Coastal Management

Coastal Management

Have you seen any of these?

Why? Lifespan Cost Problems Highest protection in the short term, lifespan about 50 years. Halts local erosion. They are very expensive to build. Erosion continues where scheme ends, need maintenance. Sea Walls

Groynes are designed to slow down longshore drift and build up the beach. They are usually made of tropical hardwoods which are more resistant to marine borers and erosion. A few are made of concrete, steel or in more recent times large rocks. They are built at right angles to the shore and spaced about 50-100 metres apart. Groynes may have a life of 15-20 years Groynes

Terminal Groyne Effect • Occurs when there are piecemeal protection schemes. • For instance a groyne field is built and sediment builds up between the groynes • The coastline continues to erode. • On the downdrift side there is a sediment deficit. The erosion of non protected side continues

The unprotected down-drift shoreline is set-back landward compared to the protected up-drift shoreline.

Terminal Groyne Effect In Action

This is a sloping feature which breaks up or absorbs the energy of the waves but may let water and sediment pass through. The older wooden revetment consists of posts fixed into the beach with wooden slats between. Modern revetments have concrete or shaped blocks of stone laid on top of a layer of finer material. Revetments

The gabion is a metal cage filled with rocks, about 1 metre by 1 metre square. They are stacked to form a simple wall. They are used to protect a cliff or area in the short term only, since they are easily damaged by powerful storm waves and the cages tend to rust quite quickly. Gabions have the advantage of ease of use and are relatively cheap but their life span is short. Gabions

Rip Rap Rock armour or riprap consists of layers of very hard rock with the largest, often weighing several tonnes, on the top. Riprap has the advantage of good permeability plus it looks more natural.

Beach Nourishment Beach nourishment, a technique used to restore an eroding or lost beach or to create a new sandy shoreline, involves the placement of sand fill with or without supporting structures along the shoreline to widen the beach. It is the only management tool which serves the dual purpose of protecting coastal lands and preserving beach resources.

Cliff Regrading Restructuring a cliff face to take away the steep gradient. reduces instability

Rising Sea Levels in Venice Rising sea levels pose a serious threat to Venice's fine buildings and unique network of canals. Once-minor floods - known in Venice as "acqua alta" (high water) - have become increasingly common, and more damaging. Now, work is due to begin on a multi-billion dollar scheme to protect the historic city with giant floodgates.

In normal conditions, the floodgates lie on the seabed. Tanks inside the gates are filled with sea water. When high tides are expected, compressed air is pumped into the gates, pushing the water out and causing the gates to rise on hinges. Once raised the gates form a slanting barrier against the incoming tide. The gates are 30 metres high and five metres thick. Protection by Barrier

A chain of floodgates will be constructed in three channels at the north and south ends of the Lido the long narrow island separating Venice's lagoon from the sea. A fourth barrier will be constructed at Chioggia, a fishing village at the southern end of the lagoon. The project is due to be finished between 2007 and 2010.

In two’s or three’s • Discuss the virtues of Soft and hard engineering techniques to slow or prevent coastal erosion. • Come up with a way or a combination of ways to try and stop the fast erosion at Great Cowden on the Holderness coast. Be ready to justify your answer!

Coastal Management