Design of Agricultural Irrigation Systems in Florida

Flow Meters

 Flow (water) meters are required to properly
 manage irrigation systems, specifically to measure the
 amount of water applied at each irrigation. Meters
 may be located at the irrigation pump to total the
 water applications to the entire area irrigated, or they
 may be located at field subunits to accurately monitor
 applications to each individual subunit. Flow meters
 are also required to continuously monitor irrigation
 pumping efficiency, to indicate clogging problems
 when decreasing flow rates are measured, and to
 allow chemical injections to be accurately made when
 chemical concentrations in the irrigation water are
 important.

 For more information on selection and
applications of flow meters, see IAS Ext. Bul. 207,
Agricultural Water Measurement (58) and Ag. Eng.
Fact Sheet AE-156, Measuring Irrigation Water (38).
For information on the applications of specific types
of flow meters, see the following IFAS Ag. Eng. Fact
Sheets: AE-18, Selection and Use of Impeller Meters for
Inigation Water Measurement (50); AE-22, Orifice
Meters for Water Flow Measurement (48); AE-25, Weirs
for Open-Channel Flow Measurement (47); and AE-
155, Shunt Flow Meters for Inigation Water
Measurement (37).

Backflow Prevention System

 Florida law requires that a backflow prevention
system be installed on most irrigation systems.
Backflow prevention systems are always required
when 1) chemicals are injected into an irrigation
system, or 2) a public (municipal) water supply is
used, whether or not chemicals are injected.

 Check all applicable local, county, or municipal
codes to determine the type of backflow prevention
device required for public water supplies. Use a
reduced-pressure zone backflow prevention device or
an air-gap separation of the irrigation system from the
water supply when chemicals are injected into
irrigation systems that are connected to municipal
water supplies.

 No backflow prevention assembly is required if
the water supply is not a public water supply (for
example, if the water supply is an irrigation well, lake
or canal) if no chemicals are injected into the
irrigation system.


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 When the water supply is not a public water
 supply, the minimum backflow prevention system
 requires a check valve, low pressure drain, and
 vacuum breaker on the irrigation pipe to prevent
 water and chemicals from flowing back to the water
 source. It also requires interlocked power supplies to
 prevent chemical injection unless the irrigation water
 is flowing, a check valve on the injection line to
 prevent water flow to the chemical supply tank, and
 a positive shutoff valve on the chemical tank to
 prevent accidental drainage from the tank.

 When Chemical Toxicity Category I pesticides are
 injected into irrigation systems and the water source
 is not a public water supply, a double check valve, low
 pressure drain, and vacuum relief valve assembly is
 required. These pesticides are marked with the
 keywords Danger or Poison on the label. When these
 pesticides are injected, 1) either reduced pressure
 principle backflow prevention devices or air-gap
 separations are required when a public (municipal)
 water supply is used; 2) only piston or diaphragm
 types of injection pumps are permitted for injection;
 and 3) pressure switches are required to shut off the
 injection pump when the irrigation system pressure
 drops to the point that uniformity of water application
 is affected.

 The Environmental Protection Agency (EPA)
requires that all pesticide products be labeled to
clearly state whether injection into irrigation systems
is permitted. Pesticide labels must also list the
backflow prevention equipment requirements and
application instructions. For more information on the
Florida backflow prevention law and equipment
requirements, see IFAS Ext. Bul. 217, Florida
Backflow Prevention Requirements for Agricultural
Irrigation Systems (52).

Filters

 Almost without exception filters are required to
prevent clogging of microirrigation systems. Filters
remove small particles that may clog the tiny orifices
in emitters. The type of filtration system required
depends on the type of emitter used and the source
and quality of the irrigation water. Filters should be
selected based on emitter manufacturer's
recommendations.

 If manufacturer's recommendations are not
available, use the equivalent of a 200 mesh screen
filter for drip systems. A larger mesh (coarser
screen) is normally acceptable for spray emitters,