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Why?

Staffordshire County Council took over responsibility for carrying out a major programme of restoration works to Chasewater’s reservoir from Lichfield District Council earlier this year (2011). 

The works are helping to make sure the reservoir remains safe in years to come, by limiting the effects of heavy rainfall and water erosion.

The Eastern dam is an earth embankment, and it is common place to carry out ongoing improvement works to a dam of its size, age and construction.

Throughout the project, LDC and now SCC have been working closely with ecologists and local wildlife groups to help plan and carry out the works with the minimum impact on local wildlife, flora and fauna, including newts and rare plants. Find out more on our wildlife page.

Throughout the works Chasewater Country Park is still open, and visitors can enjoy the mini-golf and boating lake on sunny days, and rides on Chasewater Heritage Railway, walks and refreshments throughout the season. We are very grateful to the clubs who use Chasewater Reservoir for their understanding and patience during the works.

So what is SCC doing to make Chasewater Dam safer? 

Chasewater’s main (eastern) dam is over 210 years old, and was built when understanding of how dams work was not as advanced as it is now. If we were building Chasewater dam today, we would use different materials and designs that incorporate the latest safety features.

Our engineers regularly inspect the condition of the eastern dam and reservoir, and have identified where and how improvements need to be made.

There is a very low risk of the dam failing, and by carrying out the works, and maintaining a programme of proper maintenance, we can help to drastically reduce the chances of the dam failing.

That said, it’s important to remember that, like any structure, no reservoir is ever completely safe. This is because events like major storms, mining subsidence or earthquakes can always affect the strength of a dam.

Our engineers have told us we need to complete two pieces of work, which are detailed below.

Protect against a massive storm

The reservoir’s overflow system was tested by the floods of July 2007, and thankfully it passed with flying colours.

That said, unlike modern reservoirs, our engineers have told us that Chasewater’s overflow system was not built to withstand a massive storm, the type of which is rarely seen, and that we might experience once in every 10,000 years!

We need to make sure that if such a major storm took place over Chasewater, the dam’s overflow system would be able to cope. That said, storms of this magnitude are thankfully incredibly rare in the UK, but they have happened unexpectedly in other parts of the world.

To make sure the overflow system could cope, we are strengthening and widening the spillway, weirs and culverts. This will mean that if a big storm takes place, excess rain water will be able to flow down the spillway and safely away from the reservoir, rather than over the top of the dam.

We need to prevent water flowing over the top at all costs, as if this were to happen, it could wash away part of the dam, and cause a massive failure.  

Protecting against erosion

We suspect that when the dam was built in 1799, the builders used whatever material they could lay their hands on. Unfortunately there are no records that describe what materials were used and how the dam was built, so we’ve had to carry out tests. 

Whilst we know the dam contains large rocks and stones, these do not actually give it its strength. Instead, fine particles in the dam (of less than 0.2 microns in size – a micron is 1000th of a millimetre!) give it its strength. As you can imagine however, these tiny particles can be easily washed away by water passing through the dam.

Many modern dams have impervious barriers to prevent water flowing through them. Often earthen dams are built with a clay core, which slows down the flow of water through the dam, and stops fine particles from being washed away. We have drilled into Chasewater’s dam to see if it has a clay core, but it does not.

This means there is little in the dam to prevent the fine particles from being washed away. As such, if the speed and volume of the water that passes through Chasewater’s dam increases, more and more of the fine particles will be washed away, and the dam will become weaker.

Our engineers have told us that internal erosion could lead to a natural pipe being formed through the dam, through which water would flow, causing further and possibly irreparable damage to the dam. Over time (which could be very quick) more and more the dam erode away, until the dam failed, or the pipe collapsed onto itself.

Unfortunately we cannot simply put in an impervious barrier into the eastern dam, because if we get it slightly wrong, it could concentrate a leak into a specific weak point. Instead we need to install sand filters along the entire length of the dam.

These filters are layers of very fine sand will be laid onto the downstream face. The sand will allow water to pass through, but will trap the fine particles, and prevent erosion from starting. 

Use our blog:

We have created this blog, to help answer your questions about the works, and what we are doing to protect the wildlife.

Our blog policy:
 
We have created a blog policy that we believe is fair and equitable, and one that will ensure that topics are discussed on this blog in a rational and level manner. Our policy is as follows:
 
1. All comments made on this blog are reviewed before they are published.
2. We aim to review all comments within 24 hours
3. We will attempt to provide an answer to published blog posts, where a response is requested.
4. We reserve the right not to publish comments.
5. We recognise that we will handle some potentially sensitive issues, and in order to ensure all viewpoints are aired, will aim to publish fair comments, whether negative or positive.
6. We will not publish comments that are derogatory, rude, offensive, or overtly negative.
7. We will not publish comments that are pointedly misleading, particulary if clear information has already been published on the blog about the topics under discussion.

The blog is run on behalf of Staffordshire County Council by a team at LDC. If you have any questions about the blog or this policy, please email neil.turner@lichfielddc.gov.uk or elizabeth.thatcher@lichfielddc.gov.uk

10 Responses to “Why?”

  1. Monika Turner says:

    Hi

    Please accept my congratulations on a very interesting website and thank you for the dedication and time taken to keep us informed.

    I enjoy walking around the reservoir and, naturally, am taking an interest in how the work is progressing. Last week I called into the admin block and was told that, no, a lack of funding was not the cause for delaying the work on the dam and that a contractor had been appointed. They were due to start work on 1st July and the work on the dam would be finished by September.

    Is this true please?

    Many thanks and keep up the excellent work!

    Best regards

    Monika

  2. lizziethatcher says:

    Thanks for your comments. I’m glad you find it useful.
    We are still assessing the tenders from the contractors. As you can imagine the process is complex and detailed. I’ll try to get an update on timings, but I understand the programme of works is still progressing well. Cheers

  3. peter says:

    if you look at the facing of the dam it has been coated in concrete
    and bitumen/pitch at some point was this a previous attempt to waterproof it as it looks like an add on.
    it would seem that this would be far cheaper than the proposed work does any body know the history of this
    best regards\
    peter

  4. lizziethatcher says:

    I’ll look into it for you. Cheers

  5. lizziethatcher says:

    Hi Peter, I’ve looked into this for you, and I hope this helps:

    The works that you have seen to the upstream face of the dam has been done to prevent surface erosion, rather than to waterproof it – and it likely we’ll do some patching this year. We periodically patch the upstream face because wave movement erodes the material away, but we address this by replacing it. The last time we patched to any great extent was in about 2000 or thereabouts.

    The works we are presently doing are differenct, and are designed to prevent internal erosion, which is a far greater risk to earth embankments like the one at Chasewater.

    We can’t make the dam impermeable, because we know that water flows around and under, as well as through the dam and if we were to attempt to make it impermeable there is a real risk that you increase the velocities of water through those areas where you cannot treat, or indeed where you miss.

    So both sets of work need to be carried out.
    Lizzie

  6. Martin says:

    When all the works are finally finished, will the pier be re-opened for public access?

  7. lizziethatcher says:

    I’ll find out. Cheers

  8. John Carver says:

    Hello,

    I have only just come accross this web site, and as a local resident, I wish I had found it earlier. Congratulations on providing such comprehensive answers, in both a readable and technically competent manner.

    The necessity for the work is obviously paramount, both for the general safety of the earth bank dam, but also for the one in ten thousand year storm.

    The draining of Chasewater must have been a golden opportunity for all sorts of studies to take place, Is there a list of them?

    Equally I am sure there must masses of technical photos of the project as it progressed. Are there any plans to compile a comprehensive narrative on the process as a historical technical document for the future?

  9. lizziethatcher says:

    Hi John

    Thanks for your feedback. I’m glad you find the site useful. We do have hundreds and hundreds of pages of documents as you can imagine. We recently wrote an article for International Water Power and Dam construction with gives a good overview. http://www2.lichfielddc.gov.uk/chasewaterdam/2010/10/20/international-water-power-dam-construction/

    I’m not sure if there are plans to create a summary doc, so to speak, on the project, but I can find out for you.

    L

  10. Paul Bradley says:

    Can anyone tell me exactly where the reservoir is drained from? it looks like a place under where the remaining body of water is, but equally as I know little about 18th century water engineering it could be at the base of the pier tower. I know that the convention was to have the valves in the centre of the dam, with a control building directly above (as at Edgbaston reservoir) but on looking at the dam wall from the south shore the sit of an original sluice / valve hinted at by the tower above appear to have been cemented shut. Also, what is the drain, is it a simple sink hole? Thanks,

    Paul.

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