Micro-Irrigation Resources
East Multnomah Soil and Water Conservation District 7/16/2015
Definitions
Flow The volume of water that moves through a pipe over a given period of time; usually measured in GPM (gallons per minute) or cfs (cubic feet per second).
cfs Cubic feet per second; a measure of flow.
GPM Gallons per minute; a measure of flow.
Velocity The speed that water moves through a pipe expressed as a distance over a given period of time; usually measured in fps (feet per second).
fps Feet per second; a measure of velocity.
Pressure The weight or force that is produced when an object, fluid, etc., presses or pushes against a surface in contact with it; usually measured in psi (pounds per square inch) or feet of head.
psi Pounds per square inch; a measure of pressure.
Feet of Head A measure of pressure; the amount of pressure that would be produced at a point in a pipe by a tank of water connected to it, determined by the difference in height between water level in the tank and the point in the pipe.
Friction The resistance water encounters moving through a pipe or through fittings that leads to a decrease in energy and a corresponding drop in pressure; usually measured in psi (pounds per square inch) or feet of head.
Distribution Uniformity A measure of how uniformly water is applied to an area being irrigated, expressed as a percentage.
VFD (Variable Frequency Drive) A device that controls the output speed and torque of an electric motor by varying the input frequency and voltage. By controlling the speed and torque of the electric motor of a pump, system pressure can be controlled.
Cycle Stop Valve A valve that mechanically controls the output flow from a pump to match the usage. These valves have no electronics. The valve mechanically senses downstream pressure, and a pilot valve or spring mechanically controls the valves position. A standard pressure switch and pressure tank is used for starting and stopping the pump.
Air/Vacuum Release Valve A valve for purging air from an irrigation system to ensure proper performance of the system. Air/Vacuum combination valves also allow air to enter pipelines at shut down to prevent vacuum suction. It is recommended to install a combination valve at least at the well head.
Mainline The pipe that supplies water from the well head to the point of application.
Riser/Header The pipe that brings water from the mainline to a valve for use in a field, usually from below ground to the surface.
Filter A device for removing impurities from irrigation water, so that the system does not become damaged by getting clogged.
Pressure Regulator A valve that reduces incoming water pressure to a set pressure usable by the system. A pressure regulator is used when the incoming pressure is too high for the emitters or fittings. The flow rate of the regulator should be matched with the system. Pressure regulation does not take effect until minimum specified flow passes through the regulator. It is recommended that pressure regulators be situated after valves or shutoffs. They may be damaged if left under constant pressure.
Manifold/Lateral The pipe that supplies water from the riser/header to the emitters that apply the water. They usually have many opening to allow for distribution of the water.
Zone A subdivision of a field into an area appropriate for management objectives (e.g. to group crops with similar irrigation needs, to ensure even distribution of water based on supply and topography).
Set The time a zone is in operation. Different zones may have different set times. Sets may occur multiple times per week or per day.
Emitter A fitting that applies irrigation water from a pipe to the soil.
PC (Pressure Compensating) A type of emitter or drip line that allows operation at a wide variety of pressure while maintaining constant flow. This feature is especially useful when pressures in an irrigation system vary by location due to frictional losses or topography.
Evapotranspiration The process by which moisture is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.
Available Water Capacity The range of available water that can be stored in soil and be available for growing crops.
MAD (Max allowable depletion) The maximum amount of depletion of soil moisture that can occur without stress to the plant.
Atmometer An instrument that measures the rate of water evaporation.
Tensiometer An instrument for measuring the moisture content of soil.
Calculating flows
1 cubic foot = 7.48 gallons
1 acre = 43,560 square feet
Example: Farmer Jones wants to calculate his irrigation needs. When he turns his pump on for zone A that is 1 acre, he notes that the flow meter reads 74.8 GPM. He assumes that he is irrigating ¾ of the zone, excluding paths. He wants to know how many inches he will irrigate in 1 hour.
Irrigation Rate = Flow in GPM7.48 galft3*1% of area irrigated * Area in ft2*12 inches1 ft*60 min1 hr
= 74.8 GPM7.48 galft3*1 acre0.75 * 43,560 ft2*12 inches1 ft*60 min1 hr = 0.22 in/hr
If farmer Jones didn’t have a flow meter he could estimate his irrigation by using the manufacturer specifications for his drip tape. The specifications say that the drip tape puts out 40 gallons per HOUR per 100 linear feet of tape. He has 40,000 ft of tape in his 1 acre. Again, he assumes that he is irrigating ¾ of the zone, excluding paths. Note: This method overestimates the amount of irrigation being applied because it does not account for the fact that the pump is limited by the maximum flow it can produce and instead assumes the pump is pumping as much as the drip tape can handle.
Irrigation Rate =
Flow Rating of Drip Tape in galhr per 100 ft7.48 galft3*Linear Feet of Tape100 ft*1% of area irrigated * Area in ft2*12 inches1 ft
= 40 galhr7.48 galft3*40,000 ft100 ft*1 acre0.75 * 43,560 ft2*12 inches1 ft = 0.79 in/hr
Another way farmer Jones could estimate his irrigation would be to capture the water under several of his emitters and find an average of what they are emitting. In a 15 minute test he captures the following amounts..
Container 1: 4 oz Container 3: 5 oz Container 5: 3 oz
Container 2: 3 oz Container 4: 5 oz
The average amount coming from each emitter is (4+3+5+5+3)/5 = 4 oz. So, on average each emitter in the field is putting out 4 oz/15 min * 60 min/hr = 16oz/hr. If the spacing on the emitters is 12 inches he knows he has 40,000 ft/1 ft per emitter = 40,000 emitters in his field. Again, he assumes that he is irrigating ¾ of the zone, excluding paths. So..
Irrigation Rate =
Average Measured Flow per Emitter in oz/hr7.48 galft3*1 gal128 oz*Total Number of Emitters% of area irrigated * Area in ft2*12 inches1 ft
= 16 ozhr7.48 galft3*1 gal128 oz*40,000 emitters*1 acre0.75 * 43,560 ft2*12 inches1 ft = 0.25 in/hr
Online
OSU Western Oregon Irrigation Guides:
bioe.oregonstate.edu/Faculty/selker/wo_irrigation_guide.htm
WSU Irrigation Resources: irrigation.wsu.edu
WSU Irrigation Scheduler Mobile: weather.wsu.edu/is
Agrimet: www.usbr.gov/pn/agrimet
The Weather Channel: www.weather.com
National Weather Service: www.weather.gov
Estimating Soil Moisture by Feel and Appearance:
http://www.nrcs.usda.gov/wps/portal/nrcs/detail/mt/newsroom/?cid=nrcs144p2_056492
Regional Water Providers Consortium: www.conserveh2o.org
Oregon Water Resources Department: www.oregon.gov/owrd
Oregon Department of Agriculture: www.oregon.gov/oda
Natural Resources Conservation Service: www.nrcs.usda.gov
EMSWCD: emswcd.org
OSU Small Farms Program: smallfarms.oregonstate.edu
Energy Trust of Oregon: energytrust.org
Irrigation Vendors and Services
Steve’s Pump Service: www.stevespumpservice.com
Ernst Irrigation: ernstirrigation.com
Fisher Supply: www.fisherssupply.com
Stettler: stettlersupply.com
Mitchell, Lewis, and Staver: www.mitchellewis.com
Ferguson: www.ferguson.com
Dripworks: www.dripworks.com
Your local hardware store
Page 2 of 4