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LIST OF ILLUSTRATIONS.
FIG. 30. YORKSHIRE Coast . . . . . . . . . . . . . . . . . 220 31. GROTNES ON North Shore, BRIDLINGTON . . . . . .
229 32. GROYNES AT KILNSEA . . . . . . . . . .
236 33. Box GROYNE AT TRUSTHORPE . . . . . . . .
241 34. NORFOLK COAST, AND ENTRANCE TO THE WASH . . . . . . . . 243 35 Coast, BawDSEY TO Harwich . . . . . . . . . . . . . 285 36. GROYNES AT FELIXSTOWE . . . . . . . . . . . . . . 287 37. „ OSTEND . . . . . . . . . . . . . . . . 349 38. , West KAPELLE . . . . . . . . . . . . . 351
Tue geological and tidal conditions of every part of the coast vary so much that no general laws can be laid down as to the principle on which works for their protection should be carried out, and each particular locality, if it is to be properly treated, must receive a careful examination and investigation of its characteristics.
All attempts to preserve the littoral parts of a country from destruction must be a perpetual struggle against natural causes. The erosion of the cliffs is only a part of that system of destruction by which all land above the level of the sea is being worn away, exteriorly, by means of gales and tides acting on the shores, or, interiorly, by rain and frost on the surface. In both cases the degraded material is transported and deposited on the shores, or in the bed of the sea, there to be formed into the sedimentary rocks of future ages.
The destruction of the sea-coast has been most felt along the chalk cliffs at the east end of the English Channel; and owing to the necessity of preserving the frontage of the seaside resorts, which abound here more than in any other part of England, the protective works have necessarily been of a very extensive character.
The drift and clay cliffs of Hampshire and Dorsetshire, although continually wasting away, have not received the same care, the absence of towns and buildings not rendering protection such an absolute necessity. Further west there is a less waste, the cliffs of Devonshire and Cornwall being composed of harder and more resisting material.
On the east coast the cliffs extending from Flamborough Head to the Thames consist almost entirely of glacial drift or
alluvial deposit, and consequently are subject to constant erosion. As the advantages of the bracing air of such places as Cromer and Sheringham, and as Felixstowe and Clacton, where this is combined with a southern aspect, are becoming better known, and these and numerous other seaside resorts are becoming developed, the importance of works for protecting the sea-fronts and the esplanades is realized as being a matter of urgent necessity.
The geological character of the coast north of Flamborough, and on the West Coast, is such as to be less liable to the destructive action of the waves, except where cliffs of glacial drift intervene, as along part of the Lancashire and Cumberland coasts. There are also fewer towns and watering-places. At Blackpool, however, works for the protection of the coast of a very extensive character have been carried out.
Along the Belgian and Dutch coasts, besides several important watering-places, there are large areas of land which lie below the level of high tides, and depend for their protection on the maintenance of the sand-dunes by which they are bordered, or on sea-walls and earthen embankments of a very extensive character.
The consideration whether the destructive operations of nature should be allowed to go on without check, or whether remedies should be adopted for protection, is one that resolves itself into a question of money and convenience. On those parts of the coast which have been made into seaside resorts, the maintenance of the beach, and of the sea-walls which protect the promenades, is of vital importance to the attractions of the place, while the protection of the cliffs may be important to the preservation of the buildings which have been erected on them. Along those parts of the coast, also, where the land is preserved from inundation by natural sand-dunes or artificial embankments the preservation of the beach is a matter of absolute necessity. Where, however, the land is used for agricultural purposes and is not of a more than ordinary fertile character, the cost of the preservation of the cliffs on which such land is situated may be greater than the value of the land. For example, on the Yorkshire coast the waste is probably as great as in any other part of England. From Bridlington to Kilnsea, a distance of about forty miles, the cliffs, which consist of glacial drift, are wasting at the rate of 2) yards a year, equal to about one acre per mile of coast. Groynes which were erected at Withernsea cost £370 each, and allowing eight groynes to the mile, the cost of protection per mile of coast would be £2960. The life of these groynes may be taken at thirty years. The value of the land is about £30 an acre, and allowing a loss of an acre a year per mile of coast, in thirty years the value of the land lost would amount to £900, or less than one-third the cost of protecting it.
Recently the question of the erosion of the Yorkshire cliffs has occupied a considerable amount of attention on the part of the landowners and of the inhabitants of the seaside towns situated on the cliffs. It has been stated that by reference to old maps it was found that this part of the coast has been eroded during the last two or three centuries about one mile in width, the erosion during the last ten years having gone on at a more rapid rate than at any previous period. To deal with this question, it has been proposed to obtain Parliamentary powers for the purpose of carrying out a general scheme of protection, and of taxing all land within a range of three miles, and rating the property in the towns for the same purpose. The estimated cost of a system of groyping has been put at £3000 a mile, or a total with other works of £150,000. The interest on this outlay, with repayment of capital within fifty years, is calculated to involve a charge of two shillings an acre on all land within the first mile from the cliff; one shilling on the next mile; and sixpence on the third mile; and of threepence in the pound on the ratable value of houses. It will be seen, on reference to the chapters on examples of sea-walls and groynes, that the length of time over which repayment of the loan is to be spread is put at nearly three times that which has been sanctioned by the Local Government Board for works of this character.
The proposal to add to the taxation of agricultural land in order to provide for the doubtful contingency of its being washed away three centuries hence appears to be more novel than practical.
Previous to designing works of coast defence, it is necessary to have a clear conception as to
(1) The forces in operation causing the destruction of the cliffs and the denudation of material from the shore.
(2) The way in which these forces operate.
different classes of material; and the quantity available for maintaining them.
(4) The movement of littoral drift; the agents that cause such movement, and how they operate; and the general direction of the drift.
(5) The best form of structural works for preventing the drift of material and denudation of beaches.
The waste and destruction of coasts, apart from interior causes, such as weather and landslips, due to want of drainage, are caused by the action of waves breaking against them during on-shore gales and high tides. It is essential, therefore, that attention should be given to the laws governing the action of shore waves on beaches, cliffs, and sea-walls.
As the force of the waves which beat against a cliff or seawall and cause destruction is governed by the depth of the water on the beach in front of them, it is obvious that the most effective means of protection is the maintenance of the beach and the prevention of its denudation; and, where material is available, by promoting accumulation and by raising the level of the surface, diminishing the depth of the water and the force of the waves. In endeavouring to attain this object, the works should be so designed that, while securing a level and even strand on which the waves can expend their energy with as little destructive effect as possible, the amenities of the beach, especially at seaside resorts, should not be interfered with more than is necessary.
For this purpose a knowledge of the laws governing the movement of littoral drift and of the qualities of the different materials to be dealt with must be taken into consideration, as an important factor in designing works necessary for the protection of the coast-line.
Also, in designing works of coast protection, the fact must not be lost sight of that both on shingle and sand beaches the only material that can be collected and accumulated is that which is already on the coast or is supplied from the destruction of the cliffs. There is no other source of supply. Beach material is not, therefore, inexhaustible, but, on the contrary, on many parts of the coast is limited in quantity; and the question as to whether its removal for commercial purposes should be allowed is one that requires careful consideration.