Removal of Dove Cliff weir - information page

Overview

Page created July 2019. Last updated 20 January 2021.

Our contractors, Stonbury, continue to work following current Government Coronavirus guidelines.

Archaeological discovery

The previous works carried out to isolate the temporary bypass channel resulted in a significant drop in water levels. This exposed a timber structure along the channel bed, pictured below.

Following the unearthing of these historic timbers, the project team has been working closely with key consultees, such as Historic England and the Derbyshire and Staffordshire County Archaeologists, to agree and develop a plan to both record and mitigate the exposed timbers. A strategy and programme for managing the archaeology was agreed in July 2020 and on the 6 August 2020, investigation works commenced on site.

After a thorough sampling process carried out by the archaeologists, early information indicates the timbers date back to 1296-1409 and 1485-1650. We are still not yet able to accurately determine what the structure was, but will share this information with you when it becomes available in 2021.

The archaeology investigations were completed in late September 2020 and included removing some key pieces of the structure for further investigation. The remaining sections have been reburied to preserve them for future generations.

A considerable amount of physical information has been collected in order to better understand and record the structure. We are currently waiting to receive the post-excavation programme from the archaeologists, but have been advised it will still take a few months to fully assess all of the information and produce the report. We are providing our support to all of the team throughout this process.

During the weir removal process a cross section of the old weir is being recorded by the archaeologists. Working in a water logged environment is challenging and we are taking all necessary steps to ensure this can be done safely. Below you can see a cross section of the weir with some historic timber uprights below the concrete that was used to repair the weir in the 1960s.

Bypass channel opening

With the physical archaeology investigations in the bypass channel completed, our contractor, Stonbury, completed the construction and opening of the temporary channel in late October 2020 (pictured below).

This was a critical step for the project and coincided with World Fish Migration Day on the 24 October (https://www.worldfishmigrationday.com/). This event only occurs every 2 years and aims to raise awareness of the importance of rivers without barriers for the health of migratory fish. The bypass channel enabled migratory fish to be able to swim past the weir, during all flow conditions, for the first time in many decades.

The temporary diversion of the river through the bypass channel is necessary to allow for a safe dry working environment for our contractors and for the planned archaeological investigations on the main weir to be completed.

Dove Cliff weir

Works to physically remove Dove Cliff weir began in early December 2020. This process will take a few weeks whilst archaeologists record a section of the historic structure that lies beneath the reinforced concrete and masonry. There is unfortunately an inevitable noise impact locally from the demolition of the weir and rock movement in accordance to the design, but this is being kept as minimal as possible for the benefit of the local community and wildlife.

Progress has been steady since our last update in December 2020. We have unfortunately experienced several flood events during this time, which delays progress as it floods the site making it unsafe to work. This can be seen in the 2 photographs below showing the dry working area in early December and the flooded working area in January.

The remainder of the weir removal, archaeological recording and construction of the new river banks are scheduled to be completed over the next 2 months. These are weather permitting of course, with the final sections and reinstatement of the land on both sides of the River Dove then programmed to be completed in the weeks following.

As the main weir works must continue in isolation from the river, water is being pumped into the mill fleam to ensure it maintains a steady flow. The pumps are designed to have a minimal noise impact. However, to ensure that the site remains safe to work in and the fleam is flowing, they will be running continually until the river has been re-diverted back to its original course and the fleam is reconnected.

Labyrinth weir

The Labyrinth weir construction work continues to progress and is being completed in tandem with the main weir works. Water is being pumped into the mill fleam to maintain the flow and prevent any environmental issues occurring further downstream of the site.

The photographs below show progress with the Labyrinth weir, with the majority of the structure now removed and the mill fleam river bed also lowered as required.

The red arrow highlights a point of reference between the before and after photos below.

Fish rescues

Fish rescues are being carried out as required now that the weir is isolated, with the team ready to undertake further fish rescues if any flood events occur that inundate the site. A fish rescue was undertaken at the start of January following the Christmas shut down and the ingress of flood water during this time. Very few fish were found in the working area, which mainly comprised of minnow, bullhead and grayling.

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

A national lockdown was reinstated at the beginning of January 2021 to reduce the spread of Coronavirus and alleviate the pressures on our National Health Service. During this time Government guidance is allowing construction activities to continue, similarly to the previous lockdowns 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.

Impact of rainfall in 2019

Since starting construction works in August 2019, we have experienced very high rainfalls in the Dove catchment, which has led to some very high flows. These include the second highest flow on record over the weekend of the 26 and 27 October 2019. The hydrograph below from the nearest river level and flow gauge at Marston on Dove, approximately 2 miles upstream, shows the depth (stage) of water at the gauging station over this period.

When the water depths at the Marston gauge are above 1 metre (m), shown by the blue line on the graph, the Dove normally starts to overtop its banks near Dove Cliff weir downstream, leading to potential flooding over the local area. The 2.6m peak on the hydrograph is the flood event of late October 2019, but there have been many other large flood events since September 2019 as can be seen.

The scale and frequency of the flood events had led to working conditions on site becoming very difficult and at times potentially dangerous for our contractors if they had continued. The safety of the contractor and our staff is our highest priority. 

We decided it was not safe or suitable to continue with the weir removal works until the flows were lower and could be managed in a safer manner. Construction was therefore suspended over the winter period for 2019.

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 monthly and at key times. 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