sharp point of Dungeness is constantly protected from wave action 

 by the French coast close across the Channel. Although the south 

 coast of the Ness is now being eroded, new ridges are being built 

 up on the east coast. 



Some spits, such as Spurn Head at the mouth of the Humber, 

 are predominantly sandy in character. They are built up largely by 

 the long, flat constructive waves that carry sand up the beach from 

 offshore. But sand cannot be brought in quantity from depths 

 greater than about thirty feet, so much of it must come along the 

 shore, carried by oblique waves and currents from a coast that is 

 being eroded, or from a river mouth. 



The sandy shore line features born of waves and wind can be 

 raised further by wind alone. As the desert sands are piled into 

 dunes, so are the sands along our beaches, but the beach dunes are 

 different because of the part vegetation plays. Their sand is held — 

 and more is trapped — by the growth of sand-loving plants such as 

 the dune plant known as marram grass that thrives only where it 

 is being continually buried by fresh sand. Because the plant cannot 

 stand salt water it cannot get a foothold on the dunes until the wind 

 has raised them above the limits of the highest tides. Today vast 

 quantities of sand are trapped in some of the larger dune areas 

 around Britain's coasts — the dunes of Braunton Burrows in the 

 southwest, Newborough Warren in Anglesey, and the Culbin Sands 

 in east Scotland. This sand has come mainly from the sea, first 

 washed onto the beaches by waves, then blown inshore at low tide. 



In some places estuaries or bays are almost entirely shut off from 

 the sea by the growth of spits or other barriers. In the sheltered 

 lagoons behind the barriers the land, with the help of salt marsh 

 plants, can reclaim part of its loss from the sea. Capable of growing 

 in salt water, these plants trap the silt and mud carried into the 

 lagoons by the tidal inundations. Year by year the land level is 

 raised, until eventually the marshes are covered only at the highest 

 tides ; this is the time when they are ripe for reclamation, for their rich 

 silt makes fertile land. In the Norfolk marshes nature's reclamation 

 goes on at a rate of up to one centimeter a year, but elsewhere the 

 rate can be rather quicker — particularly if it is aided by man, as it 

 is in Holland. 



Although the loss of land to the sea may be more spectacular 

 than land reclamation, in 191 1 the Royal Commission on Coast 

 Erosion estimated that on the whole Britain has gained more from 

 the sea than she has lost. Reclamation is also taking place in the 

 Danish Wadden Sea, where man is helping nature along by artificial 

 means. Active outbuilding is also extending the land seaward 

 around part of the coast of the Gulf of Mexico, particularly near 

 the big river mouths, and off the coast of northern Brazil. In such 

 places the rivers bring down great quantities of sand and clay. 

 While the sand is built into ridges by the waves, the clay fills the 

 hollows between them and forms a wide, low coastal belt of 

 accretion called a chenier plain. 



In the seemingly endless battle between sea and land, there is no 

 winner, there is only change, and in the large scale of things man 

 can only stand by and watch and attempt to understand the forces 

 great and small that change the edge of the sea before his eyes. As 

 in the past, the seas have swept over the continents and flooded the 

 land, then retreated, and so they will again and again. 



in/ef of baymouth 

 bar migrafes eastwards 



The five diagrams above show how the sand 

 bar at the mouth of Katama Bay, Martha's 

 Vineyard, was changed by wave action 

 from 1846 to 1889. Submarine sand bars 

 form at the breal<. point of waves and are 

 built up from both sides - some of the sand 

 being carried onto the bar from the seaward 

 side, some carried by the bact<wash 

 of water from the beach. 



233 



