JETTIES OR CONTRACTION if Vinu:s. The system will be given more in outline than detail, as the latter are far too numerous to be more than barely mentioned. The natural banks of the river, in those places where the current sets against them, and is likely to wear them away, are strengthened by revetment work. The char acter of this revetment varies somewhat accord ing to circumstances, but, generally speaking, is of two kinds. The first is a kind of soft bottom put on the bed of the stream at the point of greatest erosion. This consists of what are called mattresses or hurdles, which are constructed of mats of brush woven and fastened together with wire strengthened with a sort of lattice-work of heavy timbers placed on the banks and se cured by a substantial ballast of rubble-stones. A crib of timbers is first constructed in sections, amounting in all to dimensions sufficient to cover the place which is to be protected. Over this is laid a carpet of heavy brush. with the twigs of fibre running generally in parallel lines. Over this is laid another carpet of similar construc tion, with its fibres crossing that of the first at an angle usually less than a right angle, and the two are knitted or sewed together with strong wire. Sometimes a third carpet may be laid, with the brush lying at still another angle. Then another crib or lattice-work of heavy timber is laid on these carpets, and the whole is hound to gether with wire, or another series laid on top if extra strength and weight are needed. The entire contrivance is then placed in position, covering the bottom of the river from the centre of the channel to the margin of the bank. As a matter of course it is necessarily handled in sections, but the sections are placed and fastened together so as to form a continuous carpet when laid. and they are then heavily ballasted with rubble-stone, laid systematically to form an un cemented pavement over the carpet. It is found that this practically secures the mattress in position for a considerable time under ordinary circumstances, and actually prevents the eating away of the banks by diverting the course of the current hack to the desired channel. Generally it
occurs that the action of the river before this treatment is applied to it has made the hank un even. Sometimes it will even overhang the river a little, and it is necessary to'smooth the surface to afford an even bed or floor on which to lay the mattress. Instead of digging this away, the familiar method of hydraulics is utilized. With a powerful engine a stream of water is pumped through a hose, and the soft earth is readily washed into shape. The ultimate purpose of these mattresses and other devices is to secure an approximately uniform width between the hanks of about 3000 feet. When this is done it is believed that the bottom will he scoured out by the current. so that a depth of not less than sixteen I )1- eighteen feet will he secured through out the lower river. The permeable dike is a contrivance used in many places where it would be impossible to lay mattresses, where there may lie, in fact, no hank to lay them on, but a wide stretch of slack water reaching out into a lagoon. These dikes are of simple construction. consisting of rows of piles driven as firmly as may be in the soft bottom. The piles are placed from two to five feet apart. and between the rows quantities of brush are placed and fastened. The water passes through these works freely at first, hut being checked by the partial obstruction, it drops the sediment with which it is so heavily charged, and itself completes the dam which confines its course. These dikes are found to he very effective substitutes for complete dams, and are put where it would be difficult, if not impossible, to build a solid dam in the first place. Alore substantial, or rather more compactly built dams arc placed at some points where there is a tendency on the part of the river to form cut-offs. (See section Description of X at ural Feat ures.) This ten dency is perhaps the thing most dreaded and most carefully guarded against.