Joseph Gailani

Erosion Measurements in Linear, Oscillatory, and Combined Oscillatory and Linear Flow Regimes

Abstract Many contaminated sediments and dredged material mixtures of cohesive and non-cohesive sediments occur in wave-dominated environments. In-situ analysis is imperative in understanding the erosion and transport of these sediments. Recent research efforts have developed a flume with unidirectional flow that can measure in-situ sediment erosion with depth (SEDflume). However, the flow regime for the SEDflume has limited applicability to wave-dominated environments. Therefore, a unique device, called the SEAWOLF flume, was developed and used by Sandia National Laboratories to simulate high-shear stress erosion processes experienced in coastal waters where wave forcing dominates the system. The SEAWOLF is capable of testing in-situ or laboratory prepared cores. Erosion rates of cohesive and non-cohesive sediments prepared in the laboratory were determined in oscillatory and combined oscillatory and linear flow regimes. Results of these tests were compared to results from the unidirectional SEDflume. Although maximum shear stresses for oscillatory flows were as high as 7 Pa for the tests, the associated erosion rate for specific sediment over the entire wave cycle were comparable to much lower shear stresses found for constant, linear flows. For example, sediment exposed to a maximum of 7 Pa over a 15 s period resulted in erosion rates similar to results for a constant linear shear stress of 3.4 Pa. Analysis of results for all sediments tested led to a determination of values for an effective shear stress that relates wave-induced erosion to linear flow induced erosion.

Effects of Arroyo Sediment Influxes on the Rio Grande River Channel near El Paso, Texas

Arroyos that flow into the Rio Grande River channel along the U.S.–Mexico border provide intermittent influxes of sediment that may obstruct the channel and cause overflow as well as sedimentation problems downstream. These phenomena were studied using a recently developed, unique, in situ method for measuring the erosion properties of sediments with depth and at high shear stresses. Results of the investigation confirm that the arroyo sediments can affect the channel of the Rio Grande by introducing sediments that are more difficult to erode compared to those already present. Two sites were mapped and characterized in terms of vegetation and soil distribution. Sediment samples were collected, and erosion rates, mineralogy, and sediment grain-size distributions were determined. Results showed that large flows in both arroyos were capable of obstructing the Rio Grande channel by introducing sediments that were more difficult to erode than the existing channel sediments.

The SEAWOLF Flume: Sediment Erosion Actuated by Wave Oscillations and Linear Flow

Sandia National Laboratories has previously developed a unidirectional High Shear Stress Sediment Erosion flume for the US Army Corps of Engineers, Coastal Hydraulics Laboratory. The flow regime for this flume has limited applicability to wave-dominated environments. A significant design modification to the existing flume allows oscillatory flow to be superimposed upon a unidirectional current. The new flume simulates highshear stress erosion processes experienced in coastal waters where wave forcing dominates the system. Flow velocity measurements, and erosion experiments with known sediment samples were performed with the new flume. Also, preliminary computational flow models closely simulate experimental results and allow for a detailed assessment of the induced shear stresses at the sediment surface.

Shear Stress Measurements and Erosion Implications for Wave and Combined Wave-Current Generated Flows

AbstractSediment transport in wave-dominated environments is of great interest for dredged material placement, contaminated sediments, habitat protection, and other issues. The shear stress at the sediment-water interface during a wave event is an important parameter in determining erosion and transport for both experimental and model simulation applications. Sandia National Laboratories has developed a laboratory and field device called the sediment erosion actuated by wave oscillations and linear flow (SEAWOLF) flume in which high-resolution, particle-image velocimetry (PIV) has been applied to investigate turbulent flow shear stresses for a variety of flow conditions. The results of the PIV analysis for a wave cycle demonstrate a fully developed turbulent flow, relaminarization, and an explosive transition back to turbulence. In many cases, the results of the flume tests did not show good agreement with previously reported computational fluid dynamic results and existing theories, such as Blasius, for ...

Effects of Bed Load and Suspended Load on Separation of Sands and Fines in Mixed Sediment

An adjustable shear stress straight flume commonly used to measure cohesive sediment erosion rates has been modified to include downstream bed load traps. The new flume can be used not only to measure erosion rates, but also to analyze and quantify the modes of transport for this complex problem. The new device was used to study transport modes of quartz particles ranging in size from 19 to 1,250 μm . As expected, the traps captured the coarse material (bed load) and the fine material bypassed the traps (suspended load). Transport properties of natural sediments from three locations were also studied. Fine sediments with little or no sand eroded as aggregates which maintained their integrity in the flume channel while moving as bed load into the traps. Natural sediments that included high percentage of sand also eroded as aggregates. However, these aggregates quickly disaggregated. Sand moved as bed load and fell into the traps while fine particles moved predominately in suspension.

Develop accurate methods for characterizing and quantifying cohesive sediment erosion under combined current-wave conditions : Project ER 1497

Abstract : Aquatic cohesive sediments are often the final receptor of contaminants released by Department of Defense (DoD) activities. In estuaries, harbors, and channels, fine sediments can be mobilized and transported by the combined action of both relatively steady currents (forced by river flow, tides, and wind) and by the larger unsteady bottom shear stresses associated with higher-frequency oscillatory wave motions (either wind- or vessel-generated waves). Methods to measure contaminated sediment stability and erosion as influenced by wave processes are critical to assessing contaminant fate and associated risk as well as evaluating remediation options. This research focused on calibrating and verifying the applicability of a prototype flume designed to measure erosion of fine-grained cohesive sediment under combined unidirectional and superimposed oscillatory bottom shear stress. These are similar to the shear-stress conditions that exist in wave-current environments. This research will provide more accurate methods for assessing contaminated sediment stability for many DoD and Environmental Protection Agency managed contaminated sediment sites.

Fundamentals of Sediment Transport

The goals of this chapter are to (1) describe the processes that govern the transport of sediment in surface waters, (2) provide guidance for use in assessing and/or quantify sediment transport, and (3) describe the procedure to use in modeling sediment transport. A basic knowledge of these topics is requisite to understanding many of the contaminant transport processes important in sediments due to the strong particle associations of most contaminants of concern. This chapter starts with brief overviews of sediment transport – sedimentation related problems and how sediment in surface waters responds to the forces that cause water movement. Basic sediment transport processes are also defined. Section 3.2 describes pertinent properties of sediments, and transport processes for cohesive sediments. Section 3.3 provides guidance to use to assess and/or quantify sediment transport. It is often necessary for remedial project managers to conduct a Sediment Transport Assessment in support of a remedial alternatives evaluation for contaminated sediment Superfund sites. The assessment involves using a systematic approach that (1) identifies the processes and mechanisms that might result in erosion, (2) determines the most appropriate methods to use to assess sediment resuspension and deposition, and (3) quantifies sediment resuspension and deposition rates under varying flow conditions. Section 3.4 provides an overview of the procedures following in performing a sediment transport modeling study. These procedures or steps include: (1) model selection and setup, (2) hydrodynamic modeling, (3) sediment transport modeling, (4) calibration and validation of the models, and (5) analyzing model results.

Turbulence Structure in Oscillating Channel Flow

The structure of turbulence in an oscillating channel flow with near-sinusoidal fluctuations in bulk velocity is investigated. Phase-locked particle-image velocimetry data in the streamwise/wall-normal plane are interrogated to reveal the phase-modulation of twopoint velocity correlation functions and of linear stochastic estimates of the velocity fluctuation field given the presence of a vortex in the logarithmic region of the boundary layer. The results reveal the periodic modulation of turbulence structure between large-scale residual disturbances, relaminarization during periods of strong acceleration, and a quasisteady flow with evidence of hairpin vortices, which is established in the acceleration phase and persists through much of the deceleration period.

Rio Grande Erosion Potential Demonstration - Report for the National Border Technology Program

This demonstration project is a collaboration among DOE, Sandia National Laboratories, the University of Texas, El Paso (UTEP), the International Boundary and Water Commission (IBWC), and the US Army Corps of Engineers (USACE). Sandia deployed and demonstrated a field measurement technology that enables the determination of erosion and transport potential of sediments in the Rio Grande. The technology deployed was the Mobile High Shear Stress Flume. This unique device was developed by Sandias Carlsbad Programs for the USACE and has been used extensively in collaborative efforts on near shore and river systems throughout the United States. Since surface water quantity and quality along with human health is an important part of the National Border Technology Program, technologies that aid in characterizing, managing, and protecting this valuable resource from possible contamination sources is imperative.