Step #4 of the
Landscape Sprinkler System Design Tutorial
The next step in designing your irrigation system is to identify the individual hydro-zones that exist in the area to be irrigated. Different areas of your yard have different water needs. Each of these areas is called a “hydro-zone”. You need to irrigate them separately from one another to keep from drowning some plants while others are dying of thirst. For example, a grass lawn will almost always need more water than a shrub bed. Plants in the shade of a house need less water than those in direct sun. Tropical plants need more water than desert plants. Remember that over-watering plants can be as harmful to them as underwatering. Many plant diseases are the direct result of over-watering, particularly fungus and molds.
- Lawns and shrubs should NEVER be in the same hydro-zone, so start by creating two hydro-zones, lawns and shrubs.
- Shady and sunny areas should not be in the same hydro-zone. The shadiest areas are typically in the shadow of buildings where little or no direct sunlight reaches all day long. Go out and walk around your yard. Look for places where the soil stays moist when compared with the rest of the yard. Separate the sunny and shady areas of the lawn area into different hydro-zones. Do the same for the shrubs areas.
- Plants with different water requirements should not be in the same hydrozone. Show a separate hydro-zone for any grouping of plants that need more or less water than the others. If you’re not familiar with the water needs of various shrubs look them up in a good garden encyclopedia. You can also tell a lot just by observation. Do some plants in your yard seem to wilt easier than others? On large projects you may also have different soil types in various parts of the irrigated area. These may also need separate hydro-zones. This is very common for golf courses and parks.
- Never combine spray heads, rotors, or drip irrigation in the same hydro-zone. The water application rates are different for each of these, which will cause either dry or wet spots. For example, rotors often apply water at half the rate as spray heads. So if you were to combine spray heads and rotors on the same valve, and then turned on the water long enough to apply just the right amount of water in the spray head area, the area with rotors will only get half the water it needs.
The irrigation for each of these hydro-zones will need to be controlled by its own valve. This way the watering times can be individually adjusted for the specific needs of each hydro-zone. Nothing gets over or under watered. Over and under-watering is a major factor in promoting plant disease, and it wastes water. In some small yards it may not be practical to create separate hydro-zones for all the different water needs. This is an individual decision that you will need to make. Another option is to relocate or replace plants that don’t fit in well with others in the area. I often adjust the outlines of lawn areas to avoid small areas I know will have a different hydro-zone than the rest of the lawn, such as in the shade of a building, or under a large tree.
Drip Irrigation Systems:
If you use drip irrigation for your shrubs you can much more easily mix plants with varying water uses together. The best way to do this is to install two separate drip systems in the same area, one irrigating just the high water users and one just the low water users. Another cheaper, but less effective, way is to install more emitters at the plants which need more water. The disadvantage of this second method is that most water loving plants don’t just want more water, they want it more frequently, which is not possible when everything is on the same system. Irrigating too frequently is a major cause of plant disease so be warned!
Previously you wrote down your “design flow” on your Design Data Form. As you remember that was the maximum amount of water available for the irrigation system measured in gallons per minute (GPM). Hopefully you also noted on your plan the flow (GPM) for each sprinkler head. Now you need to divide the irrigation system into valve zones that do not exceed that amount of water. Remember that the valve zones can’t cross over the boundaries of the hydro-zones you drew previously. (Hydro-zones can’t overlap valve zones.) Here’s an easy way to do this:
- Add together the GPM for all the sprinklers in a hydro-zone.
- If the total GPM of all the sprinklers in the hydro-zone exceeds the design flow GPM, you will need to divide the hydro-zone into more than one valve zone.
- The total GPM for each valve zone should never exceed the design flow GPM.
- Drip irrigation and sprinkler irrigation may NOT be mixed together in a single valve zone. Fixed spray type sprinklers may NOT be mixed with rotor type sprinklers in the same valve zone. You need to create separate valve zones for each of these.
Repeat this procedure for each hydro-zone.
Lightly circle on your plan the heads that are in each valve zone as shown below.
Now identify the location where your valves will be installed. If the valves will be above ground pick somewhere they will be hidden, like behind shrubs. Usually they are placed near the water source but there is no reason they need to be. Remember that if you plan to use anti-siphon type valves they must be installed at an elevation 6″ HIGHER than the highest sprinkler head, so they will probably need to be on the uphill side of the irrigated area. The valves do not need to be grouped together in the same location, you can place them where most convenient. Placing the valves in small groups of 2 or more, close to the areas they will water, can often save money by reducing the amount of pipe needed.
Draw in a valve symbol on your drawing for each valve zone. This will represent the valve that turns on and off the sprinklers in that valve zone. See the illustration on the next page of the tutorial for a typical valve symbol.
Sprinkler Pipe Layout
Now that you have the valve zones shown on your drawing it’s easy to add the pipes going to the sprinklers. Start with one of the valves and draw a line to the closest sprinkler in the corresponding valve zone. Then draw a line to the next sprinkler in the valve zone, and the next, etc. Some helpful tips:
- For small residential sprinkler systems try using a different color pencil for the pipes in each valve zone. This will make your plan easier to understand.
- Where possible you can minimize the amount of trenching by placing pipes together in the same trench. Show these pipes side-by-side on your plan.
- Run the pipes as efficiently as possible. In most cases this will be the shortest possible route between each sprinkler, but this is where you need to just look at your plan and think about it a bit. You may find it easier to run one pipe down the center of an area and spur off of it to each sprinkler. Or it may be easier to split the piping with one pipe going to half the sprinklers and the other going to the other half. Some may want to minimize the number of trenches, even if it means using a less direct route for the pipe so two pipes can share a trench. There is no set routing pattern that you must use for the pipe. If for some odd reason you need to route the pipe all the way around the yard to get to a sprinkler only a few feet away from where you started that’s O.K. Try several different layouts until you find one that YOU like, that fits YOUR needs.
- Show no more than 2 pipes connecting to a sprinkler head– one coming into the sprinkler, and one going out. If you need to branch off from the sprinkler with a 3rd pipe, show the 3rd pipe branching off of the 1st pipe just before it goes into the sprinkler. There is no part made that will allow 3 pipes to connect together at a sprinkler head location. Study the sample drawing below for examples.
- Try to avoid running pipes within 5 or 6 feet of existing trees. The roots will make it hard to dig trenches for the pipe. With really big trees I try to keep the trenches out from under the canopy of the tree. If I need a sprinkler in that area I run the pipe around the perimeter then go straight in toward the trunk to the sprinkler head. Of course, this may not always be possible. Sometimes you will just have to go through an area with tree roots.
Splitting flows or splitting hairs? You may have heard that the flow from each valve should always be split just after the valve, with one pipe going to half the sprinklers and the other pipe going to the other half. The reasoning is that this “balances” the system. Good designers can balance the flows without resorting to this old method. You are well on your way to becoming a good irrigation designer, so you can forget about such amateurish methods! Route the pipe however you want to route it!
Determine Flows in Pipes:
In order to determine the pipe size we need to know the flow rate (GPM) of the water in the pipe. Calculating the water flow in each section of pipe is extremely easy, but many people have problems with it. They try to make it too complicated. Just observe the layout of the sprinklers and ask yourself which sprinklers are DOWNSTREAM of this pipe section. It’s simple logic, the water must flow through this pipe to reach the sprinklers downstream. Add the total GPM of those sprinklers together and you have the GPM that will be flowing through the pipe.
- Start at the valve. The first section of pipe goes from the valve to the first sprinkler head. All the water for every sprinkler operated by this valve must flow through this section of pipe to get from the valve to the sprinklers, right? So the flow in GPM for this section of pipe is the total of the GPM of all the sprinklers operated by the valve added together.
- The remaining sections are just as easy. The total flow through each section of pipe is the same as the total GPM of all the sprinklers downstream from that pipe section. Add together the individual GPMs for each of those sprinklers to get the flow through the pipe section. Don’t make it harder than it is! If you have a short spur pipe leading off to a single head, then only the water going to that head will pass through the spur pipe! So the flow for the spur pipe is the same as the GPM of that single head. Carefully study the sample design below.
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Text and Images by Jess Stryker unless noted. Copyright © Jess Stryker, 1997-2012. All rights reserved.