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Rh dams, arranged so as to retard the flow and lessen the velocity of the water from higher to lower pools without interfering with the free passage of the boats through the chutes; chutes were substituted for locks.

In 1866 the condition of the river improvements and the great change in the river trade—which loudly called for improved methods—is tersely summed up by Engineer W. Milnor Roberts as follows:

"For the purpose intended, namely, the making of an improved low-water navigation, looking to a depth not exceeding two and one-half feet, the general plan designed, and in part executed, under the superintendence of Captain Sanders, was judicious; and if all the proposed dams had been finished in accordance with his plans there would have been a better navigation, especially for low-water craft, than there has been during the twenty-two years which have elapsed since the works were left, many of them, in a partly finished condition. Some of these wing dams, as might reasonably have been anticipated, have, in the course of years, been gradually injured by the action of floods, and in