922 BEPOET— 1888. 



certain depth forming the surface of the slope, has been one cause of its failure, as 

 has been the case in other works where a paved surface not admitting the passage of 

 the sea has been placed on a substratum which does. The result is, a hydro- 

 static pressure is evolved by the difference of height of the wave outside compared 

 with the level of the water inside, which is comparatively at rest, tending to raise 

 the impermeable work forming the surface of the glacis, which, aiding the wave on 

 the recoil, may be one of the destructive agents at work. In the present case this is 

 to a great extent conjectural, and I am more inclined to think that the settlement of 

 the breastwork and inner work, and the consequent loosening of the surface work 

 receiving the direct impact of the sea, are the more immediate causes of its failure. 



The best mode of protecting the Eedoubt effectually is the next question, and is, 

 no doubt, a difficult one. The foreland along this shore is not of great extent, and 

 from the way in which it has been deepened in front of the Redoubt, the tide, when 

 once it makes, is soon over its surface, and would quickly gain on any outer works, 

 increasing the difficulty and first cost of construction as well as that of future main- 

 tenance. 



There are two modes by which the sea defences might be extended : first, by con- 

 tinuing the slope from the top of the bulwark down to the foreshore ; and, secondly, 

 by an entire reconstruction ; the latter of which courses I beg to recommend, as the 

 present heiglit of the bulwark is so great that to carry out a sea slope from that level 

 would entail a much larger surface and mass of work, and would bring it so near low 

 water as to render it almost impracticable, or else a very steep slope would be 

 required. In carrying out this work it would not be necessary to remove entirely the 

 bulwark, but to pave up to it and to cut ofE so much of the piles as interfered with 

 the level of the proposed slope. The work seaward of its present extent should be 

 formed of much heavier blocks tlian those now used, laid dry upon a foundation of 

 broken stone or shingle mixed with tempered clay above ; where less influenced by 

 the tide, on concrete. The main groynes should be repaired at their landward ends, 

 as they would form convenient bays for getting in the work, as well as limit the area 

 of damage should breaches hereafter occur. 



The sea margin of the elongation of the slope should be formed of still larger 

 stones, stepped down in a trench and founded as before described. To render the 

 sea slope more secure, I propose, in addition, tliat there should be longitudinal and 

 transverse crosses or walls, as shown in the drawing. These should be founded on 

 work in trenches, as described for the toe or sea margin of the slope. They would 

 have the effect of limiting the area of future breaches. The upper portion of the 

 slope might be continued, as occasion required, to the profile shown in the accom- 

 panying section. 



In doing this, the remains of old work .should be first removed, and I am of 

 opinion that the sea should be allowed to give its own slope to the debris over the 

 breached portion, and that it should be left to settle during the winter, and if the 

 breach extends itself westward such further exposed portions should be treated in 

 the same manner, the interstices to be filled in with broken stone and materials from 

 the old slope, and all old timber and faggots removed ; the slope to be then gra- 

 dually brought up, composed of well-tempered clay, mixed ^vith shingle and broken 

 stone. Shingle itself without such admixture appears to me a most unfit material, 

 from its character, to form the base of such a work of, for, unless in equilibrium or 

 closely confined, it will settle down and run out like water through any outlet formed 

 by a breach or otherwise. The existing groynes should be repaired near the bulwark 

 as far out seaward and as high as the beach usually collects. Any greater extension 

 or elevation appears to me useless. 



A small groyne where proposed by Captain Baillie would, in all probability, prove 

 a useful auxiliary, say 90 feet long ; but instead of placing the entire length obliquely 

 across the bay, as suggested by Captain Baillie, I propose that for two-thirds its length, 

 viz., 60 feet, it should point S.S.E., and the remaining third, viz., 30 feet, S.S.W., as 

 shown. 



The extension of the breakwater beyond the present bulwark I estimate would 

 cost 3,0001. ; the work above, 2,000Z. ; making a total of 5,000Z. 



I return herewith Captain Baillie's plans and sections (No. 3 sheets). On two of 

 them, descriptive of the Eedoubt, I have marked in red the numbers and bearings of 

 the groynes as I have distinguished them, and also the levels of the bulwark above 

 the shore. I have the honour to be. Sir, 



Your very obedient Servant, 



(Signed) J. B. REDMAN. 



