WAITARA HARBOUR.

Taranaki Daily News, Volume XXXXII, Issue 304, 20 December 1900, Page 2

WAITARA HARBOUR.

ME. MAHOHANT'S BBPORT. "Wherever sand or shingle exists along a cosst line, the tea, by a natural and unvarying process, seeks to form it into a beaoh. This varies in height andmagnitodeaooording to thestrength of the waves, which break upon it, Where a river enters the sea this beaohj making process still continues, but the river current, together with the influx and efflux of the tidal wave in and out [of the river channel, if of snffieient volume, is able to scour a bed throngh

the line ef beach. Batmen these opposing forces an unending struggle exists. Sometimes one temporarily overpeweri the other, and in turn is so overpowered, From my surveys and experiences at New Plymouth Harbonr during the past 5* years, I find that the sand drift arriving at that harbour on its natural and north-eastward travel towards Waitara,— shout thirteen miles distant—amounts to not less than 70,000 cubic yards per annum. Seeing the rivers that discharge into the sea between Hew Plymouth and Waitara, each hearing its quota of sand, etc., in flood time, I think it may be safely assumed that more than the quantity stated above it annually drifted past the entrance of the Waitara River on its north eastward journey. This fact must be thoroughly grasped and kept in foremost view if any constructive works for the improvement, of the river entrance are to be at-| tempted. So far as I am aware, this fact has not received any recognition in the previous reports dealing witbj this subject. j With this fact strongly impressed en my mind, it seems evident to mo, that: | no constructive work of any description built on the south western or' weatheri side of the river entrance can possibly be of any use. Any such training wtih or pier would merely have the effect of temporarily utit? of sand and eventuallyfesulfcin a 'geaward.progreasioifcof the* forelshdre without -effecting the. least benefioial change in the end. A training wall construction on the north-eastern or leoward side of a river entrance under the conditions stated is in a different case. It would have the effect of preventing the river channel being driven to leeward by tho waves and sand drift, and of concentrating the j whole scouring effect of the river current on the bur with tho best pos- j siblo result of which tho volume of! water in metion was capable. I For the foregoing reasons I thorougly approve of tho policy tho Waitara Harbour Board has adopted, of late yaars in concentrating all its efforts towards the construction of the north-eastern training wall and leaving the one previously constructed on the weather side without further extension.

, My opinion is, however, that seeing the prevalent directisn of the waves, and the consequent travel of the sand drift, tne line on which the entrance training walls have been placed is not aaoh as to have given the best possible result from suoh constructive works. Probably a direction 20 degrees eastward of the line of existing works would have gien better results, and if any further extension of the northeastern wajl is undertakes I i a modified" direotibn should be' adopted for such extension.

The class ef work built by the Beard is a suitable one, though there are details about it that might be improved upon. The section and details of tho plan I recommend for further extension j show how improvement might be effected. Also any such extension must be of heavier and mere expensive construction than- the work previously lexeouted on the north-eastern side.

I approve also of tbo stone pitching work the Board is executing along the river bank; this work is absolutely j necessary, and should be completed as seon as possible. It would b found [better to consolidate the earth filling [by ramming the earthwork and by facing it with about six inches of gravel before setting the stone pitching. It is quite likely that settlements miy occur with consequent displacement of the stonework during flood by continuing the present system of construction.

Regarding the condition of the river channel between the bridge and the sea, I think it is in an eminently unsatisfactory condition. In all anticipated improvement of a tidal river it is a condition precedent to successful result that every obstruction to tho full and free flow of the tidal water should be removed. The quantity of water running into and out of the river due to the tidal range is of vastly greater volume than the ordinary upland water flowing down it. It is the first of the flood and the last of the ebb tide in its passage across the bar which has by far the greatest scouring effect. This necessary flow is restricted by shoals in the river channel which will always militate against the best possible result being attained, no matter what training walls may be built to direct the wator. ; Nearly opposite the signal station is a shoal over which, at low tide, the water ripples down a fall of probably

well-nigh 18 inches: This boing situated so close to the entrance has a particularly bad effect. With a flood tide, instead of the rising water being driven swiftly into the tidal compartment, and so scouring the bar, the water merely dribbles in until it rises well above the level of the sheal. Also, en the ebb tide, the whole of the water in the tidal compartments, instead of sweeping quickly out over the bar at low water, is dammed buck by this shoal in particular, and its possible scouring effect is lost. There are other shoal places besides this which also have ill effects. Having carofully considered the case in all its bostrings, I recommend your

Board to do no further work at the river entrance until the tidal compartment of the river, between the bridge and the sea, has been thoroughly cleared of all obstructions by dredging, and has nowhere a less depth than 4 feet below low water mark for a width of 200 feet I think this would give much better results in improving the entrance than by further extension of the north-eastern training wall, with- ' out such improvement of the ebannel; i and this werk of improvement I com- - mend to your best attention. When that has been completed, no doubt but that as extension of the north-eastern wall for 200 feet, on the lines previously recommended herein, would afford sjme

further improvement. The system of dredging to be employed, together with disposal of the spoil, would require careful examination to obtain the moat economical results. If such examination proved that dredging by the Priestman process weuld be desirable, plant establishment, with spoil dumping aarangements conld be put into working order for about £2500 or £2BOO. This is the lowest possible sum that any re"»lly effective plant with a respectable output could be provided for." V, W. Maeohant, M. last. C.E. Timaru, December 7th, 1900.