COAST PROTECTION

there is a difference of opinion about the value of much of the works for coast protection, and in the opinion of some, money expended thereon does not give an adequate return. even in holland, whose existence depends on the maintenance of its sea walls and defences, authorities are divided on many important questions both of principle and practice. since rgro there has been remark- ably little development in the means adopted to combat coast erosion, and, generally speaking, the methods of construction which still find favour, not only in great britain but also abroad, are the same in principle as those which have been used for genera- tions previously. the royal commission on coast erosion, ap- pointed in 1906, whose final report was issued in 1911, collected and placed on record much useful information on the subject of coast erosion, protection and reclamation, not only relating to the united kingdom but also in reference to foreign countries and in particular holland and belgium! the recommendations of the commission regarding the control of the foreshore of the united kingdom and the constitution of a central sea defence authority have not yet been given effect to by legislative enactment. the report, however, has served to 'see reports and evidence: roval commission on coast erosion; particularly final report, cd. 5,708 (1911). coast protection dispel certain crroneous ideas, particularly as to the extent of the loss of land due to erosion in the united kingdom, and proves conclusively that the expense of protecting purely agricultural land is out of all proportion to the value of the land thereby saved from destruction. subsidence and upheaval of the earth’s crust-—it has been sometimes asserted that the continuous loss of land on the south and east coasts of england js partially due to subsidence of the earth’s crust, but there is no evidence to show that cither up- heaval or depression has, during historic times, affected the encroachment or recession of the sea on the coasts of great britain, and it may be safely asserted that the whole of the changes in the coast-line since the dawn of history have been due either to accretion or denudation. physical causes of seca encroachment—the encroachment of the sea on the coasts is due to the erosion of the cliffs and shore material. of the detritus derived from such erosion a por- tion is carried along shore by the combined action of wind, waves and tides, remaining in a state of more or less constant move- ment until it is finally deposited to swell some accreting sand or shingle bank or is driven against some natural or artificial bar- rier, where it lics and is perhaps buried under subsequent de- posits. the travelling shingle and sand or ‘ littoral drift ” is the principal source of the beach materials which form, and make good the wastage from, the foreshores of the coast. in the course of this lateral travel the particles, large and small, forming the detritus are still further disintegrated. the lighter material is carriec! off in suspension by the sea and ultimately finds a rest- ing place on the ocean bed at a level below the influence of wave action or tidal scour. the remaining portion of the solid mate- rials derived from the destruction of the clitf or shore is immedi- ately transported into deep water, the finer particles being rapidly swept away by the current until finally deposited on the sea bed, and a certain proportion of the larger material too heavy to be carried in suspension for any considerable distance, is drawn down the foreshore and the bed of the sea by the under- tow of the waves and ultimately makes its way by gravitation into deep water, where it finds a resting place. river detritus —the amount of solid matter thus finding its way into the ocean is vast and is increased by the addition of detritus brought down by rivers and derived from the land sur- face. river detritus, on reaching the sea, shares much the same fate as the material derived from the coast line. a part finds a resting-place in sand banks and alluvial deposits at the mouths of rivers and estuaries, the remainder spreading itself over the deep-sea bed. relation of littoral drift to eroded alaterial—it is impossible to form any exact estimate of the relative proportions of the material more or less immediately carried away to the deep sea and that other part which we may call littoral drift. in the case of chalk cliffs and foreshores it is probable that the immediately removed material amounts to nearly 90% of the whole, while alluvial cliffs and those consisting of boulder clay or other similar material may yield 20% to 30% of solids not at once carried away from the foreshore into the deep sea. gravel and rock cliffs naturally yield a higher proportion of heavy and harder particles. on the whole it is unlikely that on the average more than 20% of the solid material falling on to foreshores and de- rived from the decay of the coast line remains above low-water mark for any length of time. deep sea erosion.—the process of erosion and littoral drift is not confined to the foreshore and beach above low-water mark. such changes are continuously in progress below low-water mark where wave action or tidal scour is capable of affecting the sea bottom. these agencies and the gravitating tendency of the particles continue at work until a condition of equilibrium of the opposing forces is reached. it has sometimes been asserted that material is derivable from the deep sea for the replenishing of foreshores. fragments of rock, boulders and flints dislodged from the sea bed in comparatively shallow depths below low water are sometimes cast up on the foreshore, but such instances are exceptional and cannot be taken as evidence of coast protection the supply of any considerable volume of material from the deep sca bed. undoubtedly material lying on the sea bed below low water and in shallow depths is, under certain conditions, driven back on to the foreshore, but this is merely a temporary phase in the progress of littoral drift. with change of wind or tide the conditions may be reversed. effect of protective works on adjoining coast-line.—in order to increase the extent of any forcshore or to maintain it even in its existing condition, the natural and incessant losses must be made good by accretion or the trapping of material derived from other parts of the coast. this may be done in favourable circum- stances by the construction of groynes or other works similar in effect, but the accretion through their agency is in every case accomplished to the detriment of neighbouring foreshores. thus the large groynes at brighton trap for the time being the greater part of the shingle travelling from west to east, and very little passes on to the foreshore to the east of brighton, which, in consequence, has become denuded. . conditions affecting littoral drift—the direction of the pre- vailing littoral drift is in general governed by the direction of the flood tide, the prevailing winds, and the shape of the coast. authorities differ as to the relative effect of the tide and wind, and although the direction of drift is at times varied by the wind direction and the consequent wind waves, most competent authorities agree in the opinion that, in the case of england, at any rate, the prevailing drift coincides with the set of the flood tide. on the english coasts the direction of the flood tide does, in fact, in general coincide with the direction of the prevailing winds. on the east coast the drift is from north to south and on the south coast from west to east, both in the direction of the flood tide and prevailing wind. where a coast-line is broken up by deep bays and indentations no continuous drift can take place, each bay retaining its own characteristic material, which is prevented from leaving it by the projecting headlands extending to low water or beyond and forming natural groynes. numerous examples of these conditions are found on the south coast of devon and dorset. the direc- tion of the flood tide is also in many cases altered locally by the configuration of a bay, e.g., the deflection of the tide along the shores of the bay in a direction opposite to that of the normal coastal current. in cases where a coast-line is broken up by estuaries or rivers the results are variable, depending upon the continual struggle which takes place between the opposing forces affecting littoral drift and the tidal inflow and outflow of the river, the latter sometimes aided to a material extent by the addition of large volumes of fresh water. during strong winds in a direction contrary to the set of the tide the normal travel of drift may be nullified or even reversed. the accumulation of material on a foreshore is generally brought about by tidal action in calm weather. a beach which has been depleted during a long spell of heavy weather usually makes up again, at any rate to a partial extent, on the occurrence of calm sea and the cessation of wind. this replenishing is due to the return of a portion of the material previously drawn down into shallow water below low-water mark. generally speaking, on- shore gales result in the drawing down of the beach material and its gravitation towards the deep sea. off-shore winds, on the other hand, frequently lead to the accumulation of material on a foreshore. | effect of pier works and other artificial projections -—the construction of solid piers or other similar obstructions at an angle with the general shore line and projecting into the sea is, when occurring on a coast-line subjected to erosion, almost inevitably followed by serious depletion of the foreshore to lec- ward. the solid projection, which in many cases is carried suffi- ciently far in a seaward direction to reach comparatively deep water, effectually hinders the passage of littoral drift from its windward to its leeward side! thus the erosion of the ice shore 1 the terms ‘ windward" and ‘ leeward” are used in the sense understood by engineers engaged in coast protection work, viz., “ windward ’'—the direction whence the prevailing littoral drift pro- ceeds; and “leeward ''—the direction towards which such drift takes place. 667 is accelerated by the loss of the travelling mater‘al which under natural conditions makes good to a partial extent the ravages of the sea. instances of such stoppage are numerous on the english coast. the folkestone harbour pier has arrested the travel of the beach from the westward, and led to the accumulation of a large bank on that side and the denudation of the foreshore to the east of the harbour and towards dover. the construction of the harbour works at dover has stopped the eastward drift at that point and accelerated the destruction of the cliffs in st. margaret’s bay. at lowestoft the construction and subsequent extensions of the harbour pier and other works which project at right angles to the coast-line at the sea outlet of oulton broad have resulted in the accumulation of a bank of shingle to the northward and serious encroachments on the town frontage to the south of the harbour. sea w'ails—the conditions affecting the design of a sea wall differ so materially that every case must be considered on its merits and provided for accordingly. sea walls may be divided roughly into two classes, sloping and upright, each class having its advocates among engineers. generally speaking, walls having a sloping face are used in holland and belgium, whilst a vertical or nearly vertical face is more common in great britain. the immediate effect of the construction of a wall is detrimental to the beach in front of it, although affording protection to the cliff or banks behind. thus, the construction of a sea wall on a sand or shingle foreshore is in itself calculated to bring about the denudation of the beach and the wall may become before long the agent of its own destruction. whilst the wall will prevent erosion by the sea of the cliffs in rear of it, the beach in front of the wall must be protected and conserved by the construction of groynes. many walls have failed through the displacement of the filling behind them by wave action; the provision of a substantial and wave resisting surface or paving behind the wall is, therefore, of great importance, and has been too often neg- lected. suitable provision for the drainage of the cliffs, where they exist at the back of sea walls, is also a matter of high importance, which has often been neglected with disastrous results. much can undoubtedly be done by draining, sloping and plant- ing, to preserve and protect cliff faces, and these works ought to proceed simultaneously with the carrying out of sea-defence undertakings, when the cost of the latter is justified, to protect the foot of the cliff. sea walls subjected to abrasion by shingle are, if faced with concrete, very liable to progressive and serious damage. in such positions a concrete wall is frequently protected by a facing, at any rate over that portion subjected to abrasion, of hard stone or flints. for this reason also reinforced concrete is unsuitable for use in the face work of walls on a shingle beach, as the abrasion of the concrete surface soon results in exposure and deterioration of the steel reinforcement. grovnes.—\lowever effective they may be in collecting travel- ing material, groynes will not in all cases prevent the waves reaching the toe of a cliff or bank and eroding it to a greater or less extent. a combination of thet wo forms of protection—groynes and wall—is frequently desirable, but groynes alone have on many low-lying foreshores, particularly where there are no cliffs, proved successful and efficient without the construction of sea walls or protected banks, as for instance on the four miles of shore between worthing and shoreham. in some cases pro- tection of the crest of a beach above high water has been secured with success by the construction of a timber barrier or wave screen formed of piles spaced apart and driven parallel to the line of shore. groynes may be divided into two main classes: (1) high and substantially built structures of timber or other material; (2) low groynes of inexpensive and light construction usually placed at short intervals apart. in general, low, light groynes are suit- able on flat sandy foreshores which are not expose to sudden anc extensive changes of level. in any case it is undesirable to build up the planking of a groyne to a considerable height above the foreshore level existing at the time of construction, and it is preferable to raise the groyne by the addition of planking to 668 keep pace with the accretion of beach material. the use of rein- forced concrete for the construction of groynes has frequently been advocated, but is unsuitable on shingle beaches on account of the rapid abrasion of the thin concrete coverings of the stecl reinforcement. groynes, speaking gencrally, to be of maximum efficiency should be at distances apart about equal to or little more than their length. they should extend continuously from the shore or work to be protected to the vicinity of low water of spring tides. there is much diversity of opinion and practice with re- gard to the direction in which groynes should point. some authorities advocate their direction at right angles to the shore line, others pointing slightly to windward, and some authorities advocate a leeward direction. no general rule can be laid down and a plan suitable for one locality may prove a failure in another. the opinion of most authorities, however, appears to favour a direction pointing slightly to windward. removal of shingle —beach material is too often limited in quantity and the question arises whether its removal for com- mercial purposes should be allowed. the results of natural erosion and denudation are, in many instances, aggravated by this practice. the powers possessed by the board of trade provide for the issue of prohibitory orders and in certain circum- stances where the removal of beach or sand can be shown to be injurious, such orders have been frequently made. relative extent of loss and gain of land—the evidence as regards the total superficial area gained and lost in recent years on the coasts and in the tidal rivers of great britain shows that far larger areas have been gained by accretion and artificial reclamation than have been lost by erosion. evidence laid be- fore the royal commission by the ordnance survey dept. in 1907 showed that within a period, on the average, of about 35 years, about 6,640 ac. had been lost to the united kingdom, while 48,000 ac. had been gained. most of the gain has been in tidal estuaries, while the loss has been chiefly on the open coast. moreover, the gain has been due in the main to the deposition of sediment brought down by rivers and to artificial reclamation. it is, however, probable that the land lost has been more than compensated for by land naturally accreted. the report of the royal commission contains the following statement :— the erosion . . . would have been far more serious if extensive works of defence had not been constructed by local authorities, railway companies and others, at a great cost, though, on the other hand, such works in many places have been responsible for erosion of the neighbour- ing coasts by interfering with the normal travel of the beach miterial. on the whole we think, however, that while some localities have suffered seriously from the en- croachment of the sea, from a national point of view the extent of erosion need not be considered alarming. cost of coast protection.—the cost of construction of groynes varies very considerably with the design and local conditions. before the world war light low groynes might be constructed at a cost of from ros. to {1 per foot lineal, and groynes of more substantial construction at from £1 to £3 per lineal foot, while some of the large concrete and masonry groynes of the type [re- quently constructed at brighton and hastings cost as much as £7 or £8 per lineal foot. the initial capital cost of protection per mile of shore was seldom less than £4,000, even when no sea wall was constructed. under present conditions these figures should be nearly doubled. the annual charge for repairs, inter- est on capital, and replacement may be put at not less than 10% of the original capital cost. the cost of protecting purely agricultural land which is sub- ject to erosion must of necessity, under the conditions which usually prevail, be considerably in excess of the value of such land. protection under such conditions is only justified when agricultural land is in the vicinity of towns and its erosion, 1f it be not stopped, is likely to lead to those towns being outflanked by the sea, and in situations where the works have as their object the preservation from inundation of areas of low-lying land of considerable extent. it is not desirable, even 1f it were practica- ble, to prevent erosion of all parts of the coast, as the waste of the coast protection cliffs provides the greater part of the beach material which acts as the most valuable agent of protection. the expenditure incurred in the construction of sea defences by many of the coastal towns of england in recent years has been very considerable and in some cases has imposed a heavy burden on the inhabitants. as an instance the case of sidmouth, a sea- side town on the south coast of devon, having a population of about 6,000, may be referred to. asa result of exceptional gales the sea defences of the town over a frontage of under half a mile were seriously damaged and undermined between the years 1917 and 1925 and the construction of new sea walls and groynes, completed in 1926, entailed an expenditure of over £100,000. sand dunes and alluvial flats—the preservation of sand duncs is most important along certain parts of the coast where they afford protection to low-lying areas behind them, and they should in these cases be maintained and fostered by the encour- agement of the growth upon them of marrum and other grasses, which help to bind the sand together. where drifting of blown sand occurs much may be done to check it by the fostering of such grasses. the process of natural accretion on alluvial flats has been hastened in many cases by the planting of suitable vege- tation such as rice grass (spartina), and in this way land may in time be reclaimed by entirely natural means. conditions in holland and belgium a large part of holland and some portions of belgium are below the normal sea level and are protected from inundation by artificial embankments (dikes) or by narrow belts of sand dunes. the foreshore works on the coast of holland and belgium, although of great interest and attended with considerable suc- cess, do not afford examples to be followed as affecting the sea defences of the united kingdom and other countries exhibiting physical characteristics similar to those of the latter. the protec- tion works in such cases as blankenberghe, heyst ,scheveningen, callantsoog and petten are of great magnitude and the engi- neers responsible for these works, particularly in holland, have at their command the accumulated experience of centuries of sea-defence work. the local conditions with which these works have to conform, viz.: low flat foreshores consisting entirely of sand, are wholly different from those generally associated with sea-defence works in england. the large expenditure involved is justified by the necessity of securing the safety, not only of the sea-board, but of large tracts of the countries themselves. investigations in holland are said to indicate a continuous sub- sidence of the land of that country relative to the sea level, amounting to about 15 cm. per century. the north sea foreshores of holland and belgium consist for the most part of fine sand; similar deposits border the lower por- tions of the numerous river estuaries which penetrate far inland, but in the higher parts of these the foreshores are generally com- posed of fine sand covered with clay or mud. the foreshores of the north sea between high and low water have an average gradient of about 1 in 45 and the shores above high water nor- milly slope at about rt in 25. submerged sand banks more or ess parallel to the shore are a characteristic feature of the north sea and estuary coast lines of holland and belgium. these, where they exist, afford considerable protection to the sandy shores during on-shore gales. in calm weather and with off-shore winds sand accumulates on the foreshores. the two most important forms of sea-defence works in common use in ijolland are (a) groynes, (#) fascine-mattresses with stone ballasting. groynes are usually constructed at right angles to the shore line and are maintained as arule at a small height above the average foreshore level. on those portions of the north sea coast which are most exposed groynes are placed about 250 metres apart and are extended out beyond the low-water line. many of the grovnes on the dutch coast are constructed of layers of fascine mattresses covered by heavy stone, having their crests almost flat or turtle-backed with side slopes of 1 in 2, or flatter. the fascine or brushwood mattresses are held together and pinned down by rows of piles. wide brushwood aprons, with heavy stone covering forming flat slopes, are constructed on cither coates—cody side of the groyne in order to protect the flanks against scour. the groynes are carried up above the line of high water to meet the base of the sand dunes or the protecting dikes. these groynes, inclusive of the side aprons, are often of considerable width, sometimes as much as 30 metres at their deepest and widest parts. the cost of groynes built in holland has varied from £4,000 to {£11,000 cach. the underwater banks of some of the estuary channels and sea inlets on the coast of holland frequently stand at a steep slope with deep water alongside. under these conditions there is ser1- ous liability to erosion and it is usual to protect the banks both above and below water by artificial means. for many years fascine mattresses have been used for this purpose. these are made up on a convenient sandy foreshore, covered at high tide and when completed are towed to the place where they are to be used and sunk on the sea bottom by ballasting with stone. they consist of two layers of grids of brushwood, each built up of crossed rows of parallel brushwood ropes, o-4 metre circumfer- ence, and spaced o-g metre apart centre to centre, bound to- gether with a filling of brushwood in three layers between them. on the top of the upper brushwood grid some open-work par- titions are formed for the reception of stone ballast. formerly, clay mixed with a little stone was used for ballasting, but in mod- ern practice stone alone is employed, the mattresses being weighted to the extent of 1,000 kg. per sq. metre. the cost of continu- ous protection of the steep banks of the estuary channels where the depth of water alongside is sometimes as much as 30 metres, is very considerable, amounting in some cases to as much as {100 per metre run of bank. in some localities the cost has been re- duced by the construction of intermittent mattress work, leaving short unprotected stretches of bank between projecting spurs which serve to deflect the main current away from the unpro- tected embayments. in cases where the sea bed of the deep channels consists of clay, erosion is not so uniform as that of sandy bottoms and the side slope is sometimes almost vertical. in such situations rubble stone ballasting or surfacing of the bank is preferred to the employment of mattresses. the pro- tection of the shore lying between the steep submerged and partially submerged banks of the channels and the base of the dike or wall, which forms the immediate protection of the land behind, is usually effected by means of groynes. these shorcs, which are sometimes of considerable width above the level of normal high water, have in most cases flat gradients. bibliography.—w. h. wheeler, the sea coast (1902); reports of royal commission on coast erosion, 1st rep., cd. 3683 and cd. 3684 (1907), and rep., cd. 4460 and cd. 4461 (1909), fast rep., cd. 5708 (1911); a. e. carey and f. w. oliver, tidal lands (1918), d. \w. johnson, shore processes and shore line development (1919). see also proceedings institution of civil engineers (passim); a. t. de groot, de ingenieur no. 35 (1911); r. p. j. tutein wolthenius, die gido, nos. 3 and 5 (1913). cn. gg. get. e.r ww.) coates, joseph gordon (1878- _—+), new zealand poli- tician, was born at matakohe, the son of a farmer. he was elected m.p. for kaipara in ro11, and favourably impressed his leader, mr. w. f. massey, with his solid, if not brilliant, qualities. from 1917 to 1919 he served in france with the new zealard forces, in which he attained the rank of major and gained the military cross. shortly after his return home, he was invited to join the cabinet, and, as head of the public works, railways and other departments proved himself a capable administrator. his energy and sincerity amply compensated for any lack of elo- quence, and when mr. massey died in 1925 he was his obvious successor. as prime minister the chief aim of his domestic policy was the consolidation of the primary industries of new zealar d, thus paving the way for a development of secondary industries. in overseas affairs he was a staunch imperialist. coblenz, germany (see 6.612), had in 1919 a population of 57,393. new law courts, churches and a theatre were built after 1910. coblenz was bombed by the alliesin 1917 and 1918. after the armistice the town and bridgchead were occupied by allied troops under the treaty of versailles, art. 429-432, coblenz forming the second zone to be evacuated after ro years, should germany fulfil her obligations (see rhineland). coblenz was 669 the seat of the rhineland high commission, and was first occupied by american troops, becoming general pershing’s headquar- ters. on jan. 10 1923 the american troops were withdrawn and replaced by french. on oct. 21-26 1923 separatists carried out a coup, proclaimed a rhineland republic, and declared that they had been recognised as a de fucto government by the french high commissioner. the separatist leaders quarrelled among themselves, and the movement had collapsed by feb. 1924. cochery, georges charles paul (1855-10914), french politician (se> 6.619), died in paris aug. 8 1914. cochin, denys marie pierre augustin (1851-1922), french politician (see 6.619), joined the briand national de- fence cabinet on the outbreak of the world war as a minister of state and was sent on a diplomatic mission to greece. he died in paris march 24 1922. cocoa (sce 6.628).—the modcrate prices of cocoa in 1925 were largely due to the development of cocoa-growing in british west africa. in 1905 the world’s production of raw cocoa was 141,000 tons, of which 23% was grown in the british empire; in 1913 255,000 tons were produced, of which 35% was british; and in 1925 the world’s production was about 500,000 tons, of which 60°% was produced in the british empire. gold coast.—in 1922, out of a total world output of 403,000 tons, 159,000 tons were grown on the gold coast. there were no organised plantations, the trees being cultivated around the native villages. the crop is gathered, fermented and dried and brought in in small but very numerous consignments to the river and rail collecting stations, whence it is shipped down to the ware- houses at accra. the bean is not of the highest quality, being flat in shape and somewhat bitter in taste, owing to imperfect methods of native cultivation and preparation. but it is the most important cocoa available in bulk and at a low price, and forms a basis for all cocoa and chocolate productions, at its best readily blending with any other sorts. dangers to further de- velopment of production on the gold coast are the felling of the forests, causing the climate to become drier and the country more exposed to winds; and the multiplication of pests and diseases. these matters are carefully watched and dealt with by the department of agriculture and by the gold coast agricultural and commercial society. other producing areas nigeria presents conditions which make possible a production equal to that of the gold coast; 37,192 tons were exported in 1924. other important producing countries, and their approximate production in 1924, are: brazil, 70,000 tons; ecuador and trinidad, 30,000 tons each; santo domingo and venezuela, 25,000 tons each; and san thome, 20,000 tons. the bulk of high grade beans, to which the flavour and richness of good cocoa and chocolate are due, comes from trinidad, venezuela, grenada and st. lucia; and these, with the small quantity from ceylon, of the plantation variety, fetch the highest prices on the london market. the entire crop of java beans, which are comparable with those from ceylon in quality, is shipped to amsterdam and is sold there by auction six or seven times a year. during the world war, hamburg lost its position as the larg- est cocoa market: most of the gold coast crop was landed at liverpool and london, which handled more cocoa than ham- |. burg during the post-war period. london has a public auction, the prices at which cocoa changes hands being wired all over the world and forming the basis of negotiation. in 1918, prices at which the various kinds of raw cocoa should be sold in great britain were fixed, accra being quoted at 65s. per cwt. and ceylon plantation, java and samoan at 100 shillings. in 1919, when control was abolished, the price rose rapidly, and by feb. 1920 ceylon was 200s., with that of other sorts in proportion; but by 1921 the price had fallen to the normal level of 80 shillings. (c..0. 1. gb) cody, william frederick (1846-1917), american scout and showman known throughout the world as “ buffalo bill” (see 6.637), died in denver, colo., jan. 10 1917. he was buried in a tomb which was blasted from solid rock on lookout moun- tain, 20 m. from denver. : 670