We must demonstrate to the Environment Agency and Cumbria County Council that our assessment of flood risk is in accordance with National Planning Policy and that flood risk to, and from the proposed projects can be managed effectively without increasing risk to others.
We've engaged with specialists to carry out extensive hydraulic modelling studies to assess how the proposed work at all three sites may alter flows. The key findings are detailed below.
Crummock Water
Crummock Water is full nearly all of the time and flood flows are easily transmitted through the system and out into the River Cocker. Therefore, the weir does not currently provide any flood attenuation benefit to help manage flood risk downstream.
Removing the weir will lower the typical water level within Crummock by approximately 1.35 metres, creating greater natural storm attenuation capacity.
The new outlet from Crummock Water would consist of two naturalised river channels, each approximately five metres wide. The two new outlet channels, combined with a natural 'rougher' surface act as a throttle, holding back water during a storm event and slow the flow of water passing forward from the lake in comparison with the existing forty metre wide smooth outlet weir.
Work at Park Beck would also contribute to reducing flood risk. The lower course of Park Beck is currently a straight concrete channel and provides an efficient way of transferring storm water into the reservoir. Our proposed work would remove this concrete channel and return the natural curves of the watercourse. This would reduce the rate at which the water enters into the reservoir, with multiple channels that would create several points of entry during high flows and remove the pathway for flood water to bypass Crummock Water and flow straight into the River Cocker.
The combined effect of lowering the water level in Crummock Water, the two re-naturalised outlet channels and the re-naturalisation of Park Beck would all contribute towards reducing the risk of flooding.
The modelling is also assessing the impact for both flow and flood level throughout the River Cocker catchment and into the River Derwent at Cockermouth.
Chapelhouse Reservoir and Overwater
Chapelhouse and Overwater reservoirs, like Crummock Water, are not designed or operated as a flood management provision.
The weir at Overwater was designed to retain a larger volume of water than would have been stored in the natural lake. The dam at Chapelhouse was designed to create a body of water in the natural valley of the River Ellen (that is diverted around, and perched above the reservoir) to then allow water to be abstracted for drinking water purposes.
Chapelhouse does not route flood waters through it, this is done naturally along the River Ellen. The reservoir is nearly full all of the time which provides little flood attenuation provision as it acts to store and retain water 'offline' for water supply and abstraction.
Removal of Chapelhouse does little to change the natural hydrological regime. Our modelling is also assessing the impact for both flow and flood level throughout the catchment down to Maryport.
Click the links below to take a look at graphics and aerial images which help to demonstrate the existing and proposed top water levels at Crummock Water and Overwater.
Aerial images: Crummock Water and Overwater
Graphics: Crummock Water and Overwater