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ARS Home » Research » Publications at this Location » Publication #102018


item Bonta, James - Jim

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: It is known that there is spatial variation of soil characteristics over landscapes, and that this variability is important for causing rates and volumes of surface runoff to be produced. However, there is no method for including this variability into computer models of watershed hydrology. This is because there are no data available. A previous study showed that watershed runoff was greatly different on two adjacent watersheds that wer visually the same. In order to investigate the reasons for this disparity in runoff, several small 0.25-sq. meter infiltration plots will be placed over the landscape to quantify the spatial and temporal variability of runoff and infiltration. However, a flow-measuring device was needed first to accurately measure the drip flows and higher flows expected due to high rainfall intensities, and seepage flow from within the soil, both of which can occur simultaneously. The device must be able to log detailed runoff data from the plots that are isolated on the landscape from power supplies A device was developed that includes a unique nozzle design used in conjunction with a cup-type rotor and data logger to measure the range in flows from drips to larger runoff flows. The device was shown to work well under synthesized unsteady flow rates, such as might be expected under natural-rainfall conditions. The research has utility for applications other than for the small infiltration plots such as for rain gages, seepage flow studies, percolation flows from beneath lysimeters, etc. Researchers will be able to use the flow measurement device developed in the study.

Technical Abstract: 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. Runoff from small natural-precipitation infiltrometer plots, 0.25m**2, under these conditions can be merely drip flows, or they can be larger flows during high-intensity rains when seepage is occurring simultaneously. An exploratory and developmental study of a drip-flow/low-flow nozzle/rotor flow-measuring system is presented. Evaluation of different nozzle configurations led to the development of a unique nozzle that incorporated a special drip diverter, an internal flow baffle, and drip-control silicone beads, used with the rotor of a Price current meter. The nozzle/rotor combination yields a rating curve with a resolution less than design requirements, and works well with flows as high as about 6 L/min, above design requirements. Seven linear segments fitted simultaneously comprise the rating curve. For flow rates less than 1 L/min the median residual error about the linear segments was 0.002 L/min with a standard deviation of 0.03 L/min. For flows greater than 1 L/min, the median error was -0.01 L/min with a standard deviation of 0.17 L/min. Unsteady flow tests with the nozzle showed that the rating curve and nozzle/rotor assembly work well, with the median error in volume of -15 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 speed need to be measured. 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.