May 2020 - April 2021 Herts and Middlesex Wildlife Trust (HMWT)

FiveRivers were contracted by Herts and Middlesex Wildlife Trust to undertake an options and detailed designs appraisal and plan for river restoration improvements to a 7km reach of the River Ash in Hertfordshire.

The River Ash, one of the 240 chalk rivers in the UK, suffers from the pressures of over-abstraction, agriculture, impacts from sewerage, historic modifications/alterations and degraded habitat.

Project requirements

The problem

The 7km reach identified for options and detailed design works was owned and managed by the Easneye Estate, who with HMWT, wanted to see the river improved and detailed designs undertaken to provide an ‘off the shelf solution’.

The river, as mentioned, suffers from the pressures of over-abstraction, agriculture, impacts from sewerage, historic modifications/alterations and degraded habitat.

Using our extensive knowledge of designing and delivering improvements on degraded chalk stream habitats, FiveRivers were tasked with designing challenging solutions and alterations that would improve the habitat of the Ash.

Both specialist and smaller more volunteer friendly installation activities were requested to allow for a range of mechanisms for delivery of the scheme when designed.

Our approach

The solution

Dividing the 7km reach into easily identifiable sub reaches, that could be designed and submitted for consent independently, FiveRivers started by undertaking catchment walkovers with all stakeholders to determine key drivers and pressures along the 7km reach as well as understanding any constraints and previous works that may have already be undertaken. Following this initial phase technical details for improvements were drawn up and an options appraisal report produced with suggestions for enhancements on each sub reach as well as detailing findings on constraints from a desktop analysis (including hyrdology, flood risk, designated sites, heritage and archaeology, geomorphic character, ecology) and budgetary construction costings for each technique. Multiple options were suggested for each sub reach with both challenging and conventional ideas put forward for discussion. These included:

  • Bank regrading
  • Creation of inset floodplains
  • Creation of wetland scrapes and wetland pond features
  • Ditch blocking
  • Backwater creation,
  • In channel berm creation
  • Large Woody Material installation
  • Gravel riffle installation
  • Undertaking tree works to reduce shading
  • Undertaking tree planting to increase shading
  • Removal of concrete in channel structures
  • Reinstating old paleo channel
  • Hibernacula creation
Project outcomes

The results

Following agreement with stakeholders of the proposed alterations and improvements in each sub reach, the outline designs were formalised, drawn up and presented for approval. Qualitative risk assessments and, where required, quantitative flood risk modelling was also undertaken to ensure the designs had no impact on localised or downstream water levels. Construction costs were also provided to ensure any future funding bids undertaken to allow for installation were accurate. All designs, once finalised, were drawn to CDM2015 regulations to include information important to pass on in the design phases to the contractor.

All designs were submitted for consent with the Environment Agency and approved.

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Discuss your needs
Restoration of the River Ash is an aspiration that the Trust has been working on with the Easneye Estate and Environment Agency for many years. At the point the Trust commissioned FiveRivers, we had delivered some small-scale improvements as a partnership, but knew we wanted to go further in terms of collective ambitions for the river and its floodplain. Having the expertise and technical capability of FiveRivers to prepare a construction ready detailed design plan was integral. Their team really understood what we wanted to achieve and were able to factor in complexities of surrounding land use to come up with a design that suited all parties involved. Their competency was trusted by the landowner and the result is a fully permitted scheme that we have been delivering in stages as funding permits, owing to FiveRivers ability to manipulate the design into bite-size deliverable chunks. We are looking forward to seeing the scheme fully implemented over the next few years.
Sarah Perry, River Catchment Coordinator at HMWT
Luke Roberts - Design & Construction General Manager at FiveRivers (5R)

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Looking to talk to an expert?

Luke Roberts

Design & Construction General Manager

Get in touch by either phone or email to speak with Luke and discuss your needs.