Effect of flushing velocity and elapsed time on sediment transport in driplines

摘要

Dripline flushing is a maintenance procedure that is recommended for all microirrigation systems. However, flushing velocity and flushing duration, which particularly affects the design and management of subsurface drip irrigation (SDI) systems, havenot been studied extensively. A laboratory study was conducted at Kansas State University with a 10 m transparent pipe simulating a SDI dripline. Three different sediments with sizes up to 500 pm were introduced into the pipeline and their distribution along the pipeline was analyzed under different flushing velocities over various times. Head loss under the conditions of this study increased exponentially with increased flushing velocity suggesting that the flow regimes could be characterized between moving beds and heterogeneous flow. The percentage of pipeline blockage was logarithmically related to the flushing velocity, with greater than 30% of the pipeline occupied by these larger sand sediments when the flushing velocity was less than 0.3 m/s. Although flushing velocities at or near the calculated deposition velocity could remove the majority of the sediments with a short duration of 15 minutes or less, flushing velocities approximately 45 to 65% of the deposition velocity could achieve similarsediment removal with longer flushing duration (up to 180 minutes). The ASAE EP-405 recommended minimum flushing velocity of 0.3 m/s still appears adequate for most microirrigation systems operating under typical conditions. Designers are encouraged tocalculate the deposition velocity for new microirrigation systems and to use it as a flexible guideline to assess the adequacy of flushing. End-users are encouraged to extend the duration of flushing for perhaps as long as five minutes after the initialconcentration of sediments are removed to improve overall flushing. Further research is warranted to evaluate flushing velocity, but the results of this study should be representatively instructive of the phenomenon of sediment transport in microirrigation driplines during flushing.