The proposed work on this section of the Merriott stream has now taken place, with thanks to our project partners and local landowners. This can be seen in the video below...

 

 

Rational and project overview 

The Merriott catchment is classified as having poor ecological status because of low fish numbers; this is due to little available fish habitat, barriers to fish migration, and historic pollution events.  

One such barrier was a 280m-long culvert between the Flood Alleviation Scheme and the Mill House near Moorlands Road.  

The culverted field flooded in roughly the location where the new channel has now been developed.

 

We opened up the culvert and restored an open meandering stream - thus creating backwaters (to temporarily store flood water), fish passage easement features, and a riparian corridor of mosaic habitats. In addition, improvements have been made to the site and adjacent footpath for the benefit of local residents.

The new view of the river corridor habitat, as seen from the Flood Alleviation Dam (August 2023).

 

Detailed design

The detailed construction design was drawn up by Ghyston Engineering and Hydro-Morph and includes:

• Cross-sections and long-sections defining a new meandering channel that allows fish passage and improves floodplain connection, detailing suitable substrate for habitat creation and erosion reduction.
• Engineered step-pool ramps that gently lower the stream bed from the alleviation dam to the open channel at the upstream end as well as from the open channel back into the culvert at the downstream end, making the stretch passable for native fish. 
• A number of backwater areas to provide flood storage and wetland habitat. 
• Engineering drawings for a ford to allow for vehicle and livestock crossing.
• Planned construction phases, instructions to contractors, utilities and health and safety considerations. 
• Planting and habitat creation plan including securing logs in the stream, tree planting on the banks, and seeding a diverse meadow mix on disturbed ground. 

The overview design plan can be viewed by clicking here. 

The new step-pool ramps that gently lower the stream bed for native fish passage (July 2023).

 

Public access improvements

The footpath was improved by: 1) levelling and spreading stone on the surface towards the Flood Alleviation Dam 2) installing drainage ditches along the sides of the footpath and across into the stream feature near Mill House and 3) removing the hedge on the culvert side of the footpath in places of low habitat value. These measures have widened the footpath, improved the view of the field and removed the previous ‘tunnel feel’, and improved the ground conditions of the path allowing the use of the footpath in all weathers. 

 

 

Pre work surveys

Flood risk modelling

Flood risk modelling was contracted out to Edenvale Young. For flood events arising from between 1 in 2 and 1 in 100 year storm events, the models predicted flood reduction. The functioning of the alleviation dam- protection for events up to 1 in 25 years - remains unaffected. For extreme flood events (those in excess of the maximum expected once in 100 years, when the existing flood alleviation dam would be overwhelmed and Merriott already flooded) the model predicts a nil effect with possible minor increases in depth in certain areas (up to a maximum of 4cm flood depth on top of the baseline flood depth of >0.5m) and respective decreases elsewhere. Please note that the model’s inaccuracy level is ±2cm.

 

Preliminary ecological surveys

We carried out preliminary ecological surveys as well as species-specific surveys as required e.g., bat emergence surveys and eel surveys. 

Pre-work assessments determined that the grassland is semi improved with a few areas that are species rich, which were avoided during construction. The hedge between the footpath and the culvert field is mainly made up of non-native or non-valuable species. The few isolated bushes of spindle and dogwood in the hedge, as well as all other trees on site, have been retained. The site provides suitable habitat for reptiles like slow worms and grass snakes. Phased strimming was implemented to encourage reptiles out of construction areas. Whilst the potential of bats using the culvert was assessed as low, an emergence survey was conducted. Previous to the work, the site was not suitable for water voles and otters.

Drone image of the site previous to work. Image taken by Rob Treacher.

 

 

Consents

Planning Application was approved in February 2021, you can view the planning application including all engineering drawings by clicking here. 

Applications for Ordinary Watercourse Consent were also approved by the Somerset County Council in July 2020 and October 2022. 

 

 

Funding

The Merriott project is funded by multiple sources. 

The original development of this project was funded through the Hills to Levels Multiple Benefits Project, a partnership project between FWAG SW and the Environment Agency, funded by the Environment Programme (Water Environment Improvement Fund WFD GiA). 

The site work was then co-funded by the EU funding and the Somerset Rivers Authority.  

Initial work was funded by a scheme under the Rural Development Programme for England (RDPE – EU funding) called the Water Environment Grant (WEG). The scheme is designed to support delivery of projects to improve ecological status of rivers in England. The Merriott project attracted the funding because of its poor ecological status.

Additional Funding was then provided by the Somerset Rivers Authority under the Hills to Levels project. Hills to Levels is a holistic catchment management approach across catchments in Somerset, aiming to ‘slow the flow’ of water to reduce flood risk, reduce erosion, improve water quality, deliver wider environmental benefits and increase resilience on the floodplain. 

View from the Flood Alleviation Dam in high flows previous to work being completed.

 

 

Community Engagement 

Three articles were published in the Merriott Messenger which goes out to all households in Merriott. The first article, in autumn 2018, introduced the project and invited to a community event held in Merriott village hall on 24th September with more than 40 members of the public attending. The second article, in autumn 2019, discussed the results from the Flood Risk Modelling and again invited to a community event held at the Kings Head Pub on 18th November 2019. A third article, summer 2020, is updating on progress such as the detailed design, planning and footpath improvements.

It is hoped that more community engagement can follow after the works are complete to inform the local community about projects achievements and future monitoring. 

 

 

Monitoring and view to the future 

Whilst the funding ends post construction, and the management responsibility falls to the riparian landowners. FWAG is not planning to walk away from the site but to monitor the site and provide ongoing habitat management advice.  

Monitoring will include:

• Assessing which species develop on the site
• Understand / map the stream’s natural evolution: use drone footage and cross sections before, during and after construction, after the first winter etc
• Monitoring water levels in the channel and backwater areas to check whether they temporarily store flood water on the floodplain 
• Assessing whether adaptive management is required and securing funding for this 

Looking to the future, we are hoping this site will be suitable to attract maintenance funding through the Government’s Environmental Land Management Scheme (ELMS). The schemes vision is to provide public funding for public goods; in this case thriving plants and wildlife habitats, flood attenuation, and beauty and engagement with the environment. 

This project is part of a wider catchment initiative which is looking at removing further barriers to fish migration to allow migration between the two tributaries of the Merriott and potentially reintroducing brown trout form the Parrett into the upper catchment to re-establish sustainable populations. 

  

Thank you to all landowners involved: for their time, effort, and cooperation and for giving up land, and to anyone else who has helped this project to progress.