The Plug Hole
Technically known as shaft spillways but affectionately known as plug holes, the drains were designed to regulate water levels in the reservoir by letting out water when the reservoir became full after prolonged wet spells.
The water is carried away down tunnels through the dam to the River Derwent downstream.
Each plug hole has a diameter of 24m (78ft) and the drop from the exit point to the floor of the tunnel below is 20m (66ft).
These shaft spillways have been nicknamed bellmouth or morning glory - after the flower - spillways.
The Plug Hole
Technically known as shaft spillways but affectionately known as plug holes, the drains were designed to regulate water levels in the reservoir by letting out water when the reservoir became full after prolonged wet spells.
The water is carried away down tunnels through the dam to the River Derwent downstream.
Each plug hole has a diameter of 24m (78ft) and the drop from the exit point to the floor of the tunnel below is 20m (66ft).
These shaft spillways have been nicknamed bellmouth or morning glory - after the flower - spillways.