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Chiswell case study: The Scheme |
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 Flooding behind the beach during the storm of December 1978. The Island of Portland was effectively cut of from the mainland   Above: Waves overtopping the beach during the storm of February 1979. Below: The damage to property  
Repairing the breach during the 1979 event. Plant from across the Island, including the quarries, was brought in to push the pebbles back to the crest of the beach |
History and description of problems 4. It is likely that the Chiswell settlement and the southern neck of Chesil Beach have been flooded many times. The first major report of note occurred in November 1824 when, as a result of a catastrophic storm, 26 people were drowned and about 80 houses destroyed or damaged. Since that time, 22 events that have endangered lives and properties have been worthy of record, the most celebrated of which occurred in November 1936, when King Edward VIII had the misfortune of being on board a train which was stranded by floodwater at Chiswell. 5. It appears that the incidences of flooding did little to dissuade people from living in the area, or the authorities from systematically reclaiming land at the northern end of the settlement. It was in 1865 that the Weymouth and Portland railway line was constructed on an embankment which traversed The Mere, a low-lying area of marshland at the back of the Beach, within the confines of Portland Harbour. In 1902, the infilling of The Mere at its northern end began, followed by the construction of the naval oil tanks on the reclaimed area. Further reclamation of The Mere was subsequently carried out, with the last vestiges disappearing in 1977. 6. In 1978, Wessex Water constructed a floodwater culvert connecting the northern end of Victoria Square northwards to the Ministry of Defences internal surface water drainage system, discharging into Portland Harbour, with the object of providing an outlet for sea water flooding to this lowest part of Chiswell. 7. It was, however, the flooding events of the 13 December 1978 and the 13 February 1979 which prompted the promotion of the Sea Defence Scheme. The characteristics of the two events were significantly different. The former event consisted of steep waves, of about 12 second period, accompanied by a strong on-shore wind. The waves, on breaking, plunged at a steep angle, creating a strong backwash which removed material from the Beach to the sea. The Beach was progressively cut back and the crest level lowered as the erosion continued into the landward slope. The lowered crest level permitted overtopping, causing further crest lowering and more overtopping which, combined with the percolation through the Beach, eroded the landward face. The result was an inundation of the lowest part of Chiswell to a depth of- 1.2 m, the flooding of properties and the main road, and a potentially serious danger of a breach, which could have entirely severed Portland from the mainland. 8. The February 1979 event was caused by an ocean swell of 18 second period waves which arrived without warning and was not accompanied by strong winds. Higher surge conditions than in 1978 resulted, and although the deep-water wave height was less, the energy of the long period waves led to severe overtopping of the Beach and sea wall, to a lowering of the Beach crest, and to the carrying of shingle on to property. 9. From records, it was assessed that the 1978 event, which induced percolation through the Beach and overtopping, has an estimated return period of five years (storm surge flood). The February 1979 event, which caused seepage and overtopping from long-period swell waves, has an estimated return period of 5O years (ocean swell flood). 10. The consequences of the two events on the community at Chiswell and on the communication between Portland and the mainland were similar. Over 30 properties in the lower end of Chiswell were flooded and families were evacuated to emergency rest centres; all public utility services were cut on both occasions for a period of over 24 hours. The Isle of Portland, including the Naval Base, was cut off from the mainland by floodwater apart from a circuitous route through the Royal Naval Air Station at HMS Osprey. 11. The emergency services were fully committed for a period of five days for the 1978 event, and for 10 days for the 1979 event. In both cases, Wessex Water and Weymouth and Portland Borough Council (the Council) combined forces to rebuild the crest of the Beach. Although a co-ordinated effort on the part of all services was made to restore community life, it was a traumatic period for the residents and emergency workers alike. To experience such devastation twice within three months led to a plea from residents for action to be taken, and to a determination on the part of the authorities to respond. 
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