Modern station reduces risk
Selby Dam pumping station plays a vital role in protecting the Yorkshire town from flooding. Now, after refurbishment, it's all set for the future.
Yorkshire's Selby is located on the River Ouse, which has not only been of great commercial benefit to the town over the centuries, but also a considerable menace during periods of heavy rainfall. In the last decade alone, the town was at serious risk of flooding on several occasions and more than £18M has been spent on flood defences.
A key part of this defence is the Selby Dam, which runs for more than six miles and is separated from the River Ouse by its pumping station, where the dam and river meet in the centre of the town. The pumping station played a vital role protecting Selby during the floods of June 2007, when it ran continuously for more than three weeks. It is estimated that as many as 321 homes and businesses are at risk of flooding when water in Selby Dam backs up and needs pumping out.
Bruce Saunders, project engineer at Xylem Water Solutions, says the Selby Dam plays a vital role in defending the town. "Selby Dam is the main flood defence for the town and the pumping station is the key component, managing water levels in the dam at high tides, when it can’t discharge into the River Ouse."
The dam’s primary function is land drainage from rural farmland, with the pumping station structure preventing the River Ouse back flowing into the dam at periods of high tide. During periods of low tide, the pumping station is bypassed underneath, with the flow passing through a central chamber, via four flap valves into a culvert which leads direct to the River Ouse. As the tide rises, the flap valves close and water backs up in the dam. Depending on the level the dam rises to, the pumps kick-in and removes the water from the dam into the River Ouse.
Due to the sheer amount of rainfall in 2007, the original pumps were unable to cope with the sudden surge in volume of water, causing water levels to rise with Selby almost flooding. As a result, the decision was therefore taken to fully refurbish and upgrade the pumping station, with the installation of new, easy to maintain pumps, along with a series of additional control features and early warning systems.
Prior to the refurbishment the pumping station was fitted with four vertical spindle pumps dating from the 1960s. Although the pumps were used infrequently, with the exception of periods of high water flow, there were several age and maintenance issues that needed to be solved.
"The existing pumps worked well but could not cope with large surges in water volume. In addition, there was the on-going problem that the pumps were difficult to access and maintain," says Saunders. "What’s more, the shafts were greased by machines which needed checking and topping up at regular intervals, all of which added to on-going maintenance costs. In order to gain access to the pumps it was necessary to drain the respective pump cell completely."
When selecting replacement equipment, Flygt had to consider specific design criteria stipulated by the Environment Agency (EA). Due to the design of the electrical network feeding the pumping station, electrical loadings imposed by the replacement equipment could not exceed the loadings of the existing equipment. Secondly, electrical noise on the system had to be limited to the values specified in the electrical regulations, further complicated as there was no means of totally isolating the two electric feeder cables into the pumping station from the electricity supply transformer which also fed other parts of the town. Finally, the station had to be kept as fully operational as possible during the refurbishment.
A harmonic study of the electrical supply was undertaken and two 400 amp wall-mounted isolators were installed, feeding fully automated temporary variable speed drive starters. This enabled the existing pumps to be replaced one at a time, whilst always providing three fully operational pumps, during the refurbishment.
A new motor control centre, equipped with two Flygt 90kW PumpSmart variable speed drives (VSD) and two ABB low harmonic drives was the solution to the electrical noise problem. Using the VSD units meant that the electrical supply constraints could be maintained and these units could offer the EA possible future energy savings by running the pumps at reduced speeds. The proposed pumps were four Flygt PL7061 large submersibles, together with the discharge columns and pipe work.
The new control panel offers five different ways of controlling the pumps. This includes two automatic, main and backup ultrasonic controllers that automatically start the pumps as the levels rise. A third means of control is offered by automatic electrode hardwire back-up.
If this fails then there is an option of starting, stopping and resetting the pumps via telemetry, from an EA control centre. If all else fails, the pump station can be controlled manually on site.
"The pumping station has played a very important role to protect Selby against flooding over the years, and the refurbishment ensures that the town now has a modern pumping station that can defend and reduce the risk of flooding to homes and businesses," says Saunders.
In addition, the new Flygt pumps are easier to maintain and can offer energy savings when operating at reduced speeds, which is a benefit to ongoing running costs and the environment.
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