FORESHORE EROSION AT LOWER PORTOBELLO.

Otago Daily Times, Issue 17687, 26 July 1919, Page 7

FORESHORE EROSION AT LOWER PORTOBELLO.

ENGINEER'S REPORT. Tho Harbour Board's resident engineer (Mr Wilkie) submitted to the board yesterday the following report on tho erosion of tho foreshore at Lower Portobello:— On Saturday, July 5, I visited the locality refcrrod to in tho {ward's latter, and found that tho sand hills in front and to the westward of Mr Dick" u house havo boon subject to very extensive erosion by wavo action. These Band hillo cstond from high water mark back towards tho hill» for about half a irak> in depth, and are covered wifih grass and lupins. A wide, lirm sandy bsach, in places 10 to 15 chains wide, gradually slopes from tho base of tho sand hills to low water mark. It ia apparent that these sand dunes havo been formed by wind-blown sand whan tho quantity of sand entering tho harbour was much more plentiful than at present. Since tho building of tho mole and protao tive works at tna Iloads, tho supply of sand has boen greatly rcduced, and in fine weather th,9 boaoh on this portion of the foreshoro does not nralco up. The shore line is approximately normal to tho southwest winds, and in heavy weather tho wavo aotion ia expended ujion steep banks composed of loose material, and consequently much sand is being removod. That this eroding action has beeh. going: on for some yoars, and that a strip of the foreshoro same 3000 ft in length and several chains in width has been removed, is apparent from the remains of vegetable life dlssernablo on tho beach below high water mark. Some of the sand must find its way into the channel, and if not swept out by tidal scour, must bo removed by dredging, arid therefore it is advisable that tho shoro bo protected from further inroads by the sea. The building of a stone wall 3ft high, backed_ by sft of day at the foot of Bie sand hills, would bo a sure but rather expensive method of preventing denudation. This wall would be similar to the ono constructed from Spit Jetty to tho Pilot House, and, allowing for tho material costing 4s per yard, would involve an expenditure of £600. Another chcaper method would bs the construction of scrub groynes, which would serve both to protect the toe of tho sand hills from the full foroo of the wavo action, and also to build up tho beach by catching any wind-blown sand. It is estimated that these groynee would cost £200, but as their usefulness would depend upon the amount of wind-blown sand, I am not prepared to recommend their construction until, from observation extending over some months, I air> satisfied they would have the desired enect.

The report was held over to enable the engineer to make observations and report