Removal of Dove Cliff weir - information page

Overview

Page created July 2019. Last updated 1 September 2021.

This month we have progressed well and can now see the reinstatement (restoration to original condition) coming along nicely.

Project timeline

The temporary bypass channel reinstatement has progressed well. However, managing groundwater ingress into the channel has been a bigger challenge than was expected by the contractor. This has led to a slightly later completion date than originally forecast. With suitable weather and flow conditions, we will now be finishing construction in September rather than the end of August.

Please bear in mind that all activities on the project are weather dependent and the construction programme naturally reflects this.

Temporary bypass channel

The temporary bypass channel reinstatement is nearly complete and we are working on the final section which is the placing of the topsoil. This is a particularly important part of the reinstatement due to its location in the floodplain, and we are monitoring this very closely to ensure it is returned to the same condition as when we started. Once the temporary bypass channel is reinstated we will be removing the haul roads, site compound and reinstating these areas.  

Images below looking downstream of the temporary bypass channel.

Left image with fully diverted river taken on 1 April 2021.  Right image with bypass channel reinstated on 19 August 2021.

Dove Cliff weir

All construction works around the weir removal have now been successfully completed.

Following the completion of the works, the channel consists of a more natural river bend, with a deep faster flowing section on the outside and a shallower flowing section on the inside, as shown in the images below. The mill fleam has been reconnected on the outside of the bend to ensure the flows are maintained.

Below is an aerial photograph looking down at the new river alignment where the weir used to be, adjacent to the aerial view design illustration.

Above Left: August 2021 aerial photograph of completed permanent works. Above Right: Artist impression of completed project.

There will be some specific landscaping whereby we will replant native trees and shrubs in place of those that were removed to enable the works to be undertaken. This will happen in the late autumn of 2021 to align with their planting season.

Benefits of weir removal

Weirs were historically designed and installed to control water and at that time the environmental impacts of their installation weren’t fully considered or understood.  It was later discovered that they altered natural functions of rivers and their connection with the floodplain, impacting on water quality and adversely affecting aquatic ecology and the wider surrounding environment. Removing a weir improves water quality by allowing water to flow naturally.

Fish and invertebrate species also greatly benefit from weir removal as weirs act as barriers to their movement. Weir removal benefits all aspects of aquatic ecology, including recovery of the riverbed and banks, and development of a more diverse habitat.  A greater diversity of fish and invertebrate species is documented both up and downstream following weir removal.  We are already seeing the benefits of weir removal upstream of the site with the formation of gravel bars and improved habitat for invertebrates and spawning fish as shown below.

Photographs - (Above left) Exposed river sediment is important habitat for diverse communities of beetle, birds and plant species. (Above right) Dove Cliff weir with salmon attempting passage.

Outdated weirs which no longer serve a purpose frequently fall into disrepair and become economically unfeasible to maintain and replace. The public safety risk associated with these types of structures should not be underestimated.  Every year there are numerous unfortunate incidents of people drowning in the dangerous conditions around weirs.

Fish rescues

From March to June 2021 the site had remained isolated, therefore, no fish rescues were required. This was great news as it meant we had no impact on spawning coarse fish during the important breeding period.

The temporary bypass was isolated in late July. Fish rescues were carried out before completely dewatering the channel so the reinstatement works could commence.

We continue to have a specialist team ready to undertake further fish rescues if any flood events occur that inundate the site.

To date, during our fish rescues 16 different fish species have been recorded including Gudgeon, Bullhead, Perch, Chub, Dace, Stone loach, Grayling, Eel and Brown Trout.

National lockdown

To reduce the spread of Coronavirus and alleviate the pressures on our National Health Service we are continuing to follow measures to prevent its spread. As Government guidance eases, we will continue with construction activities, similarly to the previous restriction easing measures in 2020. We are working with our contractor to ensure all Government guidelines are adhered to during this period, enabling the construction works to continue.

Accessing the site

Despite the inclusion of these warnings in our updates and the site signage, we are still aware of members of the public illegally entering our live construction site. We need to remind you that there are many dangers on site due to the changing ground layout, unstable banks and structures, and deep, fast-flowing water. 

Trespassing or forcing entry into the contractors working area is an offence which can lead to prosecution. The health and safety of the public and our contractors is of the upmost importance to us, which is why we cannot stress enough how essential it is for the public to not access the site at any time.

Please can we ask, for everyone’s safety, that you refrain from entering our live construction site at all times.  

 

Background

We are removing Dove Cliff weir (pictured below) to improve biodiversity and improve fish passage through the entire Dove catchment. Dove Cliff weir was structurally assessed in 2016 and sections were found to be in a poor condition. This led to all options for managing the weir being investigated.

The best solution for fish passage in our rivers is to remove barriers, such as weirs and sluices. This is particularly important when they are in poor condition, can cost a lot of money to maintain and no longer serve a functional purpose.

Fish passes alone do not improve the habitat required for fish to spawn and grow. However, removing weirs does as it allows the sediments within the river to deposit naturally creating the right river environments.

Frequently asked questions

Will the removal of the weir effect the water levels in the river?

Once Dove Cliff weir is removed, the water level upstream of the weir will drop. The water level is expected to drop by approximately 1 metre immediately upstream of the weir. Due to the natural slope in the riverbed, the further upstream you go the less change in water level you will see. There will be no change in river level upstream of Rolleston Brook where it enters the River Dove.

The reduction in water level will be a benefit to the environment as it allows the river to function in a natural way, creating both shallow and deep sections within the river. Shallow river sections are just as important to biodiversity, especially fish, as they provide the right conditions for small fish to grow after they hatch. 

How will flows in the mill fleam be affected by this project?

Maintaining a similar flow split between the main river and the mill fleam (mill leat) was an important design criteria for this project.

Levels in the mill fleam may change this year due to current requirements for the construction works to divert water around the site and, therefore, may not reflect the historical flows until the works are completed. However, when they are completed the mill fleam will continue to experience similar flows as it has historically.

The flows in the mill fleam will be less during the construction works and more representative of low summer flows.

Further information

Look out for #Dovecliff updates on our twitter feed too @EnvAgencyMids.

We will update the site working hours if they change but they are generally Monday to Friday, 7:30am to 5:30pm.

Thank you for visiting our project information page.

Please keep visiting this page as we will be updating it regularly. This page will be open to the public until the end of construction and during the following monitoring phase.

External website links that may be of interest

https://yearofthesalmon.org/
https://www.damremoval.eu/
https://www.worldfishmigrationday.com/home