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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #115194

Title: SPECTRAL ANALYSIS OF TURBULENT FLOW AND SUSPENDED SEDIMENT TRANSPORT OVER FIXED DUNES

Author
item VENDITTI, JEREMY
item Bennett, Sean

Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 8/20/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sediments eroded from agricultural areas due to farming practices continuously enter streams and rivers. The transport and deposition of these solids and their associated agrochemicals can have detrimental effects on water quality, ecology, and river flow processes such as conveyance and the severity of floods. Traditionally, the transport of suspended solids has been related to simple characteristics of the flow, but little quantitative information exists that defines this link. A laboratory study was conducted to determine how the characteristics of the flow can be related to the transport of suspended solids. This study used a laboratory channel with triangular-shaped roughness elements on the bed ad devices that could measure fluctuations in velocity and the concentration of suspended solids. The data showed that the fluctuations in velocity and the suspended solids with time were very similar. The goal of this research is to better understand the processes controlling the transport of suspended solids in rivers. This information is important to federal agencies in their assessment of sedimentation problems and their prediction of total sediment load.

Technical Abstract: Measurements of turbulent fluctuations in velocity and suspended sediment concentration were obtained synchronously over fixed, two- dimensional dunes in a sediment-starved flow. Contour maps of turbulent flow parameters demonstrate that the flow separation cell and a perturbed shear layer are the main sources of turbulence production. Spectral analysis reveals that peak spectral energies generally occur at 1 to 2 Hz for the streamwise velocity component and 2 to 4 Hz for the cross-stream and vertical velocity components. Peak spectral energies for suspended sediment concentration occur near 1 Hz throughout the flow. Squared-coherency values for co-spectral analysis of velocity and sediment concentration are insignificant. Integral time-scales for velocity range from 0.20 s for the streamwise component to 0.06 s for the cross-stream and vertical components. Integral length scales for velocity range from 0.065 to 0.135 m for the streamwise component, which are comparable to flow depth, and from 0.020 to 0.030 m for the cross-stream and vertical components, which are comparable to dune height. For suspended sediment concentration, integral time and length scales are similar to the streamwise velocity component.