Chesil Beach - Landforms and Management

Background Information

Chiswell is a low-lying village on the Isle of Portland.  As the photographs show much of the village is at sea level.  There are approx.150 residents in 70 dwellings.  The road (A354) that joins Portland to the mainland runs close to Chesil Beach (see photo 6) on the west side of the village.  Also in the village, on the Portland Harbour side, is the site of what was for a long time Portland Naval Base (see photo 6).  It is now being used as a marina and other commercial uses. 

 

These geographical and economic characteristics of the area meant that when the village was flooded there were significant consequences for the Island.  Flood events were quite common in the past and two serious events in December 1978.  Portland was cut off for 3 days as the village was under 1.2m of water.  In February 1979 30 properties flooded and public utilities were cut off for 24hrs.  This meant that a management scheme was implemented to try and alleviate the affects as these events had a recurrence interval of 5-10 years. 

 

There were two main causes of  flooding at Chiswell: 

 

Overtopping - This is when waves and spray go over the top of Chesil Beach.  Associated with this is shingle overspill where shingle was blown onto the roads and buildings causing road closure and structural damage.

Percolation - this is where water seeps through the shingle and reaches the clay base of the beach.  The water then flows either back to the sea or down into the village.

 

The Solutions:

A new recurved sea wall (300 metres) with the aim of reducing overtopping.  other modifications were made to create a wide, stepped defence Cost 350,000 (photo 1 and 2) (1981)

Gabion mattresses (150 m) which was used to raise the level of the beach to 14.5 m with the aim of making the crest more secure. Cost 150,000. (photo3) (1983)

Gabion Boxes (photo 4) protecting the most vulnerable area by raising the height of the beach. (1983)

To prevent flooding by  percolation - A drain system has been constructed.  This involved steel piles being placed through the beach and into the underlying clay Any water that is collected is directed in to the culvert (Photo 5 and 6) and is discharged into Portland Harbour. (cost 2.5m) (1985/6)

In June 1997 the section of the  A354 was raised so that it was above the flood level of the Dec 1978 flood level to prevent the Island from being cut off. Cost 600,000.

Total cost: approx. 5 million

Since the scheme was put in place the impacts of sever storms have been reduced.  For example road closure is now very rare.  The Cove House Inn (photo 2) was damaged in 1990.  Generally, the village is going through a period of revival as the flood risk is has been vastly reduced.