How to Prevent Erosion on the Ocean Front.

Evening Star, Issue 17333, 22 April 1920, Page 8

How to Prevent Erosion on the Ocean Front.

Th« following suggestions are respectfully submitted to all whom it may concern in order to make good the beach in trout of the present esplanade by making the wall and roadway a continuous one ultimately to the limite of St. Kilda Borough. -At present the beach is in a verv rough state with boulders, the same, being denuded of the sand which made the beach such a pleasant resort for the inhabitants iof IDnnedan Some people blame the building of the esplanade wall for being the cause of the erosion, but when it is considered that the ordinary high tide mark is practically at the wall foot! it will be obvious that the tide would spend itself there, even though no wall had been built Abnormally rough seas would send the tide higher up than the line of the •wall before the same was built and a certain amount of erosion would result to the sand dunes. It may be taken as a fact that had the waU been built above the level- of the nigh tide mark, in abnormal tunes, the erosion would have been largely eliminated. fh9 wall is there, however, and the problem is how to make good the beach • in other words, restore it to its uristine condition. A series of light groynes should be set somewhat to the angle as shown on the accompanying sketch, and rising, say, 6in

[By Kohohike.]

at a time, till the boulders are covered with 12in or 18in of sand; the groynes- to bo flush with the sand at the height indicated. The expected action of the tide in receding from the groynes would be to leave layers of sand behind them, first Hushing up the boulders, then, as the groynes are built a little higher, the sand would flush up behind the wailings. The proposed sinuous wall, continuing the present wall, is meant to allow the waters to glide along, instead of striking square on and 'practically rebounding en masse, with a strong back-wash taking sand and gravel with it. It would be perfectly safe to build a wall at the line of the highest known' tide level, so as to allow the wave to expend itself.' The returning wate.s would be correspondingly thin, and would not be detrimental to the sand of the beach. To build, however, within the high tide level would necessitate the use of groynes to counteract the back-wash. Groynes - should not be set as the present ones are, but at pn easy angle to the wave force, so as to retain the sand. The two groynes at present on the St. Glair beach allow the sand to recede as easilv as it conies in. The accompanying sketch shows a series of light groyne?, set in such a manner that sand would be more likely to be held from a receding tide than grovnes set practically square to the existing wall

My proposal then, is to sink sufficient posts to enable the groynes to be securely built wifi sufficient wailings only to make flush wUh the top of the boulders, and n ♦£ tides flush U P with - sand. On this taking place, bolt on another wailing, and repeat till 12in or 18in of sand covers the boulders. Stop at that. It will be observed from the sketch that the gray .e« overlap each other. That is tor th=! purpose of more readily retaining sand while the tide is receding. ' ° As is known, the road formed as an extension of the esplanade has been practically washed away. To enable a road to be constructed that would withstand tidal action, the sketch No. 2 shows method of building—sheet piling driven some distance below low water mark, and projecting a short height above hiirh tide mark, tied together by strong wailings. From the top of the piling, and restinsr on the wailings, pitch fhe embankment sufficiently _ high to be clear of anv abnormal high tide: then fill in the embankment with ordinary filling—willows, couch grassing, or other holding shrubs could be planted, and so tend to bind the embankment right up to road level. Loose stones, though large, will not withstand recurring wave action. Stone of moderate size, properly pitched, will for certain do so. _ The proper foundation of the pitching is, in my opinion, absolutely necessary.