Case study:Alma Road Rain Gardens

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Location: 51° 38' 47.70" N, 0° 2' 3.53" W

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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	http://enfield.gov.uk/
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 projects	No

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.

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File:LBE233 - 101.pdf

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: 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 Site Edit site 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) 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) 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 Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Flood risk management, Urbanisation, Poor Water Quality Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures 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) 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