At a given location, under normal conditions a river flows with a Manning coefficient of

$0\mathrm{.}030,$ and a cross setion as indicated in Figure $3($a$).$ During flood conditions at this

location, the river has a Manning coefficient of $0\mathrm{.}040($because of trees and brush in the

floodplain$)$ and a cross section as shown in Figure $3($b$).$ Determine the ratio of the

flowrate during flood condition to that during normal condition.

$($a$)$

Figure $3$: River flows at $($a$)$ Normal condition and $($b$)$ Flooding condition