Eggington Brook

Eggington Brook

Flood Alleviation and Defence

  • Client:

    Isaac Mercer (Client being TW/BDWNT)

  • Location:

    Eggington Brook, Clipstone

  • Sector:

    Water board - Residential

  • Project Value:

    £3 Million

Services:

Bridge Infrastructure Bulk Earthworks Grading and Excavation Groundworks Land Remediation Watercourse Realignment

Project Scope

  • Manage IDB Communications, Inspections, Approvals & Permits
  • Construction of new Earth Embankment Dam & Remedial Works
  • Ecology Mitigation Management
  • Temporary Works Design & Installation
  • Site Clearance (Remove of vegetation & HL culverts)
  • Construction & Installation of Drainage Culverts & Spillways
  • Application of Bridge Deck Waterproofing System
  • Application of Bituminous Emulsion Waterproofing
  • Install Guardrails To Culverts & Hydrological Features
  • Bulk Earthworks to Eastern Zone of the Reservoir
  • Engineered Fill to Form Dam Reservoir Emb. & Culvert Support
  • Installation of S104 & S38 Works & Rising Main & Services

Project Overview

Eggington Brook runs south of the village, northwest of Clipstone and approximately three miles east of Leighton Buzzard.

The team already deployed at Clipstone working with the client's agent Isaac Mercer gave merit to ECL winning this contract.

ECL was commissioned to build a solution to works recommended on Eggington Brook under the Reservoirs Act 1975.

These works included the upgrade of the flood defences in order to withstand a 1 in 100,000 projected annual flood with the new embankment dam to achieve an official Dam/Reservoir status. Further works also included the formation of the new access road crossing Eggington Brook to connect both sides of Leighton Buzzard from the linked road between Standbridge and Clipstone.

Works started in August 2021, and the fundamental success of this project relied heavily upon the formation of strong stakeholder relations and communications to ensure all works were immaculately executed in line with strict protocols. Our existing relationships with the local authorities and comprehension of their processes and procedures were essential to the success of this project.

Project Challenges

We worked closely alongside Dr Andy Hughes BSc (Hons) PhD DMS CEng FICE FCIWEM MIM, the country's foremost reservoir dam consultant. Managing monthly meetings with Dr Hughes, the Internal Drainage Board (IDB), the Lead Local Flood Authorities and others to ensure we achieved project goals and individual requirements and ultimately delivered the project whilst focusing on sustainable development to protect and enhance the local environment.

FLOOD MITIGATION METHODS A crucial element of this project was to increase the width and height of the embankment and lengthen the low-level culvert. Making these significant alterations to the embankment whilst safeguarding water levels in the area was challenging.

Project Outcome

Working in an existing flood zone meant rigorous working methods were systematically carried out to ensure the integrity of the embankment during the progress of works. Regular water level monitoring and liaising with IDB on upstream 'events' were key throughout the build process.

The project upgraded 800 meters of flood bank with new and recycled materials where possible. As a result, flood Protection is now in place for Leighton Buzzard and the surrounding area under the Reservoirs Act 1975. We continue to manage ongoing communications whilst we wait for the complexities of the legal agreement to achieve the reservoir dam status to be finalised. As with all projects, safety remained a priority, resulting in zero reportable injuries recorded.
The results of a large number of plate bearing & shear valve tests have been carried out very effectively. Work to the Embankment is nearing completion & the standard of workmanship appears good.

Dr Andy Hughes BSc (Hons) PhD DMS CEng FICE FCIWEM MIM

The low level culvert appeared to be in a good condition and the lining appeared to be in a good condition. The upper culvert appeared to be in a satisfactory condition with good line and level.

Dr Andy Hughes BSc (Hons) PhD DMS CEng FICE FCIWEM MIM

Engineered Fill to Form Dam Reservoir Emb. & Culvert Support
Construction & Installation of Drainage Culverts & Spillways
Compaction layers around headwalls of the Side embankment
Application of Bridge Deck Waterproofing System

COMPACTION CHALLENGES 

Quality impermeable compaction layers around the headwalls of the ‘Side’ embankment were critically important to ensure zero movement of the earthwork coming up from compaction.

A series of compacted layers, the subgrade surface layer and subbase layers, were manipulated to make them stable by sheep-foot rollers and tracked machines.

Regular plate bearing and hand shear vein tests were carried out and documented for each 200mm level, qualifying the placement and compaction of materials. Reports were conducted by Dr. Hughes and favourably communicated to the IDB.

Flood defence compaction layers at the headwalls of the 'Side' embankment

 

LINING OF UPPER CULVERT

It was important to ensure that the lining of the culverts would prevent water and debris from entering the space between the upper culverts and the underlying surface, both around the perimeter of the installation and along the joints. To achieve this, we arranged for a custom-made liner from Germany to be installed in the new culvert sections as well as the extended low-level culvert. The reservoir board inspected the lining and workmanship, and confirmed that it met all necessary standards.

 

LEADING EDGE OF THE FLOOD DEFENCE

We made the strategic decision to install the screens and ducts on the downstream edge of the embankment, behind the downstream kerb. This will effectively safeguard the leading edge of the flood defence from any potential impact during future works. Placing the services away from the ‘core’ area was a crucial step in ensuring the long-term effectiveness of the flood defence system.

 

IDENTIFYING POTENTIAL ENVIRONMENTAL HARM

The same core site team delivered the project throughout, benefiting the programme due to familiarity, consistency, and the full weight of their knowledge in flood alleviation and defence works.

Multiple types of monitoring and environmental measures were successfully carried out during the project cycle to identify the potential for environmental harm, including:

  • Dissolved oxygen monitoring when working within the watercourse.
  • Water level monitoring to combat any potential flood events.
  • Areas for vegetation growth were seeded with locally indigenous species to lend to the environment.

 

EROSION MITIGATION – TRAFFIC POINTS

To mitigate erosion from heavy maintenance traffic movement, we installed a reinforced concrete structure with voids for vegetation growth which we seeded with locally indigenous species.

Flood alleviation reinforced concrete structure

FLOOD ALLEVIATION & CARBON SAVINGS

Carbon emission savings were also made by the team, who actively sought to reduce our footprint throughout the project by:-

  • Recycling bulk earthworks – Using blue clay (Class 7a) harvested (borrow pit) from the Eastern Zone of the reservoir to help fill the embankment and culverts. 
  • Sourcing local subcontractors in our supply chain. 
  • Sourcing local materials, including aggregates from nearby quarries and concrete from a local plant.

 

WORKING RELATIONSHIPS

Throughout the project, we established a strong and effective partnership with Dr Andy Hughes and the IDB.

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