Engineering Wonders of the World
Volume III

176 ENGINEERING WONDERS OF THE WORLD. to adjust the question of boundaries be- tween state and private canal lands, and to recover as many as possible Ohio Canals. . 2, 1 n . of the state lands that are tied up by ninety-nine year leases and long- time rentals. This State, with its area of 40,760 square miles, its population of 4,157,545, and its natural resources of coal, iron, petroleum, and salt, is busying itself in the matter of canal traffic and the prosperity that follows in the wake of properly managed canal systems. It is purchasing its own machinery, dredges, drills, etc., and is replacing all the old wooden locks with staunch concrete structures. The rivers in this State are being canalized to a remarkable degree, and the accompanying illustrations show the ingenious needle dams constructed to equalize the depth of the water during slack water seasons, and ’permit the utilization of the river by means of locks, even at low water, when the dams can be laid flat on the bottom of the river. The method of operation is simple but effective. The needles or pieces of timber are removed from their sockets and floated to the side of th© stream ; then, by jerking a chain—which is done by steam in a boat further up-stream—the dam collapses, unit by unit. HALF OF A NAVIGABLE PASS. A chain is attached at intervals to all the needles. When pulled it releases the needles from the frames, and allows them to float down-stream, as seen in the picture.