The River Cerne is largely a groundwater fed river with a small upstream catchment, running mainly over Chalk and Upper Greensand.  The bed armour material is mainly local flints and remains stable.  This is often overlain  by shifting seasonal banks of sandy silt with a healthy ecosystem of flora and fauna.  Due to surface run-off and at times of high groundwater levels, the river level may rise or appear coloured.

Flood Storage Area

Cerne Abbas benefits from a Category 'A' Flood Attenuation or storage Reservoir with a dam built across the valley to the north of the village.

The reservoir is designed to hold approximately 68,000 m3 of flood water over 2.18 km2 and release it slowly through a control structure known as a penstock, beneath the dam.  The height of the penstock is set and fixed but is locally adjustable in an emergency using hydraulic equipment, operated from a control position on the dam.  There is an incident room at the Blandford EA depot which is equipped with monitors receiving live images from cctv cameras in our area which includes that from our own installation here in Cerne.  Telemetry data is also gathered on site by way of water height sensors at several points in the river and this too, is sent to the control centre.  Thus controlled, the river maintains a maximum height and flow rate through Cerne Abbas and beyond downstream, in times of heavy rainfall.

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Secondary defence scheme.

Surface water from unusually heavy rain may run into the village from the surrounding hillsides  at times of high levels of groundwater.  Normally, this water runs into the gullies and culverts under Long Street and thence into the River Cerne.  In exceptional cases, the water may be in excess of what the culverts and gullies are designed to cope with, possibly exacerbated by their becoming blocked with leaves or field debris washed down.  This excess water is then captured effectively by a large steel U shaped grating across the street, and fed into the 1.2m wide pre-cast flood relief culvert.  This culvert follows the most direct route to the River Cerne downstream of the village. All culverts are remotely inspected and cleansed regularly on behalf of the council.   These assets are maintained by the Dorset Council.

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