| BERM
The Project
|
BERM
Beach Erosion in the Rives Manche
The Project Introduction Aim of the project To investigate the supply and depletion of shingle on Rives Manche beaches under present day management regimes, and to determine the sustainability of the beaches in a period of rising sea level. Project description The shingle beaches of the Rives-Manche region are a vital natural defensive barrier, helping to protect the land from wave attack. In low lying areas they are the principal natural defence against erosion and flooding. They are also a major visual and recreational amenity of great importance to the tourist industry. In addition, above the high tide mark they speedily become colonised by plants, developing into habitats of considerable nature conservation importance. The shingle on Rives-Manche beaches is composed almost entirely of flint, and derives ultimately from the erosion of the chalk strata with their included bands of flint nodules. It has long been assumed that the eroding cliffs supply flints to the beaches at a sufficient rate to compensate for the annual losses caused by wave attrition and other processes, including human activity. The shingle beaches, in other words, are thought to be a self-sustaining resource. This assumption is more and more being called into question on both the Sussex and French coasts. Long stretches of the cliffs along the East Sussex coast are now defended by sea walls, which significantly restrict the supply of flint to the beaches. In addition, the shingle on both sides of la Manche naturally drifts from southwest to northeast along the beaches under the influence of the tides and the prevailing winds. Groyning of many beaches and the construction of jetties at harbour mouths have seriously interrupted the movement and distribution of shingle. The dredging of some harbour mouths, for example at Dieppe and Saint-Valery-en-Caux, also interferes with the hydro-sedimentary system, further depleting shingle resources. As a consequence the supply of shingle to the beaches may no longer be sufficient to offset the annual losses. Also of concern is the suggestion that much of the flint that now forms shingle on the beaches was eroded from the chalk strata during the glacial periods. It is argued that rivers and streams running off the frozen Downs deposited flint gravel on the floor of what is now la Manche at a time when the sea was no nearer than western Cornwall and Brittany. Rising sea levels after the last glacial period flooded la Manche, and drove much of the flint gravel landwards, thereby creating the shingle beaches. When the sea reached its present level, 5000 or more years ago, the supply of shingle from offshore largely ceased. According to this view, the shingle that protects the present-day shoreline of la Manche is essentially a fossil deposit that is ever diminishing under the attack of the waves. If Rives-Manche shingle beaches are indeed fossil, the implications for long-term sustainable coastal management are extremely serious. Even if they are not wasting away naturally, increasing human intervention with natural processes is seriously affecting the volume and distribution of shingle along the Sussex and French coasts with impacts on the rates of coastal retreat and the risk of flooding. It is crucial, for coastal zone management in the Rives-Manche region, to ascertain whether or not the current shingle supply is sustainable. The region faces a projected sea level rise of approximately 0.5m in the next 50 years. When combined with predicted increased storminess and high tide levels there is a substantial risk that current sea defences will be overwhelmed within their engineering life-spans. However, it would be quite wrong to prejudge the issues. What is urgently needed is a transnational dialogue between experts on either side of la Manche who have worked on the problem, often from very different perspectives and without reference to each other. A more thorough analysis of existing scientific evidence and the collection of additional scientific data relating specifically to this issue is also urgently required. This project will determine the extent to which
contemporary shingle beaches of Rives-Manche are depleting and assess the
risks that this will pose for the region in the face of rising sea levels.
The study will encompass the shingle beaches of the entire Rives-Manche
region, i.e. East Sussex, Seine Maritime and Somme
Contact details Dr Cherith Moses, Dr Rendel Williams, Dr David
Robinson
Telephone: 00 44 1273 877037
Dr Daniel Delahaye, Dr Stéphane Costa (consultant)
Telephone: 00 33 2 31 56 63 84
Last updated 06/FEB/2001 MAW |