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120 THE MARINE REVIEW FIG, 2--THE POWER HOUSE UNDER CONSTRUCTION wide and has a depth of about 7 ft. at mean water. Observations ex- tending over a period of 20 years indicate that the volume of water flowing through the river at this point varies from 20,000 cu. ft. per second at low. water: to" 372,500 cu. it at: flood stage. The mean water level will be-raised about 35 ft. by the dam and the normal working head on the hydraulic machinery will be 32 ft., FIG, although this may vary from 20 to 39 ft. from high to low water. Previous to the civil war there was a large amount of traffic on the Mis- Sissippi river and except at high wa- ter the boats had to discharge their cargoes at the foot of the Des Moines rapids and be hauled over light by animal power. Commercial demands on congress, however, were finally successful in securing a lock and: canal system to pass these rapids which was opened for traffic in 1877. There are three locks with a _ net width of 80 ft. admitting 'boats up to 350 ft. in length overall. It requires about two hours for a steamboat to pass the three locks and 12 miles of canal. The lockage is free, but the expense to the government in operat- ing the system has been about $40,000 per year. 3--GENERAL PLAN OF THE KEOKUK PROJECT