The Sea Coast. J. Steers A.
Wash, and in South Holland 37,000 acres. In early days banks were often built rather prematurely, but now it is realised that the longer the period of natural accretion goes on, the better the land reclaimed. In the Wash warp begins to be deposited at about +5 feet O.D.; neap tides rise to +8 feet, and at this level Salicornia spp. appears. At about +10 feet it is replaced by grasses. Nowadays, the foreshore outside a new bank becomes grass marsh in approximately ten years, but to get the best results it is left in a natural condition for another twenty or twenty-five years. The salt marshes in the Wash carry a vegetation typical of east coast estuaries—Salicornia spp., Suaeda maritima, and Aster tripolium give place to Puccinellia maritima and Obione portulacoides along the creeks. Spartina townsendii has been introduced. In 1925 there was a little at Wolferton and on the banks of The Cut; today there are extensive areas between Wolferton and North Wootton. Since Puccinellia is much grazed, there is no further development until the marsh is embanked. Limonium and Armeria are absent, and the only other species worth noting is Cochlearia officinalis. An interesting fact is the speed at which the ordinary halophytes2 disappear once a marsh has been reclaimed; even within a year they have been replaced by docks, nettles, thistles, buttercups, and daisies. Since 1932 much of the reclaimed land has been ploughed, and it yields good crops. The saline origin of the ground still, however, shows in the drainage ditches; in one example in a ditch of a marsh reclaimed in 1904, Puccinellia maritima remained the dominant plant in 1945. A pond in a reclamation made in 1865 was 80 years later still fringed by Scirpus maritimus, Puccinellia maritima, Aster tripolium and Spergularia salina. If water drains from the upland, fresh water aquatics only come in very slowly.1
Here and elsewhere accretion on the natural marshes is encouraged by cutting ditches, or grips, running up and down the marsh. A fall of about two feet a mile is given to them, and the excavated material is usually dumped on the seaward side. This helps to produce calm water and foster deposition. If any erosion of the excavated material takes place it is spread over the grassland. The ditches are found to help the ebbing tide and to aid the consolidation of the deposited material before the next tide covers it. They are about 60 or 70 feet apart, and cut when the marshes reach about +10 feet O.D.
Apart from local variations in the nature of the marshes, exposure, and other factors, the process of reclamation in the Wash is virtually the same as that in other parts of the country. If a rapid survey is made of our coast, it will be noticed that great changes have taken place in Romney Marsh and around the Parrett mouth in Somerset, and in the reclamation of the extensive Fenlands of East Anglia and Yorkshire. More modern changes are rapidly taking place in Southampton Water and Poole Harbour and other places on the south coast. This is mainly the result of the introduction of Spartina townsendii, a plant which first appeared in 1870, and since then has spread very rapidly, and has been planted on many other parts of the coast to help reclamation. “The stout stem bears stiff erect leaves: from the bases of the stems stolons radiate in all directions, binding the soft mud; and feeding roots, mostly horizontal in direction, ramify through the surface layers of the mud, while stouter anchoring roots extend vertically downwards. The leaves offer broad surfaces to the silt-bearing tidal water, and their points catch and hold fragments of seaweed and other flotsam. The thick forest of stems and leaves breaks up the tidal eddies, thus preventing the removal of mud which has once settled on the marsh …. No other species of salt-marsh plant, in north-western Europe at least, has anything like so rapid and so great an influence in gaining land from the sea.”2
Another district in which there has been a good deal of reclamation is Morecambe Bay. Although local conditions favour the process, the results are not of any great value, since it is sand rather than silt which is deposited. The sand is derived mainly from Triassic rocks and boulder clay, and is chiefly quartzose and well rounded. Since, however, it is free from silt it is more or less useless. This fact was strongly emphasised by the Royal Commission (1911), and in their report they also noted that of one thousand acres reclaimed near Morecambe, nearly half had been abandoned.
In the Solway and other firths of Scotland, considerable reclamations have been carried out. There is no need to detail instances, since it is clear that as far as natural and sheltered conditions are concerned, localities in the firths are obviously suitable for this purpose, partly as a result of seaborne silt, partly of river borne material. Around Dingwall, for example, the Conon and Peffery rivers deposit a great deal of sediment. On the other hand, diversity of interests must be considered. It may seem an obvious advantage to take in more land, but on the Clyde some reclaimed lands had to be removed, since they were detrimental to the more important navigation interests.1
A word is desirable about the lateral spread of natural marsh. If comparisons are made between two separate editions of the six-inch Ordnance Survey of selected areas, the spread can be measured. Since the surveyors were probably not ecologists it is not always clear what boundary they took for the vegetation. In certain cases known to the writer, however, reasonable measurements can be made in this way. Nowadays the quickest method is to compare two air photographs of the same place taken a few years apart. Anchor marsh, a small enclosed marsh on Scolt Head Island, was almost bare of plants in 1920, but in 1939 it was thickly carpeted and a good deal of mud had also accumulated. Holme marsh, near the entrance to the Wash, seems to have developed from a sand flat enclosed in part by a shingle ridge to its present fairly advanced state since 1858,
Loss and gain of land are going on constantly. Erosion is nearly always more spectacular, especially if houses or other buildings are caused to fall. Yet it is the slow unnoticed process of accretion in estuaries and other places that is the more valuable. The Royal Commission in 1911 found that in total area, accretion far exceeded loss. No other comprehensive measurements have been made since then, but we can assume without any doubt that the statement is still true.
If, however, we go back in time, even only for a century, we are soon in difficulties. Much of our present fairly detailed knowledge depends mainly on present-day observations and measurements—all too few—specifically designed to tell us of loss and gain. The large scale Ordnance Survey maps are nearly always our first reliable means of measurement, and they date back only to the early decades of the nineteenth century. Earlier maps are seldom reliable; sometimes particular surveys are very helpful, but it is rare to find anything before the eighteenth century on which accurate distances can be obtained. This does not mean that early maps are useless; far from it. They must, however, be used with great caution and their information, where possible, checked in other ways. Erosion and accretion are both irregular in their rates of action, and for this reason alone averages over a long period must not be taken as holding good for other periods of similar length. All kinds of factors may intervene; a sand bank may be thrown up offshore or in front of a cliff and so hinder direct erosion; wearing down of the shore platform may allow bigger waves to break near the cliff foot and so increase the rate of loss; if the sea is cutting into land sloping upwards to the interior the rate will gradually decrease, since the waves have to remove an increasing amount of waste per unit of advance; the exact converse of this may lead to quicker erosion. These and many other local factors must be taken into very careful consideration if we delve back into the past and try to estimate loss or gain in early times.
The growth of certain shingle spits and forelands can be traced with some approach to accuracy over long periods. Orford Ness illustrates the point well. In 1601 it was carefully mapped by Norden, who made a survey of the whole Manor of Sudbourne. The maps are on a large scale and the spit itself seems to have been as carefully surveyed as the farm land. Figure 7c shows the position of the south end of the spit in 1601. We know that, apart from minor setbacks, the spit lengthened until it reached a maximum in 1897, in which year a great storm did much damage along the east coast, and cut off about a mile of its distal end. Since then its history can be traced from various editions of the Ordnance Survey. Before 1601 the evidence is far less reliable. There is in the British Museum an Elizabethan map which is undated, but probably was made about 1590. It shows