Exmouth Warren, and its threatened destruction (1872)
|Author(s):||Martin. J. M.||Origin:||DA Transactions|
|Topic(s):||environment and maritime||Year published:||1872|
|Location(s):||Dawlish Warren, Exmouth, and River Exe||Pages:||84-89|
By J. M. Martin, C.E., F.M.S. (Read at Exeter, July, 1872.)
The encroachment of the sea on the Exmouth Warren was the title of a paper read by Captain Peacock, F.R.G.S., originally, before the Exeter Naturalist’s Club at Starcross in the summer of 1869, and subsequently, at the meeting of the British Association held in this city in the same year.
At the first meeting of the club in 1871, Captain Peacock called the attention of the members to the changes which had taken place since the reading of his paper; which changes, though continuous, were comparatively unnoticed, as there had in the intervals been no such gales as that which in January, 1869, swept away so much of the Warren.
Between these two periods there was considerable discussion through the medium of newspapers; there were leaders written by their respective editors calling attention to the serious consequences to the commerce of Exeter that might ensue upon an extension of the present or the formation of a new breach in the spit of land which lies at the mouth of the river Exe; the subject was more than once broached in the Town Council, and a formal resolution even was moved on one occasion to the effect that “it was desirable the Council should take means of ascertaining the probable effect the washing away of the Warren would have upon the navigation of the River”.
But since then next to nothing has been heard of the matter, which would probably not have been the case if heavy weather had prevailed; and I should not now have brought the subject before this Association, were it not for the purpose of taking advantage of this meeting to again call public attention thereto in the presence of representatives of Science on the one hand, and, on the other, of that commerce which is presumed to be threatened with extinction or thereabouts, if the encroachments of late years so great should continue.
The Warren, as is well known, consists of two parts, an inner and an outer, having at high tides a considerable sheet of water between them. The inner portion consists chiefly of a low ridge of sand, and a considerable expanse of mudflat or ooze. No change, so far as I have been able to ascertain, has occurred in this portion that can for one moment be compared either in extent or importance with those which are known to have been going on for the past century on the outer Warren, or that portion next the English Channel; which comprises, or rather did comprise a century ago, a continuous ridge of sand-hills of varying height and of considerable width, flanked at the eastern extremity by a sandy bluff of about fifty acres in extent, and twenty to twenty-five feet in height. Inside the Warren, and protected thereby, is a pool with deep anchorage, called Exe Bight, where ships of considerable burthen may lie safely, and it is to this anchorage that injury would in the first place arise in the event of a breach in the inner Warren, which is composed of sand, in places only a few yards in width, and which is itself protected by the outer Warren.
I have prepared a diagram of the seaward portion of the Warren, on which are delineated the outlines thereof at four different periods, ranging over the past eighty-five years. It shows that a considerable area has been washed away from the whole sea-face, that gaps have from time to time been made in the once continuous frontage, and that the detached bluff has totally disappeared. To convey an idea somewhat commensurate with the extent of this encroachment of the sea, I will merely state that at the time the oldest of these maps, bearing date 1787, was constructed, the high water channel between the bluff and the land on the Exmouth side was about 430 yards wide. Twenty-two years later, in 1809, the bluff had been so far lessened on the side of the channel that the distance across was ninety yards greater. Thirty years later still, in 1839, this once extensive bluff was represented by three little sandy islets, and has now entirely disappeared; the width of the channel having increased in eighty-five years to 970 yards, or more than double its width eighty-five years since.
Besides the detached bluff some 25 acres of the eastern end of the ridge, which has a tendency to turn northwards from its original line of direction and travel up the river, have also disappeared.
About 600 yards west of the present extremity of this ridge is a gap through which the tide flows at spring tides to a considerable depth, filling the space between the inner and outer Warren previously referred to. A sheet of water existed here as long ago as the date of the oldest trustworthy map I have been able to discover, viz., in 1787, but it had then no direct communication with the English Channel, being filled through a channel leading from a point between Exe Bight and Exmouth Passage, so that the water required to fill it had first to pass through the navigable portion of the river between Exmouth and the Warren.
The channel above referred to is now closed by the dam of the Exe Bight Pier and Oyster Company.
This gap, or breach, in the outer Warren was made in 1859, at a point just eastward of the site of a previous breach made in 1824, which breach was promptly closed by the then authorities, whose works still remain to testify their efficacy. The 1859 breach was at first comparatively small, but doubtlessly growing larger. Suddenly, in the storm of January, 1869, it was enlarged to five times its previous width. It became a formidable breach 130 yards wide, and the bottom thereof was degraded to near low-water mark. Since January, 1869, we have had no such storms as that, yet the breach has gone on widening, until at this moment it is 240 yards wide, having nearly doubled in width in three and a half years of comparatively smooth weather.
Altogether, I estimate that of the seaward face of the Warren, a portion equal to more than 100 acres has been removed by oceanic and fluviatile degradation. This process is still going on, and is seriously weakening the barrier between the English Channel and the Harbour of the Exe.
Probably many years will elapse, if this action is not intensified by storms, before it will ultimately be broken down; but its constitution is destroyed; it is, so to speak, on its last legs; and if it receives many such shocks as that of 1869, or if the inner Warren should be broken through, the most serious consequences to the Port of Exeter may be expected; the navigation will be stopped, the occupation of the canal will be gone, and the Exe Bight anchorage will become what Captain Peacock so graphically described as a “dangerous bay of shoals”.
The vast mass of material that has been thus removed must surely have been deposited somewhere; and it would be interesting to ascertain, with some approach to accuracy, what changes have taken place in the bottom of the estuary during the period under observation; but I fear that, beyond bare outline, no trustworthy account exists of the progress of changes that after a lapse of time may be found to have been quietly going on, and producing serious results.
The question naturally arises out of the foregoing remarks —If the consequences of this degrading action of the sea are likely to be so serious, what course can be adopted to repair existing damages and prevent their further extension?
Another question must be first answered, viz.: What is the history of the Warren? what formed it? and what is now destroying it? The answer to this appears to be, that the prevalent winds and waves along the coast have forced northward and eastward the débris of the cliffs which bound the south-eastern part of this county, which must in the lapse of ages have been, from the friable nature of the rocks, enormous in quantity; that this débris has formed in the shelter of the rocks at the mouth of the river a gradually protruding tongue of land, in a direction continuous with the line of coast, checking the turbid water of the estuary, which deposits its sediment on the river side thereof.
This action is likely to go on until only such a channel is left as the effluent water from the estuary at ebb tide is able to keep open, when, under ordinary circumstances, so long as the conditions under which the spit is formed remain unchanged, the spit itself remains stationary, subject only to such minor changes as are caused by abnormal agencies; the action of these being afterwards modified by the general action of the continuous agencies.
Supposing that now, from some cause, the supply of the materials forming the spit ceases, the same action of the elements which tended originally to form it being directed upon the spit itself would naturally wash it away, and the materials of which it is composed would be gradually drifted towards its extremity, and either carried by the flood-tide into the estuary, or by the ebb into the sea; either to form shoals, or to be carried under the stream, and along the coast on the opposite side of the river. This action is to be observed in this case, the heaviest materials of which the Warren is composed being exactly analogous to those on the coast from Teignmouth upwards, with this addition, that amongst the larger gravel and pebbles found on the north-east side of the Warren, opposite the Exmouth Docks, occur large fragments of limestone, with the edges of their fractures only slightly rounded, and, with that exception, looking just like the pieces of stone which are to be seen wherever masons have been at work. As these fragments, if found at all, are certainly not so numerous along the line of coast west of the Warren, it seems to me extremely probable they are the chips of the blocks of limestone used in forming Brunel’s railway wall along the coast. If this assumption be correct, it would seem that the foregoing scheme of the formation of the Warren is at least probable; and this being so, we can find, at any rate, one cause of the cessation of the supply of material to the Warren in Mr. Brunel’s sea-wall itself; for since its construction only a very small fraction of the immense amount of rock previously falling into the sea, to be ground up into gravel and sand, could possibly find its way there. I do not presume to say that this is THE cause why the Warren has decreased in size, for it is evident the Warren was lessening before the railway was constructed, but I do believe it is aiding in its destruction.
To attempt to permanently fill the gap by artificial means would tax the resources of a more wealthy and enterprising community than ours, and require a larger inducement than we possess; but some action could be taken to prevent further injury, and the same action would have the effect of strengthening, and to some extent restoring to its original form, this barrier against the incursion of the sea.
If it be granted that this theory of the formation of the Warren be correct, it would follow that any means that would arrest the comparatively small flow of shingle and sand now drifting along the coast, would have a tendency to reduce to a minimum the waste going on, and if the means were adequate, and the supply of materials sufficient, to check it entirely, and build up a new rampart instead of the old.
As Devonshire men, most if not all of us have seen the effect the groins constructed for the protection of the South Devon line of railway have had in retarding the drift of gravel towards the mouth of the Exe (I do not attach so much importance to sand, because that is much affected by wind; and if once the gravel beach can be established, sand will by the same action of the wind form dunes beyond it), how that the gravel has risen to the tops of the groins on the windward or south-west side, and even swept over them; whilst on the north-east or lee side the beach is no higher at the head of the groin than at the toe or point thereof, the differences in level amounting sometimes to as much as twelve or fifteen feet, and the increased height on the windward side extending to the extremity of the groin itself.
The same effects can be seen at any harbour or projection on the coast from Exmouth to Hurst Castle, and it is owing to this uniformity that I am inclined to attach a faith to the use of groins that I at present deny to any other mode of dealing with the difficulty.
There are other points, such as, for instance, the preservation and improvement of the Exmouth Channel, that will demand, as well as those already adduced, the most careful attention, should the matter ever have to be practically considered; but I know that the time at my disposal, and I think, perhaps, the scope of the Association, forbids going further into detail, besides which I feel that I have already occupied the attention of the meeting sufficiently long; but if an excuse or an apology be needed for obtruding this twice-told tale on your notice, the first must be that I know great interest therein is felt by a large number of gentlemen present, and the second that until I had actually surveyed the Warren, and the gap therein, I had no conception of the vast extent of the waste that had been going on, and having become possessed of this knowledge, I deemed it proper to direct the attention of the Association thereto.