Trent Valley Drainage Board Update Report Part 2
Sutton-on-Trent Parish Website
Continued from Part One:
The largest contributor of flow to the village centre is Cuckstool Dyke. Options to mitigate the flow by partially diverting it elsewhere or introducing online storage (flood embankment) have not yet identified a financially viable option. Storage requires a reservoir of circa 80,000 m3 capacity, placing any structure within the requirements of the Reservoirs Act and adding substantially to both Capital and Operational costs. The option of transferring some of the flow to the River Trent to a former outfall at Carlton on Trent does provide some benefit, but that benefit is limited under all storm flow scenarios, and certainly not sufficient to justify capital investment. This scenario does lead to an increase in risk of agricultural flooding to the south of Sutton on Trent which might be considered acceptable if there were substantial benefit within the village. However that benefit does not materialise.
The Board are looking at alternative routes to transfer intercepted flows from Cuckstool Dyke to the Trent and will be undertaking high level modelling of options shortly and expect to have a workable solution by the end of May 2021.
Cuckstool Pumping Station
A flap valve which became detached towards the end of December has been refitted and the seating of the second flap valve resolved so that both flap valves now operate correctly. A quote for a new flap valve has been received and the plan is that one of the flap valves will be replaced with a new one, allowing the second flap valve to be replaced by the removed flap valve once it has been refurbished. There have clearly been issues with the flap valves both this year and last, and if they do not seal when the Trent is running at high level, the pumps not only have to cope with flows from Bulham Lane Drain and Cuckstool Dyke – they also have to pump whatever runs back from the Trent.
One of the recently refurbished pumps is anecdotally not working properly – this has to be proved. Flow monitoring equipment has been installed to validate pump output. This can only be fully proven when the Trent is high – ie flap valves submerged, so the results of this testing are awaited. Initial results, without the benefit of the pumps working at maximum head are being reviewed on 12-1-21.
There have been suggestions that the pumps may be inadequately sized. Flow monitoring will validate the true output which will lead to decisions on the capacity of the pumps. The pumping station structure is sized for the existing pumps, so any increase in physical pump size is going to require significant work. The pumping station is noted to have worked effectively until the recent pump refurbishment, which does indicate that proving that the pumps do what they are supposed to do as the first step.
Pumps operate on start and stop levels and the volume pumped between start and stop is a function of the upstream volume and the rate at which it is replenished. The way that the Cuckstool pumps have been starting and stopping is being assessed from telemetry records to see if there is a hydraulic restriction upstream is preventing water from getting to the pumping station quickly enough. Clearly when the water levels in the pumping station forebay are high the pumps should be working continuously. Consideration is being given to widening the watercourse immediately upstream of the pumping station to form a larger sump which will allow pump start levels to be set lower, but still allow the pumps to operate at low flows without being starved of water. In particular, starting the second duty pump earlier ie at a lower level will have some benefit, providing that this does not lead to ‘hunting’ because of the stop level.
Issues with the set up of the automatic weedscreen are being addressed on 12/13 January 2021 by the installer of the new equipment.
The Board are updating all telemetry and a new remote telemetry unit with improved functionality will be operational at the pumping station site by the end of May 2021.
Neil Kemble, Engineer, 11-1-21.
- 01623 238712
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Newark, Nottinghamshire, NG23 6PX