Reduce pressure in your irrigation system with pressure regulators of various kinds.
Problem #1: How to keep even pressure when water has to run downhill
Good news! Gravity is not all powerful when it comes to water flow. We can intervene with pressure regulators.
If you ran a line of poly tubing straight downhill you’d run into trouble.
If you left it up to gravity, your drip irrigation system would be trickling out water at the top of the hill, and shooting out high pressure water at the bottom of the hill.
First trick is to run the line at an angle down the slope, to decrease the gravitational pull.
Second trick is to use pressure regulators as needed. To keep the water pressure even, simply add pressure regulators at intervals along the line. Lay down a short run of poly tubing then add a pressure regulator. Repeat as you go down the hill.
Problem #2: Keep water flowing evenly along a long line
You might have a pressure tank that gives you low water pressure. If you have a long line of plants to water, and your pressure is low, you could have very low water pressure by the end of the line, with inadequate water coming out of the emitters.
Solve this problem by running poly tubing down one side of the plants, across the bottom, and up the other side, connecting the poly tubing again to form a rectangle around the line of plants.