Hilton Grace Woods Flood Alleviation Scheme

Introduction

Hilton Grace Woods is a small community woodland nestled within the housing estates of North Halewood. Its unique shape creates long woodland avenues that define the character of the site. The site is owned by Knowsley Council.

In 2020/2021 an issue of flooding was reported coming from the wooded greenspace and as a result was flooding the gardens of residential properties of Yelverton Close (6 properties). These houses are located north of the site and their gardens are at the base of a shallow sloped green space. During periods of heavy rainfall, surface water would drain from saturated ground in the grassed areas of the site and pool up on low ground between the access path and the Yelverton Close properties. With the properties being on a lower level than the path, the water would naturally build up against the boundary fence and generate surface water flow into the residential gardens. These flooding issues to various extents have been occurring regularly, but increasingly so every winter.

Pre Construction, During Construction and Post Construction images

Pre Construction

During Construction

Post Construction

Project Design Strategy

With no drainage connections possible, the scheme’s strategy was to limit the flooding of the properties by using the path to create a barrier and a scrape to hold the water away from the houses. This has involved raising the path running behind and parallel to Yelverton Close properties. In sealing its surface with tarmac and cross falling the water away from the properties, a barrier has been created, minimising the surface water flowing to the houses and instead directing the water towards an adjacent land drain. This in turn feeds into a wetland scrape which increases the water holding capacity of the site away from the housing.

The benefit of the simple design is the three defences to flooding. Firstly, in initial heavy rainfall events, the scrape fills up. Secondly, when the rainfall event is prolonged, the land drain has water holding capacity. Then thirdly, in extreme conditions, when both scrape and land drain are at capacity the path itself will hold the water back from the properties, enabling the flood to form a wet woodland area.

The wetland scrape will enable the scheme to have environmental benefits as this will help increase the biodiversity of the site’s habitat. As holding the water in one location while it slowly dissipates will make the scrape a seasonal wetland habitat enabling differing species to establish.

Project Key Milestones

In 2023, in consultation with the in-house Council team, WSP consultants designed the scheme up to the production information stage, with the new raised path and wetland scrape to deal with heavy rainfall periods on site.

With a successful application to access the Environment Agency Quick win funding, the project was given the go ahead in summer 2024.

Following a simple tender process, this scheme was successfully completed in August 2024.

Contact Details

Email address: ess.enquiries@knowsley.gov.uk

Disclaimer

Information on this page has been provided by Knowsley Metropolitan Borough Council and was correct at the time of upload. The Flood Hub is not responsible for any information held on this page. For any enquiries, see the Contact section of the page.