1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



269 



TVealt's Quaiierly Papers on Engineering. — Part 4. London, 1844. 



The present part of Weale's Papers has two original articles by 

 Capt. Vetch and Mr. Clarke, and several valuable papers republished. 

 It commences vcith a very interesting article by Capt. Vetch, of the 

 Royal Engineers, on the Construction of Harbours of Safety in the 

 Downs; reclaiming the Goodwin Sands and Sandwich Flats. Of the 

 practicability of these undertakings we are fully convinced, and also 

 of the very great advantages which wo\ild accrue to the commerce of 

 the empire from such an enterprise ; as, however, the method pro- 

 posed by the gallant captain is novel, we should not like to commit 

 ourselves to the opinion that it is jier se the most efficient, though we 

 are bound to admit its ingenuity, and the prima-facial evidence of its 

 applicability. The principle on which the author proceeds informing 

 his roadstead is thus explained, and is one, which, although pregnant 

 with the most valuable results, has not been always duly borne in 

 mind. 



ON HAVKNS OF SAFETY, BY JAMES VETCH, CAPT. R. E., F. R. S. 

 Of all the natural havens which occur on the east and south coast of Eng- 

 land, that formed by the Isle of Wight is the most complete. It has two 

 large openings or entrances, great capacity, and good anchorage, and it may 

 be pretty safely assumed that the best harbours for ail purposes are those 

 formed by an island lying near the main shore, and with tlie channel between 

 them, sheltered by projecting paints or banks; if we can therefore, by any 

 reasonable means, convert the Godwin Sands, the Scroby Sands, and the 

 Smithick Bank into islands, we should render the Downs, Yarmouth Roads, 

 and Bridlington Bay, havens of the best qualities ; but other advantages re- 

 sult from converting these barrier sandbanks into islands, since, by raising 

 their crest above high-water mark, they cease to be hidden dangers, and it is 

 obviously more prudent to build on the foundations laid by nature, and to 

 complete her works, than to extend long piers or breakwaters into deep 

 water for the purpose of inclosing an anchorage, not only without any assist- 

 ance from natural circumstances, but possibly in direct opposition to them. 



+: * * * 4: 



The great question that now remains to be solved is, whether it be possi- 

 ble in a reasonable time, and at a reasonable expense, to raise the crest of the 

 Godwin Sands above high-water mark ; and the writer is of opinion that the 

 same may be accomplished, first, through the means of alight but strong frame 

 work of malleable iron with other concomitants ; secondly, through the cir- 

 cumstance of the low prices to which iron has now descended ; and, lastly, 

 by means of obtaining the operation of nature to accumulate sand around and 

 within the contrivances erected to catch and retain it ; and without under- 

 valuing the application of iron framings for breakwaters under other condi- 

 tions, the writer considers the superior utility of the principle will become 

 most manifest in the conversion of sandljanks into islands. * * 



The Godwin Bank is of an oval, or rather egg shape, the extreme length 

 measured from the three fathom level at the north sand head to the same 

 level at the south sand head, being 17,980 yards, or 10} statute miles nearly, 

 and the extreme breadth from the west excrescence at the Bunt Head to tlie 

 Barrier Edge, being 7667 yards, or somewhat better than 4:5 statute miles. 

 The extent of the portion of the bank which is left dry in spots at low water 

 is 12,364 yards long and 6532 yards broad, that is, about seven statute miles 

 by 3j^, or 3-7. The elevated spots inclosed within the last dimensions, at 

 ordinary spring tides, are left dry at low water to the amount of 34 to 5 J 

 feet ; average 4 J feet ; and at these times their surfaces remain dry and 

 workable upon, for three hours, and the rise and fall of tide being 16i feet, 

 these spots are covered on the average at high water to the extent of 12 feet. 

 The nature of the sand is remarkably clean and free from clay and mud, as 

 might naturally be expected from the constant washing to which it is ex- 

 posed, and Mr. Smeaton, who landed upon the hank in May, 1789, states 

 that he " visited and landed upon the Godwin Sands to have a" view of them, 

 and examine their nature, and found that though of the nature of a quick- 

 sand, clean and unconnected, yet the particles lay so close that it was diffi- 

 cult to work a pointed iron bar into the mass more than to the depth of six 

 or seven feet." Captain Bullock, who made a boring lately, found at the 

 depth of 71 feet the sand become so dense and cohesive as to break the 

 borer in the efforts to make it penetrate lower, and it is stated that Captain 

 Hewett was unable to bore to a greater depth than 8 feet. 



Capt. Vetch then proceeds to make some ingenious remarks as to 

 the probable nature of the substratum under the Goodvf ins, and bis 

 views on this question seem to us to be well founded. We do not 

 accord with him, however, as to his next point, combatting the received 

 notion of the origin of the Goodwin Sands from the submersion of a 

 part of the Earl of Kent's estates. We are rather afraid that our en- 

 gineer has been induced to take such a course from the motive he 

 assigns, of combatting possible prejudice that if "the locality was once 

 firm land, incapable of resisting the sea at a former period, it is im- 

 probable that it can be regained or resist for the future," rather than 

 by a comprehensive view of the evidence on the subject. The nega- 

 tive evidence of present submarine appearances would be just as con- 

 clusive against the inundation of the Zuyder Zee or of Zealand, or 



against the serious abrasions of our eastern coast, by which, in our 

 own time, villages and parishes have been worn down into the domain 

 of the sea. We know that other districts have been lost for want of 

 attention to their sea banks, and we can see no reason why the strong 

 traditional evidence of the submersion of the Goodwin district should 

 be doubted, or that any argument should thence be drawn against its 

 subsequent recovery by the resources of engineering science, either 

 under the direction of the gallant engineer or some other colleague 

 equally able to grapple with the opposing difficulties. To proceed 

 with the Captain's plan. 



The writer proposes to conduct a spinal embankment or nucleus of the 

 nascent island along the sandbank as would readily permit the tides and de- 

 positions to visit both sides of it. The spine may he carried down the mid- 

 dle of the bank, or along the most elevated ridge, and if of a concave form, 

 greater sheUer would be given for the deposition of material, and the writer 

 wonld prefer following such a line as would serve so far for a barrier bank to 

 the island when completed. Thus on the Godwin Sands it is proposed to 

 carry the spine or nucleus breakwater parallel to the great crest of the sands, 

 as particularly developed along the eastern margin of the bank, and at the 

 average distance of 500 yards from the edge, that the artificial harrier may 

 be secure from damage by any temporary shifting of the outline of the bank, 

 and also that sufficient space may he left outside the spinal embankment for 

 the deposit of matter, which being sustained in reverse, would not be so sub- 

 ject to be carried o(i by currents or storms as at present, and would afford 

 mutual support to the spine. 



The specific mode of construction is thus detailed : — 



To meet the condition of the Godwin Sands in constructing the spinal em- 

 bankment, it is proposed to use iron rods, in a position nearly vertical, pene- 

 trating 74 feet into the sands and rising 7J feet above their surface ; the up- 

 right rods to be about one foot apart, and arranged in square frames of 12 

 feet each side ; and these squares complete, (called iron gabions, for facility 

 of description,) will each contain 48 iron rods on a space of 12 feet square 

 penetrating the sand 7i feet, and considering what has been stated of the 

 tenacity or closeness of the sands at that depth, it may safely be allowed 

 that so great a number of prongs will give tlie gabion all the strength that 

 can be required against any lateral force applied above the level of the sands, 

 and so far from seeking to go deeper for a foundation, it might be better to 

 employ means to prevent any farther settlement of the gabions. The iron 

 gabion being fixed, and the rods inserted in the sand to the depth stated, it 

 is next proposed to floor the interior space with hurdles, and on these to line 

 the gabion with one row of fascines firmly fastened to the iron rods ; and 

 this first stage of the structure to remain, without further addition, until the 

 action of the sea has heaped up the sand externally and internally to the top 

 of the fascines, when a second floor of hurdles and second row of fascines 

 will be introduced, and the operations continued until the gabion is filled. 

 The gabions now described form but the first tier in the structure, and when 

 the interior and exterior surface has become elevated seven feet, a second 

 tier of gabions is to be keyed on to the first, and these last treated as the 

 first. In the foregoing manner the author merely attempts to raise a barrier 

 one foot high at a time, and composed of materials not oflFering a solid re- 

 sistance to the waves, but calculated to receive and retain the sand on either 

 side as thrown up. It will he obvious that on such a surface as that of the 

 Godwin Sands, and where we cannot safely plant a heavy structure or acquire 

 a solid foundation, that we must endeavour to supply these deficiencies by 

 embracing and holding on by as broad a surface as can conveniently, and 

 economically be attempted ; and with this principle in view, it is proposed 

 on the hue of spinal embankment to lay down two parallel rows of gabions 

 36 feet apart, bonded and tied together with cross rows at every 36 feet, by 

 which means a base 60 feet wide would be procured for the spinal embank- 

 ment, and by the numerous cells of which it is composed, every facility 

 would be offered for the accumulation and retention of sand, &c., an object 

 which would be still farther attained by throwing out ribs from the spine at 

 suitable points to intercept the passing sedimentary materials, and these ribs 

 embracing the sand to a still greater extent of surface, would increase the 

 stabiUty of the spine. 



The proposed spinal embankment or breakwater on the Godwin Sands will 

 employ about two tons of malleable iron per lineal yard ; and the expense of 

 the materials and structure, per Uneal yard, may he roughly estimated at 

 £24 ; and the cost for 12 miles, or 21,120 hneal yards of spinal embank- 

 ment, at i24, gives a total expense of £506,880. The first tier of gabions 

 would cost about £253,440, and if the whole was finished in four ye rs, the 

 expense would be about £125,000 per annum. 



We should observe that this ingenious paper is copiously illustrated 

 with copper plate engravings. 



The second paper is Sir J. Renuie's Report on Holyhead and Port 

 Dynllaen Harbours, already known to the public. 



The third an Investigation of the Comparative Loss by Friction in 

 Beam and Direct Action Steam Engines. By Wra. Pole, C. E., Pro- 

 fessor of Civil Engineering, Bombay. This is the paper which was 

 read before the Institute of Civil Engineers, and reported in this 

 Journal of last year, page 170, the present paper is illustrated with 

 mathematical formulae and engravings. 



23 



