View All Articles 72 - Eccleston Dam on the River Yarrow - Information from Lower Yarrow Flood Action Group, Croston. Huge THANKS extended to L.Y.F.A.G. for all their efforts. View Attached File

Eccleston Dam on the River Yarrow - Information from Lower Yarrow Flood Action Group, Croston. Huge THANKS extended to L.Y.F.A.G. for all their efforts.

3rd of March, 2024

L.Y.F.A.G has  given the P.C. details about the operation and capacity of the dam located on the River Yarrow in Eccleston which  regulates river levels to try and prevent flooding further down river as the Yarrow  flows through Croston. Please see attached file below. 

Here's a summary of the key points:

Purpose of the Dam:

  • The purpose of the dam is to keep the River Yarrow  level low enough to prevent flooding of roads and properties in the village. It achieves this by impounding water upstream of it.

Closing Operation:

  • The dam starts operating when the river level rises to 3.36 meters.
  • The first penstock closes fully when the river level reaches 3.36 meters.
  • If the river level rises to 3.42 meters or higher after 90 minutes, the second penstock closes by 33%.
  • If the river level remains at 3.42 meters or higher after another 90 minutes, the second penstock closes by 66%.
  • If the river level remains at 3.42 meters or higher after an additional 90 minutes, the second penstock closes fully.
  • The closing process takes a minimum of 4.5 hours from fully open to fully closed.

Raising Operation:

  • The penstocks start to be raised when the river level drops to 3.31 meters.
  • The first penstock is raised by one stage when the river level drops to 3.31 meters.
  • If the river level remains at 3.31 meters or lower after 90 minutes, the first penstock is raised by another stage.
  • This process continues every 90 minutes until both penstocks are fully open.
  • The raising process takes 7.5 hours from fully closed to fully open.

Capacity of the Basin:

  • The basin can hold 1,300,000 cubic meters of impounded water before water would start to run over the spillway on top of the dam.
  • At this point, the river level at the dam would be 8.1 meters.
  • The highest recorded level at the dam since becoming operational is 6.7 meters, which is slightly less than 50% of the basin's capacity.

Sources:

  • Details about penstock closing/raising procedures are from an email from James Chapman (EA) dated 5 June 2023.
  • Details about the basin capacity are from a graph received in an email from Chris Tomlin (EA) dated 14 December 2022.

Many thanks to all those volunteers involved in L.Y.F.A.G. A huge amount of work has been undertaken by these volunteers over the years and on behalf of everyone who has benefitted from their efforts, the Parish Council extends  most sincere gratitude and appreciation to this group for all that they have achieved.