GROINS AND SAND

Evening Star, Issue 14531, 6 December 1910, Page 4

GROINS AND SAND

OBSERVATION v. TEXT BOOKS. MR PETOE-s" OPINIONS. This morning a reporter called on. Mr F. W. Petre, architect, and asked whether he, as an old resident of St. Olair, would give his opinion on tho proposal to protect the St. Clair foreshore by means of more groins, as recommended in Mr Furkert's report. Mr Petre replied.: It is not an engineering question at all. It is a matter concerning which any intelligent obsorver can form an opinion. In my judgment, the groins are not only 11601065, but absolutely harmful. Let mo put it this way: The whole of the- sand, or nearly the whole of it, that comes into tho St. Clair comer of tho beach depends upon the north-cast wind blowing it along tho foreshore. The groins, especially tho easterly one, act a? n check to the travelling of the sand along tho beach. It has to surmount each groin in turn and do a certain amount of steepiochasiii'i before it can got to tho come where it is wanted: So by extending the groins between high and low-water mark yon would simply check tho motion of the Kind. Ono can see how this comes about. The sand that has retired from the St. Clair end has slipped into the sea owing to the wave action digging out the sand amongst fhs breakers. In one night there was a dead drop of tho whole beach at that end. The text book is evidently the might of these groins. People- have locked up the Jest boohs io see what is the cause of tho denuding of sandy beaches, and this is the result. Where beaches are denuded by tho action of tho wind the groins answer admirably. But in this case- they are tho worst possible thing, because they prevent tli© sand, which is abundant at the Lawyer Head end. from coming to St. Clair, where it is difficult to keep it supplied except by that means. Very little comes in on the waves. If you want to see how the evil woiks. look at tho natural groin of the headland above the baths. There is no sand on the south, side of itnothing but boulders—because the sand has always been slopped in its drift along the bca.'li by this natural groin. 'Die only rand on the second beach is a very small quantity brought in by the waves. To sum up, the sand that is deposited at the St. Clair end owes its presence to the action of the. wind, not tho waves—it is v, ind-borne sand—and anv groin at that end must interfere with tho supply. It is

:> Jong timo fiinco (southerly weather preva:led and brought the St." Gair beach to its present low level. Since then we liavo had a lot of north-easterly wind, and under Iho old conditions the sand wot.ld be all back by now. but it is not so. If anyone rroes thero when a north-east wir/d'_ is blowing ho will we the sr.nd travelling and being stopped by the groins, and to put in more groins o't extend the present ones will onlv intensify the evil.