Browsing by Subject "Erosion"

Now showing 1 - 15 of 15

Air fall ash and tuff
(2009-03) Barker, Daniel S.
Erosion of a sharp density interface by homogeneous isotropic turbulence
(2019-05) Lagade, Joel Albano; Johnson, Blair Anne
Desalination, commonly used for potable water production, generates brines that are ultimately released back into the environment. Desalination brines discharged into coastal regions with weak currents and mild bathymetry, such as the Gulf of Mexico, do not necessarily mix with surrounding natural waters and remain stably stratified (Hodges et al., 2011). Because dense immobile saline layers from these discharges can cause hypoxia and threaten local ecosystems, we are conducting an experimental study to investigate the effect of turbulence on a sharp density interface to identify mechanisms of turbulence that promote and/or inhibit interfacial erosion. There remains a gap in the literature regarding the interaction of mean shear free homogeneous isotropic turbulence with a sharp density interface, a critical component in understanding dynamics across a stably stratified system. To address this fundamental question, we use randomly actuated synthetic jet arrays (RASJA - Variano & Cowen (2008)) to generate homogeneous isotropic turbulence, absent mean shear, above a dense fluid layer. The Richardson number is varied to ascertain the thresholds at which the density interface erodes and mixing between the stratified layers occurs. As in Johnson & Cowen (2018), who characterized the mean shear free turbulent boundary layer at solid and sediment beds, particle image velocimetry is used to complete a statistical analysis of the turbulent flow field at and above density interface. Simultaneous laser induced fluorescence measurements are obtained to capture erosion, sharpening, and mixing. Statistical metrics of the turbulence are coupled with the evolution of concentration profiles and mixing, which is determined by measuring temporally resolved isopycnal displacements. In the current work, we provide the first experimental data to test quantifying entrainment across stratified fluids as described and applied in direct numerical simulation studies by Zhou et al. (2017). By examining the interplay between mean shear free homogeneous isotropic turbulence and a sharp density gradient, we aim to deduce under what environmental conditions it is sustainable to discharge brine into relatively quiescent flows, considering key factors such as ambient turbulence and relative salinity variance between the brine and surrounding waters.
Gravity Work
(2009-04) Barker, Daniel S.
Hillslope seepage erosion, spring sapping, and knickpoint migration : evidence of groundwater sapping Middle Trinity Aquifer, Honey Creek Basin, Comal County, Texas
(2005) White, Kristin Miller; Sharp, John Malcolm, Jr., 1944-
Geomorphic features within Honey Creek basin are consistent with formation by spring sapping which is the erosion of soil and rock by groundwater. Geomorphic evidence includes: swallow holes (stream swallets) that pirate spring discharge into the subsurface, groundwater piping and seepage along weathered marly slopes, headward erosion at knickpoints and spring orifices, fracture controls on incised streams, and generation of alluvium from scarp collapse. Erosion pins were used to measure erosion and sediment accumulation on marly slopes. Aerial photograph interpretation, Arcview GIS, 3D Analyst, and Geoorient techniques were used to evaluate the physical hydrogeologic features (potentiometric surface, karst springs, recharge features, knickpoints, and fractures) and their relationship to surface erosion patterns. Honey Creek basin is underlain by interbedded marl and limestone units of the Cretaceous Middle Trinity aquifer. Springs and caves provide a window into subsurface processes, including flow direction along preferential flowpaths and perched water tables. Precipitation affects spring discharge and water table levels in both stratigraphically perched aquifers and deeper aquifers. Upland karst features allow recharge of surface water to focus flow into spring conduits that rapidly discharge into streams following intense precipitation. Spring conduits and upland creeks feed into intermittent tributaries, then into perennial channels of Honey Creek and the Guadalupe River. Perched aquifers focus flow toward intermittent springs, while perennial springs are supported by a deeper regional system. Transmissivity is high within rock units that contain solutionally enlarged fractures and spring conduits. Elsewhere, the transmissivity of limestone and marl is generally low so that preferred flow pathways concentrate spring discharge where hillslope erosion has intersected bedding planes, conduits, and fractures. As springs discharge into local surface water bodies, erosion occurs at the spring orifices causing headward erosion along the pathways. Dominant fracture trends within the basin are generally aligned with the northeast-trending Balcones Fault Zone and a secondary fracture distribution to the northwest. These trends strongly influence spring location and sapping
Impacts of unpaved roads on runoff and sediment production in Culebra, Puerto Rico
(2019-12) Mclaughlin, Preston Wyatt; Ramos-Scharrón, Carlos E.
Terrigenous sediment delivery into tropical coastal waters from unpaved road development is a key stressor influencing the global decline of coral reef ecosystems. Higher turbidity of coastal waters from this terrigenous sediment can result in smothering, bleaching, and reduced photosynthetic activity for coral reefs. Since the 1990’s, the small Puerto Rican municipality of Culebra has experienced significant rates of land development, and an expansion of its unpaved road network, which has been identified as the contributing factor responsible for the continuous decline of the island’s live coral cover. This research focuses on quantifying runoff, and sediment production rates for Culebra’s unpaved road and undisturbed surfaces at the plot (~3 m²), and watershed (~1 km²) scales. A total of 46 rainfall-runoff simulations, and 119 Guelph permeamter tests were conducted to collect this data. Results indicate that only 1.2 mm of rainfall is required to produce overland flow on unpaved roads. At least 7.9 cm of rainfall is needed to generate overland runoff on undisturbed hillslopes. Erosion rates were greatest for recently graded road segments, with an average annual erosion rate of 54.65 Mg ha⁻¹ yr⁻¹. Unpaved roads that have been left ungraded for over one year erode at about half this rate (29 Mg ha⁻¹ yr⁻¹). Undisturbed surface erosion was negligible in comparison, with a mean rate of 0.05 Mg ha⁻¹ yr⁻¹. Based on this data, there are up to five orders of magnitude difference between erosion rates of graded unpaved roads and natural soil surfaces in Culebra. Within one year, a total of 335 storms occurred between. Around a quarter of all recorded storms produced overland runoff on unpaved road surfaces. Hurricane Maria was estimated to be the only storm that year to generate overland flow on undisturbed surfaces. ArcGIS was used to identify segments of road most likely to transport overland runoff to the coastline, as well as segments generating the most erosion. Sediment production rates for the study areas ranged between 3.1 and 10.9 Mg yr⁻¹. This information is beneficial towards documenting the overall effectiveness of erosion mitigation structures built to reduce terrigenous sediment transport produced from these roads
Joints in igneous rocks
(2009-03) Barker, Daniel S.
Kinematic restoration of the Costa Rican convergent margin : exploring the effects of a rough subducting seafloor
(2020-12) Gose, Brooklyn Nicole; Bangs, Nathan Lawrence Bailey; Barnes, Jaime Danielle
The Costa Rican convergent margin has been a primary site for studies of subduction erosion because it is a documented example of an erosional subduction zone with tectonic erosion by seamount, plateau, and ridge collision. Previous work has explored both modern-day and historical evidence for ongoing subduction of a rough seafloor at Costa Rica that has left erosional scars on seafloor bathymetry, but the impacts on slope sedimentation, the tectonic removal of pieces of the upper plate, and the long-term sub seafloor geologic record left behind from these events is poorly understood. To further explore the effects of subducting plate bathymetric features on the long-term structural and stratigraphic record, this study used three-dimensional kinematic restoration to examine trends in uplift and subsidence over time and potentially identify periods of seamount subduction. This study utilized a 3D seismic reflection volume along with interpreted well log data to create a finite element model of major structural and stratigraphic features within the study region. The 3D model was then kinematically restored using Paradigm’s SKUA-GoCAD Kine3D, providing a 2.2 Myr history of three-dimensional motion for the modeled area. Results start at 2.2 Ma when subaerial uplift elevated the margin 1.2 km corresponding to a regional unconformity established from drilling. This event was followed by a period of subsidence before a short pulse of uplift occurred in a ~9 km wide circular area on the shelf. Recent (1.3Ma – 0Ma) enhanced subsidence in the same region has led to the formation of a circular bathymetric depression on the seafloor that resemble similar features farther north interpreted as seamount impacts. This leads me to conclude that a subducted seamount (~9 km at the base, 1.5 km height) passed through the study region ~1.8 Ma leaving behind a weakened region of underplated sediments. Over time, basal erosion of this area has removed 180 km³ of material. The models reveal that seamount subduction causes erosion both by transfer of material from the upper plate in front of the seamount, and by weakening the upper plate to promote erosion in the wake of the seamount, resulting in distinctive seafloor indentations.
Lava domes
(2009-03) Barker, Daniel S.
Mass balance of Martian sedimentary fans and valleys
(2016-05-20) Shover, Katherine Rose; Holt, John W., Ph. D.; Kim, Wonsuck; Moscardelli, Lorena
Dozens of sedimentary fans have been identified on Mars and have been interpreted as alluvial fans or deltas. However, the extent to which these deposits represent the complete eroded mass of the valleys that drain into them, the extent to which erosion has removed fan material, and the extent to which sediment bypass occurred during fan deposition into a distal water body remain unknown. This study investigates the role of emplacement versus modification following deposition in a catalog of martian fans to determine the extent to which such deposits have been preserved. A mass balance approach was taken; by calculating the present volumes of fans and the valleys feeding them, the percentage of eroded valley sediment that has accumulated and remained within the fan deposits can be determined. Based on measurements of 32 valley and fan volumes calculated using CTX stereo DEMs, we find two major classes of landforms: isolated inlets with lower stream orders and fans of approximately equal volume to the source valleys, and regionally-integrated valley networks with higher stream orders and much smaller fan volumes than valley volumes. If stream order correlates with valley age on Mars, then these results imply change in martian erosion and deposition patterns over time. We infer that hydrodynamic sorting in older, wetter systems resulted in preferential deposition of fines in fans formed by higher stream order valleys, and, ultimately more erosion in these fine-grained deposits, while younger, drier systems created deposits with intermixed sediment sizes that remain preserved today due to the greater protection of the fines from post-depositional erosion. These observations are consistent with a waning hydrologic cycle throughout martian history.
A predictive model for sand production in poorly consolidated sands
(2010-12) Kim, Sung Hyun, 1983-; Sharma, Mukul M.; Prodanovic, Masa
This thesis presents a model for the process of sand production that allows us to predict the stability of wellbores and perforation tunnels as well as mass of sand produced. Past analytical, numerical, and empirical models on material failure and erosion mechanisms were analyzed. The sand production model incorporates shear and tensile failure mechanisms. A criterion for sand erosion in failed sand was proposed based on a force balance calculation on the sand face. It is shown that failure, post failure sand mechanics and flow-dominated erosion mechanisms are important in the sand production process. The model has a small number of required input parameters that can be directly measured in the lab and does not require the use of empirical correlations for determining sand erosion. The model was implemented in a numerical simulator. Three different experiments using different materials were simulated and the results were compared to test the model. The model-generated results successfully matched the sand production profiles in experiments. When the post-failure behavior of materials was well-known, the match between the simulation and experiment was excellent. Sensitivity studies on the effect of mechanical stresses, flow rates, cohesion, and permeability show qualitative agreement with experimental observations. In addition, the effect of two-phase flow was presented to emphasize the importance of the water-weakening of the sand. These results show that catastrophic sand production can occur following water breakthrough. Finally the impact of increasing sand cohesion by the use of sand consolidation chemicals was shown to be an effective strategy for preventing sand production.
Pyroclastic flows and surges
(2009-03) Barker, Daniel S.
Scoria (cinder) cones
(2009-03) Barker, Daniel S.
Spatter
(2009-03) Barker, Daniel S.
Using GIS and the RUSLE model to create an index of potential soil erosion at the large basin scale and discussing the implications for water planning and land management in Morocco
(2015-12) Clark, Madeline Lacy; Eaton, David J.; Hajji, Mustapha
Severe erosion rates endanger the drinking water and agroforestry sectors in Morocco. To determine ways to improve erosion mitigation in Morocco, this study examined the political landscape underpinning research and policy implementation nation-wide. It also conducted a case study for erosion modeling in the most important river basin for drinking water in Morocco, the Bouregreg Basin. In this case study, 15 erosion scenarios were constructed in ArcMap according to the Revised Universal Soil Loss Equation (RUSLE), the most commonly used tool to predict erosion in Morocco, to determine the effect of variation in data inputs on the quantity and severity of sheet and rill erosion. Results indicate that average annual erosion rates in the Basin are minimal to moderate, with localized areas experiencing severe rates over 25 tons/hectares/year, indicating that channel and gully erosion rather than sheet or interill erosion dominate in the basin. Increased DEM resolution from 30 to 90 meters amplified predicted erosion rates by a factor of 10, and variation in precipitation between the highest and lowest agricultural years yielded a difference in maximum erosion rates of nearly 60,000 tons/hectares/year. These results indicate that the spatial resolution of datasets and variation in climatic factors produce substantial differences in model output and may bias policy-making in light of variation in data management practices and the potential effects of climate change. In order for Morocco to reach its goal of implementing Integrated Water Resource Management (IWRM), operators and researchers should collaborate at the basin level and establish best data management practices in the drinking water and agro-forestry sectors of Morocco. To achieve these changes, this study recommends that decision makers reexamine how they fund and support erosion research and mitigation, and that all stakeholders coordinate to both compile data to develop empirical and process-based erosion models fitted to Morocco and calibrate these models through investing in representative field studies.
Wind Work
(2009-04) Barker, Daniel S.