Kenneth Pye Associates Ltd.
 Scientific Research, Consultancy and Investigations

              
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Coastal processes and prediction of morphological change in the Dingle Marshes area, Suffolk
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The coastline between Walberswick and Dunwich takes the form of a sand and shingle ridge, behind which are the low-lying Dingle Marshes, and the adjoining Westwood, Oldtown and Corporation Marshes. The shingle ridge has been artificially maintained for many years in an attempt to maintain the crest level at or above c. 4.0 m OD. The barrier has been retreating landwards for several hundred years at a long-term average rate of c. 1.0 m per year. In recent decades the central section of the barrier has receded more quickly than the northern and southern ends, creating a more arcuate plan form. The sediment volume in the central section has been progressively reduced, with the result that it has become increasingly difficult to maintain the height and width of the ridge. The barrier has naturally been prone to periodic wave over washing and breaching, and there have been several significant breaching events in the last 20 years, most recently on 31 October to 1 November 2006 when a c. 2 km length of barrier was levelled by waves and tidal ingress to c. 2.0 m OD. During this event four major and one minor tidal scour channels were created through the barrier, the deepest being located near the northern end of Dingle Marshes. Given the projected increase in sea level over the next 100 years, the continued maintenance of the barrier as an adequate tidal defence is likely to become unsustainable. Several options for managed retreat and realignment of the barrier have been suggested. However, a careful balance needs to be stuck between the cost of maintaining the barrier in a sustainable position, and the loss of freshwater wildlife habitats on the marsh areas behind. 

Reconstructions of the coastal environments between Dunwich and Walberswick from historical maps and
documentary evidence between 200BC and 2003. Beneath, an indicative prediction of the morphology in the 22nd
century under two scenarios: (a) 'do nothing'; and (b) maintenance of the Westwood Marshes embankment.

Observed (black) and predicted (red) tidal levels recorded at Lowestoft during the passage
of a storm surge between 30 October and 2 November 2006. Although the maximum tidal
height was not exceptional, the tide hardly retreated, so that water levels were constantly
above the predicted level of high tide for approximately 20 hours.

Lidar image of the coastline between Dunwich and Walberswick, including Dingle Marshes. The heavy black lines
show the positions of existing embankments, while the red arrows show the positions of breaches in the shingle
barrier during the storm surge on 31 October to 1 November 2006. The light blue areas show the land below
1.3 m OD and indicate the marshes which would be flooded if there were no embankments in place.

    
The Dunwich-Walberswick shingle barrier, Suffolk,  in June 2006 (left), and again in November 2006 (right) after
breaching by a storm on 31 October to 1 November 2006. Dingles Marshes are to the right of the photographs.

    
Tidal channel formed following storm-breaching of the          The saline lagoons and brackish marshes of Dingle
Dunwich-Walberswick shingle barrier, Suffolk                      Marshes, protected behind the artificially nourished
                                                                                           sand-shingle ridge

Publications and Reports

Pye, K. and Blott, S.J. (2006). Coastal processes and morphological change in the Dunwich - Sizewell area, Suffolk, UK. Journal of Coastal Research 22, 453-473.
(click to view the abstract of this paper)

Pye, K. and Blott, S.J. (2006) Walberswick to Dunwich Tidal Defence Scheme: Comments on the Preliminary (Do-Nothing) Ecological Appraisal Report with Background Information About Coastal Processes and Morphological Evolution of the Area. Report prepared for RSPB. Kenneth Pye Associates Ltd., External Research Report ER606.

Kenneth Pye Associates Ltd. - Environmental Consultants
Page last modified: September 03, 2007