A Treatise On The Principles And Practice Of Harbour Engineering

-'3- HARBOUR ENGINEERING. takes an initial slope of 1J or 2 to 1, which subsequently may become modified to 2 or 3 to 1. Fascine work has been largely practised as a substitute for stone in cases where the bed of a river consists principally of quicksand incapable of supporting any great intensity of pressure. And as most estuaries are of a sandy nature, more or less uncertain and treacherous, it is a system which naturally suggests itself, in those cases, for adoption. Circumstances are particularly favourable to fascine work, for instance, in the sodden, low-lying land on the shores of the Netherlands, and at the outlets of the fenland on the east coast of this country. The nature of fascine work has already been alluded to in connection with its employment for jetty construction (p. 171). For that purpose it is chiefly built up in the form of mattresses which are equally suitable for covering a large area of sloping bank, and for being raised in tiers. Where mattresses are not essential, faggots, or “ kids,” as they are locally called in Lincolnshire, consisting of 6-feet lengths of thorn branches, cut from hedgerows, and made FASCINE WORK ANO ENCLOSURE EMBANKMEHT Scale ^AA *> Mléet Fig. 212. —Fascine Work in the Wash.1 beim* 'rLaliiTb up into bundles 3 feet in girth, may be utilised. These are lighter to lift and easier of manipulation. They are placed overboard, and weighted with sods and clay until they sink, the wall being built up in this way, witli the kids overlapping each other in transverse layers. lhe interstices of fascines in a waterway rapidly fill with a deposit of earth and detritis, which soon solidifies, and the whole becomes a tough, composite bank, closely cohesive, and, at the same time, fairly flexible; so that it any undermining should happen to take place, no sudden, abrupt fractures would be produced, but the mass would settle uniformly, and no part of it would have any tendency to slip out of position into the fairway of the channel, as sometimes happens in the case of rubble walls. Moreover, the tenacity of brushwood offers effective protection, not only from the ordiuary scour of streams, but from the wash of passing vessels and the discharge of heavy rainfalls during periods of low water. Arrangement of Walls. —-Training-walls are either single or double. Single walls only are necessary when the nature of the flow is such that erosion is confined to one side of a river, as is the case at bends. In inter- mediate positions and straight reaches, and also in places where it is desirable to direct a stream across from one bank to that opposite, two parallel walls 1 Min. Proc. Inst. C.E., vol. xlvi., Plate 8.