Jess Stryker's Landscape Sprinkler Design Tutorial Step #4  Hydro-Zones & Valve Zones

Hydro-Zones:

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 seperately 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. Reember 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.

Using a pencil lightly outline the different hydro-zones in your yard on your plan. Some hints:

• 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!

---

Valve Zones:

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:

1. Add together the GPM for all the sprinklers in a hydro-zone.
2. 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.
3. The total GPM for each valve zone should never exceed the design flow GPM.
4. 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.

Previous Page of Tutorial     Sprinkler Design Tutorial Index     Next Page of Tutorial

Glossary    Conversion Formulas    About the Author

Comments?   Questions?   Product Data & Reviews   More Irrigation Tutorials!

www.IrrigationTutorials.com

Use of this tutorial is subject to the conditions and limitations listed on the disclaimer page.

Jess Stryker's Irrigation Tutorials
Copyright © Jess Stryker, 2001
All rights reserved.