Take the water surface as the section 1, and the section of the small hole as the section 2:

The water surface height is h 1 (i.e. the required water depth), and the pore height is h2=0, p 1=p2=0 (gauge pressure), and v 1=0.

In a steady state, the inflow and outflow of water are equal.

Velocity of outflow from orifice: v2 = (150cm3/s)/(0.5cm2) = 3m/s.

Le Bernoulli equation: ρ GH 1 = 1/2 * ρ * V2 2.

9.8 1h 1=4.5

H1= 0.46m = 46cm.