Browsing by Subject "erosion"
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Item Antecedent and anthropogenic influences on the Galveston Island shoreface(2009-05-15) Pitkewicz, Jennifer LynnGalveston Island, Texas has been experiencing high rates of erosion in recent years, spawning an interest in developing complex beach management programs. However, before any effective management project can be implemented we must understand all of the processes that control the shoreface. It is only recently that scientists have begun to recognize the importance of the role that the geologic framework plays on the coastal evolution of the shoreline. In this region, it is the antecedent geology as well as the anthropogenic obstructions which are the key factors controlling the formation of the modern shoreface. This study defines the extents to which these antecedent and anthropogenic factors influence the shoreface as well as refines the geologic interpretations offshore of Galveston Island. Using sidescan sonar, CHIRP seismic sonar, multibeam bathymetry data and sediment cores, the shoreface and subsurface geology were modeled. It was determined that the thickness, extent and slope of the modern sediment in the nearshore environment is controlled by the topography of the Beaumont Clay, a consolidated clay deposited during the Pleistocene. Anthropogenic obstructions, including the Galveston Seawall, groin and jetty system, have changed the sediment transport patterns in the region and have created a system of erosion and accretion not only along the shoreline, but for the entire length of the shoreface.Item Erosion and Sedimentation on the Carnegie Ridge, Eastern Equatorial Pacific(2014-11-17) Brooks, Caroline KellyThe Carnegie Ridge is an aseismic ridge that bounds the south flank of the Panama Basin. Dynamic sedimentation around Carnegie Ridge is shown by evidence of erosion, dissolution and re-deposition of pelagic sediments where erosive episodes have carved out relict landscapes. I examine three aspects of these features: 1) What are the mechanisms involved in the erosive episodes; 2) Can the ages of the erosive events be constrained; and finally 3) Can the transport mechanism be identified? The extent of erosion and re-deposition was studied during the R/V Melville cruise MV1014 from October to November 2010 to compare with geochemical estimates of sediment focusing. The MV1014 cruise acquired geochemical, geological and geophysical data to compare with earlier surveys and scientific drilling. Large-scale erosion, presumably driven by massive, density-driven deepwater spillover events from the Peru Basin, created a prominent valley named Sand Dune Valley in the study area. A second, smaller valley, known as Western Valley, was likely formed by medium-scale erosion catalyzed by a ridge jump with subsequent normal faulting forming a fault scarp which has intensified near-bottom currents. Smaller-scale erosional events created small-scale surface sediment truncation. Utilizing a seismic stratigraphy developed by comparing seismic horizons to the sediment columns at DSDP Site 157 and ODP Site 846, and exposure of diagenetic chalk along the valley floors allowed a reconstruction of the timing of these highly erosive episodes. Two major erosive episodes are proposed to have occurred at ~5 Ma and ~3Ma which removed as much as 75 km3 of sediment. The erosive episodes may be linked to a ridge jump of the Galapagos hotspot at ~5-4 Ma and the final closing of the Isthmus of Panama ~3Ma. Sediment transport regimes for the Quaternary were determined using horizons dated at 2 Ma (PL-2), 1.7 Ma (PL-1) and 84 ka (Q-84). Isopachs created using the three horizons concluded that the dominant transport regime occurs to the NW of the study area with strong lateral transport to the sides of the valleys.Item Flow assurance and multiphase pumping(2009-05-15) Nikhar, Hemant G.A robust understanding and planning of production enhancement and flow assurance is required as petroleum E&P activities are targeting deepwaters and long distances. Different flow assurance issues and their solutions are put together in this work. The use of multiphase pumps as a flow assurance solution is emphasized. Multiphase pumping aids flow assurance in different ways. However, the problem causing most concern is sand erosion. This work involved a detection-based sand monitoring method. Our objectives are to investigate the reliability of an acoustic sand detector and analyze the feasibility of gel injection as a method to mitigate sand erosion. Use of a sand detector coupled with twin-screw pumps is studied under varying flow conditions. The feasibility of gel injection to reduce slip and transport produced solids through twin-screw pump is investigated. A unique full-scale laboratory with multiphase pumps was utilized to carry out the experimental tests. The test results indicate that acoustic sand detection works in a narrow window around the calibration signature. An empirical correlation for predicting the twin-screw pump performance with viscous fluids was developed. It shows good agreement in the practical operational limits ? 50% to 100% speed. The results indicate that viscous gel injection should be an effective erosion mitigation approach as it reduces slip, the principle cause of erosive wear. To correlate the performance of viscous fluid injection to hydroabrasive wear, further experimental investigation is needed.