THE HARBOR.

Gisborne Times, Volume XXII, Issue 1789, 21 June 1906, Page 2

THE HARBOR.

(To the Editor Gisborne Times.) Sir, —Tho next poins in Mr Siev~ wright’s letter that to me seems to require consideration is the sand drift along the Waikanae beach, the very existence of whioh Mr Sievwrigbt appcirs to doubt, but whioh I submit is fully demonstrated by the constantly increasing quantity of sand deposited aloDg the groin. More* over, anyone throwing in the water a floating body, as I have done at various plaoes along the beach, would soon convince themselves that an easterly current does exist ; even by watobing the small rollers they will see them flaw np the beach, curl to the eastward in returning, and carry the sand with them. The cause of this currant is the stream coming down the big river and meeting the flawing tidal current; the resultant of these two forces must be a current along the beach ; there is nowhere else for it to go; it is continued along the beach till meeting with the waters of the Turangamu. If is again carried by this new force into the bay to follow the endless round again and again, | and so this part of the bay is steadily filled up by the alluvial deposits brought into it by the rivers. The advocates of g oyne extension urge that wave action at the end of the groyne will keep the river free from this travelling sand, but they evideotly overlook the fast that ordinary wave action is only exerted in a vertioal direction; and although the waves are apparently travelling at a great speed, they oarry nothing with them until they break. This can easily bo seen by throwing a floating body on a wave, when it will not be seen to bo carried forward by it, but will float, indepen lently of the wave, at the velocity and direction of the tidal, or other current that may bo flowing. Watch aoy waterfowl riding on waves for an illustration. Therefore, wave action can only ass'st in cleating the end of the groin, by stirring up the mud from the bottom, in common with other parls of the Bay of equal depth, whilst its removal will depend upon the tidal current, which wo must remember is ebb, as well as flow. The flowing ourrent would probably oarry some of the deposit higher up the Bay ; the ebb would, with equal probability, bring it back again. It has been objected, that it is not the sediment brought down by the rivers that is filling up the Bay, but a deposit brought in from the ooean by the flowing tide, and this deposit causes the bar at the entrance to tho river. But, if this were so, why is that part of the Bay south of the breakwater not fi'lmg up ? It is sub-

jeet to the flowing tide equally with other parts, and beiDg deeper, therefore, less subjsot to wave aotion, ehou'd fill up qu : cker in proportion, than those shallower parts more disturbed ; but yet, I think I am correct in saying, its dopth romains constant. I should bo very glad to be convioced that ooly an insignificent quantity of mud comes down tbe Turanganui ; for then, inetead of suggesting a cutting on the Bouth side of the breakwater bb a new outlet for the river, I would suggest tbe erection of a weir at that plaoe to provide for the overflow, but yet of sufficient height to dam the river beck to high-water level. This wou'd greatly improve both rivers in many ways, bus I will leave those who are not afra'd of the mud, to advooate it. Will any of them accept the responsibility of doing so ? 1 1 conclusioo, I may say, I have only made use of Mr Sievwrigbt’d loiter, because it gave me an opportunity of opening ads oussion upon matters (as I consider) of great importance to the district at thopre- i sent time,—l am. eto., i THQS. L, LEWIS, C.E, .