Determine the depth for the assumption that the flow is in the lowest and next section of the channel

$($a$)$ Calculating the hydraulic radius and using the Manning equation with this assumption, what is the depth for a flow rate of $10$

$\frac{m^3}{s}?$

$($b$)$ Is the value of the depth larger or smaller than the height $h_1+h_2?$

$($c$)$ Is the assumption that the flow is only in the lower and next higher section of the channel valid?