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Flooding and storm damage: Media saturation

While most people hope for a dry summer, for a team working on a United Utilities project in Salford, staying storm-free is more critical.

Reservoir: The circular tank will store stormwater and release it when the weather has eased

The circular tank will store stormwater and release it when the weather has eased

Heavy rain complicates most construction work, but when that work involves cutting into a storm water overflow pipe, poor weather could do more than just delay the project. And, when the site in question is almost within sight of Salford’s Media City - home to both ITV and the BBC - a storm during the critical stage of the operation could cause flooding to the surrounding area and become national news.

In a bid to stay out of the headlines, the GCA joint venture of Galliford Try, Costain and Atkins has been keeping a close eye on the weather as it prepares to work 24 hours a day on a storm water storage scheme for United Utilities (UU).

“In Salford we have two Unsatisfactory Intermittent Discharges (UIDs) that share the same outfall into a major watercourse,” explains UU project manager Steve Taylor.

“The aim of this project is to build a 4,500m3 tank to store storm sewage and prevent the discharge in periods of heavy rainfall. The tank will store the excess water until the storm abates, when it can be pumped back to the treatment plant. But if the storage capacity of the tank is exceeded, the tank will include a static screen that will prevent raw sewage from entering the water course.”

With the BBC and ITV studios so close by, any flooding would be sure to make the news

This £13M scheme is one of 211 similar UID projects underway in the area as part of a £620M investment.

While its concept is straightforward, finding a plot to build the tank has taken several years, due to the high level of development in the area, so it is being squeezed into a former landscaped area within metres of industrial units and next to a cemetery.

Cementation installed 133, 1,180mm diameter segmental cased piles for the secant pile wall that forms the circular tank and the outline of the diversion chamber around the existing outfall pipe.

The 80 piles constructed for the tank are 23.8m long, extending 1m below the formation level of the tank base, while of the 53 installed for the diversion chamber, 16 sit above the culvert and are 6.5m deep, while the rest extend to 15.5m.

With the capping beam on and the piles in place, the focus now is on the excavation, and this is where the GCA team has been praying for a good summer.

Next phase

To construct the next phase of the storage tank, the existing pipe needs to be broken out and the temporary works for the new diversion chamber built, so a storm at this point would be challenging to say the least.

“There have been modifications to the treatment plant at Salford to increase capacity, but the storage is still needed to reduce the risk in heavy rainfall, and there is still a risk of the weather causing issues during the construction,” says Taylor.

Once the pipe has been broken, GCA will install a temporary flume to carry the flow in the pipe - an operation that will take two to three days to complete.

“We will closely monitor the weather and work 24 hours a day in this phase to minimise the risks,” says GCA senior site manager John Holding.

“There is an alarm at the Salford works and on the spill weir, so we would have a few hours of warning before flow would reach the site, but there is potential for the flow to reach up to 6,000l per second.

“With the BBC and ITV studios so close by, any flooding would be sure to make the news.”

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