Author
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Replogle, John |
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Submitted to: Journal Hydrologic Engineering
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/10/2008 Publication Date: 1/25/2009 Citation: Replogle, J.A. 2009. Tests of concepts for streamflow sampler design. American Society of Civil Engineers. Journal of Hydrologic Engineering. 14(1):65-74. Interpretive Summary: Total-load sampling of stream sediments is of particular interest in forest fire areas because of the impact of increased erosion on reservoirs and the need to evaluate imposed watershed treatments. Sediment monitoring in streams, particularly total-load sampling has been a perpetual problem. Usually a combination of three devices are used, one for bedload, another for suspended load, and a third for measuring channel flow rate. A total load sediment sampler that can perform all three of these functions is proposed. It requires installation in sites that can provide a step overfall height about equal to the maximum channel flow depth. The concept is based on a long, wide, and moving conveyor belt, with slots in the belt, onto which the stream to be sampled discharges. All flow drops through the slots, and with equal sized slots each must catch a similar proportion of the total flow and the included sediments. Hence, only one slot needs to be collected. For practical purposed, a test rack with several slots represents a short section of the total conveyor belt, and is traversed left and right through the falling nappe. The concepts are extended to the condition with a stopped belt where several sampling-slot rack sections are equally spaced beneath the overfalling water. A 'proof of concept' sampler assembly of the stopped-belt system performed well. The sample catch across the stream was within about 4% of expected, which is not as accurate as the traversing system, but offers a total load sampling method even where motorized equipment is difficult to install or where electric power is not available. Prospective users of the sampling systems include the Natural Resources Conservation Service (NRCS), Environmental Protection Agency (EPA), U.S. Bureau of Reclamation (USBR), the Army Corps of Engineers (COE), and other soil and water conservation agencies in various states. Technical Abstract: Total load sampling of stream sediments is of particular interest in forest fire areas because of the impact of increased erosion on reservoirs and the need to evaluate imposed watershed treatments. Total-load sampling has been a perpetual problem in sediment monitoring. Usually a combination of bed load sampling devices, suspended load suction samplers, and some kind of flume, for total flow rate, is used. A total load sediment sampler that can perform all three of these functions is proposed. It requires installation in sites that can provide a step overfall height about equal to the maximum channel flow depth. The concept is based on a long, wide moving conveyor belt, with slots, onto which the stream to be sampled discharges. All flow drops through the slots, and with equal sized slots each must catch a similar proportion of the total flow. Hence, only one slot needs to be collected. It is practical to replace the conveyor belt with a rack having several slots that represent a short section of the total conveyor belt, which is then traversed back and forth on a track through the falling nappe. Laboratory tests of this proposed sampling-assembly rack indicated that its constructed width is related to the channel depth and the sum of the slot openings. When the rack slot-width sum is more than half the channel overfall depth, the system under sampled from 0% to 2 % but when it is less than one-third of the over fall depth, the system under sampled by over 8%. The concepts are extended to the condition with a stopped belt where several sampling slots are equally spaced beneath the over fall. A 'proof of concept' sampler assembly of the stopped-belt idea was built and tested. The sample catch across the stream was within about 4% of expected, offering a total load sampling system where motorized equipment is difficult to install, or electric power is not available. General and specific design and construction suggestions are presented. Further extensions of the concept to test set-ups for irrigation sprinkler uniformity tests are discussed. |
