IWS were approached by the Environment Agency to identify a solution to mitigate issues caused by the main streets within Elford being lower than the peak flood level of the river. When the River Tame was in flood, river water would not only enter the village, it would also prevent the main culvert that runs under the village from discharging collected water into the river.
The catchment area meant that flows of up to 3700 l/s could enter the culvert at the top of the village.
The only land they had access to was an existing open topped storm culvert approximately 3m x 2m, within a fenced compound.
Due to the site restrictions a conventional pumping arrangement into a discharge pipe was not possible as a new pumped discharge could not be accommodated. The possibility of installing a discharge pipe within the gravity culvert was considered but the high flows meant that the head required and power needed was beyond the capabilities of the local network. IWS suggested an innovative solution, developed in two parts:
- The creation of a flood wall to prevent river water from entering the village with an actuated penstock housed on the downstream side of the wall. This would close when the river was in flood
- Installation of a large axial pump that would lift the water over this new wall and allow the water to run in by means of gravity to the river
The Design
Hydraulic modelling was developed by IWS, this determined the upstream hydraulic gradient and determined the water level in the pumping chamber to prevent the lowest gulley in the village from surcharging.
The downstream system curve was then determined and the head loss over the weir wall to ensure the full flow could be achieved by gravity, once the water had been lifted over the weir wall.
This determined the height of the flood / weir wall, the height of the structure and in turn the lift required from the pumps. IWS engaged with Flygt Pumps and requested the development of a hybrid with an oversized impeller on a smaller motor.
The Construction
The nature of an axial impeller and the proposed control through inverter drive enabled this to be achieved without overloading the smaller motor or the limited incoming supply.
The civil works were undertaken by an appointed contractor, within the confines out the existing site, without road closures or damage to the existing fence line.
IWS undertook the complete MEICA installation including the installation of a new radio system, which communicates with an existing telemetry outstation housed within the river gauging station.
Commissioning
Before works were completed and commissioned, a flood event occurred; fortunately, the pump and MCC had been installed. Late one evening with water rising from road gullies and in front of an increasingly large crowd of worried-looking residents, the plant was put into operation by the designer. The penstock closed the pump started and the water levels were drawn back into the gullies and the operation handed over to the local Environment Agency site personnel.
