Eyewitness accounts of the great flood of 30 January 1607 tell of "huge and mighty hills of water" advancing at a speed "faster than a greyhound can run" and only receding 10 days later. The flood reached a speed of 30mph and a height of 25ft. It swept up to four miles inland in the Bristol area, north Devon, Pembrokeshire, Glamorgan, Monmouthshire and Cardiff - and up to 14 miles inland in low-lying parts of Somerset.
But it is still not certain exactly what sparked the disaster which killed so many. For centuries it was thought high tides and severe storms were to blame, a theory accepted by Dr Kevin Horsburgh from the Proudman Oceanographic Laboratory in Liverpool, who said a massive storm surge, formed by a combination of high tides and hurricane winds, may have been to blame. Tsunami theory But a tsunami theory was put forward by experts from Bath and Australia in 2004, supported by evidence of deposits of sand, pebbles and shell at various locations around the Severn Estuary where flood waters swept in, including Hill in South Gloucestershire. It's believed these deposits may have been brought in from the open ocean. Dr Roger Musson, head of seismic hazards at the British Geological Survey, confirms the theory is feasible, saying there are other examples of earthquakes in the area caused by an ancient fault off south-west Ireland - but adds that he believes a storm surge was more likely the cause.
 | | Several pamphlets recorded the disaster |
Risk managment experts, who have run simulations of a storm surge coming up the Bristol Channel today, say that in a worst case scenario the flood heights would top existing defences and cause flooding over an extremely large area. The cost of such a disaster would be about £13bn, with 80% of these losses occurring in the cities of Bristol, Cardiff and Gloucester. However, the chances of it happening again are said to be small, with the probability that such an event would take place on average only every 500 - 1,000 years. Pamphlets of the 17th Century depicted the great flood as a destructive and violent event, four hundred years later a similar killer wave could prove just as disastrous. | 
