Measurement of bedload discharge in nine Illinois streams with the Helley-Smith sampler

Abstract

Samples collected with the Helley-Smith bedload sampler can provide useful information about transport of sand-size sediment in Illinois streams. Samples provide the basis for bedload-discharge rating curves for the Rock and Kaskaskia Rivers and Henderson Creek. Rock River data cover a wide range of flow conditions and yield a well-defined curve. Data from Henderson Creek cover a much narrower range of flow conditions and show wide scatter. Only three measurements define the Kaskaskia River rating curve, but these cover a range of flow conditions and fall on a straight line. Comparison of measured bedload discharge with bedload discharge computed for selected flow conditions from channel characteristics allows the selection of an appropriate indirect method for determining bedload discharge for the Spoon, Kishwaukee f and Edwards Rivers. No one indirect method best represents bedload discharge in studied streams. No bedload-discharge rating curve was developed Jfor the La Moine River, because the two measured bedload discharges are not sufficient for development of a rating curve and do not agree well with discharges computed by any of the three indirect methods. The dominant size of bedload particles in all streams sampled is in the range from 0.25 to 0.50 millimeters. Sampler efficiency has not been determined for grains finer than 0.50 millimeters and bedload-discharge rating curves presented should be used with caution. Data from two of nine streams sampled give results which cannot be used at this time. Clogging of the sample-collection bag by fine sediment may have been significant in the Green River, and because the effect of clogging has not been defined, the data cannot be interpreted at this time. Samples collected in the Vermilion River were judged not to be representative of the true bedload transport, possibly because large bed material grains or high flow velocities interfered with the operation of the sampler. INTRODUCTION Erosion of soil from farmland and deposition of sediment in navigational channels and reservoirs are major environmental issues in Illinois. Accurate measurement of sediment transported by streams is critical to evaluation of these issues. Although there are well-established techniques and equipment for measuring suspended sediment/ there is no widely accepted procedure for measuring bedload. The Helley-Smith sampler (Helley and Smith, 1971) is one instrument that has come into wide use for measurement of bedload, although tests on its sampling efficiency are still being conducted. In 1978, the U.S. Geological Survey began sampling bedload in Illinois streams with the Helley-Smith sampler to provide data to estimate the volume of sand-size material entering the Mississippi River and its tributaries, the Rock and Illinois Rivers. The first sampling sites were on the Rock River, Henderson Creek, and the Green River. In 1980, sites on the Vermilion River and the Edwards River were added to the sampling program. In 1981, sites on four additional streams were added the La Moine, Kaskaskia, Spoon, and Kishwaukee Rivers. All sampling sites are at long-term Geological Survey stream-gaging stations (fig. 1 and table 1). Purpose and Scope The purpose of the present study was to analyze the bedload discharge measurements, to develop bedload-discharge rating curves for those sites with sufficient record, to determine the usefulness of each sampling site for measurement of bedload discharge, and to evaluate the suitability of the Helley-Smith sampler to Illinois streams. Methods of extending the rating curves or developing curves for stations with few measurements also were to be investigated, using bedload discharges computed from channel geometry and bed material characteristics for selected flow conditions. Three available methods for such computations (indirect methods) were chosen: the Meyer-Peter, Muller equation (Meyer-Peter and Mflller, 1948), the Einstein method (Einstein, 1950) and the Schoklitsch equation (Shulits, 1935). In this report, a description of methods used to measure and compute bedload discharge is followed by the description and evaluation of each bedload sampling site. For each site, channel characteristics that relate to sediment transport are described, measured and computed bedload discharge are presented, suspended-sediment samples are discussed in relation to bedload samples, a bedload discharge-rating curve is presented if one was developed, and an evaluation of the site in terms of bedload sampling is given. A final section discusses the more important points brought out in the analysis. Acknowledgments The bedload sampling was done in cooperation with the U.S. Army Corps of Engineers, Rock Island and St. Louis Districts. Data analysis was carried out in cooperation with both the U.S. Army Corps of Engineers and the Illinois Department of Transportation, Division of Water Resources. The assistance of Charles W. Farnham, U.S. Army Corps of Engineers, Rock Island District, who provided unpublished data used to determine water surface slopes for the Rock River, is gratefully acknowledged. The thoughtful report review of Claude N. Strauser, U.S. Army Corps of Engineers, St. Louis District, was also appreciated.