact forename Jamie
Main contact surname Kukadia
Main contact user ID User:London Borough of Enfield
Contact organisation London Borough of Enfield
Contact organisation web site
Partner organisations Thames 21, Greater London Authority
Parent multi-site project

Case_study:Rewilding Enfield's Urban Rivers

This is a parent project
encompassing the following

File:Artsists Sketch.pdf

Project summary

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Alma Road is situated in Ponders End, a deprived area in the London Borough of Enfield. The area is known to suffer some localised surface water flooding, due to the impermeable nature of the surroundings created by the expanse of hard-surfaces, lack of green spaces and inadequate capacity in the existing drainage system.

This part of Enfield is generally low lying, as it forms part of the Lee Valley. The natural flow path to the nearby watercourse, Brimsdown Ditch, a tributary of the Salmons Brook/River Lee, is obstructed by the adjacent railway line and exacerbates surface water flood risk. When it rains the runoff from Alma Road picks up a large amount of pollutants, drains into the highways gullies and is fed into the Brimsdown Ditch.

Rain Gardens are a type of Sustainable Drainage (also known as “SuDS”) which mimics natural drainage by allowing water to soak naturally into the ground.

The project will retrofit five Rain Gardens into the highway realm, with a total area of 200m2 along a 200m stretch of Alma Road, with the aims of:

• Reducing surface water flood risk on the highway, as highlighted in the London Borough of Enfield’s Local Flood Risk Management Strategy (2015) • Water quality improvements to surface water runoff and the receiving Brimsdown Ditch by removing runoff from the conventional drainage system • Improving biodiversity by planting a wide variety of species • Horizontal traffic management by slowing down traffic in proximity to the school, bus stop and several wide junctions that are currently not pedestrian-friendly • Aesthetic enhancement of the road and the surrounding area • Improving public perception of SuDS through school and community engagement. • Inspiring more green infrastructure SuDS development across the borough

In later phases, the Alma Road Rain Gardens will be complemented by an additional 400m of SuDS features along the highway and across the 7Ha site of the Alma Regeneration Project.

Monitoring surveys and results

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The functionality of the Rain Gardens will be monitored by the Structures and Watercourses team from the London Borough of Enfield during and after rainfall events, and during dry weather spells.

Local perception of Sustainable Drainage Systems is also being noted. Alma Primary School have been particularly perceptive to the project and have engaged their pupils in "River" sessions with Thames21. As a result, the Primary School are keen to employ their own SuDS features within the school premises, and have already retrofitted several Thames21 Rainplanters intercepting roof runoff.

Lessons learnt

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Image gallery

File:LBE233 - 101.pdf

Artists Sketch.jpg

Catchment and subcatchment


River basin district Thames
River basin London


River name Salmons Brook
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 136
136 m
0.136 km
13,600 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Suburban
Waterbody ID GB106038027960

Other case studies in this subcatchment: 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 River Restoration at Laymer Road, Salmons Brook at Grange Park


Name Alma Road, Enfield
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 Yes
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present No
Species of interest
Dominant hydrology Quick run-off
Dominant substrate
River corridor land use Urban
Average bankfull channel width category
Average bankfull channel width (m)
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Project background

Reach length directly affected (m)
Project started 2015/04/01
Works started
Works completed
Project completed 2016/03/31
Total cost category
Total cost (k€)
Benefit to cost ratio
Funding sources 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

Reasons for river restoration

Mitigation of a pressure Flood risk management, Urbanisation, Poor Water Quality
Other reasons for the project


Structural measures
Bank/bed modifications
Floodplain / River corridor Sustainable urban drainage ponds (SUDs)
Planform / Channel pattern
Other Rain gardens
Non-structural measures
Management interventions
Social measures (incl. engagement)


Hydromorphological quality elements

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Before measures After measures Qualitative Quantitative

Biological quality elements

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Physico-chemical quality elements

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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

Additional documents and videos

Additional links and references

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Supplementary Information

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