The Froude number of flown in a rectangular channel is 0.8.

The Froude number of flown in a rectangular channel is 0.8. If the depth of flow is 1.5 m, the critical depth is

F_r =	V
	√gy

q =	Q	=	AV	=	B ⋅ y ⋅ V	= V_y
	B		B		B

⇒ V =	q
	y

F_r² =	V²
	gy

=	q²	×	1
	y²		qy

=	q²	×	1
	g		y³

y_c³ =	1
	y³

∴ y_c = (F_r²y₃³)^1/3
= (0.8² × 1.5³)^1/3
= 1.292 m.