Irrigation system

1. A gravity irrigation system comprising:

a distribution piping having apertures to distribute water to a field;

a valve located upstream of the distribution piping, the valve configured to limit a pressure of the water being delivered to the distribution piping;

a sump configured to receive the water at a lowest elevation of the field;

a depth sensor disposed within the sump;

a return pump disposed at least partially within the sump and configured to move the water to an elevated portion of the field;

a motor configured to drive the return pump;

a power source coupled to a variable frequency drive, wherein the variable frequency drive is configured to power the motor and control a motor speed proportionately to an indication of the depth sensor; and

a transfer piping coupled to an outlet of the return pump and configured to bring the water from the return pump to a check valve and from there to the distribution piping at a low pressure side of the valve.

2. The gravity irrigation system of claim 1 , wherein the return pump has a maximum dynamic head of 5 feet while outputting at least 600 gallons per minute.

3. The gravity irrigation system of claim 2 , wherein the motor to drive the return pump has a maximum of 3 horsepower.

4. The gravity irrigation system of claim 1 , wherein the system includes a first meter to measure an input flow rate from the distribution piping and a second meter to measure an output flow rate of the return pump.

5. The gravity irrigation system of claim 1 , wherein the valve is a butterfly valve.

6. The gravity irrigation system of claim 5 , wherein the butterfly valve is set in a first position to reduce a head from the transfer piping to a maximum of 5 feet when the return pump is not operating, and in a second position that varies in response to a sensed pressure in the distribution piping to maintain the head at a maximum of 5 feet when the return pump is operating.

7. The gravity irrigation system of claim 1 , wherein a pressure relief element is disposed at the outlet of the return pump to return water to the sump when an output pressure of the return pump exceeds a set point.

8. The gravity irrigation system of claim 1 , wherein the distribution piping is 10 mil thick lay-flat polyurethane piping.

9. The gravity irrigation system of claim 8 , wherein the apertures are aligned with furrows in the field and are custom-sized to uniformly distribute water to every furrow.

10. The gravity irrigation system of claim 1 , wherein the power source coupled to the variable frequency drive is a wire coupled to an electrical grid.

11. The gravity irrigation system of claim 1 , wherein the power source coupled to the variable frequency drive is a wire coupled to the output of an electrical generator powered by an internal combustion engine.

12. The gravity irrigation system of claim 1 , wherein said power source coupled to the variable frequency drive is a wire coupled alternately to an electrical grid or the output of a solar photovoltaic array.

13. The gravity irrigation system of claim 1 , further comprising a support structure built atop and attached to the sump to support the return pump, the attached motor, and the variable frequency drive.

14. The gravity irrigation system of claim 1 , further comprising a pump panel, wherein the overall footprint of the sump, the return pump, and the pump panel is less than 900 square feet.

15. The gravity irrigation system of claim 1 , wherein the return pump is formed at least partially of polyvinyl chloride.

16. The gravity irrigation system of claim 15 , wherein the return pump further includes a discharge element, a first transition element and a second transition element, wherein each of the discharge element, the first transition element, and the second transition element are formed at least partially of polyvinyl chloride.