4 8 THE IMPROVEMENT OF RIVERS. 



propelling, being provided with a pair of side paddle-wheels 21 feet in diameter. The 

 draught was designed to be 48 inches. The boilers are seven in number, set in three 

 batteries, and with a working pressure of 170 pounds. The pumping outfit consists 

 of a centrifugal pump with a 32-inch discharge, capable of delivering not less than 

 1000 cubic yards of sand per hour through 1000 feet of pipe, and is operated by a pair 

 of horizontal tandem-compound condensing engines of i6-inch and 26-inch cylinders, 

 and 20-inch stroke, direct connected. The sand agitator is of the water-jet type, acting 

 under a pressure from a duplex pump of 60 to 100 pounds per square inch. The pipe- 

 line is of J-inch steel plate, in 50 feet sections, supported on pontoons and with swivel 

 joints. Twenty anchor piles, 35 feet long and 1 1 inches outside diameter, of metal from 

 J inch to j -inch thick, were supplied with the dredge. 



Full quarters were constructed on the hull, including laundry, bath-room, machine- 

 shop, and refrigerating and electric-light plants. 



Dredges for Improved Rivers. - The best type of dredge for a river possessing 

 locks and dams, where these are sufficient in importance to require annual service of 

 this nature, is the dipper dredge, fitted for use with a grapple bucket also. Its capacity 

 should be not less than 2 yards, as small dredges are very uneconomical, costing 

 almost as much in operation as large ones. The machinery should be of special power, 

 as part of the work will consist in tearing out wrecks, snags, old cribs, etc., and the 

 strength of all parts should be designed accordingly. The limiting depth of water in 

 which to work should be 18 or 20 feet, as the dredge will then be practically independent 

 of summer rises, and can work on uninterruptedly. This is sometimes a matter of 

 much importance, as we have more than once seen important works delayed in times 

 of pressure because a rise of a few feet put the dredges out of operation, their limit of 

 depth being 1 2 to 1 5 feet. The coal capacity should be ample, so that the work can be 

 carried on for- several weeks away from the base of supplies. 



In the last few years steel-hulled dredges and scows have come into use, and have 

 given excellent satisfaction. They are much stiffer than the wooden hulls, and give 

 no trouble from leakage, and if they are occasionally painted appear to outlast two 

 or three of the usual type. 



The scows should always be of the side-dump variety, so they can be used for 

 backing dams, filling washouts, etc. The bottom-dump is usually inapplicable for 

 this, as it needs a depth of water of 8 to 10 feet for dumping. 



Dynamite. Dynamite is principally employed for the removal of snags, rocks, 

 etc. Its use for assisting in the removal of sand-bars has often been proposed, but 

 seldom applied, and then with uncertain measure of success. It was used on the 

 Brunswick Bar in Georgia from 1891 to 1895, and also at Aransas Pass, Texas. At 

 the former locality about 100,000 pounds were used, with the result as shown by surveys 

 that the four years' work had only deepened the channel 1.7 feet. Dredging was then 

 resorted to, and a further depth gained by this means of 1.6 feet in eight months, or 

 almost as much as in the whole four years preceding. 



