DEEPENING OF CHANNELS IN RIVER BARS.

Grey River Argus, Volume XXI, Issue 2307, 31 December 1875, Page 4

DEEPENING OF CHANNELS IN RIVER BARS.

We recommend the following, from a correspondent of the ' London Mail', to the attentive perusal of our readers : — * The Board of Army and other Engineers, who recommended the adoption of the jetty system in deepening the, channel over the bar at the mouth of the Mississippi River, is now in session at New York examining the plans of Captain Eads,- who has the work in charge; Sir Charles Hartley, the British Engineer, who constructed the improvements at the month of the Danube, has visted this country at the request of Captain Eads, and will be consulted in the prosecution of the work. The desire is to make the improvement permanently successful in deepening the channel, and everything possible will be taken advantage of for the purpose. The jetty system' was adopted by Congress , upon the recommendations of the Board above referred to, and work ordered upon the South Pass, the contractor not to be paid until'2of t. depth of water is secured. On June 14 the work began, and. although little more. than two months have elapsed, Captain Eads announces that the progress already made indicates such success that he expects the largest ships visiting American waters will be able before the close of the year to enter the Mississippi without risk or delay. The South Pass former!} had generally 7ft. of water ; now this has been deepened whereever the works have been constructed to at least 15ft. The plan adopted is simple yet ingenious. The object is to confine the current within straight parallel walls, so proportioned in width to the body of water flowing through, as to produce a velocity which will force the stream to scour out a channel for itself to the required depth. The chief difficulty was devising the means for building these walls and making them secure upon the very unstable foundation. The current passes over sediment many feet in depth and between banks of similar sediment, all deposited by itself. Thus the bottom and banks are all composed of soft mud, in which works of stone" would soon sink. Piles (by themselves) or cribwork, or any Bimilar wall, would be soon undermined, and to meet this difficulty it was determined to build the walls of the Pass with broad flat mattresses of willow brush lashed securely together and anchored to an interior row of piles, which they in turn protect. At first the piles are driven along and inside the line proposed for the bank, and the mattresses of willow brush are then constructed 40ft. wide and 2ft. thick firmly lashed together by crossbars fastened with hickory pins, and are towed into position and anchored outside the piles. Being then weighted with stone, they sink to the bottom, and the deposit of sediment from the current is so greac that in a few hours the interstices will be so filled as to make them a solid mas? and the sediment will continue gathering upon them, laid one over another until the mass beaomes more solid and enduring than any portion of the natural bank. The . resistance ; offered *by theflolk"»«-ferasir effectually nreventsjfche^iipacement of

any of the sediment lodged in the interstices, and when completed the wall of mattresses and mud will perfectly protect the row of piles from the current, and the entire mass is covered with a firm stone' paving to prevent injuries from storms. The outer ends of the walls which are exposed to the action of the sea will be constructed of a stronger and broader mat-: tress, so as to present a solid and more durabte work. It has been noticed in the Mississippi that the most onduriug and hardest removed bar is that caused in a brief period by the deposit of sediment from the current in the top of an uprooted tree which happens to lodge in the channel, and the plan of building these mattressess walls is of the same character, the current doing a good deal of the labor. Years will of course be required to complete the jetties entirely, but the expectation is that the channel will quickly deepen wherever it is confined by them within narrow limits. Of the preliminary lines of piles there have been 9,860 ft. driven on the jetty for the eastern side of the South Pass, and 1,950 ft. on the western Side. Of the mattresses foundation 3,500 ft have been securely laid mostly on the eastern side. The river's own deposits anchor these jetties more firmly than is possible by any other attainable method, and about 309 ft. linear of these mattresses are daily placed in position. The work is one of interest abroad as well as here, for the commerce of all nations seeks the mouth of the Mississippi. ' •