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Irrigation Glossary



Backflow Any unwanted flow of used or non-potable water or substance from any domestic, industrial or institutional piping system into the pure, potable water distribution system. The direction of flow under these conditions is in the reverse direction from that intended by the system and normally assumed by the owner of the system.

Backflow prevention device [BPD]  Safety device which prevents the flow of water from the water distribution system back to the water source.

  • Air gap  Physical separation of the supply pipe by at least two pipe diameters (never less than one inch) vertically above the overflow rim of the receiving vessel. In this case line pressure is lost. Therefore, a booster pump is usually needed downstream, unless the flow of the water by gravity is sufficient for the water use. With an air gap there is no direct connection between the supply main and the equipment. An air gap may be used to protect against a contaminant or a pollutant, and will protect against both back-siphonage and backpressure. An air gap is the only acceptable means of protecting against lethal hazards.
  • Atmospheric vacuum breaker [AVB] Backflow device configured with a single moving part, a float, which moves up or down to allow atmospheric air into the piping system.The AVB is always placed downstream from all shut-off valves. Its air inlet valve closes when the water flows in the normal direction. But, as water ceases to flow the air inlet valve opens, thus interrupting the possible back-siphonage effect. If piping or a hose is attached to this assembly and run to a point of higher elevation, the backpressure will keep the air inlet valve closed because of the pressure created by the elevation of water. Hence, it would not provide the intended protection. Therefore, this type of assembly must always be installed at least six (6) inches above all downstream piping and outlets. Additionally, this assembly may not have shut-off valves or obstructions downstream. A shut-off valve would keep the assembly under pressure and allow the air inlet valve (or float check) to seal against the air inlet port, thus causing the assembly to act as an elbow, not a backflow preventer. The AVB may not be under continuous pressure for this same reason. An AVB must not be used for more than twelve (12) out of any twenty-four (24) hour period. It may be used to protect against either a pollutant or a contaminant, but may only be used to protect against a back-siphonage condition.
  • Double check assembly [DC] Two internally loaded, independently operating check valves together with tightly closing resilient seated shut-off valves upstream and downstream of the check valves. Additionally, there are resilient seated test cocks for testing of the assembly. The DC may be used to protect against a pollutant only. However, this assembly is suitable for protection against either backsiphonage or backpressure. 
  • Pressure vacuum breaker[PVB] Backflow device configured with a spring loaded float and an independent spring loaded check valve.Check valve which is designed to close with the aid of a spring when flow stops. It also has an air inlet valve which is designed to open when the internal pressure is one psi above atmospheric pressure so that no non-potable liquid may be siphoned back into the potable water system. Being spring loaded it does not rely upon gravity as does the atmospheric vacuum breaker. This assembly includes resilient seated shut-off valves and test cocks. The PVB must be installed at least twelve (12) inches above all downstream piping and outlets. The PVB may be used to protect against a pollutant or contaminant, however, it may only be used to protect against backsiphonage. It is not acceptable protection against backpressure. 
  • Reduced pressure principle assembly[RP, RPA, RPZ] Consists of two internally loaded independently operating check valves and a mechanically independent, hydraulically dependent relief valve located between the check valves. This relief valve is designed to maintain a zone of reduced pressure between the two check valves at all times. The RP also contains tightly closing, resilient seated shut-off valves upstream and downstream of the check valves along with resilient seated test cocks. This assembly is used for the protection of the potable water supply from either pollutants or contaminants and may be used to protect against either backsiphonage or backpressure.

Back pressure Increase of pressure in the downstream piping system above the supply pressure at the point of consideration which would cause, or tend to cause, a reversal of the normal direction of flow.

Back siphonage  Reversal of flow (backflow) due to a reduction in system pressure which causes a negative or sub-atmospheric pressure to exist at a site in the water system. 

Basic intake rate (of soil) Rate that (irrigation) water enters the soil at the surface.

Basin irrigation Irrigation by flooding areas of level land surrounded by dikes. Used interchangeably with level border irrigation, but usually refers to smaller areas.

Beneficial uses: Beneficial use of water supports the production of crops: food, fiber, oil, landscape, turf, ornamentals, or forage.

Best efficiency point: Highest efficiency on a pump characteristic curve.

Best management practice An irrigation BMP is a voluntary irrigation practice that is both economical and practical and is designed to reduce water consumption and protect water quality while maintaining a healthy, functional landscape.

Black water Water containing liquid and solid human body waste generated through toilet usage.

Blaney-Criddle Method Air temperature based method to estimate crop evapotranspiration.

Bog coefficient Inverse of scheduling coefficient but using the wettest 1%window instead of the driest.  Gives no indication of the location of dry areas. 

Border dike Earth ridge or small levee built to guide or hold irrigation or recharge water in a field.

Border ditch Small excavation used as a border of an irrigated strip or plot with water being spread from one or both sides.

Border irrigation Irrigation by flooding strips of land, rectangular in shape and cross leveled, bordered by dikes.  Water is applied at a rate sufficient to move it down the strip in a uniform sheet.  Border strips having no down field slope are referred to as level border systems.  Border systems constructed on terraced lands are commonly referred to as benched borders.

Brake horsepower Power required to drive a pump.

Brake horsepower hour Measure of work input into a pump or other device.

British thermal units {BTU} Amount of heat required to raise the temperature of one pound of water from 63 to 64 degrees Fahrenheit.

Bubbler Water emission device that tends to bubble water directly to the ground or that throw water a short distance, on the order of one foot, (300 mm) before water contacts the ground surface.

Bubbler irrigation Application of water to flood the soil surface using a small stream or fountain.  The discharge rates for point-source bubbler emitters are greater than for drip or subsurface emitters but generally less than 1 gpm.  A small basin is usually required to contain or control the water.

Bulk density of soil Mass of dry soil per unit bulk volume (generally ranging in value from 1.3 to 1.6 g/cc) 

Bulk density of water Same as density of water. Mass of water per unit bulk volume. (approximately 1.0  g/cc, 62.4 lb/ft3)

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