England & Wales Climate action and sustainable development

Flood mitigation in Waltham Forest, London: Innovative flood resilience efforts and sustainable solutions

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Waltham Forest Council shares how they are proactively addressing flood risks to the community after experiencing £16m in flood damage in 2021. In the aftermath, they have enhanced flood resilience through natural mitigation, road transformation, and household actions, like installing water butts. Efforts include wetland creation and local road alterations for sustainable drainage, all to reduce risk and promote community engagement in one of the most diverse and densely populated London boroughs.

Summary

In 2021, heavy rainfall overwhelmed the drains and caused £16m in flood damage, including serious water damage to 28 local schools. We know extreme rainfall events are becoming more frequent and that the effects won’t be felt equally; people in deprived areas are the worst affected.

That’s why, at Waltham Forest Council we are taking action. We are working with local community groups to build flood resilience in three ways:

  1. Natural flood mitigation
  2. Transforming local roads
  3. Direct household action

What did we do?

Although the largest reductions in flood risk are likely to come from capital investment. Our ‘Lower Floods’ project offered to install specially adapted self-emptying water butts and low-cost water-saving devices at residents’ homes. The water butts were adapted and installed by our own in-house company Service Store.

What was the impact?

We estimate that the 1,000 installations could slow 150,000L of water during each heavy rainfall event. The Council’s partnership with the National Flood Forum helped build fantastic engagement with local community groups. As a result, ‘word of mouth’ was the main reason for the uptake by residents. Household action can offer a better cost benefit (litres per £) and build support for future action.

Flood mitigation in Waltham Forest

Waltham Forest is a Borough in the North East of London. It is the most densely populated outer London Borough and home to an estimated 278,400 residents. It is also one of the most diverse areas in the country with regard to ethnicity, and Waltham Forest is ranked 12th most deprived of the 32 London Boroughs.

Heavy rainfall in Waltham Forest in the summer of 2021 overwhelmed the drainage network and resulted in more than £16.4m in flood damage. The storm intensity and severity equated to a 170-year return period in some places. As extreme rainfall events become more frequent, the capacity of the surface sewer network is more often exceeded (typically designed to withstand only 1 in 30 year events).

There is a known inequality with regard to social deprivation and people worst affected by flooding, and deprivation also constrains community preparedness when these events occur. The Council is responding to this by working with local community groups and partners to build resilience across the borough through a range of initiatives around delivering natural flood mitigation projects to reduce flood risk to properties and commercial premises. These initiatives involve:

Constructed wetlands, basins, and swales enhance amenity space to improve water quality and biodiversity

The South Chingford Flood Mitigation Project (derived from the South Chingford Flood Study Report) has completed three schemes:

  1. Rolls Sports Ground
  2. Memorial Park
  3. Larkswood Playing Field

The project will completely remove 64 properties from flood risk from a storm event, which has a 5% chance of occurring each year, and 72 properties from a storm event, which has a 1% chance of occurring each year. Another 821 properties will also receive a reduction in flood risk.

The Chestnuts Field Flood Mitigation project will include the creation of a vibrant wetland ecosystem in the heart of Walthamstow. The scheme comprises three interconnected wetland basins providing 2750 m3 of attenuation. The scheme has been thoughtfully designed with the community in mind – with two new viewing platforms and seating areas, people can relax and enjoy the views of the new wetland amenity area. This transformative project will include new planting and improvements to the public highway on Spruce Hills Road and Sturge Avenue. This will reduce flood risk to local properties by introducing new carriageway levels and a raised junction table that is designed to divert surface water towards the Wetlands. The Council intends to create a nature trail route to illustrate the wildlife flood mitigation benefits for community interaction.

The Fillebrook Flood Alleviation Scheme provides flood mitigation over two sites:

  • Phase 1 at Leyton Sixth Form College
  • Phase 2 within the new Fillebrook Park at the Whipps Cross redevelopment site

The benefits will reduce the flood risk to residential and non-residential properties in the immediate and downstream area and provide amenity, biodiversity, ecology, habitat enhancement and educational value. At Whipps Cross Hospital, a series of six basins, six swales, and ten tanks, giving a total storage volume of 2,260m3, will be provided. This will capture overland surface water flows from the Fillebrook catchment. At Leyton Sixth Form College, a single swale and tank will provide additional surface water capacity to complement the flood mitigation scheme at the Whipps Cross Hospital site. The scheme sits at the edge of the College’s playing field. With a traffic-calming raised road surface it will divert surface water from Peterborough Road to the proposed scheme.

Transforming local roads that are susceptible to flooding to include Sustainable Drainage (SuDS) and storm water storage

Local highway transformations like Esther Road and Kings Passage include permeable paving and raingardens, which enhance walking and cycling opportunities in the area. Raingardens along Forest Road to Blackhorse Road station form a naturalised corridor leading to Walthamstow Wetlands.

Brooke Road, Oliver Road, Chestnut Avenue North and Chestnut Avenue South scheme was developed due to severe local flooding during the summer storms of 2021/2022. Local properties and St Mary’s Primary School were severely flooded, causing major flood damage and disruption to the area. A scheme was developed, jointly funded by Waltham Forest Council, Thames Water and the Department of Education. This project consisted of the introduction of a permeable pavement with below-ground attenuation tanks in Brooke Road/Oliver Road and with raingardens provided adjacent to the school. Also, a permeable road pavement was provided to Chestnut Avenue North and South, supplemented by the introduction of rain planter units within the school. The scheme provided a total attenuation capacity of around 500m3.

The National Flood Forum engaged with the local community, and the communities’ views on the proposed schemes were sought through a public engagement programme that used drop-in sessions at local venues to obtain feedback on the scheme proposals.

Supporting direct household and community action

As noted above, the most significant reductions in the likelihood of flooding are expected to come from capital investment schemes, however, flood mitigation doesn’t stop there. Waltham Council has been proactively encouraging collective community action to address climate-related challenges. These types of projects can offer a better cost benefit ratio to capital schemes (£ per litres saved) and bring positive engagement to generate momentum.

The Lower Floods project has been doing just this by installing low-cost water-saving devices in homes, such as tap aerators and specially adapted self-emptying water butts. Using funding from the North London Waste Authority has meant it’s free of charge to residents in specific parts of the Borough. The Council’s partnership with the National Flood Forum has enabled close engagement with local community groups, leading to high levels of participation from residents. The delivery partner is the Council’s own in-house contractor Service Store. Their adaptive approach and quick response time have been a key part of successfully following through from sign-ups to installs. A proactive door-knocking approach when the Service Store is on the streets undertaking installs has encouraged neighbours to sign up. ‘Word of mouth’ is proven to be the main reason for uptake by residents. The project has gained enthusiastic support locally, residents are motivated to collectively reduce the risk of future flooding in homes. Each 210L water butt can capture and slow the first 15mm of flood water that lands on a typical 20m2 of roof. It’s estimated that the 1,000 installations could slow 150,000L of water during each heavy rainfall event.

A community-led flood mitigation scheme at Greenway Avenue is being developed with local community residents and Walthamstow Cricket Club. This scheme includes the introduction of retrofit SuDS features, including swales, detention basins, reprofiling and shaping of the existing drainage ditch to laneway, reprofiling of the laneway surfacing, and the installation of rainplanter units to local properties and the Cricket Club. Greenway Avenue residents and the Cricket Club were badly affected by flooding during the summer storms in 2021/2022.

Clustering projects in areas of high flood risk: Complementary to Lower Floods is an innovation project led by Thames Water and funded by Ofwat – offering free rainwater planters to local residents in specific streets to help ‘slow the flow’ of rainwater into the sewer system. The purpose of these modular devices is twofold; to help prevent flooding by attenuating rainwater runoff from roofs and to provide some rainwater for reuse. The rainwater planter does this with two tanks: one of them is a permanent water reservoir which holds 30 litres, and the other is a larger 235 litre tank which slowly self-drains to ensure there is capacity in the tank for the next storm. This project tested social and financial incentives to encourage residents to install these devices, as well as utilising the Our Rainwater digital platform. By clustering the installs in streets with high flood risk, these projects work together to reduce stormwater entering the sewers to avoid exceedance events.

Comment

The Council has learned that empowering individuals to tackle community flood risk can be effective in efforts to scale up solutions across communities. This is done twofold: first, by utilising community communication channels, and second, by amplifying resident-focused narratives. Sharing personal stories from residents on their experience of past flooding and illustrating how neighbours can help by installing water-saving devices and welcoming SuDS schemes in their local road network has contributed to better awareness of flood mitigation potential and higher participation across the borough.



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