BATE OP EROSION OF THE SEA-COASTS OP ENGLAND AND WALES. 931 



7. ISLE OF GRAIN. 



To the Secretary of State for War. 



■Westminster, S.W., February 21, 1867. 



Sir, — Acting on instructions from the War Office of August 22 last, accompanied 

 by various plans and sections showing the works in progress at the Isle of Grain and 

 the extent of the encroachment of the sea on the shore, I proceeded to Sheerness on 

 August 27 and made several inspections at low water during the then spring tides. 

 I also again visited the site in October last in reference to borings then in progress, 

 and also again on the completion of the last, to satisfy myself as to the real character 

 of the substratum, respecting which great doubts had been expressed. 



In the course of my inquiry I received every assistance from the then commanding 

 E.E. officer at Sheerness, Colonel Freeth, and from the officers at the Isle of Grain 

 fort. 



My instructions inform me it is proposed to protect in the most economical 

 manner the foreshore of the property of your Department. 



From the plans placed before me and from my inspections I draw the conclusion 

 that the waste of the shore is to a certain extent local, viz., that the material, the 

 London clay and sand and gravel thereon, and the alluvial deposits southwards, are all 

 easily acted on by the sea at high water, and that the material abraded is redis- 

 tributed upon the foreshore ; a comparison of the early plan made for the Board of 

 Ordnance in 1784: with those of the present day shows this, and that the high-water 

 mark is much further inshore and the low-water mark further out. To the north of 

 the fort at the boundaiy of the property of your Department the sea has gained to 

 the extent of 700 feet and to the eastward of the fort the low-water mark is nearly 

 a corresponding distance further out. 



To check this action, I recommend the construction of stone slopes of Kentish rag 

 paving on a bed of concrete, separated into bays by sheet piling, and these again 

 subdivided by lateral piling, as shown on the accompanying drawing. 



North and south of the pavement I recommend the construction of two low 

 groynes, as shown at the north end, in a direction N.E. by B. by compass, and that at 

 the south, E.S.E., and two at the north and south ends of the fort frontage, each 

 bearing E.N.E., also opposite the north and south extremities of the battery, that at 

 the north end to bear east by compass, and that at the south to bear E.S.E., viz., six 

 groynes in all. 



As regards the frontage of the battery, I do not recommend quite the same treat- 

 ment as for the rest of the frontage. 



For the frontage generally, I consider that the paving should be brought up above 

 high water until it intersects the glacis slopes, and that north and south and between 

 the fort and battery it should be brought up to the level of the adjacent low land or 

 summits of the neighbouring walls, and that the foot or toe of the slopes should be 

 sheet piled, with a deep trench at back for a rough deposit of stone to form an abate- 

 ment at foot. To the southward this becomes more necessary from the nature of the 

 ground, and the toe will have to be increased in depth more especially corresponding 

 with the frontage of the battery. 



Certain borings were taken in 1861, the results of which were placed before me, 

 as also the details of the foundations of the Martello Tower on Grain Spit ; from 

 these it was clear that there is following the contour of the hill above a considerable 

 inclination of the London clay to the southward. 



Looking to the uncertainty respecting the level of the London clay opposite the 

 battery, I recommended the sinking of two additional boreholes north and south of 

 the battery frontage next the sea, adjacent to and 40 feet west of the two black 

 beacons. 



The general result was, at the outer or north beacon for a depth of 35 

 feet (22 feet below Ordnance datum) nothing but layers of modern alluvion 

 were met with upon a crust of gravel, into which the boring was carried 5 feet, 

 40 feet in all : this boring was abandoned from the tools failing. At the inner or 

 south beacon similar material was passed through for 45 feet, when blue clay 

 was reached, and bored into for 7 feet 6 inches, a total depth of 52 feet 6 inches. 



From the fact that the pipes were drawn before I had the opportunity of examin- 

 ing the strata in the second or south boring, a third was made at my request 320 

 feet north of the south beacon and in a line with the other two, which proves 

 that the solid London blue clay is 45 feet from the surface of the ground, or 32 

 feet from Ordnance datum and 26 feet below low water; from the borings of 



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