MR HEALE'S REPORT ON THE NEW RIVER HARBOR.

Southland Times, Volume 2, Issue 103, 19 October 1863, Page 5 (Supplement)

MR HEALE'S REPORT ON THE NEW RIVER HARBOR.

S^THe Mi^o^^^ciM Report; of ; the jo&l for publici|tHni /i— ; i |siß^Sb^^i^^^p^|t|nges \ the; !&6nel of the harbor, nedr rs lthe Bombay : ijcfc^ begaif^to 7 'excitpj' attention and l^^iiC-^sl^i^^K^OtJ^^^y ■ Sear views rt upoih the subject without iccurate -plans^ X tbofe^the>yery first: importunity of Vsendirigs a competent inrvevor to sufWHhe" ha>Tsr, and <F S, as far*af# oilier ■ engagements, jould p^Mef^watclvßd.and assis^d--,f'this wfe^Tl^Ma^iSiriOtyet quite »mpleteainrife^yidrograpbjcalsportiojn, lilt it is suffici^nUyjadvancedrfto^how, : #j clearly the nature* of "the; action; rbich .ha«-bepnrg>>ing'onvJws^«A^:^ ■■ j "' I submit;h ! iwewi^ oted by Mr 'Baj^er,; showirig.f theijforjm f ; the sboals&n^^annel* ;as^tlSeys6w nl and, W,s W^Bmd^m^, i,py frqittrMr f Thomspn'dssurv^y made 1 1856, a work of unimpeachable ! acctiicy in all it* essential points;;^ j I On compariiif these two, it will bje i )e n that the -coWex Hide of the great' ioal| which .formerly .extended from ie northern shore in; tthe direction -pf, ie Pjlot Station, has been worn away y the action of the tide; and thatia ; Jit, which in-1856 was-quite^narrow, nd ran inwards fro.m,tbe^b a^onl^about! iree-fourths v of a mile, fias become e^-" ;nded to within less, than a^cablejs ingth of the s ßombay Itofck? and'ap"roaches the Oberon Rocks so closely b almost to closethe inshore chanhbl tihat point. ',' ;,'. r . . • . It is evident that this action, by which boiitone and a half" millions of cubic let of sand has; been deposited in eonLuation of the spit as it then stood, inst have been going on ever since '856, and probably it commenced long:; Ifore; bu'tit nafturally would not be |nch noticed until its Jesuits began to 111 upon the navigation of the harbor. \ i The practical effect, of^e change ras first felt upwards of a year ago', jhen the Aphrasia grounded on. the Rowinp end of the spit, where not long ■fore the channel had been • perfectly Kfe. Soon after a more serious acciKnb resulted from it. ' ; MTbe growth of the spit continually: Rifted the channel, and, consequently,: He run of the tide closer to the shore Bj.the vicinity of the Maori Kalnga. Kis scoured away the sand hear the Beach, and gradually denuded a small | ■itch of rocks which, at the time of: Er Thomson's survey, were in shallow, piter, nearly buried in sand.but which-, ■j the change I have described, came B)jbe pointed rocks, standing up quite Bjtbe fairway of the channel. On one ■these the Guiding Star steamer struck ■id was lost. . . : ' ;v~?-^ ■_;;'■ \ Hn the. course of [■<& few days the Ittque Eucalyptus.iand soon after her Kbther vessel, touched these rocks, L firsCbrought into the Hannel, seemed, toypaa.ny .persons as if bad been, newly^. created. The Kfnnel ever since has heen forced more. B| more over towards .the land,f until Bw the only passage, for vessels rth be- ■ Ken or inshore of these^TOcks'; and Be inshore channel, which alone is ■liable 'over' the bar, is jal most cut off Bin the main course of the tide and Bn the upper part of the harbor. The Bjfth of water' at this" 'points is only Bfjve or thirteen- feet at low water H^ngs, so that vessels of considerable HlPght can only cross it about high then, being the change which place, it .becomes , necessary Ist. Its causes. . , .. : H| 2nd. The probable result from the H| continued action of the same causes.^ ' ! "*• .■'■ ' ■||3rd. Whether any artificial means } H| can [be employed to vary them, qr to, avoid any further injurious consequences, or to : expedite any beneficial ones, which may result from them. whole of the slioals, and the: and western shores/ at the of the harbor^ consist of perfectly K 1 an d loose quartzose sand, having gravity not 2. 'material, must; possess a high Of and it may be laid as a principle that the banks of it can have np stability bethat of the, influences which act them. . .Their form is,in fact, an resul|^of a 'the motion of the water of passing through and over that . motion being very . slightly only by the inertia of the sand, form will promptly alter as soon changes take place in. the direction, or volume of the' currents, the , eqilibrium' is ' such that the tide exactly brings back and reall the sand carried down by or else a supply is perpetually forward to make good the porsize of the channel, under such must be ia direct proporquantity of , water which in and, out during ebb and flow, depth must depend upon whether tend to contract it in h -P'ondulj. to expand it later- ■ • •■ . -' ! ■•-■■' •"•" ■.■■'"■ the amount of water in the is very lai-ge, quite sufficient favorable circumstances to scoop deep and wide enough to all the purposes of the .most commerce. section of the Oreti .Riyer^abo^e of' the Makarewa ii at its summer level about four hundred

s(|uareH feet>^ana" i|C velocity on^tbec '; J^li^A^wo^and-ialia jf| iniies^plr lionr^lj^imdan septiontduring* thej&reefpasfc? xti^t}sW£as>een pall \ %*. hundred^ sgUOT^^t^-MdJ-l^^yfil^^ l6iei^Bk^M^% ftr^Koti^ ;|l%eV Makare wa n*a^ 7 of ; tli.e^yi^ume olf^tM Oreii } and ;he vVaikiwi. Waihopai, antt; -^number of smaller sti^ajtHis^^^ tmajcjeu up in 1 ho" aggre^a^^i f oiu^ oi^injotiless than one hundred and tenf thousand cubic feet per mWu ?^ilr^«ai|ei| and tyro hiindred th^sa^d f iri^s^itsotfs^o?f: fioodw But thi£ 'gf^at^Wonßtant^^ discharge ljs;4 mere-tr"jfle compared .witli- .the .tida.l waters flowing th¥b'ugtflhVHead^ o?he esteary Rovers an w arear of r Jabout- eighteen-and a-hjalf .BqUa*rjßimile3,of.Whi«h lit'inay be roughly estimated that one-half is coyered at .low wafes a^bl r receives and discharged In^ea^Hide'-tfie fall depth of the rise and fairat the^Headj, and T the '-M&ssxk '6f,Hbiat '^MS^'^i *iiMW p ' r *V .;\: ] I '"'■ __This,great-discharg'6 df water neees- . ■saTijyr t £uppp>es frovefcyilaSgeWfifice of" discharge, and—in- fact between the; Horseshoe 'Channel 'and ' tfre ..Bombay ! =R?6'cfi,'<th f e cnanri'ei 1 a?low ? !^wa&r- -Kaa i |a ' bread.th jpf^qnite a. quarter r of .a mi^e, the depth* varying from twelve to thirjty , feet, and the ! total" 'dimensions of the channeljCannQ.t be- less jthangithls at^any point lower down,, but must, in fact, be . greater^ since f>the ! voftfcity; of the !euirent is less ;-j if,' therefore,] the depth of the channel be less^ it must 'arise, froii unfavourable circumstances leading to its divergency in width. . i : i .;•.■■•: The :V circutnstances under which the current of the harbor meets the sea are, in some- r espec ts ? , f a you rabley Th us, i t flows into Foveaux. Straits, which are effectually ' projected from . the ~gf?zi\ swell of. the Southern Ocean by StewartjS Island. "The advantage' which the harbor enjoys in this respect. over, .those op the west'coastjof tjie Isjand .is immense, and -is"i clearly marlfed'hy <the fact that the sea rarely r . breaks all acrosjs the channel "of th& New River, in which there is ; sixteen feet- of 'waterj while it frequently breaks all. across the chanjnels of Ihe Kaipara and Manukau, in which there are upwards of thirty feet of water. \".' ',''...' But the unfavourable circumstances •o tHe'm'out 1 ! of the New' River arethese : The .southern shore, which consists •o° a pretty straigh' rosty ' c ich, of which Omawi Island may be considered the outer extremity,; greatly overlaps the North Head, which lies to the north east of Omawi Island, at a distance of two-and-a-half mites. Now, the best course for the channel, and that which the ebb tide would naturally take, lies along the southern snore ; and a channel there, with the full force of both ebb and flood tides flowing through it, would ahvays be deep, because confined by the rocky shore •; but the flood tide, coming in from the westward, strikes all along the oblique lineofthe bar, and '; in its present condition sweeps over it, and the prevailing wiads being in the '■■ same direction, the v waves of transla-;! tion ". roll at continually varying angles over its long outer edge, smoothing every inequality, and causing the tide j to spread itself evenly over the whole I breadth, and consequently to a very j shallow depth. A portion of the ebb follows the course so laid open to it, and thus the scour of by far the greater part of the tidal currant is wasted with- : out any useful effect on the harbour channel, with the further disadvantage of cross actions of the tides, the flood running, until quite recently, at right angles to the course of the ebb. While, however, the tendency of the flood-tide is thus to force its way in from- the North-west, and so to keep open a broad shallow channel all along that line, there is another and an opposite influence at work, which, when favourably directed, may effectually conItrol the former one; and which, I j think, has done so in comparatively jrecent times. There 1 can be no doubt 'that here, as under similar circumstances" elsewhere, great quantities of sand 'travel continually from west to east. I Now, if undisturbed by the harbor tides, this would be deposited on the northern iparttf what is now the Bar, and would form a great triangular spit running out from the Northern Head, and the har bor would then be in its best condition. I I think that the form of the channels shown on the earliest map, and all the changes which are known to have taken place, afford a strong presumption that, this was once the case, and that a breach was subsequently made through this spit near its southern extremity, probably in a season of great floods following a very fine one, when the channel had become contracted by a diminished flow of water. As soon as this breach was made, the tides, especially the flood, would be divided into two branches at an obtuse angle inside the bar. Along the line of contact of these two currents a space of slack water would be formed, and any sand brought to that point by the force of the current would fall. This appears clearly to bs the origin of the spit, as 1 find it on Mr Thomson's chart. It is obvious that such a spit, especially at the commencement, when it was still small, would be subject to great and sudden changes as the circumstances of strong westerly winds, or of great r YjX floods, gjyre preponderance to the rolling in of the 'flood-tide through the breach in the bar, or to the efflux of the ebb by the inshore channel. This quite agrees with the earliest accounts we hear of the harbor, when it is stated that-/ or a short time the inshore channel was almost closed near the Pilot Station. : ' It is quite clear that, for the past seven years at least, this outer or bar 'channel has continually increased in width, and so has more and more let in the floodrtide and also the action of the

wb^te^ ;^onVexC^av«^e4,'«s^hiln a feyr years : 4^? jfchS^niJScds <!*£ a t 4h>ee-^burths f\ A: sgprt Breaking seairoUs Cm with westerly, wijOds^and so displaces sand ,along, ' t^^ge|of, -the^ shoals, and • the' ftbiK^ngs" it oy|t^ind:depQ3itsri^on the dividing? spit. :; |;i j Tills action Kas^tiow gone on sO faf, that it isno-longeV a conflict betWejeri -two x ary' ciirreritSj for/;tha.t ?of the inshore' channel Js t almost extinguished. It is c.lear- thai by far th^ greater part oftthe {ebpj as^well 31s the flood, mow "ftaßWs.Jby i: yiie i ,.BHndi .Chann<el, and the greatest hope -I have of a speedy improvement of the hafbor is Based on the { expec,tationithatithe;:impact of the ebb* against*. .. the, .lo^er part of the dividing spit' below/the Pilot Channel ;niay_Wear through it at that point. ■■: «#f j this were to h'appeh) I have] no doubt thafc a ; iyery great and rapid im--prOvedißnt'df theliarbbr« would be the immediate result ; the channel would then be nearly straight^and would meet ithe prevalent winds and sea at a: very j oblique^anglp, f whit;h ; would be so favor- \ able t'b tie. passage of the tides, in that dire&jiiony .'tliatXcbiMJeiVe ' that the passage the. tide, over the bar would cease , Or .nearly so, and then it would injmediat^y^ shoa) T tlp ; the dividing spit would constantly work over towards the shore until the inner channel became obliterated, and the mouth of the harbor would ultimately, return to what I conceive to have been its former and normal condition-, Of a single wide and deep channel, flowing pas^t the South Head, with a great continuous .sand : spit extending from the north sh of e. It is, of course, impossible to predict the ; time which these*hanges may take, to j come about, but I have a strong con- ' viction that the action going on tends in that direction. I have given the most anxieus consideration to the question, whether any improvement can be effected by artir ficial means? The conclusion I come to is, that it is impossible to effect any immediate advantage,, and that the attempt might be disastrous. To effect any sudden changes, a decided obstruct tion must be opposed to the current ; but the instability of the foundation is such, that the eddies which would be immediately produced by such obstacles would scour out deep holes around the ends ofvthem, and might have the very opposite effect of deepening the channel attempted to be closed, or of open'n^ new ones in the most undesirable positions. ' lam convinced that the only remedial measures- which can safely be adopted are such as will gently assist) the natural tendencies, and not oppose them. Now., it is clear to r me that the condition essential for the well-being of the harbor is, that the whole of the tide should be deflected on to the south shore, at the least possible an«?le with ; it. The diminution of this deflection 1 by the we ring away of the shoal, as described, is clearly the proximate cause of the present inconvenience, and I think that the gradual restoration of it is the only means by which any re • turn to a better condition will be effected, or by which any available channel can be permanently maintained. f I conceive that in the condition in which this spit is shown by Mr Thomson's chart, a work of very moderate extent p.nd cost would have secured its permanence, and have effected a considerable improvement to the harbor ; it is a much more arduous task now to replace a shoal which has been removed, and to obstruct a channel which has beenfermed, but I still think that both may be gradually done by aiding the ; tendency of the sand to deposit at that ' : point. The only way in which it can be prudently attempted is, in my opinion, by a training wall starting from the shore as an abutment, arid carried along nearly in the direction of the margin of the portion of the shoal which remains, so as to bo almost parallel with the present course of the ebb tide. I believe the effect of this would be to produce still water behind it, in which sand would rapidly be deposited. As such an effect resulted, the work could be gradually carried forward, never pushing it far beyond where it was effectually backed up by the sand, and so ultimately the "Blind Channel" might, I conceive, be obliterated, and the northern shore be carried forward nearly as far as the southern ; if this. Work succeeded in only a moderate degree, the whole of the ebb aud flood waters would be confined to one channel of moderate breadth, and I have no doubt that it would, in that case, be of such a depth as would admit ships of any size required by commerce. But I wish to be quite understood that such a work must necessarily be tentative only. That success cannot be with certainty counted upon, and thatj under the most favorable circumstances 5 the benefit would be very slow and gradual. lam,therefore,unwillingtourge it strongly, or to raise any sanguine expectations, Still, since if successful, the advantages would be very decisive— -as the first steps would not involve a very large cost, and as the probable results would soon become apparent, and the experience" gained would certainly be valuable, if only to prevent any more costly or hazardous schemes, 1 should certainly be glad to see the experiment tried. ;.'.; i I conceive that the work at first would be .eiactly of. the, character of the groins frequently used in fixing the beaches in England; composed of piles and 1 planking, and that for the first thousand yards, which would be ample for the initial experiment, the work would only average about five feet in

andjj^^ m^re-th^n^i^^r:^urnning fpbt. When the^effect of tiiis^^wasideyeloped it would heHqufite JtittLe ibiiforjm -Hah 'estimate jfor the larger extension of it, j „ .phave'the honor td^be, ! , -' " '. -Sir, : -- ■ j .rYourvmost'olrcdietff. servant, j „,h ;p, t M K f ... -. i: ' v^hief Surveyor. To His Hotior-the Superintendent, ; ,^^:w£>:^ 'Southlarid.' ■£•:• * ; vj \ ■-■'■