Clypse Reservoir

Clypse and Kerrowdhoo Reservoir as seen from above The Clypse Reservoir is the upper of the two reservoirs in the Groudle valley and impounds the upper reaches of the Groudle River above Onchan.

It was constructed by Douglas Waterworks Company during the period 1875 to 1878 to the designs and under the supervision of Daniel Cregeen, a local engineer. It is formed from an earth embankment which has an upstream slope of 1 in 5 and a downstream slope of 1 in 4, the upper part of the upstream face of the embankment is protected from wave action by carefully placed stone pitching. The downstream face is predominantly covered by grass but with areas of bracken and brambles.

The embankment is made watertight by a central concrete core which is taken down just below the level of the natural stream bed into the underlying boulder clay. The draw-off works comprise a 12 inch diameter pipe for the supply pipe and an 18 inch diameter pipe for the scour pipe both of which are controlled by downstream control valves located in the small masonry valve house at the toe of the embankment.

The reservoir contains water to a depth of 40 feet and stores 32 million gallons up to the level of the overflow cill at 450 feet above ordnance datum. The overflow is formed from a concrete channel. There is a small residuum lodge at the top end of the reservoir to trap sediment brought down the River during storms. The flow into the reservoir can be by-passed around the eastern flank of the reservoir by means of a concrete bywash channel. The 12 inch supply main from the Clypse Reservoir towards Onchan originally ran down the valley below the eventual top water level of Kerrowdhoo Reservoir. This main was re-laid during the construction of Kerrowdhoo Reservoir, to run along the left bank of the new reservoir. A valved connection was provided into the Kerrowdhoo main to provide an alternative source of supply from the Clypse Reservoir should it be necessary to take Kerrowdhoo Reservoir out of service for repairs, etc.

Following completion of the Kerrowdhoo Reservoir, the normal mode of operation of the Clypse Reservoir became to feed water down into the new lower reservoir. The original agreement for purchase of the Kerrowdhoo site required a supply of water to be provided in perpetuity to the Kerrowdhoo Farm fields to the west of the new reservoir, and the Clypse supply main is therefore still kept charged to enable this supply to be maintained. The catchment area covers 562 acres and rises to over 1,000 feet at Slieau Meayll.

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