Upgrade and improvement works needed to be carried out on a dam and reservoir which feeds a Water Treatment Works. This included work on various main feed valves and pipework, along with work on the compensation flow pipework and valves.
Two sets of overpumping were required so that the Water Treatment Works had a continuous feed from the reservoir and the compensation flow kept within the regulated levels.
There were two main challenges with this project, the first one being the location as the reservoir and dam are remote and difficult to access. The second was that the water for the treatment works needed to be drawn from 5m below the water surface to ensure and need to be supplied at a constant pressure across varying flow requirements. This is because the water is currently drawn from that point so to keep water quality the same the overpumping needed to be taken from the same point and also the current gravity fed system provided a constant head of pressure to the work regardless of the flow required.
Taking this into account, using a pontoon and submersible pumps would not work as they would not draw the water from deep enough. The other method of using diesel run surface pumps next to the reservoir wouldn’t work due to the limited space available, the running costs and having fuel next to the water, which was an unnecessary risk in case of spillage. The flow needing to be replicated for the treatment works was up to a maximum of462 l/sec and the compensation flow required was a minimum 160 l/sec. Due to the sensitivity and importance of the project multiple planning meetings were attending by our Solutions Team discussing all areas and scenarios with the client to ensure that the solution provided had adequate redundancies in place for any situation.
The Selwood solution
The solution identified for the treatment works main flow was to use three NZ pumps, set up in duty/assist/standby, and to float the suction pipe workout, using pipe floats, by a distance of over 30.0m towards the middle of the reservoir with a 5.0m down pipe attached on the end to where the water was needing to be drawn from. This allowed more flexibility with the pipe work than a pontoon and meant that any maintenance required on the pumps could be carried out easily. They were tethered to the shore using suitable pump chains to prevent excessive moment and drag and also anchored to the bottom by a specialist dive team.
The NZ pumps are electric so as no on-site power was available for use super silent bunded generators were set up in a nearby carpark, removing the potential risk of diesel spilling into the reservoir or water course. This was also convenient for refuelling. Selwood Inverter panels were used and commissioned by our electrical team to automatically provide and maintain a continuous pressure to the Water Treatment Works, replicating what the current system was providing. This allowed the overpumping to provide the controlled flow required to the treatment works without upsetting the normal working process.
For the compensation flow, 2 NZ pumps were set up in a duty/standby configuration in the same way as the other pumps. A data logger and flowmeter were used so that the client could track the flow and ensure that it stayed within the regulated limits. As there was no mobile network signal available any reliable telemetry solution would have been difficult so Selwood provided expertise on site resource during critical phases of the works providing the client with additional resilience and piece of mind.
The Water Treatment Works has been able to function without interruption or delay whilst the maintenance and upgrades works took place and the compensation flow was maintained well within regulatory levels.