Underwater Surveys Benefit Prevention of Coastal Erosion

The town of Dunwich on the coast of Suffolk has nearly all been lost to coastal erosion.

Once a thriving sea-port is now a historic site of marine archaeological interest. The first mention of a settlement in this area was ‘Dunmoc’ in the 7th Century. In the Doomsday book (1086) there is one church but within 150 years the population had grown to about 5000 and was considered to be the 6th largest port in England.

A measure of the importance of a settlement is the number of religious buildings in the town and this peaked at 18 in 1225. However after this point the town seemed to undergo a fast decline in the following 250 years.

Coastal erosion due to storms and changing currents have moved the coastline at least 1500m further inland.

Today there are less than 50 houses which could be claim to be part of the ‘extended’ Dunwich village. Most buildings at that time would have been made mainly of wood and thus would not have survived.

Churches and other religious buildings however were more likely to be constructed of stone and therefore it is the remains of these that may be present underwater.

Several surveys were conducted over a 4 year period (2008-2012) using sidescan sonar imagery and multibeam bathymetry at the highest resolutions.

These underwater survey techniques can get a reasonable level of understanding however the fine detail is masked due to the dark and turbid waters in the area which precludes the use of underwater photography.

Therefore a diver-held DIDSON sonar system was used to target individual features previously identified.

The DIDSON works at 1.8MHz and can be held by a diver like a video camera with a head-up display or mounted on a tripod.

Press Release, October 14, 2013