The future of Cannop Ponds: Frequently asked questions

Tree roots exposed alongside water

Frequently asked questions

Why is change needed – why can’t everything stay as it is? 

As large bodies of water, held back by earth dams, Cannop Ponds fall under the remit of the Reservoirs Act 1975. We are legally obligated – for the safety of communities downstream – to address several issues with the ageing reservoir dams and their spillways at Cannop Ponds. 

The more we looked at what would be needed to address the issues with the Ponds, the more we could see opportunities to improve the site for the community and wildlife, whilst also protecting those downstream.  

Read more about the history of the project here.

How have you made a decision? 

Over the last 2-years we have carried out site investigations and survey work.  We produced 4 potential options that could meet the project objectives and sought the community’s views on those options. 

The 4 options have been evaluated against the project objectives.  During this process one of the options was ruled out as it did not meet a key project objective to reduce flood risk downstream.  The analysis provided an objective assessment from which a decision on the best way forward has been made. 

Full details of the assessment can be found in the Outline Business Case which was approved by our Executive Board in January 2024.

What will happen to Lower Cannop? 

Lower Cannop will continue to be a large lake in the heart of the Forest of Dean. Engineering works will be carried out to build a new larger spillway and make the existing dam watertight, protecting the dam from the risk of failure. 

The new spillway will be a reinforced concrete structure, replacing the existing channel. It will have a greater capacity than the existing channel and project further into the reservoir to make sure it can cope with the volumes of water from future storms.  The exact dimensions will be confirmed during the detailed design stages to follow. 

At the same time a cut-off wall will be constructed along the length of the dam, to prevent water continuing to seep through the earth embankment. This will mostly be hidden below ground level and will likely be constructed from steel sheet piles. 

See artist's impressions here.

What will happen to Upper Cannop? 

A more natural approach will be taken at Upper Cannop, which will minimise the necessary and intrusive engineering works. This will retain significant areas of open water, as well as providing marsh and reedbeds. This new mixture of habitats will be beneficial to a range of wildlife.  

  • Shallow edge habitats will help boost numbers of invertebrates and plant species, that will in turn support a greater number of wintering bird species such as the mallard, gadwall and tufted duck that will be attracted to this shallower water to feed.   

  • There will be greater foraging opportunities for rare bat species such as the lesser horseshoe bat and Natterer's bat  

  • Species like otters will continue to benefit from ample foraging opportunities whilst potentially benefit from reduced disturbance. 

  • Greater area of breeding habitat for amphibians and dragonflies. 

See artist's impressions here.

Why can’t Upper Cannop be kept as it is?

The earth embankment at Upper Cannop is in a poor condition and would require very substantial engineering work which would significantly impact the visual appeal of the site.  A more natural approach will see the current embankment retained and a focus on improving wetland habitats for wildlife whilst reducing the overall volume of water held so that Upper Cannop no longer qualifies as a reservoir. 

Will I still be able to visit? 

Yes, in the long-term Cannop Ponds will continue to be an important place for local people and visitors. We will continue to welcome people of all ages, abilities and backgrounds to enjoy the wellbeing benefits of nature and the outdoors.  

Accessibility will be improved, to provide a space that everyone can enjoy. 

There will be a period of time for construction, during which access will be restricted. The details for this are being worked on and will be shared when we know more. 

When will work start, and how long will it take? 

The next stage of the project will be to develop the concept design further and to engage again with the public and other stakeholders later this year. The design will then be developed further prior to submitting a planning application in the winter. 

Assuming a successful planning application we hope to be able to start work in 2025. Works could take a couple of years to complete 

How much is the project going to cost? 

Initial cost estimates have been developed for the purposes of comparing the different options considered in the Outline Business Case. A detailed cost plan will be developed for the confirmed option as the design is developed beyond the concept stage. 

The initial costs in the Outline Business Case include significant assumptions and simplifications. They should therefore not be considered as an accurate reflection on the likely final cost. They do however provide an indication of potential costs, which at this stage are in the range of £4.2M to £8.5M. 

What will be the impact on flooding? 

The changes at Cannop Ponds will increase the storm water storage capacity, and therefore reduce downstream flood risk for any given storm.   

The current dam structures are vulnerable to high storm flows and risk being ‘over-topped’ as the spillways are too small.  Over-topping is a common cause of dam collapses world-wide, and climate change modelling shows the increased likelihood of high and extreme storm flows.  The new spillway at Lower Cannop will be able to carry substantially more water to manage this risk into the future.  

What will be the impact on wildlife? 

In the long-term, the changes at Upper Cannop will substantially benefit wildlife and complement the retention of the large body of water at Lower Cannop. The project has identified the protected species that use the Ponds and will need to safeguard these through the design and construction phases. 

Both Ponds work in tandem to deliver the multiple objectives of the project, including improving the overall wildlife value, as well as the now legal requirement to deliver biodiversity net gain.  

Upper Cannop will retain areas of open water for aquatic species and our native fish, alongside benefits for other wildlife including wetland birds, dragonflies and otters, achieved through creating more diverse and dynamic habitat such as marsh and reedbeds. 

In the short-term – there will be a construction phase, where we will be governed by an Environmental Impact Assessment, and a Habitat Regulations Assessment which are both designed to protect wildlife during and after construction projects. We will work with experts and regulatory bodies to mitigate the impacts and to ensure the site delivers the planned habitat improvements as quickly as possible following completion of all works.  

What will be the impact on the heritage features? 

Upper and Lower Cannop Ponds were built around 200 years ago to provide water to Parkend Ironworks. 

The dams and spillways have changed significantly over the intervening decades, and the heritage value is less about the structures themselves, and more about the landscape heritage of the water bodies in the valley. 

Retention of the Lower Cannop dam allows for interpretation of the Bixslade Tramway Crossing, and its historic rationale, taking stone from the quarries high up on the valley sides, down to the ‘railway’ in the valley bottom.  

The current stoneworks are part of that same landscape heritage and will be largely unaffected by the project. A significant extent of the earth embankment at Upper Cannop will be retained, again making that link to the past, however the spillway will be removed, and other alterations made to implement the project.  

What will happen to the hydroplant?

The hydroplant will be removed and will not be replaced. The existing hydroplant isn’t very efficient due to the way the reservoirs work. Hydroplants need more stable conditions with constant high flows – the flows at Lower Cannop peak and trough too much, and this won’t be altered by the new scheme.

Useful links

A drone image taken above Cannop Ponds
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