Guidelines for Drip Irrigation on Hillsides

Slopes create some unique problems for drip irrigation systems. These problems are not hard to solve, but if not considered and/or addressed they can create a mess.

Sample Design:

Drip System Sample Design

Drip System Sample Design Sample Design of a Drip System on a Slope

An easier to read, higher resolution (656 kb) pdf version of the drip system design shown above can be downloaded by clicking on the image above, or click here. The pdf version includes a copy of the planting plan that goes with the drip system. The plans print out on 5 standard letter-size sheets of paper. I suggest you click on the image above to download it and then print it for a visual reference before continuing. (Yes, this is a real design for a site on a hillside overlooking the Pacific Ocean in Ventura, California. No, it’s not my house. Our house has a fine view– of two cats in the yard!)

Type of Emitters to Use:

When installing drip irrigation on a slope or hill side, it is best to use pressure compensating emitters. Pressure compensating emitters apply a more uniform rate of water on slopes when compared to a standard emitter. This is because as the water is pushed in a tube or pipe up a slope the water pressure in the pipe or tube decreases. When water flows in a tube or pipe down a slope the water pressure in the tube increases. As the water pressure changes, it results in a change in the rate of water flow from the emitter. Using pressure compensating emitters solves this problem. I suggest using a diaphragm type pressure compensating emitter. For more information please see the Drip Irrigation Emitters page.

Drip Tube Orientation:

One trick for installing drip systems on slopes is to try as much as possible to keep the drip tubes running horizontal to the slope direction. In other words, try to keep the drip tubes as level as possible. A typical design would have either a pipe or drip tube running from the control valve vertically up or down the hillside. Check valves would be installed at periodic intervals on this pipe or tube (I’ll explain more about the check valves later.) From this vertical pipe or tube, the drip tubes would branch off and run horizontally across the slope to the plants. Does that make sense? No? OK, a picture helps, so take a look at the Sample Design of a Drip System on a Slope at the top of this page. This plan is a map view, so you are looking down at the drip system just like when reading a map. Notice the light gray color contour lines that indicate the slope. The contours are labeled at the ends with the elevation, such as 117.00′, so the line labeled 118.00′ is one foot higher than the line labeled 117.00′. Next, look for the tube that runs up the slope on the left side of the area with the check valves shown on it. Now look for the tubes that branch off it, you will notice most of the emitters are on these tubes, which run more or less horizontal to the slope.

Low Emitter Drainage:

When a drip system is installed on a slope a problem called “low emitter drainage” occurs. Each time that the drip system is turned off the water in the tubes drains out through the lowest emitters. This causes a small puddle to form around the low emitters, and the area around these low emitters becomes saturated and over watered. Sometimes this low emitter drainage is not a problem, it just depends on where the drainage is occurring. If the drainage is occurring in an area where it doesn’t create a problem it is likely not worth dealing with it. However, most of the time the water is going to create a problem, such as a mud pit, mosquito farm, or worse. In the case of our sample design low emitter drainage would cause water to drain out of the emitters just behind the retaining wall. This would be a very bad situation, as the water could build up in the soil behind the wall and the weight of the water could push over the wall. As a general rule, if the difference between the highest and lowest elevation is 0,5 meter (1.5 feet) or less, low emitter drainage is typically not a big enough problem to worry about. If the elevation change is greater than that there are two ways to deal with it.

The first way to reduce low emitter drainage is to use special emitters with built-in check valves. The check valves inside the emitters keep the water from draining out of them when the system is turned off. These special emitters are limited in how much water they can hold back, each brand is different so you need to consult the manufacturer’s literature. A typical emitter with a built-in check valve holds back the water from an elevation change of about 1,3 meters (4.5 feet). What that means is that if the slope or hill is more than 1,3m high the check valve will not be able to hold back the water and some water will still leak out. If this were the case you would have to also use a secondary check valve on the tube, as described below. Many designers don’t bother to use emitters with check valves. They just use standard emitters and put up with a small amount of low emitter drainage. If the change of elevation is more than about 1 meter (3 feet), they will use check valves on the tubes as described in the next paragraph.

The second way to reduce low emitter drainage is to install check valves on the tube at periodic intervals. This is the method used on the sample design. The check valves prevent the water from flowing down to the lower part of the tube(s). This does not completely eliminate the low emitter drainage, but it reduces greatly the amount of water that drains out. It basically spreads the problem out so that the water drains through many emitters rather than just a few. But this is still much better than having all the water in all the tubes drain out through just a few emitters. The check valve is typically a small spring-operated type check valve. A check valve is installed on the tubes at intervals based on the height of the slope. Typically check valves are installed at about 1m (3 feet) of elevation change intervals. The number of check valves needed depends on how many tubes you have running vertically up and down the slope. Thus the reason I recommended having most of your tubes run horizontal. In the sample design I was able to limit the number of check valves to 3 by using a single tube to run up the slope and keeping all the other tubes horizontal. When you install the check valve you need to note that it will have a direction of flow arrow on it, be sure to install it with the arrow facing the correct direction. If the check valve has an adjustable spring tension set to the least possible tension if the water is flowing through it uphill. If the water is flowing through the check valve downhill set it to 0,15 bar (2 PSI). Most spring-type check valves come factory preset at 0,5 bars (5 PSI) so you will need to adjust them down. The manufacturer should have literature telling you how to adjust them.

This page is not intended as a full guide to drip irrigation on slopes. This page is a supplement to the Guidelines and by itself is not a complete guide to drip irrigation systems. Please also read the Drip Irrigation Design Guidelines at the link below.