PORT MOUTHS AND SCOUR.

Manawatu Herald, Volume XXXV, Issue 1115, 28 June 1913, Page 4

PORT MOUTHS AND SCOUR.

TALK WITH MR REYNOLDS, C.K. As instance of the effect of scour upon the approach to a harbour when the outflowing tidal currents have been properly trained and guided, the following particulars regarding Nelson harbour are in* teresting—perhaps the more so because the conditions governing the approach tQ Nelson Harbour and Napier Inner Harbour are analogous. So says Mr Leslie H. Reynolds, C.E., who is the designer of the Nelson works, and who has also investigated and reported on Napier Harbour, Speaking to a reporter this

week, Mr Reynolds said ; “The old entrance and approach to Nelson Harbour had a low water depth of from seven to eight feet. This was discarded in favour of the new entrance through the Boulder Bank, where the depth seaward ranged from nine leet near the shore to 17 feet at lew water over a distance of more than half a mile out. My scheme provided for an entrance of 500 feet bottom width, with a depth of 15 feet at low water. The Nelson Harbour Board, however, decided to execute a cut of about half the width recommended. Therefore practically only onehalf of the tidal volumes allowed for in my scheme find ingress and egress through the new entrance. Notwithstanding this, however, the scour has been instrumental in cutting an approach to sea for a distance of about 1800 feet and over an area of 14>4 acres with a depth of from 42 feet to a minimum of 25 feet at low water spring tides, and over an area of 30 acres with a minimum depth of 17 feet at low water extending to sea for over 2000 feet.” Mr Reynolds went on to say that, had a full width entrance been cut (and consequently the columns of the tidal outflow doubled), the scour would have been very much greater, and in his report of March, 1913, to the Nelson Harbour Board, he had advised that if the cut through the Boulder Bank were enlarged, and certain dredging carried out inside the harbour, vessels of the Athenic class, or larger, could be handled and berthed at Nelson.

Mr Reynolds stated that Wanganui furnishes another instance of-efficient scour due to efficient training of the currents. He is confident of obtaining 32 feet depth at the entrance and lower reaches of the Wanganui River, and he was emphatic in his opinion that, when once the entrance to the inner harbour has been widened and deepened, and the moles extended on certain lines which he has recommended, no further dredging will be necessary. The increased scour, he held, will maintain a depth in the approach of from 29 feet to 30 feet out to sea at low water. In connection with the port of Wanganui, it is of interest to record that the Union Company’s salvage tug Terawhiti (drawing over 13ft.) worked the Wanganui bar recently an hour before low water.