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Dam is a critical piece of work in flood defence

Anthony Myatt, Project Manager of Morpeth Flood Alleviation Scheme on Skinnery Bridge overlooking High Stanners. GM031547

Anthony Myatt, Project Manager of Morpeth Flood Alleviation Scheme on Skinnery Bridge overlooking High Stanners. GM031547

Last week the Herald reported on the progress of the town centre elements of the Morpeth Flood Alleviation Scheme. Now Chief Reporter ANNA SMITH highlights other aspects of the work as outlined by Environment Agency Project Manager Anthony Myatt and Flood and Coastal Risk Management Director Ian Hodge.

The dam

RESIDENTS of Morpeth will be familiar with many of the town centre works going on to improve flood defences, but one of the most important elements of the alleviation scheme is being constructed out of public view, upstream at the Mitford Estate.

The Environment Agency is building a complex floodwater storage system on the estate, which will be capable of holding back 1.3 million cubic metres of water.

The dam will reduce flood flow to Morpeth town centre, providing some level of protection to all properties. It is a key part of protecting the area from a one-in-137-year flood event, the same as that seen in 2008.

The project so far has seen access roads built, the River Wansbeck temporarily diverted and nationally important native white clawed crayfish relocated by hand.

Work is running to schedule for completion by autumn this year.

Project Manager Anthony Myatt said: “In terms of the programme, the dam is the critical piece of work and that is still on schedule for completion in the autumn. The work to date has gone quite well.

“The river diversion is complete, all the culverts have been installed and we are in the process of starting construction on the inlet and outlet structure. We are awaiting final approval for the materials so we can start getting ready for the dam construction.

“We expect to get to the spring or early summer before diverting the river back.”

Mr Hodge, of the agency’s Flood and Coastal Risk Management directorate, said the dam location has changed slightly from the original plans after assessing conditions on site.

“When we first looked at the dam, we looked at it as a desk-top exercise,” he said.

“We looked at all the features, such as the amount of water we needed to store and a location where we thought we could put a dam to ensure that capacity. That was all in outline, but when you come to look at the detail there are further things to do, like site investigation to check the ground conditions.

“We had to make sure the location was able to withstand the water pressure and we had to take the views into account of the landowner. We wanted to get both the best solution for the landowner and the scheme design and also consider the impact on the Mitford Estate itself.

“The dam now is in the ideal location for getting the maximum flood alleviation benefit downstream.”

Mr Hodge said that criticism of the Mitford Estate has been unfair and that without the landowner’s consent the project could not have gone ahead.

He said: “The upstream landowner doesn’t benefit directly from the scheme and they are impacted quite dramatically by the construction work. It is only right that they have compensation for that impact.

“There have been comments about us bending over backwards for the upstream landowners. No way. We have dealt with that very professionally and have had private negotiations about compensation packages, which are related to the impact on the landowners.

“The dam upstream was the only technical solution and the location was the only place we could put a dam of the size and capacity we needed.

“If we hadn’t managed to get the agreement of the landowner, this scheme could not have happened.”

Cotting Burn

Some properties in Morpeth have not been flooded by the Wansbeck, but have been inundated three times in four years by the Cotting Burn.

The Environment Agency is now finalising a design for a floodwater storage dam on the burn that would provide protection to a one-in-100-year flood standard.

Mr Myatt said: “We are just in the process of finalising a storage solution for the Cotting Burn. The idea has always been that the level of protection for the Cotting Burn would be for a one-in-100-year event.

“It is a much smaller scheme, but the same principle as what we are doing at Mitford.”

Surface water

Local authorities take the lead in addressing surface water flooding problems, but the Environment Agency offers support in terms of sharing data and giving advice.

It is currently working on plans with Northumberland County Council.

Mr Myatt said: “As part of the partnership with Northumberland County Council we are working to develop a solution to surface water flooding.

“We haven’t got much detail yet and we have to prepare a business case.”

Mr Hodge added: “This is a separate project from the Morpeth Flood Alleviation Scheme, but there may be an opportunity to work with the contractor to link work into the overall scheme.”

Previous work

Work is clearly still ongoing to deliver the £24million flood alleviation scheme, but the Environment Agency also completed £2million of emergency repairs to defences after the 2008 flood. In addition, work was carried out to the burns.

Mr Hodge said: “Following the disaster in 2008 we repaired all of the existing defences and did some emergency work. We invested £2million in emergency work and carried out repairs on some of the culverts, such as on the Cotting Burn and Postern Burn.

“It was quite a significant amount of work at the time.”

Wansbeck Street

The Herald has previously highlighted complaints from residents in Wansbeck Street that their homes have been left out of the flood alleviation scheme.

The Environment Agency has offered property-level protection, but says the cost of building a flood wall is too high to justify the work.

Mr Myatt said: “Because of the condition of the existing river wall, for us to provide a flood defence we would have to rebuild the existing wall and provide a flood wall on top. The costs associated with that would be around £1million. Unfortunately, to protect seven properties it is not a sufficient return on our investment.

“We share the concerns of residents there and we are providing them with some form of property-level protection to ensure that they have some form of protection up to a one-in-50-year event standard. They will also benefit from the dam upstream.”

Mr Hodge added: “Any work there would only benefit those seven properties. I think the cost would be £1million plus because there are risks associated with taking down the existing walls and building from bedrock so the cost per property would be £143,000. Regrettably, the economic case just doesn’t stand up.

“Overall, the £21million to £24million scheme will deliver substantial benefits from flood risk to more than 1,000 properties and it is about an eight to one return — for every £1 invested, the return is about £8 in reduced costs in the future from flooding.

“We have to look at the cost benefit for everything we do and to invest £1million would need a much bigger return than we can achieve from the seven properties in Wansbeck Street.

“We do need to look at options to protect the properties there and we are committed to do that. We don’t want those properties to be excluded, but we have to take account of economic pressures and the economic viability.”

Dredging

Many residents have questioned why the Environment Agency is not dredging the Wansbeck to alleviate flood risk.

Mr Hodge says that while such action may be beneficial in some areas, it is not suitable for Morpeth.

“Dredging is in the press a lot at the moment,” he said.

“The agency will always look at dredging as a potential solution to increase flow of watercourses. In some circumstances it will be an appropriate solution, but for a watercourse the size of the River Wansbeck, and the flood flows, which could involve hundreds of cubic metres of water, the undertaking would have to be extremely significant.

“It is also a very sensitive site environmentally. We have to consider the flora and fauna, and if we take material out we have to be very careful about where we dispose of it.

“There are lots of sources of silt upstream that moves down continuously so dredging simply will not work.”

However, the agency will continue to survey the river to assess whether some gravel needs to be removed on a smaller scale from localised areas as part of channel maintenance.

Last week, it had a remote control boat in High Stanners to take measurements.

Mr Myatt said: “The remote control boat was carrying out survey work in the river to determine the current bed levels.

“This is done on a period basis to ensure that the flood defences aren’t being compromised by a build-up of silt or gravel. The survey will be used to identify whether gravel removal will be required.

“The remote control boat is a new piece of equipment that means that the survey can be carried out quicker and safer than traditional methods.”

Information centre

After seeing the strength of the Morpeth community, the Environment Agency decided to trial the idea of having an information centre available for residents throughout the flood works.

It has been a huge success, with hundreds of inquiries made. Mr Hodge said: “Having the shop front is very unusual for us. Because Morpeth has such a strong sense of community and we are working in the town on the scheme we thought we would benefit from having a shop front to enable people to keep in touch with us on a daily basis and to provide information and reassurance.

“It has been really positive and there has been real value in doing that.”

Mr Myatt said: “We are here to listen and for people to talk to us. We want to hear about any concerns they have.”

The centre is open on Tuesdays, from 1pm to 5pm, Wednesdays, from 9am to 1pm, Thursdays, from 2pm to 6pm, and Fridays, from 9am to 1pm.

 

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