Green-tech helps to reduce the risk of flooding in Leeds

Project: Leeds Flood Alleviation Scheme Phase 2

Location: Leeds, West Yorkshire

Client: Leeds City Council

Main Contractor: BMMjv (BAM Nuttall/Mott MacDonald Joint Venture)

Landscape Architect: BMMjv (BAM Nuttall/Mott MacDonald Joint Venture)

Products/Services Supplied: Coir Edge Sods, Coir Log Rolls, Rock Rolls

Leeds City Council is working with the Environment Agency on their Flood Alleviation Scheme Phase 2 (FAS2) to reduce the risk of flooding of a 14km stretch between Leeds Train Station and Apperley Bridge.

The project is designed to protect 1,048 homes and 474 businesses through a combination of traditional engineering methods and natural flood management. Due for completion in Spring 2024, it is expected that the flood risk will be reduced to a 0.5% probability of occurring in any given year (a 1-in-200-year level of flood protection).

BAM Nuttall is a construction and civil engineering company that delivers key pieces of infrastructure across the UK, from railways to wind farms. They use digital engineering and a net zero carbon approach, placing sustainability at their core.

Part of the scheme included work on the bank of the river Aire upstream of Kirkstall Bridge using an earth embankment or steel sheet piled flood walls in some areas. The embankment will tie into flood walls, that will extend up to the existing Kirkstall Bridge. This section of railway line connects Leeds with Shipley and Bradford and has flooded several times in the past, and currently remains at risk.

Alongside the embankment and flood walls, 2.4 hectares of landscape and ecological enhancements are being implemented in Kirkstall Meadows. This work includes the creation of wetland scrapes and various interventions to support local wildlife.

The project was subject to planning conditions that required reinstatement or protection of vegetated features along the riverbank where the construction of hard flood defences would otherwise have compromised the permanent river-side ecology.

Sub-agent Jim Mitchell, comments, “Green-tech was chosen as the products they offered were designed exactly for this purpose. They were able to supply products that complied with the project specification and offered expert advice on alternative solutions that improved buildability and function’.

For this part of the project, Green-tech supplied 45 pre-established Coir Edge Sods which comprise 5 different aquatic plant species mixes. This unique system incorporates pre-established vegetation within the face of stone-filled gabions which is an integral part of the erosion control solution for a water’s edge, even where the projects require hard engineering solutions. This innovative, green erosion control system helps when the stability of engineering with gabions is combined with the benefits of immediate vegetation to provide rapid environmental and ecological regeneration.

20 gt Coir Log Rolls were supplied. These are cost-effective and an excellent technique for establishing marginal vegetation around lake edges, streams, and river banks. Compressed coir fibre encased in woven polyethylene or coir netting, gt Coir Log Rolls can be supplied pre-established with UK native species or unplanted.

These were accompanied by 20 gt Rock Rolls - designed to help reduce and prevent long-term erosion and allow for the ground to stay stabilised. Commonly used around watercourse shorelines, high-flow riverbanks, and streams, gt Rock Rolls are UV-stabilised polypropylene mesh filled with gabion stones. They are ideal for creating a solid foundation for installing pre-vegetated coir products - the roots of the emergent plants grow into the voids of the rock rolls, giving long-term erosion control and bank support. Gt Rock Rolls installed below coir units can also be used to support a filter fabric or biodegradable matting.