Question 1199689
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Incomplete post...<br>
(1) You didn't ask a question<br>
(2) 400 feet (presumably directly downstream) from the base of the dam, we need to know how far the elevation changes in those 400 feet in order to be able to solve the problem.  It doesn't make sense to assume that 400 feet from the base of the dam the surface of the river is still at the same elevation as the base of the dam.<br>
Re-post -- providing a clear and complete description of the problem, and asking a question.<br>