190 Chapter 10: Appendix
Irrigation System, Drip or Trickle (441): A planned irrigation system in which
all necessary facilities are installed for efficiently applying water directly to the
root zone of plants by means of applicators (orifices, emitters, porous tubing, or
The applicators can
perforated pipe) operated under low pressure (Figure
be placed on or below the surface of the ground (Figure 2-2 1).
water quality may not be significantly affected by transported substances
because runoff is largely controlled by the system components (practices).
Chemical applications may be applied through the system. Reduction of runoff
result in less sediment and chemical losses from the field during irrigation. If
a chemical hazard may exist to
excessive, local, deep percolation
shallow ground water or to areas where geologic materials provide easy access
to the aquifer
Irrigation System, Sprinkler (422): A planned irrigation system in which all
necessary facilities are installed for efficiently applying water by means of perfo-
rated pipes or nozzles operated under pressure.
Proper irrigation management controls runoff and prevents downstream surface
water deterioration from sediment and sediment attached substances. Over irri-
in runoff
gation through poor management can produce impaired water
as well as ground water through increased percolation. Chemigation with this
system allows the operator the opportunity to mange nutrients, wastewater and
pesticides. For example, nutrients applied in several incremental applications
based on the plant needs may reduce ground water contamination considerably,
compared to one application during planting. Poor management may cause pol-
lution of
and ground water. Pesticide
from chemigation may also be
hazardous to vegetation, animals, and surface water resources. Appropriate
safety equipment, operation and maintenance of the system is needed with
chemigation to prevent accidental environmental pollution or backflows to water
sources.
Irrigation System, Surface and Subsurface (443): A planned irrigation system
in which all necessary water control structures have been installed for efficient
distribution of irrigation water by surface means, such as furrows, borders, con-
tour levees, or contour ditches, or by subsurface means.
Operation and management of the irrigation system in a manner which allows
little or no runoff may allow small yields of sediment or sediment-attached sub-
stances to
waters. Pollutants may increase if irrigation water man-
agement is not adequate. Ground water quality from mobile, dissolved chemicals
may also be a hazard if irrigation water management does not prevent deep per-
colation.
irrigation that requires the drainage and removal of excess
waterfrom
may discharge increased amounts of dissolved substances
such as nutrients or other salts to
Temperatures of downstream
water courses that receive runoff waters may be increased. Temperatures of
downstream waters might be decreased with
systems rvhen excess
water is being pumped from the field to lower the water table. Downstream tem-
peratures should not be affected by subsurface irrigation during summer months
if
the water table is not required. Improved aquatic habitat may occur if
or seepage occurs from surface systems or from pumping to lower the
water table in subsurface systems.
Chapter 1 O-1 90:
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