The dam wall does not have a traditional spillway to control water height but discharges into a tunnel under the side of the valley, via a large bell-mouth drop-shaft overflow in one corner, a feature not normally seen on Pennine dams ⁬which usually have masonry spillways [REF].
On the dam wall near the drop shaft is an ingeniously-designed emergency overflow consisting of three metal troughs that when full tip water over a wall where it runs across the road and back into the river below.