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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASAE.  VOL. 43(6): 1489-1498 . (doi: 10.13031/2013.3048) @2000
Authors:   J. V. Bonta, V. C. Goyal
Keywords:   Infiltration, Infiltrometer, Spatial variability, Hydrology, GIS, Instrumentation

Runoff is generated on landscapes in a deterministic and random, but unquantifiable manner, and measurements of the spatial variability of infiltration and seepage under natural-precipitation conditions are highly desirable. Runoff from small natural-precipitation infiltrometer plots (0.25 m 2 ) under natural conditions can be merely drip flows, or they can be larger flows when runoff is produced simultaneously from high-intensity rains and seepage. A study of a drip-flow/low-flow nozzle/rotor flow-measuring system that met design requirements for runoff measurement is presented. Comparison of different nozzle configurations led to the selection of the rotor of a Price current meter, in combination with a unique nozzle that incorporated a drip diverter, an internal flow baffle, and drip-control silicone beads. The best nozzle/rotor combination yielded a rating curve with a resolution less than design requirements, and worked well with flows as high as ~6 L min 1 , greater than design requirements. A combined function using linear segments for low flows, and a 4th degree polynomial for high flows, comprised the rating curve. The average residual error about the function was 0.113 L min 1 . Unsteady flow tests with the nozzle showed that the rating curve and nozzle/rotor assembly worked well, with the median error in volume of 21 mL for 12 synthesized events. The device is a standalone measuring system that can be placed anywhere on the landscape, and only electrical pulses, representing rotor-rotation speed require measurement. The nozzle/rotor system can be used for other applications in which drip and low flows need to be measured, such as for rain gauges, percolation flows from lysimeters, spring flows, etc.

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