COAST DESTRUCTION AND DEFENCE.*
ONE result of the changes in the unknown ages of geological time is constant,—the steady encroachment of the sea. Here and there land may snatch a small advantage over salt water, and a delta fill up, or a _coral bed grow into an island, but the net result is that soundings and the evidence of the distri- bution of plants and animals show us that where narrow creeks of water separated continents broad tracts of interfluent ocean now roll, and that there is no reason why at the close of a remote, unthinkable, but inevitable lapse of time the greater part of the land surface may not be reduced to mere islets, surrounded by a vast and almost lifeless ocean, so salt that no creature can live in it but the brine shrimps and the other entomostraca which survive in the Salt Lake of Utah or the Dead Sea.
Recent years have added so much to the financial value of the English coast-line that, apart from such remote antici- pations, there has been every reason to combat the encroach ments of the sea, especially at those points where seaside towns have sprung up, and have rendered every acre of great value to the owners of the soil. At Cromer, Sheringham, Bournemouth, and numbers of other older and established watering places the sea has to be fought, and at present it is by no means certain whether it has been defeated.
Mr. W. H. Wheeler, a practical engineer, the author of two valuable works on The Drainage of Fens and on Tidal Rivers, gives in a new volume on The Sea Coast a most interesting summary of what is known of the present conditions of the shores of England. Its practical object is to give some data as to the best forms of sea-walls and groynes. But this is preceded by an account of the natural agencies for destruction and protection, such as the action of shore waves, the move- ment and formation of pebble beaches and sands, and the transporting and depositing power of waves. Briefly speaking, the best natural coast protection is a pebble beach. Yet these beaches never rest in situ, and are themselves derived from the previous destruction of land. There is a littoral drift which slowly " shoves " the pebbles onward along the coast, where they are only arrested by natural juts or groynes, which stop the drifts and bank up the pebbles in such a way as • The Sea Coast : (1) Destruction, (2) Littoral Drift, (3) Protection. By W. H, Wheeler, M.LC.E. London s Longman and Co. DOD. gd. net
toiproteat the bays between-them. There are a large number of. famous pebble . banks along , our shores, some of.which have done the work, not only of protection but of reclamation, in a more thorough Manner than any engineer could afford to attempt. The tendency a the sea-wash is to push the pebbles along into banks parallel with the shore. These gradually elongate,and passing onwards, block the mouths of rivers, or en- close long tracts of shallow sea, which in time fill up. At Ald- borough the travelling shingle has prolonged the course of a river for nine miles, protecting all the inner land from the sea. At Chesil Bank it has made an inland lagoon ten and three- quarter miles long. In the Solent five miles of such bank, three being submerged, run out to Hurst Castle. Barnstaple boasts a bank of large boulders, those at the bottom weighing as much as a hundred and fifty pounds. Such banks are seen at Shoreham, Lancllig, and at Weybourne, in Norfolk, the most striking of any except Chesil Beach. For at Weybourne the bank runs on till it projects far into the sea at Clay, and after blocking a river there has passed on, and grown so fast, with a " nose " of sandhills added to it, that it has been prolonged some hundreds of yards in human memory, judging from the successive erection of look-out and Coastguard huts, which were originally at the extremity. Dungeness is a mass of deposited shingle, six miles wide at the base and three miles long, and grows so rapidly that it has travelled eastwards at the rate of two and a half yards annually since the lighthouse was built in 1782. It now increases at the rate of two hundred thousand tons of shingle per year.
Unfortunately, great as is the mass of pebbles at places, there is "not enough to go round," a fact which, besides mating the artificial protection of coast costly and difficult, suggests the question, Whence did the pebbles come, and when P They do not come from the bottom of the sea, for at Weybourne and Cley, for example, the sea bottom is sand. In many eases they do not come from the destruction of the cliffs, for the pebbles are not the same as those in the cliffs, but belong to formations inland. There are also far too many of them, and also far too much sand, which is only pebbles ground smaller, to be formed in any recent epoch. In More- cambe Bay there are ninety thousand acres of sand, as much as the whole area of the New Forest. There are eighty-four thousand acres of sand-beds in the Wash. Nowhere on the ad- jacent coast is there, or was there, material in recent times in the shape of stone to be ground down into this vast weight of sand. There is plenty of earth, and the earth deposits all along the Norfolk coast from Brancaster to Blakeney grow fast now. But -there is not sufficient stone on any adjacent part of the coast to make either the sand-beds or the shingle banks from. In other places the destruction of the chalk cliffs from age to age provided a quantity of flint, which can be recognised by its colour. But in many pebble banks the hue of the stones shows that they were derived from inland gravel-beds, perhaps brought down adhering to glaciers and ice. In others the origin of the beaches can be identified or conjectured. Thus when the Solent took the place of the land between Hamp- shire and the Isle of Wight, the whole of the flints which once studded the chalk were left as possible beach pebbles. The great bank running from Weybourne to Blakeney is probably made and extended by the drift from the vanishing cliffs at Sheringham, Cromer, and elsewhere near. The net result is that whatever fresh natural protection accrues to the coast in places is caused by destruction of cliffs at other places, and that failing this accumulation of coast-drifting shingle arti- ficial defences must be made. These are either groynes or barriers; run out seawards to stop the march of the drifting shingle coastwise, or sea-walls. There is no general agreement among engineers as to the best form of either groynes or sea- walls, even where the conditions are the same as those met-with on other parts of the coast which have been experi- mented upon.
At ninety-six places on our coasts artificial means of arresting ind piling up the drifting shingle have been used, while the number of sea-walls passes counting. The artificial maintenance of sand dunes is not much practised in this country, probably because the parts of the coast which they fringe are considered to be adequately protected, though
where that is not the case, as opposite the reclamations made , Tie French Revolution and Religions Reform: an Account of Feeleoiastiral by the Earl of Leicester at Holkham, the " hills" are easily oi.itri,..)thtweetehsp,ot.frif in Franc. front to Mi.. By William raised by half burying faggots and letting the sand blow in Loma Hodder and gioughtnu. from the sea over them, and then planting the mounds with marram grass. The control of sandhills by planting is now well understood. In Australia a long frontage of sandy coast was planted with a grass which not only held the sands firm, but proved excellent cattle food. On our shores there are three main sand-containing grasses. One is mat grass, with an under- ground creeping stem. It will branch out starwise from a centre, and form a circle twenty yards in diameter. Another is the famous "marram," which the Dutch call " helm," which is planted in drifting sand in tufts two feet apart, and soon grows sufficiently to prevent the " hills " from shifting. The third is " sand sedge," which is as effective in building up sandy coasts as the fresh-water sedges are in collecting and retaining alluvium.
Mr. Wheeler describes most patterns of sea-wall existing in England, as well as the various means used for keeping or collecting beaches and sand in front of threatened spots.
Theoretically, the groynes are preferable, for they endeavour to enlist natural forces in aid. It is of immense importance, where the safety of miles of coast, and sometimes of thousands of acres of reclamation, is involved, that the right kind of groyne should be used. Unfortunately what suits one place does not suit another, and a groyne which would help shingle to accumulate on a given piece of coast might cause such a scour as actually to cut the beach away elsewhere. The two.
rival kinds are the tall groynes and the low ones. The latter aim at building up beach gradually, the former at arrest- ing the progress of the littoral drift in a great mass.
Favourable examples of the working of the low groynes of a kind invented by the late Mr. Case, " expenditor " for Romney Marsh, may be seen at Dymchurch, where, instead of placing more than £100,000 worth of heavy groynes outside the threatened wall, low groynes of ingenious construction, following the natural inclination of the beach, were built rapidly and cheaply, at the rate of one per day. The result was that after ten miles of coast had been provided with these, at a cost which, including the re- pairing of the sea-bank, was only £19,000, " the foreshore was built up to the natural inclination of repose, and is now undisturbed by gales, and the beach has been changed . from mud and sand with pools of water to a well-consolidated mixture of beach and sand." Where there is no natural beach for groynes to accumulate, sea-walls
become the only alternative. Of all the forma - in use Mr. Wheeler considers the most effective to be one having an elliptical form at the bottom, dying out into a vertical line at the top, the bottom slope conforming to the natural angle of the beach (p. 87).
This is a good instance of a book written on a technical subject for readers of general education. It is full of facts, and provides the large class of owners of coast land, seaside town authorities, and Government officials 'who have to report on coast protection with the power of noting for themselves what has been done elsewhere. Landed pro- , prietors often incur great expense and loss in shore protection works. undertaken with insufficient knowledge or not very well informed " expert " advice. We know of more than one case in which, if a landowner had had the local information at his disposal which reference to Mr. Wheeler's book would give him, many thousands of pounds might have been spent tc advantage instead of uselessly.
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