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Drip
Irrigation Design Manual |
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This manual includes
design steps, design layout, technical data, and detailed layouts
of the A1 drip line, single outlet drippers and TOP drip heads
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Introduction |
 Whether it's a lawn or landscape
area, proper irrigation water management is essential to promote
a healthy landscape while maximizing existing water resource
use. Until a drought
occurs, the evidence of improperly designed or maintained irrigation
systems usually goes unnoticed. It's not until the water supply
is low or water restrictions are enforced that we realize that
many of our irrigation systems are extremely inefficient. These
problems can stem from a number of sources, including poorly
designed and installed irrigation systems, lack of appropriate
maintenance, and improper placement of sprinkler heads that do
not consider runoff potential, terrain difficulty, and windy
sites . As long as water remains relatively inexpensive, irrigation
will remain a low priority, resulting in over irrigation. In
todays market, drip irrigation has made great strides
in becoming recognized as a water management tool, helping architects,
contractors and users to customize their irrigation system to
meet specific needs. Drip Irrigation is the slow application
of water directly to the plants root zone. Maintaining an optimum
moisture level in the soil at all times results in less water
lost to the sun and the wind. No water is wasted on non-growth
areas, and the root zone is maintained at its ideal moisture
level, combining the proper balance of water and air for a very
efficient irrigation system. |
Advantages and Benefits
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Water Efficiency: By applying
water only where it is needed, with less runoff, less deep percolation,
and less evaporation from leaves and soil, the uniform application
of water use in drip irrigation systems can achieve high water
efficiency.
Reduced Pest Problems and Weed Growth:
Watering only the roots
of your plants with drip irrigation cuts down on water-borne
pests and fungal diseases that spread by water movement, as well
as the germination of weeds in the area between your plants.
Reclaimed Water: Using drip irrigation below ground eliminates the
potential risk of disease caused by bacteria and viruses in reclaimed
water.
Versatility: Low volume irrigation systems are designed for
placement in both new and existing landscape areas, and are ideal
for installation on difficult terrain such as on slopes, in oddly
shaped areas, and on windy sites.
Root Zone: One of the most important aspects of drip irrigation
is the fact that, in many instances, a totally new and more favorable
root zone environment is created and a relatively constant soil
moisture level is maintained. This fact has important implications
because it bears upon questions of plant water requirements,
tolerance and control of disease.
Durable: All DIG products are designed to withstand the
harshest conditions in commercial installations. They are manufactured
of high quality, highly durable plastics and contain added quantities
of the compound Carbon Black, making them resistant to the damaging
effects of ultraviolet rays. |
Disadvantages:
- The system requires a pressure
regulator and filter.
- The drip tubing can be susceptible
to damage from household pets.
- A filter is required to guard
against potential clogging of the drippers and drip line.
- You cannot see a drip system
working as you can a conventional sprinkler system.
- Drip irrigation creates a smaller
wetted area, so control is more critical in replacing the water
used by the plant to avoid stress.
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Design Criteria |
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When designing a system, depending
on your layout, you have three options:
- Individual ( button) drippers
with a .5, 1, and 2 gph (for individual shrub and trees)
- TOP 12 outlet drip head (for
individual shrubs and trees or spaced planting)
- A1 pc drip line with preset
spacing (for dense planting)
Designing with option 1 or 2
requires many of the same rules; The TOP system uses PVC pipe
for lateral and sub laterals as with a sprinkler system. Button
drippers use drip hose for laterals. Button drippers and TOP
are ideal for virtually any shrubs, trees or group of shrubs
and trees, but are most efficient when plants are not concentrated.
To cover densely planted areas, ground cover or a complete wetted
area, use option 3 with A1 pc drip line. Designing with this
option uses many of the same rules as a sprinkler system such
as application rates, operating pressure, flow rates and overlapping
coverage. A1 uses a single dripper flow rate with preset spacing
and equal spacing between the laterals. These drawings illustrate
some ways you may lay out a individual dripper or drip line in
a landscape area. |
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In any design that you do,
make sure to plan for the future. When plants mature, they may
require more water. Watering times can be lengthened to meet
those needs, but generally in option 1 and 2, more drippers should
be added to supply the maturing plant. Also, new plants may be
added to the landscape, so leave some room in the overall design
by having about 20%-30% more water capacity available. A 3/4"
or 1" valve will almost always provide more than enough
water for individual zones.
Site
Survey
Start by making a sketch of the
areas that you want to water. Use graph paper with 1/4"
squares. This will make drawing to scale easier. Identify the
site's water sources, pressure (test water pressure) and flow
rates, type of water ( pump, well, or city line) retaining walls,
paved areas and slopes. This will require measuring the area
that you wish to irrigate. If you select option 1 or 2 with individual
drippers for the installation, make sure you note the locations
of trees, shrubs, and group of plants. Identify type of soil
and try to separate your plants into categories: shrubs plants,
and trees. Based on their sizes and location you will determine
and select your choice of drippers, layout, flow rates and spacing.
If you select option 3 with A1 drip line for the installation
you do not need to categorize the plants because the method you
use is for a complete wetted area. |
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Determine
Soil Types |
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Wetting pattern by
soil type |
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When water is applied slowly to
the root zone at a single point, it is acted upon by the forces
of gravity (downwards) and capillary action (radially outwards),
producing a wetted pattern characteristic of the soil type and
application rate. To determine which type of soil you have in
a given area, take a handful of dry soil, grip tightly and release. |
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Sandy (coarse) soil |
Will crumble and fall apart |
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Loam (medium) |
Will hold together but easily
break apart |
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Clay |
Will mold without breaking |
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As described earlier, we recommend
using individual drippers or TOP drip heads on trees, shrubs
and individual plants. A1 drip line is best used on ground cover,
dense planting, hillsides and on very coarse soils as water will
percolate downward before it can spread far enough horizontally.
Drip irrigation is ideal in areas where it is windy, since high
winds will disturb the spray pattern of the sprinklers.Soil is a storage room of
plant nutrients, and the medium through which water and nutrients
move. It is the anchor for plants and the reservoir of water
for plants' growth.There are various types of soil with differing
characteristics, which determine what types of plants can be
grown. Each type of soil will require a different layout. In
sandy and light soil, the water will tend to go straight down,
so we recommend using the A1 drip line or a TOP closely spaced,
12"-16" apart, with .5 gph or 1 gph drippers. In loamy
soil, the water will move slowly and will spread evenly, so here
you can use .5 gph or 1 gph drippers with a 18" to 20"
spacing. In clay soil, the water will be absorbed very slowly,
and we recommend .5 gph drippers, TOP, or A1 drip line at a much
wider spacing, 18" to 24" apart. |
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Soil Water Relationships |
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A micro irrigation system is
essentially a transportation system which delivers water to a
point in or near the root zone. The final link in this transportation
system is the soil. The soil's physical and chemical properties
determine its ability to transport as well store water and nutrients.
In the next few paragraphs we will try to explain the soil and
water relationship, and the mechanisms by which moisture is transported
and stored within the soil.
Capillary moisture: is the water held in pore spaces by
the surface tension between the water, and the soil particles.
Capillary moisture is the primary force in spreading the water
horizontally and it is a primary source of water to the plant.
Gravitational water is free water in the soil which will
move downward under the influence of gravity. After the soil
is saturated, the gravitational water will percolate downwards,
leaving the soil at field capacity.
Field capacity is a measure of the water held by the
soil against the influence of gravity. If soil is saturated by
rainfall or irrigation and then allowed to drain freely for 24
hours, the soil is usually at field capacity. For most plants,
a soil moisture content near field capacity is the ideal moisture
level for vegetative growth, because there is a good balance
between soil moisture tension and aeration. The soil will lose
very little water after it has drained to field capacity if there
are no plants growing in it. Plants will remove water by transpiration
and reduce the soil moisture. On hot days, the plants may use
water faster than the soil can supply the roots, or faster than
the roots can supply the rest of the plant and the plant will
wilt. Normally, given sufficient soil moisture (you can keep
using your irrigation system) the plant will recover during the
night.
Permanent wilting point is the soil moisture content at which
the plant wilts and remains in a wilted state ceasing normal
growth and transpiration.
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Moisture holding capacities of
different soils |
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Soil texture |
Field capacity % |
Permanent wilting point % |
The difference
in available moisture % |
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Sandy |
9 |
2 |
7 |
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Loam |
34 |
12 |
22 |
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Clay |
38 |
24 |
14 |
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