ls^5.] 



THE CIVIL i:\GI\KER AND ARCHITECTS JOURNAL. 



309 



I1ART50URS OF REFUGE AND DEFENCE. 

 By John Rookf, Esq., Amlior of Givhgy r.s a Science. 

 Ilarloiir in Dunr fiii;/. 

 Adnii'ing pivpn pxcpptioiis, propospd toI>p arwwprcd in (lii' arlic]p, 

 lie H;ir!'(»r Ciitnmissi<iiiprs Iuivp most jii't'y recommended llie con- 

 striidi'Mi ( f ii Ilailmiir rf Rcfiipe in Dc\er Hnv, vviUi :i pier run out 

 onllie West from Clieesniiin's Ile;i<l into 7 f.illinm of watrr, iiloiig 

 willi works finillv errlosing 520 acri-s up to low water mark, or 3SU 

 oeres witlioul til'' two fatlu.in line. Vi I Sir William SyniomU wiili 

 eon A ia«tice dis^ent-i from this report " heoanse" he "rannol reeom- 

 niend'a close harbour at Dover, where the pilots consider the hohliic 

 prou'id generally indillerent : and the engineers say it will silt np." 

 1.0. kiag nevertheh ss to Dover as a harlionr of refuge, defence, and 

 oH'ence, it become.s exceediig'v de.-irahle that the defects connected 

 with a national work, as staled hy Sir William Symonds, should be 

 saiisfactori'y reconciled. Moorings may he amply provided for; and 

 the harhour'prciposed should not be left n mere shingle trap. But lids 

 objection sliouir! be repaired by !lie construction of a pair of Ir.ips 

 , ne on its Western extremity, and a corresponding one on the eastern 

 side thereof, as shown ia tlie'di; gram here annexed, d d. With these 



previsions admitted, we shall find tie leading incidents at Dover, 

 »peakirg in a physical sense, admirably adapted to the construction 

 of a complete harbour of refuge, piovided the Work requireil were 

 • ftectively completed. This subject is capable of the most distuict 

 illustration iii physical experience. 



ylclioti of Sill and Shingle. 



As o-( olrgical results, we find along the Sculliern and Eastern shores 

 of Great Britain, frc in Torbay to Saint Abbs Head, no portion of the 

 coast free from .iral untroubled by masses of moving silt and shingle, 

 attributable to the debris dropping fronj variotrs projecting clilfs along 

 this sea line, composed as they ;!re of the newer orders of tossiliferous 

 strata, in connexion with silt carried to the sea by the several land 

 streams within these given points of coust. In proof of this, none of 

 the coast from Land's End to Exeniouth, where the older rocks ob- 

 tain, more free from silicious debris ai.d mouldering materials than 

 the newer fossiliferous strata, is liable to either barred rivers or the 

 objrcticm of moving silt and shingle, perplexing harbour construction 

 by artificial means. 



Among the remarkable instances shown experimentally, the rivers 

 Tamar iind Tlym, the F.il, the Dart, the Fowey, and the Avon, may 

 be fairlv stated in illustration of the theoiy here brought into view. 

 t)n this line of coast, indeed, not only rivers incoHsiderab!e in their 

 v(.b me of back water, but even streamlets, offer favourable incidents 

 for harbour construction. Not to say that such facilities are eminently 

 geologic.il in their structure, as well as ad. qualely freed from silt and 

 he;. dies of drifting shingle. But the instant we go eastward of Tor- 

 bay, to the river Exe, u considi r.ble stream mainly from ort' new red 

 sandstone, we not only find the channel of navigation barred, but per- 

 plexed by shifting sand banks ; and this is almost uniformly the rule 

 up to Saint Abbs Head. G'-okgy, as a science dependir g on physical 

 laws, accouritsfor the prevalence of such a rule undeniably. 



These proofs show lliat any coast with an aderpiale depth of water 

 inshore, where sill and shingle aie rot driveir along shore by the scour 

 ol tides i.m! the violence ot winds, uray be f.ivoui..ble to the construc- 

 liiuof secure and permaneit harbours. But sueli mateii.ds ilo pass 

 all. I'g the coast at Dover, and ins. much Dover is ineligible on ordi- 

 nary ii:eans lor the constiuclion of a baiboiir of refuge; on the other 

 b,.nd, etleclually check ai.d stop tie movunent of silt and shing e 

 aloi g the coast Iroiii off Dover, and It bi conies decidedly favourabli.' 

 for It:'' coilMruclioii ol the nectss.iry works required. Hence, I woul.l 

 fiipgf^sl an elongation of the pier r« sling in Cheesmau's Head, aud 

 bei.i Westwaru, ..s shown in the aeci mpauying diagram, a a, so as to 

 aHord :in etlicient shingle trap, wliicli, coiiibiueil witli a similar form on 

 the basleru exlreiuiiy of the liaibi ur, as given iii the diagram re. erred 



to, would arrest the course of silt and shingle drifting alongshore, and 

 prevent a silting up of Dover ilirbour, as contended by the engineers 

 referred to by .Sir William .Symonds. 



Eff.cicncy a/ Shingle Traj.s. 



It may be said that s'lch shingle traps would be liable to beach up. 

 TriK . Yet the very admission of the fact proves their efliciency, and 

 piiints out a direct remedy in their ready and progrissive eh ng ilioii 

 in currespondence with results; probably enough eventually providing 

 tlie groundwork of a milit.iry railway along shore, ami hearing move. 

 able l>at!eries to any point of Ibe adjacent coast ;issailrd by foreign 

 iiivaders. For the construction of an artificial beach might he compi- 

 ralively easy, when the resting poii t of such a structure were efli- 

 cienllv laid. In this respect Dover is pre-eminently advantageous for 

 the artificial attainment of a h.iibi.ur ol refuge. The heights .ilreadv 

 fortified would command and protect such a line of railw.iy; and bat- 

 teries might be then formed on the Western and Eastern piers at d d, 

 when beached up on their open sides, for the protection of the en- 

 trances of the harbour; besidis the facility of s])eedily ernb.irking 

 troops under the extended works and results here suggested, promis- 

 ing an expectation eventually th.it a bre.ikwater alone should lie within 

 the r.uige of flowing and ebbing tides in adv.ince of Dover Harbour. 



Hence the problem of its form involves the highest resistance against 

 the violence of tides, by the application of the weakest works advis- 

 able ; effective strength being thereby brought more fully within avail- 

 able means. It is [iroposed tint the breakwater shall, in the form of 

 a ship, hold its extremities to the fl.jwiug and ebbing tides, so that the 

 moving body of waters be merely divided, instead of being stemmed 

 and repelled as in the instance of the Plymouth Breakwater; rather 

 h dancing than restraining the tid.d waters, and producing an easy 

 dilliision of those waters within the area of the harbour, so as to pre- 

 seive a scour amidst gentle eddies drifting each vessel to its berth, in 

 place of violent rebounds arising from directly lineal action on abut- 

 ting points. By the two inner jetties, a a, resting on the breakwater 

 it is proposeil to equalize and protect the moving waters wilhin the 

 harbour during the action of flowing and ebbing tides, and direct u 

 light sciiur from the convex range of the deep water and doited line /, 

 on the inshore and concave form of the shallow water line c. The 

 form of the Western and Eastern piers at (i (/, would contribute to 

 ste.idy and ease tile water at the two entrances. It may be, liowevi r, 

 s.iid that the jetties, a a, are not essenlial to the scheme. Granted : 

 yet the equal distribution of scour they would provide for, the strength 

 they would add to the breakwater, and the security they gave to the 

 best portion of the harbour, would seem to recommend them eveutu^illy. 

 They may be said, indeed, to be evssential to the physical b.il.ince .md 

 diffusion of waters within the harbour; and therefore form a leading 

 feature in the scientific b dance of smooth and yet gently flowing 

 waters, drifting vessels into the centre of the harbour, and next dis- 

 posing of them around a deep and central aiichor.ig.^. Perhaps a sin- 

 gle jetty in the centre might answer equally well ; still the problem 

 they involve is one of vast moment in harbour ei gineering. 



Ill conclusion, it would be useless to construct a little harbour at 

 Duver; — none of the leading conditions admit of a successful prosecu- 

 tion of such a scheme. It would be equally ill-advised to construct a 

 harbourincomplete iudetails; — a mereshingletrap would be the result. 

 '1 he ground would be better as it is, than disturb.'d by projecting 

 points producing little benefits and great evils. Once begun, the entire 

 works should go on vigorously, lest shingle were brought into the bay 

 and stuck there ere the two extreme traps were completed. With 

 the anchorages of Dungeness and the Downs, Westward and North- 

 ward of Dover, an artificial harbour there would add another trophy 

 of Art combined w ith Nature to the many national blessings we enjoy. 

 Dungeness as a splendid anchorage and a great shingle trap, so justly 

 admitted as geological in its structure by .Sir Johu Rennie, it would 

 be exceedingly ill-advised to lay the imperfect hand of Art upon as a 

 corrective of the perfect laws of Nature. It is there the natural tides 

 overlap each other, Westward and Eastward ; the result is a huge de- 

 posit of shiugle on the side of Ei. gland, whilst it is driven eastward on 

 the side of France from Cape Hlancie z. Pevensey Bay is another of 

 these natural deposits of shingle on the side of Englanil ; and I'egwell 

 Bay also. These deposits should be promoted by artificial works 

 adapted to their purpose, as the sure uu.ile of improving the ch.innels 

 of navigation. Little groins, like little harbours, are next to useless. 

 A large groin bearing on Dmigi ness from the westward of Folkestone 

 — a pier composed ot loose stones, and a second commencing at the 

 cliffs eastward of Hastings bearing on Deadly Head, would slop the 

 [uegress of shingle dulling along the coast, and provide two addi- 

 tional liHrboiirs, wbidi, aecoidii.gly as they lie^clied up, might le 

 elongated indetermin;iie.y, providing at the same time advanced bat- 

 teries on the waters of oui shores. I his pair of groins ne. d be begun 



41 



