Answer
The river has a depth of $~~4.0~m$
Work Step by Step
We can find the depth of the river:
$A_f~v_f = A_{i1}~v_{i1}+ A_{i2}~v_{i2}$
$w_f~h_f~v_f = w_{i1}~d_{i1}~v_{i1}+ w_{i2}~d_{i2}~v_{i2}$
$h_f = \frac{w_{i1}~d_{i1}~v_{i1}+ w_{i2}~d_{i2}~v_{i2}}{w_f~v_f}$
$h_f = \frac{(8.2~m)(3.4~m)(2.3~m/s)+ (6.8~m)(3.2~m)(2.6)}{(10.5~m)(2.9~m/s)}$
$h_f = 4.0~m$
The river has a depth of $~~4.0~m$
