# Estimating pressure and flow velocity at entry and exit points of pipe used for irrigation

I am trying to calculate exit pressure of water from a pipe where the water entry is approximately 100m below ground. I know the exit flow velocity of water (20 GPM or 1.2618 litres/second); this was estimated as this is the required flow velocity to irrigate an acre of land. A centrifugal pump is used to draw the water from underground; this pump is above ground and therefore is not submerged in the water. I have made a crude illustration to visulaise my question (it is worth noting that the pipe diameter does not change throughout the length of the pipe, it remains the same even if not shown accurately in the diagram). So, my assumption for the pressure at point 2 is the culmination of all pressures casued by the atmosphere and teh various sediments of rocks and soil, from some preliminary research I found this to be about 5 atm (would this be a reasonable estimation for a ground depth of 100m?). However, I am getting confused by the flow velocity at point 2. I think it should be 0 m/s, as teh water is drawn from a stationary reservoir but it doesn't make much sense for the initial velocity to be 0 m/s, otherwise how would water be drawn up?

If I have the flow velocity and pressure at point 2 I could then use Bernoulli's equation to calculate pressure at point 1 (making height 0 at point 1 and -100 at point 2).

Any guidance would be greatly appreciated!

• Point 2 is within a porous medium, correct. Is this horizon artesian, or is it pretty close to hydrostatic? Do you know the permeability or hydraulic conductivity of rock in layer 2? You need to help of a groundwater hydrologist for this. Oct 1 at 11:58