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oust be installed correctly, following the manu- <br />T's specifications. At each selected well, a TIM <br />stalled inline in a full- flowing, acceptable test <br />i of pipe on the discharge side of the pump <br />the measurement of water velocity was made. <br />)wmeter location was in a straight, constant - <br />.er length of pipeline without turbulence - <br />ig obstructions (elbows, valves, pumps, and <br />;s in pipe diameter) for a certain distance <br />)m and downstream from the flowmeter installa- <br />iint. The distances required usually were related <br />iiameter of the discharge pipe at the measure - <br />:)cation. The desired distance upstream for any <br />-ter without a straightening vane installed was <br />diameters and for flowmeters with a straight - <br />vane was 5 pipe diameters. At some wells, slight <br />ing modifications, such as adding a pipe elbow, <br />wade to the discharge pipe downstream from the <br />-ter measurement location to maintain the <br />�d full- flowing condition in the pipe. <br />Two types of TFM's installed during this study <br />;1) the propeller flowmeter manufactured by <br />)meter, hereinafter referred to as make M; and <br />rotating -blade flowmeter manufactured by <br />Scientific Corporation, hereinafter referred <br />lake S. The pre- existing types of TFM's <br />(1) the propeller flowmeter manufactured by <br />)meter, hereinafter referred to as make X; <br />propeller flowmeter manufactured by the <br />r Corporation, hereinafter referred to as <br />3; and (3) the propeller flowmeter manufactured <br />Rockwell Corporation, hereinafter referred to <br />w R. <br />Twenty of the TFM's installed during this study <br />prototype, rotating -blade flow sensor developed <br />Signet Scientific Company (Tim Quinlin, <br />e Fischer Inc., oral commun., 1999). Because of <br />- development limitations, the 10 Signet TFM's <br />-d in 1997 were in irrigation wells that had a <br />rge pipe with a diameter of 8 in. or more, and <br />installed in 1998 were in wells that had a <br />rge pipe with a diameter of 6 in. or more. <br />The cumulative volume pumped, as indicated by <br />gs of the TFM's, was recorded on an irregular <br />During a site visit, a well discharge measure - <br />vas made by reading the register dials of the <br />)nd timing the index wheel for one complete <br />tion, then dividing the indicated volume by the <br />d time; the procedure was repeated nine more <br />the recorded discharge was the average of the <br />10 values. The volume of water pumped between site <br />visits was determined by recording the register dials <br />of the TIM at the beginning of each visit. The total <br />volume of water pumped at a study site during 1998 <br />was determined as the difference between TFM read- <br />ings made at the beginning and the end of the moni- <br />toring period. <br />Portable Flowmeter Measurements <br />During each site visit, electrical power measure- <br />ments and other onsite information were recorded, and <br />measurements of instantaneous discharge were made <br />using as many as three different types of portable flow - <br />meters—a manometer, an ultrasonic flowmeter, and a <br />propeller -type meter. These portable flowmeters <br />provided three different methods to determine the <br />average velocity of water flowing through the <br />discharge pipe. The average velocity, multiplied by the <br />cross - sectional area of the discharge pipe, was used to <br />compute the discharge in gallons per minute. When- <br />ever possible for the PCC tests, instantaneous <br />discharge measurements were made using all three <br />portable flowmeters during each site visit. All PCC <br />test measurements were made after the drawdown of <br />the pumping water level had stabilized. <br />To compute well discharge for two of the three <br />portable flowmeter types (manometer and ultrasonic <br />flow meters), the inside pipe diameter was needed; <br />therefore, throughout the study, inside pipe- dimension <br />measurements were made consistently. The pipe -wall <br />thickness was measured during each site visit using an <br />ultrasonic thickness gage. The outside circumference <br />of the discharge pipe was determined using a thin, <br />flexible metal tape. <br />The first type of portable flowmeter, a manom- <br />eter, measures differences in water pressure in an <br />upstream and downstream direction and could be used <br />in all the discharge pipe sizes in this study. A device <br />referred to as a "Collins Meter ", hereinafter referred to <br />as method "C ", was used to determine the average <br />water - velocity distribution across the inside of the <br />discharge pipe. A pitot tube that had two orifices (one <br />oriented upstream and one oriented downstream) was <br />inserted across the diameter of the discharge pipe and <br />a manometer used to measure the pressure difference <br />between the dynamic (upstream) and static (down- <br />stream) orifices at two different points in the pipe's <br />cross section. The measured pressure difference is <br />;omparison of Two Approaches for Determining Ground -Water Discharge and Pumpage in the <br />.ower Arkansas River Basin, Colorado, 1997 -98 <br />