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United States Department of Agriculture

Agricultural Research Service

Title: Water Sampler and Flow Measurement for Runoff Containing Large Sediment Particles

Author
item Bonta, James

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 1998
Publication Date: N/A

Interpretive Summary: Representative sampling of small flows of runoff water that have large sediment concentrations and large rock particles is difficult. This is because the larger particles of sediment tend to be transported in the bottom of the flow, especially rocks. Splitting the flows to obtain a representative sample is difficult. A new sampler was designed to sample sediment-laden flows containing large rock particles. The approach to the sampler is a flow-measuring device that mixes the flow well. The entire mixed flow is diverted on a timed basis to obtain one flow-weighed, representative composite sample. The sampler works well in indoor and outdoor applications, and has utility for erosion studies where large particles of sediment require sampling, such as in erosion studies in strip mines. Recommendations presented will make the sampler more reliable. The sampler can be used in other applications where small flows need to be sampled, such as with rainfall simulators and lysimeter runoff and percolation. The results will be useful to Federal and State, and university researchers.

Technical Abstract: A flow-measuring and composite water-sampler system was needed for sampling sediment-laden flows containing large rock particles from strip-mine spoil erosion plots. The median percentage of soil particle sizes greater than 2 mm was 25%. The modified drop-box weir was used for measuring flows, and for providing a well-mixed water and sediment flow that could be sampled. A new ("diverter") sampler was designed to divert the entire flow from a waste position to a sample position, and precluded the need to subsample (split) the weir flows. Indoor testing of the sampler showed the sampler worked well with the modified drop-box weir. Field evaluation showed the sampler and drop-box weir worked well under natural rainfall when all components were working properly. Divert times measured with a stop watch were not necessarily representative of actual sampler fractions. Divert times are useful for initial system setup and quality control purposes. The modified drop-box weir worked well, but occasionally larger rock particles would lodge in the head-measuring slot. Recommendations for improvement in sampler and weir operation are given. Use of the sampler in other applications is also discussed.

Last Modified: 10/20/2014
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