PATEA HARBOUR IMPROVEMENTS.

Taranaki Daily News, Volume XXIII, Issue 126, 22 June 1901, Page 2

PATEA HARBOUR IMPROVEMENTS.

MR. LESLIE REYNOLDS' REPORT. $ Wi'ST PIER RECOMMEMJED/SI Sin,— Prom my inve'tipation of that portion of the Patta river extending ff-oru tie b-uige s award, and a s-tidy of the varinus <t>ta submitted to rap, I ain now in a prs'tion to repoit as to 'lie present londitio,) of 1 hat portion of ile tiwr. iind to advise upon wtnt, in my &pi ior, is tbe suitable and tvjuomicil method of improving tht entrawy. Dia'it'g firstly with the conditions of the r'vn', I find that when the soundirgs taken for the purpose of this re port are compared with ihe-'.o by Mr. Thompson in 1877, there has been a general shoaling, averaging absmt two feets in depth, from th;Ilacbour Board wharf to the pnin' where the lower tide guage is fixel. The tionndings wpre taken, ai near t •-; I CiulJ locate them from the plan:;, upon the lities of the ecc'ious of the year re f erred to, In 1897, Mr. Thompson again ex-j amined your harbour, and reported thereon. Unfortunately the plans whith. aocornpanied that report were not available at the time of my ex- i amination, otherwise, I should have taken further soundings in positions < orresponding with the sections thereon 'hown, Thess pUns, however, have I since been forward, d to me, and I find that the positions of five of the sections lastly taken by Mr. Thompson, practicilly coincide with the po i'ioriS of sections t.ken in 1887, and thosi obtained by and in thope five oases nearly the *arne diminu ion in' depth is noticeable. Mr. Thompson, in his report of 1897. stated es follows :—" I enclose two sheets of drawings, No. 1 contains a plan of t! e taken from Mr. Finnwty's recent suivvy, and on ih I have plotted the positions of the b undings taken by me in 1877 for the Government, and aUo tbe pititfons of those jus* liken together whh a longitudinal section of the rivtr showing tbe deepest water from the bridge to the boulder bank in 1877, and to the bar as at present. From this it will be noticed that there is at le'S 1- . an increase of 5 feet in depth, tlt» old soundings show 3-3, and the new 8 3 below low water spring tides. I may mention that formerly there was often much ltss than 3-3, at times only a few inches."

From the published reports it would appear that your Board sccept-d the statame&t in the above portion of Mr, Thompson's report a* referring t o the entire length of tbe channel from the bridga to the entrance, whereas, I read it that five feet iecreas<3 of depth, referred only to that portion, diieotly subject to the deepening scour due to tbe breakwater, that is from the tideguago expending some little distance seaward of the present works, Ailer de»Kng with the depth at different poicts, Mr. Taocaps n, in summing up on this bend, concludes that, except at one po : nt where the depth was 5.3, there wai a navigable depth of fully six foet iu the fairway from tho bridge seaward.

From tho result of Mr. Thompson's investigations one must conclude that a considerable poition, at least, of the shoaling has occurred within the last fout years, I would expect that owing to tho clearing of the bosh and the opening up of the country inland, resulting in a ocmsiderablv greater portion of silt than formally being discharged in'p tha river along its banks, and from its tributaries, Bhoaling in lo 1 " 8" reaohes would follow, but I am unable to account for such rapid contractioa as would appear from tha soundings to have, occurred within recent yen's.

The accompanying dr-w'ne, No. 1, indicates tbe positions o' tbe fections and the depths of water et different pwiods upon which they were taken, ■ind from it will b9 s°en that mv observa'ions limit the navigable d»pth in the fair »ay, at low spring tdes at from 3ft6into4ft.

With regard to tbe fall in the river, £ find that the surfac.i inclination from the town wharf to tho pilot gusge s\t the period of low water springs, and under normal conditions ofri»er discharge is din, but from the pilot guage to the seiward end of tho present wo ki t l ere is an abnormally rapid fall, which during the period of two-thirds ebb tide, at the date of my iasp-ction, amounted to 18in.

Tris very exce ß sive inclination in the wator sivfaci seaward of the guage, varie l , as the conditions which I shall sh r'ly explain and thrruph which it is brought about, in p«rt alter. It is very evident' that serious throttling of "ho ingoing and out-going currents occur at this point, and that the tidal volume of the estuary, and the beneficial scouring effects of tha in-going and cut-going waters, are "oosidenbly h-mp-rrd and curtailed. The of throttling referred to lies in the fact that the bottom at this po'nt c nshts r.f pap*cl»y and heavy shingle, and also by the sand and the shingle tr*pp«d at the prior, of th l * eistern pier bing curried up to this point by the rip of the waves along the breakwater, and landed ou tho west flank of the ohanm-1 just below the tide gauge.

With th* extent of works nowcins'runted, it : s st this point that whit may bo termed the final struggle within thec-ntritpce takes placa botweenthe sea forces and the efflux currents. The seis when running with a wes'erly bias and a'" periods of fl jod tides, drives a portion of the Rhingle and f-and traveling akng ihi const into the ont-anfe, and this in turn i= carried in by the rip of thn fallowing w-tves, as as'ha shinglo ard p<ipa c'av point shown on p'an. Here the r : p is dell ctt d towards the western side f t,ho ehinnfl,the shinglo being thrown up on that sid", thereby narrowing and cmfining'iheartaunt'l throttling occurs, tho i.ormal out-going seour not being sufficient to remove it. During flood or 1 f.-eirei d«po?it is s award, but it rapidly reforms when nonfal coitdiMons again obtain. Tho ihro'tling which I have referred to is in ruy opinion a serious detriment to the beneficial scouring effec's which w. nld t>e rorifiderably augmottte.d we*'o 'bo cause of thrittliug removed. The f-x ; ent of the papi re-f should be exploi ed by boring, and any reef 'wvross tho channel blast-'ief out so as to enlarge the water way, and give freer ingress and egress to the current*, care taken to leivo suffic'ent fioting |to tho toe of the wall, and to deflect i-ha course of the currents the'efrom. jThis wou'd, however, only j n nnvft one of tho as the sea j forces would st'll rwmain to drive and pile up tho shingle and narrow the cliunnol cs at prasm*', ar.d the ooly practical method of eiadica'iug tho trouble due to sea action would be to construct a western pier to protect the entrance, and to allow the coastal drift to pass on without Wing trapped within, the channel.

! WiiST PiEtt RECOMMENDED. Aftc* consideiing the conditions affecting the entrance, I am decidedly j of opiuion that the construction of a western pier is of primary importance, and upon accompanying drawing, No. 2, I have shown the position which I sbouH recommend as most suitable, and for c mipirison have »lao shown the position of the works recommended by the lute Sir John Ocode. Upon referi ing to the drawing it will be seen that the wettern pier would commence at the extreme point of the luff <ind extend seaward a distance t f

(iOO feet, in a line practically par-lkl o that iecouitnendt,d by Sir John '''oodo, but somo 250 feet nearer the; present work*. Ic will at onca be' evident from the drawing, by adopting i bis position, th.it fer the earne length ! of pitr, practically twice the protection I would be afforded to tbe entrance, tV>e line of channel remaining as originally : designed. ! I am tioroughly satisfied thit were! he west piertocs'ruoted, as above out- j lined, tha entrance would he effortudly j pro'.ectol fr. m the western se.-s, and ' the direction of the channel, except I within small limits, permanently Used, and the depth of water on the bar I materially increased. Indeod, there, are few c-ses in one's experiences whe r e | comparatively so small an extent of 1 works as now recommended, would bring about such bene6cial results. The direction of the out-going currents, under normal conditions, is ii a line tangential to the seaward end of the curved channel to the eastward. With the protection wh'ch would be effected by the western pier, tbe outg ing currents would hold up to the line of channel it is nought to maintain, and would impinge directly on the bar. CONBTBUCTION. The method of construction for the we<t pier, which I have to recommend, and upon which the estimates are based, is shown upon the accompany- { ing drawing, No. 2, from which it will be 89on that the first 500 feet of con-1 crtte is deposited in mass, and to a height of 6ft. above the level of high wat»r spring tid. s. From this point seaward the construction would consist of a foundation of conorete deposited in big blocks of seven toon weight to approximately half-tide levjl, and capped with concrete in mass, similar to the in-sbore portion. The materi-1 would be deposited from trucks railed out on the pier coping, and by thiinethod the expensive item of f tagiag would be eliminated. Tin work throughout would be of a permanent and substantialchaneterj-whicb could be extended at any time its required, r.r as fund* permitted. The work yard and mixing machinery would be located as shown, under the lea of the bluff, and the material for the concrete con veyed from tbe west beach to the works by means of an eeri&l tram. / ESTIMATES. I estimate the cost of constructing tho west, pier extending from the bluff to poiDt B upon plaD as follows: £. West Pier from Bluff to point B. 600f»et 9,800 Aerial tram, cranes, mactinery, and gcnoral plant 3 830 I Engineering and supervision ... 1.f.00 £15,130 I would mention that I estimate the cost of constructing the pier to point A on drawing for a length of 500 f et at .£10,700, but in view of the cot siderably greater benefits to the entrance which" | would follow thscoisruc.iou to GOOfeet, j I would re commend that if po sibie this extent be carried out. > It will be se?n from drawing that, an extension of a further 100 feet .has be n shown, or in all a distauce of 700 fe >v\ from the bluff, and I estimate the cost of constructing this ex eat of pier -as follows:

West Tier from bluff to point 0.700 feet 4 . .. 15,800 Aeriel tram, cranes, roachinery, and general plant .. 3,900 Engineering and supervision 2,000 £21.700 The foregoing estimates havo benn based upon rates for material and labour which should allow of th v work beiog substantially and thoroughly exeou'ed. It will be noticed that nothing has b'-en allowed for the selling value of the plant upon completion of the woik. Should this it9m beconside'ei, I judge a 1-giti-mate estimate of gelling value at £1,500. OUIDB PIBB. As I haye been requested by your Board to report upon the Guide Pier with regard to it* effect up >n the entrance, its d'sgßH and cost, I will new briefly touch on thesi ditfe eut points. The Guide Pier exerts a beneficial effect in tint it confines the eutgoiug currents to one cm se and, especially during periods of flood", is instrumental in straightening up the channel seaward, but b'jing whit should lo itimate'y be considered an " interal wo k," ite'off c 5 is perhaps not so farreiching as may general'r have been an'icipated. With regard to the d-sign and co't, there appears (o be som» controversy as to whether the Guide Pier is constructed in accordance with fher'esigns supplied by Sir J. Good 3, and whe'lien thu sheeting is on the proper side.' The d.si>;u has ba«n immaterially altered in so far as that the piles have been drjv»n vertically instead of being slightly spleyed, which, tog. ther with the additional diagonal bracing addei, was -a wise provision, and ns f »r thy sheet piling, it ia uuqu sLmably on the side intended by Coode, and in the correct p sition mndoub'edly. I cannot, of course, judge to what depth thu pilos have been (irivon, bul 1 have no' hesitation in saying thut the superstructure has bton fairly well carried; out.

With regard to cost, howeve', I estimate that tho work should hav<> bein f flicion'ly comptotod for £4OOO. In connection with ihe Guide Pier, I must, point out that ia the event of tlvi we-tein jier not bciug pioceedsd with shortly, the seaward ecd if tho Guide Pier whi-;h now leceiv-s tho full bufl'eting of the waves, must b > protected ; the only satisfactory method of accomplishing tlrn will bo to fill ii the last four bay* wi h concrete -m.JI i uM le, t)get'ot- with an apron of ha-y boulders «t the p lint, Cheaper we Ivmls might be devised, but in view of the wave force aod the cutting action of the Band, more durable ma'erial than timber is necessary. ' In conclusion, I would thank the members of your Bo u'd, ivljo your eecletary (Mr IJonrr), and the harbourmaster for the'r assistance rendered me du iog my visit.