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(3)Tj
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(aid in understanding the size of this unit, it is )Tj
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(compared with a more familiar unit: )Tj
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(1 ft/sec = 0.68 miles per hour \(mph\) )Tj
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(To avoid excessive pressure losses due to friction )Tj
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(and excessive potentially damaging surge pressures, )Tj
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(most irrigation systems are designed to avoid )Tj
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(velocities that exceed 5 ft/sec: )Tj
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(5 ft/sec = 3.4 mph )Tj
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(Irrigation water velocities and flow rates are )Tj
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(sometimes mistakenly used interchangeably. )Tj
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(Velocity and flow rate are two different \(but related\) )Tj
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(Q = a v )Tj
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(where: )Tj
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(Q= flow rate, )Tj
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(a = cross-sectional area of flow, and )Tj
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(v = velocity. )Tj
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(The equation of continuity states that the flow )Tj
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(rate can be calculated from the multiple of the )Tj
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(velocity times the cross-sectional area of flow. )Tj
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(In pipes flowing full, the cross-sectional area of )Tj
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(flow is the cross-sectional area of the pipe. In open )Tj
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(channel flow, it is the cross sectional area of the )Tj
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(As an example of the application of the equation )Tj
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(and a 2-inch diameter pipe, the flow rate from the 2 )Tj
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(inch pipe would be four times as large as the flow )Tj
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(rate from the 1-inch diameter pipe. Note that the )Tj
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(squared and 1 inch squared = 1 inch x 1 inch = 1 )Tj
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(square inch, while 2 inches squared = 2 inches x 2 )Tj
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( SUMMARY )Tj
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-59 -25 Td
(The amount of irrigation water pumped, applied, )Tj
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(convenient to do so. That is, the volume can be )Tj
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(over which the depth was applied. )Tj
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(The pumping rate, application rate, or plant )Tj
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(water use rate is measured in units of volume \(or )Tj
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(depth\) per unit of time. The volume can be )Tj
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(calculated from the flow rate times the duration )Tj
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(\(time\) of flow. The depth of application or use can )Tj
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(the duration \(time\) of application or use. )Tj
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(Velocity refers to the speed at which water flows )Tj
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(\(distance per unit time\) as opposed to flow rate )Tj
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(\(volume per unit time\). Thus, the terms flow rate and )Tj
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(velocity cannot be used interchangeably. Both the )Tj
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(velocity and cross-sectional area of flow must be )Tj
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(known in order to calculate flow rates. )Tj
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