Irrigation Units
Flow
gpm - gallons per minute
gph - gallons per hour. Typically used for drip emitter flow rates.
gpd - gallons per day
mgd - million gallons per day
cfs - cubic feet per second. There are about 450 gpm in 1 cfs. 1 cfs is about 1 acre-in/hr. In other words 1 cfs will cover 1 acre in 2 feet of water in one day.
cfm - cubic feet per minute
cu. yd/min - cubic yards per minute
acre-in/day - flow that would cover a perfectly flat acre of land one inch deep in one day
acre-in/hr - flow that would cover a perfectly flat acre of land one inch deep in one hour. This is approximately equal to 1 cfs.
acre-ft/day - flow that would cover a perfectly flat acre of land one foot deep in one day
lps - metric liters per second. 1 lps is about 16 gallons per minute.
lpm - liters per minute
lph - liters per hour
cu. m/hr - cubic meters per hour
cms - cubic meters per second (1 cms is a lot of water! About 16,000 gpm.)
Area
acre - acres = 43560 square feet
sq. feet - square feet
hectare - metric measure of area = 10,000 square meters (100m x 100m area). There are about 2.5 acres in one hectare.
sq. meter - square meters
sq. mile - square miles. There are 640 acres in a square mile.
Distance
ft - feet
in - inches
mile - 1 mile = 5280 ft
mm - millimeters
cm - centimeters
m - meters
km - kilometers
Volume
cu. ft. - cubic foot of water
gal - gallons
cu. meter - cubic meters
liter - liters. 1000 liters fit inside a cubic meter.
acre-in - amount of water that would cover a perfectly flat acre of land one inch deep
acre-ft - amount of water that would cover a perfectly flat acre of land one foot deep
Pressure
ft of water - Feet of water. Also known as feet of head. The pressure at the bottom of the given depth of water in feet. Used by engineers to design systems. About 2.3 feet of water is equivalent to 1 psi.
m of water - meters of water. The pressure at the bottom of the given depth of water in meters. 1 m of water is about 9.8 kPa
kPa - Kilopascals. 1000 pascals. 1 pascal = the force of 1 newton on 1 square meter
atm - Atmospheres. Equal to about 14.7 pounds per square inch.
in of Mercury - Inches of mercury. Pressure at the bottom of the given depth of mercury in inches
psi - pounds per square inch. Sometimes referred to colloquially as “pounds of pressure”.
Power
hp - horsepower
kw - kilowatts
Precipiation
in/hr - inches per hour. This is a common measurement of an irrigation system’s application rate. It is important to know to understand how long to leave the irrigation system on.
in/day - inches per day
in/month - inches per month
cm/hr - centimeters per hour
cm/day - centimeters per day
cm/month - centimeters per month
gpm/acre - gallons per minute per acre. This is commonly used to design irrigation systems. 7 gpm/acre is a common design number for eastern Washington.
cfs/acre - cubic feet per second per acre
lps/ha - liters per second per hectare.
cms/ha - cubic meters per second per hectare
Salinity
dS/m - deci-siemens per meter. A measurement of electrical conductivity (EC). Salty water conducts electricity more readily than pure water. Therefore as salinity increases, EC increases.
mS/cm - milli-siemens per centimeter
microS/cm - micro-siemens per centimeter
mg/l - milligrams of dissolved salt per liter of liquid. A measurement of total dissolved solids(TBS) equivalent to parts per million (ppm).
ppm - parts per million. Parts of salt per million parts of the total solution. Equivalent ot milligrams per liter.
tons/acre-ft - tons of salt per acre-feet of water.
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