The commissioning of the Mitford Dam in Morpeth, UK, saw the completion of one of the UKs most ambitious flood alleviation projects which included the Environment Agencies biggest ever dam. ACE were the full mechanical and electrical contractors of this project, working with the Environment Agency and main contractor Balfour Beatty. The whole project was valued at around £27m of which the mechanical and electrical contract was worth approximately £800k.
A common problem that is met by every flood alleviation scheme, is that the flood waters blocked from the protected area must be displaced elsewhere which is why, when the Environment Agency looked at flood protection for Morpeth, they had to re-evaluate this problem. The flooding that affects Morpeth is traditionally caused by the volume of water flowing from the upper section of the River Wansbeck, and when this reaches the town of Morpeth the subsequent breach affects thousands of homes and businesses.
The approach of the Morpeth flood alleviation scheme was to divert and store water in a large reservoir which could then be used to control the flow of water being passed through the town. The new reservoir needed to be capable of holding 1.4 million cubic metres of water which would remove the need for excessively high flood walls being built in the historic town.
The main feature of the reservoir is the large dam which stems the flow of the River Wansbeck during times of flood. This huge structure utilises five 3m x 3m ACE penstocks, which had to be designed to withstand pressures of up to 12.5MwC. The frames of the penstocks had to be large enough to allow the doors to be lifted completely clear in time of normal or low flow.
While the dam’s main aim was flood protection, this wasn’t allowed to sacrifice fish migration. To this end the second penstock was mounted in a lower position than the other four doors, which would allow the migration of trout and salmon. The five large doors are accompanied by a smaller 1.8m x 1.8m penstock door to allow crayfish and eel migration, which meant the critical migration path, would stay open.
The key to successful operation of penstocks are the large hydraulic actuators which allow the doors to be controlled with accuracy to regulate the downstream flow. This would allow the operators to manage the discharge from the lake and keep flow at a level that would not overwhelm the existing and new flood defences in the town.
As Balfour Beatty knew that ACE had a reputation for completing projects of this scale, being able to offer £5m of professional indemnity insurance, and also having a portfolio which included being a major contractor on the construction of the Uk’s largest ever Pumping Station (St Germans) they decided to entrust this major part of the project to ourselves. The project at St Germans involved installing 4m flap valves, 4m penstocks and 4m wide stoplogs that could be stacked to 11m in height.
The project at Morpeth utilised a wide variety of specialist skills from the team at ACE which included the design of the door, able to withstand the pressure requirements, fabrication, testing and installation and the project management in multiple areas.