How will the reservoir be refilled with water?
Toddbrook Reservoir will be allowed to re-fill naturally. A managed process is in place to make sure this happens gradually and safely.
The water level will rise as rain runs off from the surrounding catchment area and falls into the reservoir.
The reservoir valves and high volume pumps will be used to prevent the water levels from rising too quickly. Water within the reservoir will be held at increasingly higher levels to allow for monitoring to take place. Once assessments have confirmed it is safe to do so, the water will be allowed to naturally rise to the next level.
How much water will the reservoir hold after the refill?
The reservoir will be able to hold a similar amount of water as prior to the incident – a capacity of c. 1.29 million cubic metres of water. The new structures are designed to a higher standard and limited space within the reservoir has been taken by their construction.
How will we manage the rising water level?
Since 2019, we have kept an operating water level at 12 metres below capacity by using the reservoir valves and high-volume pumps. The pumps remain connected to the reservoir and are in place to transfer water to the River Goyt.
The first phase of the refill will allow the water level to rise by four metres. We will then use the valves and pumps to hold the water at this level for four weeks while we carry out monitoring and assessments.
Following this - and once assessments confirm it is safe to do so - we can begin decommissioning the current pumping set up, with plans in place to replace should it be required. We will then allow the water level to rise in one metre intervals, controlling levels with the existing draw off pipes, the new high capacity draw off and the by-wash through the new structure. We will hold the water level for a week every time it rises by one metre, with smaller steps are planned for the final stages. This will allow for monitoring at each stage to confirm the refill is safe to continue.
How long will it take for the reservoir to refill with water?
At least 16 weeks but probably a little longer.
The timing and speed of the refill is dependent on the weather. If we have a drier spring then the process will take longer than if we have a lot of rain. The managed process for gradually refilling the reservoir means the water level can't rise too quickly. There will be at least 12 weeks during the refill where the water in the reservoir is held at set levels to allow for assessments.
This means that, even with a lot of rain, the quickest the reservoir is expected to refill is 16 weeks.
To be at full capacity, the reservoir water level needs to rise by 12 metres. We expect the water level to rise by the first four metres fairly quickly. It will then be held at this level for four weeks.
The pace of the refill is likely to slow down for the remaining eight metres. This is because the slope of the reservoir embankments means more water is needed to achieve each extra metre in height. At this stage, the water level will be held each time it increases by a metre to allow for monitoring.
The gradual process has been designed to ensure the reservoir refills safely.
What monitoring is in place during the refill?
A re-fill plan is in place and we will monitor the reservoir closely throughout the refill process. Our monitoring is focused on the integrity of the dam.
We will be monitoring the dam for any observed movement. We will also be monitoring the core temperature of the dam. A change in temperature could be an early sign of water leaking into the dam before it becomes visible.
The water will be held at increasing levels for set time periods to allow for this monitoring to take place. If there is no indication of temperature change or movement then the decision will be made to continue the refill process.
We will be monitoring the dam structure for any movement using traditional surveying methods and surface laser scanning models.
We have carefully installed a system to monitor the core temperature of the dam. Any changes in temperature could be an early indication of water entering the structure in a way that would not be visible otherwise.
Any unexpected observed changes in movement or temperature would cause the refilling to pause while further investigations take place.
What if monitoring shows any signs of a potential problem during the refill?
Safety is paramount and the gradual rise in water level will be a phased and monitored process. This monitoring will allow us to identify any potential issues early and to respond quickly.
If any of the monitoring indicates doubt over the integrity of the works then water levels will be held and lowered as needed. This will allow for any required investigation and mitigation works.
The reservoir valves and new high-capacity draw-off are in place to hold and reduce the water level, alleviating any pressure on the dam structure.
We are also keeping local emergency resilience teams updated as the refill progresses.
When will the pumps be removed?
The high-volume pumps will only be removed once the works have been confirmed to be safe following the monitoring and testing during the first stage of the refill.
