*** Requires the function: BisectNM
Find: y = critical depth in the equation
0 = 1 - ((Q^2)/(g*(Ac^3)))*B
where: B = 3+y, and Ac = 3*y + ((y^2)/2)
Substitute B and Ac:
0 = 1 - ((Q^2)/(g*((3*y + ((y^2)/2))^3)))*(3+y)
Difficult to isolate y on the left side (analytical)
Hence, numerical method is preferred
Find the root: y to make f(y) = 0
y = independent variable
fy = f(y) = dependent variable