CORRESPONDENCE.

Temuka Leader, Issue 231, 5 February 1880, Page 2

CORRESPONDENCE.

[Wa do not hold ourselves responsible for the opinions expressed by our correspondents] MILFORD HARBOR. to tf:s editov.. Bin, —Tn a let Lor I noil reused to the Chairman of tho MilVd Hai-bom-Board a short time since, with releienro to Sir John Coode's report on the feasibility of the scheme, I mado a few brief i-em:i"ks upon the great stress which he lays lip on the travelling end the inadequacy of the scoirking power of the river Opihi as being indefensible from the facts of the cape. I also promised to enter more full y into the matter after seeing the plans which accompanied his report, not having mypelf a copy of those documents which we v e funvsbed to Sir John from my surveys ud designs. With rtgard to the depth of water in the Inge mi, Fir Jdm states that, " excepting the f=mall nrut opposite

Mill Cn ok, in and near the line of outlet chin mi 1 which existed when t' ft survey w\m made in October la« r , the greatest depth was from 3ft to 4ft at low water <>f ordinary spring tides." This fo far is true in tie present state- of the estuary hut no mention is made as to tiie . : e|»th of this "small area," which may be said to contain even now some 12 to 15 acres, and has a depth of water of from lOffcto 12ft at low tide, and 17ft to 19ft or 20tt at high tide ; and where after a flood I have soundo 1 a depth of 22ft, as stated in my report of Oct. 29, 1877. Nor is any reference made as to the probable extent and depth of this " small area " were the mouth permanently opon< d in the manner proposed. In that case I have no hesitation in saying, 1 feel confident tiiere would be an area of from 25 to 30 acres in and near tlio line of outlet channel scoured ont and maintained to a depth ranging from 12 ft to 19ft or 20ft at least at high water ; and further, I feel sure that there are responsible contractors in the Colony that would guarantee the maintaiuence of the above depth for less than my estimated COS+.

fc>ir John Coodc is rightly of opinion that "existence or non-existence of a channel depends, ;- under present conditions, upon the relati ns between the scouring power of the tidal waters combined wth that of the fresh water discharge of the river Opihi,and its tributaries on the one hand, and on the quantity ot shingle transported along the coast by the waves of the sea on the other." With this proposition 1 entirely coincide, but differ most materially in his estimated power of the fresh water discharge which is as much underrated as is that ot the travelling shingle over-rated. In the first place tfie river Opihi is not entirely dependent on the rainfall as Sir John Coode has calculated, but quite as much upon' the melting of the snow if the high ranges where the river and its tributaries have their rise, and it is well knowr that the rainfall is much greater in high levels than over c miparatively low-lying districts like that of Oamaru, from whence his record ot the rainfall is taken ; be sides, copious springs are so numeious throughout the bed of the river as to cause a largo body of water to flow in the dry est season, and which, together with the Ud?.i influx nnd efflux alone, to say nothing of the periodical floods,which are both frequent and extremely heavy would be sufficiently powerful to maintain a navigable channel througout the year if assisted j u tho manner propose; 1 with regard to the quantity and rafe at which tho shingle travels Northward, I have already stated in my reports on Milford and Timaru, and in my letter -to the Chairman above referred to, that I differ both with Mr Carruthers and Sir John Coode in their estimate on this question, and I do so not from a mere cursory glance of a fow moments'duraMon, whieh has characterised kiir J. Coode's inspection ot the New Zealand harbours, but from a personal knowledge of the coasts of this colony during the p*st seven years, and more particularly the ISast coasts of the Middle Island, from liiverton to Kaiapoi, and having in that time specially surveyed and reported upon those parts of tho coast where tho greatest quantity of shingle prevails, such for instance as tho Kakanui, Tunaru, Mi'ford, Lake Edesmere, and Forsyth, &c. ; and from close obs rv.ition and study of this subject in many parts of the world, I emphatically deny that the quantity or rate at wl.ich the slung l ** travels is in any place like those gentlom-jn would lead one to suppose. Probably, the greatest quantity moved along the coast in a heavy south-cist sea is between the Waitaki and Tiinavu, from tho simple fact of tho waves striking tho beach more obliquely on this particular part than elsewhere, and hence the reason of the large accumulation of shingle at the Washdyke, and for tome distance northwards, which is the accumulation probably of thousands of years. At the Mi'ford Lagoon, from the more easterly direction the coast lino takes towards tho Peninsula, and the tendency the waves have to break in a ?'ne prrallcl with the coast, in a'l heavy southerly seas, the waws here invariably strike the beach directly at right angles, and therefore little or no change is observable in the movement of the beach, except at the mouth, where from an accumulation of water in the lagoon to a ccrta'n height above the ocean level, or from a flood in the river it bursts, and a mass of shingle s simply carried out a short distanco to sc* for a time, to be piled up again 1 y the ocean wavo so soon as tho flood in tho river ceases and the water in the lagoon is lowered to a sea level. But were a pjiirof solid masonary piers built out th'.'oogh tho shingle bank into deep water, as proposed by me, so as to concent'Mte the scouring power of tha river and ebb tide upon a fi.:ed channe 1 , and at tho same time prevent the shingle bank from foiling into the channel Ip.te'Tally, the mass cf shingle cast out to sea as just described, would, by the force of the waves, be thrown as before towards tlio beach right and left of the piers, v here it would f> r over remain, as it could not enter the channel, by reason of the ebb tide, which is double the strength of the flood in passing to seaward through tho entrance thus formed. Sir J Cooue, however, is if opinion that " by time these structures had reached the points contemplated for their termination, the shingle along the would have advanced so far seaward as to travel around tho end of tho southermost work, and in the absence of the requisite scouring power would inevitably block up the entrance

channel between the moles for a considerable portion of each year." I have already shown, from observations acquired on the spot during 1 a constant residence of over three months while surveying the locality, and from periodical vi-'its during the past three years, that the ''existence or non-existence "of such a channel " is not affected by the " (Quantity of shingle transported along the coast" at this part, tlie quantity transported being insignificant ; but by the mass of shingle at the mouth b?ing alternately cast our to sea bv the river flood, and again thrown back into its former position by the fore? of the waves te seal up the entrance until the next flood, and which operation would be effectually prevented by the formation of the works proposed. Besides, even were the shingle to accumulate behind the South mole at the. rate stated by Sir J. Coode, th*» effect would be that the wave breaking here direct on the beach, and not obliquely as at I'imaru, wcull tend to pile it up rather than allow it to extend into deep water, as is the case in a marked degree at the termination of the shingle beach close to the mouth of Lake Forsyth, where the shingle is piled up to a considerable height, .descending precipitously into deep waters at this junction with the rocky cliffs of the Peninsula, in fact, deep water runs close in shore along the whole length of the coast from this point to near tho month of the Rakaia, but nowhere does it beooui" so suddenly deep as at the entrance, of Lake Forsyth, from which northward not a particle of shingle is discoverable. Moreover, the shingle does not always travel north ; it does so only as long as the heavy southern seas prevail. I have frequently witnessed at Mil ford, and at the mouths of Lakes Ellesmere and Forsyth, the shingle and the floating debris discharged from the rivers and lakes carried a long distance south during a continuance of strung northeasterly winds, and in a calm sea there is no perceptible movement whatever north or south, which, shows that the littoral current exercises little or no power in this direction, but that whatever movements takes [lace, [h entirely duo to the direction and force of the wave breaking upon the beach.

Again, Sii J. Coodo states that " instances can he adduced whore navigable approach of limited depth lias been found and maintained across the line of shingle drift, but where even

a moderate amount of success has been achieved, there tho travel of the shingle cr sand lias been much less formidable in extent and. less persistent ?n\ continuous in character than along the sea '.■oat at Milford." Here I must first take leave to state tl at, the only portion of the bank divided the lagoon at Milford trom the sea that can be designated " shingle ds-ifl" is that portion only—seme 20 chains in length, by about G or 7 chains in width at base—which peviodoaiby forms the mouth, in a'lernate'y swept out to se:» by the xfver, and again cast into its form- r position by the f\ ree of waves in the manner already described, but for the rest of the bank, it is firm, solid, ani stationary, and has remained so as long as any one can re. ollect. 1 maintain, therefore, as far as tho general physical features are concerned, in spite of the travelling character of the shingle which has b"en so greatly exaggerated, especially in reference to this part of the coast, thr.t they are for more favourable at Milford for the formation of an efficient and extensive h:.rbour at comparatively small cost, than many harbours of Europe and elsewhere with which I am personally acquainted, ond where a?i extensive shipping trade exists. For example, I need only instance the ancient harbours along the north coast of France and Belgium—such as Boulogne, Calais, Dunkirk, and Ostend, all of which are s : mnly excavated out of the scabcaoh, with r arallel } iers extend in from the shore into the sea for a great distance. At the large shipping port of Dunkirk, the channel between the pirrs is period ; eal I y scoured out by artificial maims ; a la.ge rrservoi., built at great cost, b:mig situate lat tin upper

end of the harbour or channel find filled with water by means of one of the numerous canals intersecting the country which hero converge. The water thui accumulated is suddenly 'et off into the channel of the harbour by the Bimultaneous lilting of a number of floodgates at tho bottom of the reservoir, and rushing with force along tho whole length of channel to the sea at low tide, serves as the only means of scour ; a similar method is adopted at the oth<-r ports named. How insignificant is the above compared to the mighty scouring power nature has given us at Milford, and if utilised in the manner proposed, will work day and night at no cost. I may fat'ther instnnco the mndfrn harbours of Port said and Amsterdam, both excavated out of tho sandy beach, haying no scouringpo\vfrs,but dependent entirely upon dredging, and yet adtrr'ting ships of the largest draught. The latter, including tho French and Belgian ro ,- tsjust named, are situated on t'ie Coast of the North Sea, open to heavy north-west hurricanes which aro so frequer.t on that coast during the winter. Oth«r disadvantages under vhlch the above-named ports labour as compared with Milford, are tho shallow foreshores of interminable sand winch is easily disturbed by the strong littoral currents that hero prevail, as well as the heavy seais which at times break upon th« coast ; and to seaward t.ie numerous dangerous shoals and sandbanks stretching the who'e distance from the Straits of Dover to the river Scheldt.

Viewing-, therefore, tho above physical features with those ot Milford, where an

extensive and comparatively deep estuary exists, perfectly sheltered from all'paints of the compass, and within a stone's throw of the deep ocean wrW, which latter is entirely free.from shoalf*, rocks, or foul ground in any quarter, -t is man'fesf that <» navigable channel could be maintained at r comparatively small copt between the ocean and lagoon sufficiently de«-p to allow veseels drawingfrom 15ft to at least to enter in safety at high -va+er of an ordinary tide, and which could be guaranteed by the,,*formation, in the first instance, °fW provisional works at my estimatejdW cost.

1 now come to the last part of the subject, which is in reference to my estimates. Sir John Coodc having acknowledged the soundness and suitableness of the design put forward by ma and also of the mode of construction to be adopted, nevertheless estimates its cost at an extravagent rate, namely a tr.tal of L403,3»6 for the moles and wharf wsllings which comprise together a total length of 3,85-> feet, being at the raieofLl2() 7s 9d per foot lineal.

But it must bo observed that of the above total length, the two moles only compute a length of 600 ft and 350 ft respectively, equal to a total length of 950ft,f and this portion being much more than double the sectional area of the remaining work, when calculated separately, according to Sir John's figme 1 ?, is made to cost over L2oo per linrd foot sum mere than three times greater than what the Timaru mole is now being built for in a depth of 17ft of at low tide and 24ft at high tide —namely, at an average rate of L6O per foot lineal. I acknowledge that the prices furnished by me to Sir John were very liberal, and that the quantity of material shown in the design is somewhat n* re than is necessary to resist the impact of the wave, but withal, my estimate of the 950 ft of mole in 20ft of water at high tid", bears favourable comparison with that now being done at Timaru— LGG per foot lineal.—l am, &c, T. M. HARDY JOHNSTON.^ Christchurch, Jan. 26. m/M

• Thi3 mode of clearing the harbour of silt las for years past been assisted, by a, very efficient system of dredging. THE L \TE ~SHOOTING~OASE., TO THE EDITOR OF THE TEMXJKA LEADER. Bik, —I beg to contradict n statement thai lias got abroad, in reference to the above case. It is currently stated that I pave my man (Dauber) a gun for the express purpose of shooting any person stealing my fruit. This is not the truth, as the gun used by Dawber belongs to my foreman—not to me. It was taken there by the owner for the purpose of amusing bvpe self by shoobing spar'-on's. —Yours, etciK»a ¥ll. WHEELBiNDf;