January 2022 Herts & Middlesex Wildlife Trust

FiveRivers were contracted by Herts and Middlesex Wildlife Trust (HMWT) to develop a river restoration scheme within the Upper Lea operational catchment, specifically focusing on the River Lea, part of the Lee Water Body under the Water Framework Directive. Currently rated as ‘Moderate Ecological Status’ due to sewage discharge issues, the river fails to achieve ‘Good Ecological Status’. The project aimed to enhance the river’s physical condition to bolster resilience against low-flows and floods, while fostering macrophytes, invertebrates, and healthy fish populations. Priority riparian wetland habitats was targeted for improvement to support diverse avian, invertebrate, and mammalian populations.

Project requirements

The problem

The project spanned two kilometers of the River Lea, divided into four distinct sites: Lemsford Springs, Stanborough North, Stanborough South, and Stanborough Reedmarsh.

Lemsford Springs, situated within a HMWT nature reserve, features a semi-natural river course alongside a freshwater lagoon primarily managed as a watercress bed.

Stanborough North and South sites are characterised by recreational amenities and artificial modifications, including a boating lake and straightened river sections. The final site, Stanborough Reedmarsh, hosts a local nature reserve with a Reedmarsh ecosystem fed by natural springs, though some have ceased to flow, leading to habitat degradation.

Our approach

The solution

Following a number of site investigations and extensive consultation with Herts & Middlesex Wildlife Trust (HMWT), we created concept and detailed designs for each site.

At Lemsford Springs Reserve:

We designed bank protection and reinstatement measures along sections prone to erosion and piping, safeguarding water quality within the reserve’s lagoons. This included creating earth/brash berms on outer meanders where there is erosive pressure, coupled with hard logs deflectors and small area of channel resectioning and waterproof the bund. Further bank protection and reinstatement works were proposed through the installation of coir matting and hydroseeding to encourage vegetation establishment.

Replacement of a timber bridge deck with anti-slip boards, installation of a new boardwalk to replace a natural footpath causing excessive bank erosion and the replacement of an existing failed section of boardwalk over one of the reserves lagoons. We also included for the replacement of failing sections of Nicospan revetment with brushwood berms.

At Stanborough Reedmarsh:

We proposed tree works along channel banks to improve daylighting and acquire materials for natural in-channel features, including brushwood berms and large woody material deflectors. 100 meters of otter fencing was also specified on both sides of the River Lea downstream of A1(M) to encourage otter migation through a tunnel culvert under the motorway. Earth-filled berms with brushwood substructure were also included within the design to protect and reinstate poached bank areas and improve Angling  access. Bat and wagtail boxes were also included under the road bridge to provide nesting and roosting opportunities.

Within the adjacent Reedmarsh, hydrology enhancements were proposed including Reedmarsh lowering, ditch network restoration through timber channel blocks, willow carr management and additional wetland features to improve the priority habitat.

Works at Lemsford Springs and Stanborough  Reedmarsh will progress through to construction this autumn delivered by FiveRivers in-house Build team.

Project outcomes

The results

Upon completion of the River Lea river restoration, significant outcomes were achieved at Lemsford Springs Reserve and Stanborough Reedmarsh.

At Lemsford Springs Reserve, comprehensive Soft / green bank protection measures were implemented with further works preventing potential breaches and enhanced vegetation.

At Stanborough Reedmarsh, improvements were made to the habitat through:

  • Tree works improving habitat complexity
  • 100m Otter fencing supported species conservation efforts.
  • Earth-filled berms were constructed
  • Bat and wagtail boxes were installed to provide nesting opportunities.
  • Timber channel blocks enhanced hydrology in the reedbed drainage channels.

This has been a complicated project to manage and design given the number and diversity of interested parties to satisfy, including an Angling Club, Local Authority and Leisure Company, and has taken several years to complete. FiveRivers have been very patient and good about incorporating changes to the designs all the way through the project, following further stakeholder and EA consultation. We are pleased we now have a jointly agreed plan that will enhance the resilience of a much-loved river and better connect two important wetland nature reserves for wildlife. We look forward to monitoring the outcomes and successes in years to come.

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Luke Roberts - Design & Construction General Manager at FiveRivers (5R)

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Luke Roberts

Design & Construction General Manager

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