Question

You are charged with the task of restoring a 4000 m long reach of river that was channelized (straightened and bound by earthen dikes) 70 years ago. At a particular design flow, the channel currently has a width of 15 m, a mean depth of 1.2 m, n = 0.030, and drops 2 m in elevation over its 4 km length. Upstream of this reach, a dam is in place and it is operated for downstream irrigation uses, therefore its design flow will not change. You need to restore the river to a course that is similar to its former natural state (meanders and bends). A planner has given you specifications for the new channel, and with the new meanders and bends, it will be 6000 m long, with the same starting and ending locations as the present channel. The width of the new channel is to remain 15 m.

How rough will your new channel need to be to retain its current 1.2 m depth (that is, what will the new n value have to be) at the design flow?

Answer 1