7-Second and Concluding Report on the Erosion of Dover Cliffs, from St. Margaret's Bay to Folkestone, a distance of about eleven miles, addressed to the Committee, May 1893. By Captain S. GORDON MCDAKIN.

The cliffs, composed of chalk, reach an elevation of 525 feet on the west at Folkestone, and 400 feet to the east of Dover, to about 200 on the south side of St. Margaret's Bay; the High Light, South Foreland, 374 feet; and 88 to the north of St. Margaret's Bay.

The coast has been compared with the 6-inch Ordnance map of 1876, and marked at twenty-four principal stations and eleven intermediate ones with marks at about 2 feet above the shingle on plane of marine erosion: these marks are bore-holes 3 inches deep by inch wide. This form was chosen as not so likely to be tampered with as other marks, and because they would be difficult to imitate without a special tool. Each year has a different mark.

The hole with the circle drawn round it is the test-hole, the others are only indicating marks.

As in the former reports for 1890-1891, the changes are rather those of the undercliff than the cliffs themselves; this applies especially to the Folkestone Cliffs and West Cliffs, Dover.

In last year's report the foretold likelihood of a slip has been confirmed by a tremendous fall from the Abbot's Cliff, which is here 450 feet in height, amounting to many thousands of tons.

To the east of Dover (Cornhill) stations Nos. 5 and 6 in soft white chalk have lost half an inch in twelve months. Stations 1, 2, 3, and 4, in harder beds, particularly that of No. 4, in very hard nodular chalk, exhibit little or no erosion.

West Cliffs, Dover. The sea has here attacked the undercliff and talus. The marks 1, 2, 3, 4, on large detached block, have disappeared by the block having been overturned, displaced, or buried, the actual erosion of the surface not amounting, on an average, to more than about half an inch in twelve months in exposed situations, and washed by every tide. At No. 6, a large detached mass, the marks of last year (1892) are intact on two faces.

Folkestone Cliffs. Great inroads have been made on the undercliff of the Warren in three years. The mark at Station No. 1, lost sight of last year, was found again, even the mark .. of 1890 being intact, although 2 and 3 have disappeared. At No. 4 last year's mark (... 1892) also was intact, but 5 and 6 are lost or covered by falls of the cliff.

St. Margaret's Bay, four miles east of Dover.-South side of bay, mark at Station No. 1 disappeared. Stations 2 and 3 intact, but a soft band of chalk close to beach is here very much undercut by the sea, so that large masses may be expected to fall. North side of bay, mark at Station 1 of last year (... 1892) had been tampered with, an attempt having been made to cut it out; but taking the general surface and depth of hole, the marine erosion was imperceptible. Stations 2 and 3, only reached by storm-waves, were intact. The cliffs are here quite perpen

dicular, and about 88 feet in height. Since the 6-inch Ordnance map of 1876 was published there has been no great loss of land, but several heavy falls of cliff, amounting to some thousands of tons, as at the Cornhill Coastguard Station, two miles east of Dover, on February 23, 1891, and the still larger one at the Abbot's Cliff Coastguard Station (Lydden Spout) early in the present year.

The recession of the coast line westwards from Dover to Folkestone is no doubt caused by the uncertain foundation of underlying Gault clay, which retains the water passing through the porous chalk, the sea carrying away the débris: this is particularly the case where groynes or piers at right angles to the shore have intercepted the shingle coming from the west, that to the eastward of such obstructions gradually passing away in that direction, and not being replaced by fresh accretions from the west. The shore, being undefended by the shingle beach, is exposed to wave

action.

The Folkestone pier intercepts the shingle that at one time defended East Wear Bay, the Folkestone Cliffs, and the West Cliffs, Dover. The Admiralty Pier, Dover, has in like manner robbed the foreshores of the Esplanade, Dover, and the East Cliff, Dover, of their shingle, making costly revêtements and sea-walls necessary.

APPENDIX III.

VARIOUS SCHEDULED RETURNS: REPLIES TO PRINTED QUERIES CIRCULATED BY THE COMMITTEE.

Hampshire Coast.

By RICHARD F. GRANTHAM, M.Inst.C.E.

1. Part of the coast of Hampshire, east of Christchurch, opposite Highcliffe, and the village, of Newtown.

2. a. Cliffs composed generally of a bed of sharp gravel, varying from 13 to 18 feet in thickness, overlying the slippery Barton clay. b. 80 to 100 feet.

3. Nearly east and west.

4. South-west.

5. South-west.

9. a. I have not had an opportunity of measuring this. d. From 3 to 4 inches. 10. I should say stationary.

13. The degradation of the cliffs is due to the water issuing from the base of the gravel over the slippery clay surface.

14. The face of the cliff has slipped away at a rate of 3 feet per annum, taking an average line of about mile in length during the last twenty-two years. This is the rate as ascertained during that period, and it is probable that this has been the average rate for a longer period.

The shingle beach appeared to me to be stationary; so now that drains have been laid up the slipped slopes of the cliff to remove the water issuing between the gravel and clay, the slopes will become consolidated, and slipping will no longer take place.

15. It must be explained that the course of the channel of the river Avon formerly ran parallel to the beach eastwards for some distance from its mouth in Christchurch Harbour, but certain works executed some time ago by some landowner at the mouth had the effect of diverting the course straight out to sea, and thus the channel parallel to the beach has become stopped. No doubt this is the cause of the present stationary character of the beach, for otherwise erosion would take place, and the slipping of the cliff further facilitated by the undermining of the toe.

16. No. 17. No.

Sussex Coast.

By RICHARD F. GRANTHAM, M.Inst.C.E.

(1) Opposite Lancing.

1. Sussex coast, opposite Lancing. It is that portion which lies between 'Shop's Dam' and the gap in the Worthing and Lancing Road, referred to in my father's returns, Nos. 11 and 12 in the Committee's Report, dated 1885.

2. The main features of that part of the coast are described in those returns, but I have, within the last two years, constructed nine groynes between Shop's Dam and the gap in the road, a distance of about 1,100 yards.

3. That is westwards of the groynes erected under my father's superintendence; but I have had an opportunity of making a survey of that part of the coast, which shows exactly the rate at which the sea has been advancing opposite Lancing. 8. Partly of shingle, partly of sand foreshore. Opposite the Coastguard Station, west end of Lancing, chalk rocks and flints, covered with seaweed, can be seen at low water slightly above the level of the sand foreshore. In storms the flints are loosened, raised up, and washed up on the shore.

9. The shingle lies in the form of a high bank, thus:

FW.O.S.T

Sand

FIG. 2.

Surface of land

The base of the shingle bank is about 500 feet broad, and the top of it is about 6 feet above H.W.O.S.T.; the land behind is below the level of H.W. Formerly, in storms, the sea washed the shingle back, encroaching further and further on the low-lying land. There is a 'fall' of shingle, but this varies according to the state of the sea. It is generally just above H.W. springs. 11. I think that until the groynes were erected the quantity of shingle remained constant, but it was perpetually being driven back.

12. a, b, and c. The new groynes point south-east at a rather greater inclination with the shore line than those erected by my father. Their length is 300 feet, and the width apart is 400 feet, except the three groynes at the west end, which are 350 feet in length and rather closer together. d. The top end is 18 feet above O.D. and 8 feet above H.W.O.S.T. e. Timber partly memel, partly

beech. f. Although they are not yet planked up, and although there has been an unusual number of heavy gales during the past winter, 1893–94, they have completely arrested the encroachment of the sea, so that no damage has been done, nor has any shingle been swept back over the tank. The groynes will be planked up in time as the shingle and sand accumulate.

13. a. No. d. No.

14. Before the groynes were erected the sea had washed the shingle back, so that opposite the Coastguard Station at Lancing the high-water mark was at the date of my survey (1891) 320 feet further inland; and at a distance of 160 yards west of Shop's Dam, 70 feet further inland than it was at the date of the Ordnance Survey (1875).

15. The influence of the new groynes in accumulating shingle had at first a slightly deteriorating effect on the accumulation at the groynes my father erected, but the gales of the past winter have brought up an immense quantity of shingle, and those groynes are now filled again.

16. No.

17. No.

(2) Between Selsea Bill and Chichester Harbour.

1. Sussex coast, between Selsea Bill and Chichester Harbour.

2. Low cliff, varying from 4 to 11 feet above high water ordinary spring tides. The cliff is composed of loamy clay mostly, but at the west end of the bay there is gravel and sand about 4 feet below the surface. Clay appears on the shore at low water.

3. North-west to south-east.

4. South-west.

5. South-west. When the wind is westerly or south-west the shingle travels from about mile east of Chichester Harbour eastwards to Selsea Bill, and from the mile east of Chichester Harbour westwards. When the wind is easterly the shingle travels westwards from about 2 miles east of Chichester Harbour.

6. Flood tide eastwards; ebb tide westwards.

7. (1) a. 16 feet 6 inches; b. 12 feet 6 inches. (2) Probably about 9 or 10 chains; say 200 yards at springs, more at very low springs.

8. Sand mostly. There is some mud near the cliff, opposite Bracklesham Farm. Shingle lies up against the foot of the cliff all the way.

9. a. Varies from 15 yards east to 24 would vary in different seasons. cover it.

yards west at ordinary seasons, but these b. High water, spring tides, does not quite c. I have stated this in answer to Question 5. d. About 9 inches across every way. e. The shingle formed one continuous slope when I saw it, and I should not think this varied.

10. I should say the quantity of shingle was generally maintained, the quantity depending on different seasons.

11. Some has been taken away for repairs of parish roads; but this is only a small quantity, and the removal is now stopped.

12. A weak form of groyne has been tried both at Thorney Farm and at Cockham

Manor. The piles at the former are still standing, but those opposite Cockham
have disappeared. They were evidently weak. and required so much repair
that they were abandoned. a. At right angles to the shore. b. and c. They
appeared about 100 feet long, and from 80 to 100 feet apart.
timber.

e. Beech

13. a. From the end of Bracklesham Lane, and from the end of Cockbush Lane. b. and c. Repair of parish roads by the waywardens. d. I should say not. 14. All the way along, at a considerable rate. a. From 6 to 8 feet per annum opposite Bracklesham Farm; about 8 feet between Bracklesham Farm and Cockham Manor Farm. b. 10 to 13 feet opposite Cockham Manor Farm. c. During the winter 1891-92 the rate must have been from 15 to 20 feet opposite Cockham Manor Farm, from the appearance of the remains of parts of the cliff. d. These measurements agree with a comparison of the 1-inch Ordnance map, surveyed in 1805, and the 6-inch Ordnance map, surveyed in 1873. 15. There is nothing along this line of coast to cause an accumulation of shingle, so what is there is deposited and left to be carried on or taken away by the sea.