National Sedimentation Laboratory Research Articles

The LTAR cropland common experiment in the Lower Mississippi River Basin.

The Lower Mississippi River Basin-Long-Term Agroecosystem Research Site (LMRB-LTAR) encompasses six states from Missouri to the Gulf of Mexico and is coordinated by the USDA-ARS National Sedimentation Laboratory, Oxford, MS. The overarching goal of LTAR is to assess regionally diverse and geographically scalable farming practices for enhanced sustainability of agroecosystem goods and services under changing environment and resource-use conditions. The LMRB-LTAR overall goal is to assess sustainable row crop agricultural production systems that integrate regional environmental and socioeconomic needs. Primary row crops in the region include soybeans, corn, cotton, rice, and sugarcane with crop rotations influenced by commodity crop price and other factors. The field-scale common experiment (CE) includes four row crop farms (26-101 ha) established in 2021 and 2023. Three fields are managed with alternative practices, including reduced tillage, cover crops, and automated prescription irrigation, and three fields are managed with prevailing farming practices, consisting of conventional tillage, no cover crop, and nonprescription irrigation. Treatment effects on crop productivity, soil quality, water use efficiency, water quality, and carbon storage are assessed. Research from the LMRB CE will deliver outcomes linked to overarching LTAR network goals, including innovative agricultural systems, strengthened partnerships, data management technologies, and precision environmental tools.

Experimental Investigation of a Moored, Circular Pipe Breakwater

Floating breakwaters are commonly used for shoreline protection in coastal areas and may offer a relatively cost-effective method for embankment protection in irrigation reservoirs. This study explored the potential use of a moored cylindrical floating breakwater design constructed from corrugated irrigation pipe and included a preliminary investigation of the performance of a floating breakwater that was subjected to regular waves of varying height and period in a laboratory wave tank. Experiments were carried out at the USDA Agricultural Research Service (ARS), National Sedimentation Laboratory in Oxford, Mississippi. The model breakwater was made of a 17.8-cm outer diameter, high-density polyethylene (HDPE) corrugated pipe section, filled with water and restrained under two mooring configurations using steel mooring lines attached to the floor of the flume, either vertically or at an angle on each side of the breakwater. The draft of the breakwater was varied between approximately 87% and 143% of the outer diameter by adjusting the tension of the mooring lines. Additional controlled experiments were performed using the same pipe section under fixed conditions. Waves were measured using capacitance-type wave staffs located both upwave and downwave of the breakwater, and mooring forces were measured using force gauges. Experimental results indicated that the floating breakwater arrangements studied show potential for usefulness in field application, as wave heights were reduced by as much as 60% in some cases. Cable-moored models performed best when fully submerged relatively close to the still water surface. Mooring line slackness reduced the effectiveness of the model in wave attenuation but also reduced the amount of force incurred by the cable mooring system. The cylindrical model best attenuated shorter waves of low to moderate steepness.

WAVE SETUP ON VEGETATED BEACH: LABORATORY EXPERIMENTS

In this study, wave height evolution and wave setup were measured in a laboratory wave tank with a sloping beach covered with rigid and flexible artificial vegetation under regular and irregular wave conditions. The experiments were conducted in a 20.6 m long, 0.69 m wide and 1.22 m deep wave tank at the USDA-ARS National Sedimentation Laboratory, Oxford, MS, USA. Regular and irregular waves were generated using a computer controlled piston type wave generator. A plane wooden beach with a 1:21 slope was constructed at the down-wave end of the wave tank, 11.5 m away from the wave paddle. Rigid vegetation was constructed out of wooden dowels and flexible vegetation was constructed using polyurethane tubes. Both vegetation models were 3.1 mm in diameter and 0.2 m long and had a population density of 3,182 stems/m2. The results were compared with those from experiments on a non-vegetated plane beach. Both rigid and flexible vegetation models reduced the wave height and wave setup substantially, but rigid vegetation typically performed better in reducing wave setup. For some of the experiments, no wave breaking was observed over the vegetated models, indicating that wave attenuation due to vegetation reduced the shoaling rate. For other experiments, wave breaking was observed and wave height attenuation was very small; however, wave setup was still significantly lower than in the plane beach experiments.

USDA-ARS National Sedimentation Laboratory: A Historic Perspective

Most authorities concede sediment from soil erosion to be the largest single stream pollutant. Physical damage from sediment includes reservoir storage loss, navigation channel filling, stream channel morphology alterations, ecological impacts, and clogging of drainage pathways. Ultimately, soil erosion is a very expensive problem. In the United States, accelerated soil erosion has been an ongoing issue since the establishment of the colonies. Through the initiative of great minds and the labor of countless individuals, the USDA was established and continues to fight for the people, providing assistance, guidance, and research. In this manuscript, the historical groundwork is laid for the establishment of the USDA-ARS National Sedimentation Laboratory (NSL) and a synopsis of NSL research is provided. This brief perspective of soil erosion research conducted on behalf of the people is but a small portion of the illustrious history of the USDA.

Acoustic measurement of suspensions of clay and silt particles using single frequency attenuation and backscatter

The use of ultrasonic acoustic technology to measure the concentration of fine suspended sediments has the potential to greatly increase the temporal and spatial resolution of sediment measurements while reducing the need for personnel to be present at gauging stations during storm events. The conversion of high-frequency attenuation and backscatter amplitudes to suspended silt and clay concentration has received relatively little attention in the literature. In order to improve the state of knowledge, a laboratory investigation was undertaken by the National Center for Physical Acoustics in cooperation with the USDA-ARS National Sedimentation Laboratory. In these experiments, two immersion transducers were used to measure attenuation and backscatter from 20MHz acoustic signals propagated through suspended clay (smectite and kaolinite) and silt particles. The resulting data includes attenuation values for a wide range of concentrations (0.3–14g/L) and particle sizes (0.03–14μm diameter). Attenuation curves for each particle were compared to the theoretical attenuation curves developed by Urick (1948) and Sheng and Hay (1988) for scattering as presented by Landers (2010) [5,11,12]. In addition, it was found that the backscatter signal could be used to discriminate between suspensions dominated by clay or silt.

Design and implementation of a passive acoustic bedload monitoring surrogate system

Various methods of employing passive acoustics to monitor bedload transport by listening to noise generated by colliding gravel have been explored in both the lab and field. Expanding upon this research, a hydrophone-based passive bedload-monitoring system was designed, tested, and deployed by researchers at the University of Mississippi and the National Sedimentation Laboratory in Oxford, MS. A series of laboratory experiments was used to measure the dependence of acoustic propagation on various parameters such as depth of the water and placement of the hydrophones. These tests employed a calibrated acoustic transmitter to broadcast tones of various frequencies across a gravel bed. Additional flume tests used a motorized carrier to drag rocks across the gravel bed, allowing a known sediment flux to be measured acoustically without any flow noise. The hydrophone-based system was deployed on the Trinity River, Weaverville, CA, in the summer of 2012 and the Elwha River, Port Angeles, WA, in the summer of 2013. Both deployments were co-incident with physical bedload measurements taken by Graham Mathews and Associates. The design of the acoustic system, methods used to analyze the data, results from laboratory experiments, and preliminary results from field data collection will be presented.

A Phenomenological Study of Sediment Transport in Shallow Overland Flow

<abstract> Abstract. Soil erosion is a highly complicated phenomenon consisting of many component processes. On upland areas, these processes are usually thought of as detachment and transport of soil particles by rainfall and surface flow. One of the most difficult processes to quantify is sediment transport. This process depends on a host of factors including sediment type, size, size distribution, and concentrations on one hand and the flow regime relative to rates and velocities on the other hand. The effect of all of these factors is influenced by soil surface cover and surface roughness conditions. The National Sedimentation Laboratory has in recent years conducted a series of basic laboratory studies to better understand sediment movement in shallow overland flow. These experiments involved super-critical flow regimes in a 7 m long and 10 cm wide channel in which sand-size material was seeded at the upstream end at controlled rates in a super-critical flow regime with Froude numbers >1. Particle sizes were coarse sand (1000 to 1400 μm), medium sand (600 to 850 μm), and spherical glass beads (600 to 1000 μm). Measurements included particle velocity and particle concentrations using photonic probes. Three modes of transport were noted: a saltation mode at low concentrations, sediment waves in which sediment moved in regularly spaced waves, and a meander mode. The latter two modes were attributed to particle interactions. The transported sediment was continuously collected at the downstream end by a rotating sampler. A curvilinear increase in transport rate was noted with an increase in seeding rate until a critical saltation limit was reached, after which a decrease in sediment movement occurred with the formation of organized sediment structures. The small structures were waves with spacings of the order of magnitude of tens of particle diameter, while the larger-scale meander had wavelengths of hundreds of particle diameters. The measured pseudo-equilibrium transport rates were smallest in the meander mode, followed by the wave mode. A relationship was obtained that described the transition from the saltation mode to the wave mode in terms of a critical solid concentration.

The National Sedimentation Laboratory: 50 years of soil and water research in a changing agricultural environment

AbstractThe papers in this issue are based on selected presentations made at a symposium convened to celebrate the 50th anniversary of the founding of the National Sedimentation Laboratory (NSL) of the US Department of Agriculture (USDA), Agricultural Research Service (ARS), located in Oxford, Mississippi. The mission of the NSL is to find solutions to problems associated with soil erosion and sediment delivery from upland areas, erosion and sedimentation in stream channels, the impact of sediment and other agricultural contaminants on the biological well‐being of receiving surface water bodies, and the loss of nutrients and agricultural chemicals from agricultural activities on the landscape. The papers in this issue present a broad overview of current research activities by NSL scientists and their colleagues. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Reply To Discussionby Xixi Wang, Assefa M. Melesse, Steve W. Kelsch, and Wanhong Yang1

JAWRA Journal of the American Water Resources AssociationVolume 42, Issue 6 p. 1715-1716 Reply To Discussionby Xixi Wang, Assefa M. Melesse, Steve W. Kelsch, and Wanhong Yang1 “Adapting Existing Models to Examine Effects of Agricultural Conservation Programs on Stream Habitat Quality”2 F. Douglas Shields Jr., F. Douglas Shields Jr. Respectively, Research Hydraulic Engineers, USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, Mississippi 38655-2267; and Assistant Professor, Department of Geography, University of North Carolina, Chapel Hill, North Carolina 27599-3220 (E-Mail/Shields: dshields@ars.usda.gov).Search for more papers by this authorEddy J. Langendoen, Eddy J. Langendoen Respectively, Research Hydraulic Engineers, USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, Mississippi 38655-2267; and Assistant Professor, Department of Geography, University of North Carolina, Chapel Hill, North Carolina 27599-3220 (E-Mail/Shields: dshields@ars.usda.gov).Search for more papers by this authorMartin W. Doyle, Martin W. Doyle Respectively, Research Hydraulic Engineers, USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, Mississippi 38655-2267; and Assistant Professor, Department of Geography, University of North Carolina, Chapel Hill, North Carolina 27599-3220 (E-Mail/Shields: dshields@ars.usda.gov).Search for more papers by this author F. Douglas Shields Jr., F. Douglas Shields Jr. Respectively, Research Hydraulic Engineers, USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, Mississippi 38655-2267; and Assistant Professor, Department of Geography, University of North Carolina, Chapel Hill, North Carolina 27599-3220 (E-Mail/Shields: dshields@ars.usda.gov).Search for more papers by this authorEddy J. Langendoen, Eddy J. Langendoen Respectively, Research Hydraulic Engineers, USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, Mississippi 38655-2267; and Assistant Professor, Department of Geography, University of North Carolina, Chapel Hill, North Carolina 27599-3220 (E-Mail/Shields: dshields@ars.usda.gov).Search for more papers by this authorMartin W. Doyle, Martin W. Doyle Respectively, Research Hydraulic Engineers, USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, Mississippi 38655-2267; and Assistant Professor, Department of Geography, University of North Carolina, Chapel Hill, North Carolina 27599-3220 (E-Mail/Shields: dshields@ars.usda.gov).Search for more papers by this author First published: 10 August 2007 https://doi.org/10.1111/j.1752-1688.2006.tb06032.x Discussion No. 04180D of the Journal of the American Water Resources Association 42(6):1711–1713 (Copyright © 2006). Paper No. 04180 of the Journal of the American Water Resources Association 42(1):25–33. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume42, Issue6December 2006Pages 1715-1716 RelatedInformation

Utilizing a modified surface roughness parameter for describing rough surfaces with an equivalent impedance

Previous experimental and field work has shown that rough surfaces may be modeled acoustically as though they were smooth surfaces with a modified surface impedance. In these works the roughness length scale used was a single parameter equal to 1/2 of the average height of the surface roughness elements. Recent experiments have suggested that this simple form for the roughness parameter may yield incorrect results for certain conditions such as grazing incidence over impermeable surfaces or sparsely scattered roughness elements. Modifications to this roughness parameter will be investigated. Specifically, the influence of the slope of the roughness elements, which is quantified using the standard deviation in height and the correlation length, will be investigated. [Work supported by the USDA ARS National Sedimentation Laboratory.]

Wave propagation in a unique class of inhomogeneous porous materials

A system of equations describing wave propagation in a unique class of inhomogeneous porous media is presented. The specific porous medium considered consists of an elastic matrix whose pores are filled with a viscous compressible fluid. The two components, solid and fluid, are microscopically homogeneous but the porous medium is inhomogeneous because the unperturbed porosity varies with position. Volume-averaging theorems are used to construct the general equations which form the basis for the analysis. It is shown that, in general, the presence of a porosity gradient introduces new coupling terms between the fluid and solid phases in the equations of motion. Since inhomogeneity usually implies anisotropy the problem is further specialized for the case of transverse anisotropy. It is further assumed that the wave propagates in the direction of the porosity gradient, which is a principal direction of the anisotropy. The equations are compared to recent work describing rigid framed grounds with exponential porosity profiles. [Work supported by ONR and USDA ARS National Sedimentation Laboratory.]