Comparison of drip-flow/low-flow measuring devices for infiltrometer runoff measurements

Runoff is generated on landscapes in a deterministic and random, bur unquan tifiable manner; and measurements of the spatial variability of infiltratio n and seepage under natural-precipitation conditions are highly desirable. Runoff from small natural-precipitation infiltrometer plots (0.25 m(2)) und er natural conditions can be merely drip flows, or they can be larger flows when runoff is produced simultaneously from high-intensity rains and seepa ge. 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 Pric e current meter, in combination with a unique nozzle that incorporated a dr ip 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 similar to 6 L min(-1), greater than design requirements. A combined function using li near segments for low flows, and a 4th degree polynomial for high flows, co mprised the raring curve. The average residual error about the function was 0.113 L min(-1). Unsteady pow tests with the nozzle showed that the rating curve and nozzle/rotor assembly worked well, with the median error in volu me of -21 ml for 12 synthesized "events". The device is a standalone measur ing system that can be placed anywhere on the landscape, and only electrica l pulses, representing rotor-rotation speed require measurement. The nozzle /rotor system can be used for other applications in which drip and low flow s need to be measured, such as for rain gauges, percolation flows from lysi meters, spring flows, etc.