Thesis advisor: Noah P. Snyder / Global studies assert that anthropogenic activity now leads to disproportionately higher rates of landscape change compared with background geomorphic processes. This study explores the relative influence of anthropogenic, glacial, and geologic processes on erosion rates (E) in the northeastern United States (NEUS) by analyzing published erosion and sedimentation data across multiple methods and timescales. I compile erosion rates and sediment yields from records of stream gauging, reservoir sedimentation, lake sedimentation, cosmogenic nuclides in stream sediment, and thermochronology. These data serve as a comparison point for quantified volumes of sediment deposited in valley bottoms as a result of European settlement in the NEUS, where glacial history may influence the availability of erodible sediment and, as a result, the relative magnitude of deposited sediment. I hypothesize that E in the formerly glaciated region will be lower than unglaciated E over last century (stream gauging and reservoir sedimentation) timescales due to the erosive power of continental glaciation and resultant thin upland soils, and that there will be an increase in E evident over the last century as a result of human influence. 499 sites with location data were compiled across the NEUS, converted to erosion rate (mm/yr) and sediment yield (Ys; t km-2 yr-1), and analyzed using statistical z-tests to determine whether the population means are significantly different. Mean E from all record types across both the glaciated and unglaciated NEUS exhibits a range smaller than one order of magnitude (0.012-0.055 mm/yr), much less variable than order-of-magnitude differences reported by other researchers comparing modern and geologic erosion, both regionally and globally. Last century timescales exhibit higher E in the unglaciated region than the glaciated region, but only reservoir sedimentation shows a significant difference in E between regions (0.012 vs. 0.055 mm/yr; glaciated and unglaciated, respectively); stream gauging E did not exhibit a significant regional difference, likely due to the large basin sizes, short measurement timescales, and disproportionate spatial distribution of the measurements. E does not increase from geologic to last century timescales: late Quaternary (lake sedimentation and cosmogenic nuclide) records consistently yield lowest E, with geologic (thermochronology) records showing the highest E in both regions, perhaps indicating the relative importance of E over timescales during which major orogenies were occurring in the NEUS. The similarities in mean E and large range of the distributions of all timescales, however, point to the relative stability of E over time in the NEUS. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Digitized by Kansas Correctional Industries

Ecosystem engineers can govern ecosystem dynamics, yet ecosystem consequences of trait variation within engineering species are often overlooked. Combining field and greenhouse experiments with mathematical modelling, this study aimed to assess the relative importance of heritable and non-heritable trait variation within the engineer species Spartina alterniflora in controlling salt marsh erosion. In the field experiment, plots along a devegetated shoreline were restored with wild and cultivated sources to test whether populations exerted different control on erosion. The greenhouse experiment investigated whether genotypic trait differences were conserved when genotypes were exposed to elevated nutrients. A modelling approach was used to extrapolate empirical findings to temporal and spatial scales involved in landform evolution, considering spatial patterns in trait variation. The field experiment revealed that erosion rates were higher in plots planted with a wild, non-local source population as compared to plots planted with cultivars or local genotypes. Differential erosion could not be explained by differences in biomass, suggesting that other traits and resource use are stronger determinants of erosion. In the greenhouse experiment, cultivars and wild genotypes exhibited trait-specific differences in phenotypic plasticity under changing nutrient availability. Nutrient regime and heritable trait differences explained 70% of observed variation in soil shear strength. Soil shear strength increased when plants received more nutrients, but plant genotype had an equal or larger influence on soil characteristics. Model simulations suggested that older marshes (with large clones) and genetically diverse marshes (with high spatial variance in soil shear strength) may experience higher mean erosion rates. However, simulations also showed that average erosion rates are easily underestimated if the observation period is short, as variability of annual erosion rates and the probability of mass failure events were also mediated by clone size and composition. These findings illustrate that heritable and non-heritable trait variation interact with environmental conditions and landform history, together driving geomorphological processes crucial to the persistence of coastal marshes. Consideration of these interacting factors is needed when deploying ecosystem engineers for habitat restoration. / 1 / Brittany Marie Bernik

A set of solutions to the cohesive soil erosion problem were developed through this study. A first device, the Erosionometer, was developed to perform a quick and reliable test to determine the critical shear stress of soils. The Erosionometer is based on physical shearing of the soil surface and has been calibrated through comparison with piston flume measurements of critical shear stress for entrainment of various fluvial bed sediments. This device is portable, easy to deploy in the field and in the laboratory and allows engineers and researchers to cover a sizeable terrain by performing many tests in a short timeframe, with immediate results. A modification to the Erosionometer was made to allow for subjecting the soil sample to a pressure differential while testing for critical shear stress. The added functionality is intended for investigating the effect of pressure gradient on the erodibility of cohesive soils by allowing for the erosion test to be conducted under a high pressure head while the other face of the sample (away from the flow) is maintained at zero head. Testing demonstrated that a positive pressure gradient on the eroding side (high pressure on flow side) can significantly increase the critical shear stress of cohesive soils, which is in line with other research available in the literature. The results show a simple linear relation between pressure differential and critical shear stress. Practical implications of these results are discussed. A second device, the Erosion Rate Meter, or ERM, was developed to test cohesive soil samples to determine the rate of erosion under various levels of bed shear stress. This device, while being portable and fast to setup and run, is a very realistic simulation of the flow-bed interaction and allows for a direct measurement of bed shear stress on the soil sample and a precise measurement of the erosion rate. An obvious outcome of using the ERM is the easy development of erosion rate vs. bed shear stress relationships or models to characterize the different soils for design projects or further research. Of the 16 tested cohesive soils, all but two demonstrated a linear relation between erosion rate and bed shear stress. The testing systems and methods developed in this research provide a comprehensive solution to the erodibility of cohesive soils from investigation to design. Significant improvements are achieved over existing systems in the speed, reliability, accuracy, and cost of estimating the erodibility of cohesive soils.

Research Doctorate - Doctor of Philosophy (PhD) / The impact of a small particle with a wear surface can lead to very high strain-rates in the material being encountered. Often predictive erosion models are based on material property parameters taken from quasistatic test conditions. However, the material properties of the impacted wear surface can change dramatically with strain and strain-rate, leaving some doubt as to the validity of an erosion model based on quasistatic parameter values. In this study, a new stress-wave monitoring process is developed for the study of material characteristics and erosion phenomena, at strain-rates approaching 10e6s-1. For this study a newly designed piezo-electric transducer was used to monitor the stress-waves produced by small erosive particle impact events. A computational study was also conducted to aid in the transducer design and location distance from the impact source by considering the effects caused by spatial averaging. Spatial averaging affects the recorded stress-wave signal and is caused by the curvature of the stress-wave as the wave passes through the flat piezo-electric sensing element. This study was conducted using a computational and experimental approach. The joint study allowed significant knowledge to be gained for the study of elasto-plastic impact and stress-wave motion. Finite element analysis (FEA) was used to model the experimental system in detail. The stress-waves produced by the experimental process were directly compared to the FEA model. Once the FEA model was validated, detailed information from the impact event at the surface could be obtained from the model, which would otherwise be difficult if not impossible to obtain experimentally. The issues of wave dispersion have been an underlying problem in the correct interpretation of stress-wave phenomena for many years. The impact of the wear surface causes stress-waves with many frequency components, each component propagating through the wear material at distinct wave velocities. Wave dispersion causes the initial stress-wave pulse to be dispersed into many waveforms. In this study the longitudinal stress-wave was the main waveform studied. FEA simulations were conducted for a purely elastic impact and an impact causing significant plastic deformation of the surface. A comparison between these waveforms showed that in the case of impacts causing plastic deformation, the initial part of the stress-wave, measured from the time of arrival to the first peak, corresponded to the elastic stress component of the impact event at the surface. The characterisation of the waveform in regards to elastic and plastic stress components at the surface was significant for validating model parameters of the Johnson-Cook material model. The stress-wave monitoring process was applied in the first instance to erosive particle impacts to AISI 1020 steel at impact velocities up to 104m/s. A specially designed erosion apparatus, fitted with a modified double disc system was used to impact the 10mm thick steel plate. The piezo-electric transducer was firmly clamped to the rear surface, directly behind the point of impact to obtain the stress-wave signals produced by impacts of 0.4mm zirconia spheres. The study showed that the contact interface of the wear material and the piezo-electric transducer could cause a phase change and amplitude reduction of the stress-wave transmitted to the transducer at wave frequencies above 0.9MHz. The results showed that the most likely cause for the phase shift to occur was the restriction of tensile stresses across the contact interface. For wave frequencies below 0.9MHz, no phase shift or amplitude reduction was apparent in the experimental stress-wave recordings. The combined experimental / FEA study was shown to be able to validate the strain-rate parameter of the Johnson-Cook model. The parameters, which could not be validated by the stress-wave monitoring process, were the parameters relating to plastic deformation of the surface, which were the strain-hardening terms of the Johnson-Cook model. These terms were later validated by studying the extent of plastic deformation at the surface, which occurred in the form of impact craters. By comparing the predicted impact crater depths from the FEA model with the experimental results, the strain-hardening parameters of the Johnson-Cook model could be validated. The robustness of the stress-wave monitoring process was proven for the impact study of ultra high molecular weight polyethylene (UHMWPE) and vinyl ester resin (VER). Unlike AISI 1020 steel, little is know about the high strain-rate response of these polymers. Initial estimates of material property parameters were made by applying computational curve fitting techniques to the stress-strain curves of similar polymers, which were from published results obtained from split Hopkinson’s pressure bar method. The impact and stress-wave study showed UHMWPE and VER to be highly sensitive to strain-rate effects. The main effect was a substantial increase in hardness with increasing strain-rate and it was considered that the hydrostatic stress component contributed to the strain hardening of the polymers. The stress-wave monitoring and FEA computational techniques developed in this study were implemented in the development of an improved erosion model. The model form is similar to that of the well-known Ratner-Lancaster model. The Ratner-Lancaster model assumes wear rate to be proportional to the inverse of deformation energy, where deformation energy is approximated as the product of the ultimate stress and ultimate strain. The improved Ratner-Lancaster model uses the Johnson-Cook model to obtain the von-Mises stress as a function of strain. The area integral of the stress-strain curve is used to derive the deformation energy capacity of the material in the deformed zone close to the surface. The model accounts for strain, strain-rate and thermal effects and is therefore more soundly based on material deformation characteristics valid for erosion events than the Ratner-Lancaster model assumptions. The model developed in this work was applied to the erosion study of 1020 steel, UHMWPE and VER, with good correlation being obtained between experimental erosion rates and model predictions.

The erosion behaviour of clay soils has been investigated through a comprehensive program of laboratory testing. Three different erosion test methods have been employed including the rotating cylinder test (RCT), the hole erosion test (HET), and the slaking test (SLT). A new rotating cylinder test device is designed and manufactured capable of testing disturbed and undisturbed soil samples in saturated and unsaturated states. Details of the equipment along with its calibration, testing and sampling procedures are provided. The HET has been reviewed and modified to provide consistent test results. In addition, the slaking test has been customised to accept samples identical to those used in the RCT. A total 111 RCT, 139 HET, and 108 slaking tests have been conducted and analysed. Typical shapes of the erosion curves are identified, based on a wide range of shear stresses and erosion rates analysed. Correlations are presented between the RCT and HET, and between the RCT and SLT to allow characterisation of clay soil erosion in a consistent and unified manner. The erosion modes of clay soils are investigated and categorised into three main groups: ???dispersive erosion???, ???saturated non-dispersive erosion???, and ???unsaturated non-dispersive erosion???. It is shown that soils falling in the same category exhibit near identical erosion characteristics. Factors affecting clay soil erodibility are investigated and displayed for each erosion mode. All findings are presented in a unified framework. A suggested procedure is provided for the evaluation erosion potential in clay soils for practical applications.

The northern sector of Waihi Beach is an example of chronic erosive tendency. The sediment deficit along the area of beach fronting the seawall means that there is often no beach at high tide. This existing situation, and the various remedial options suggested, has created an emotive issue for beach residents. Accordingly, the current study was undertaken to identify and evaluate the fundamental coastal processes impacting upon the erosion at northern Waihi Beach. Methods used to investigate this problem included: beach profiling and shallow water hydrographic surveying; mapping of sediments and the distribution of bedforms on the inner shelf using side-scan sonar, identification of nearshore sediment transport pathways from sediment textural analyses; collection and analysis of nearshore wave and current data; and numerical modelling of wave refraction and sediment transport processes. A side-scan sonar survey, ground-truthed by surficial sediment analyses and underwater video and diver observations, indicated that the shallow inshore zone is characterised by a relatively featureless seabed dominated by fine sands. Large shore-normal sand ridges (η=0.4-2.5 m, λ=300-1400), with crests oriented northeast to southwest were identified between 15-30 m water depth offshore northern Waihi Beach. These very pronounced features consist of coarse megarippled (η≈0.12 m, λ≈1 m) sediment. Sediment textural analyses revealed that offshore sediments vary from fine to coarse sand, showing a seaward-coarsening progression. Beach sediments consist of predominantly fine sands, with a slight inferred fining in grain size that occurs towards the northern end of the beach. This is possibly a result of lower wave energy when subject to swell and sea waves from the north, due to sheltering in the lee of Rapitiotio Point. 80 days of wave and current data were collected offshore northern Waihi Beach, during two separate deployments in Nov/Dec 2007 and May/June 2008. The summer deployment was characterised by waves from a northeast-east origin (Hs=1.09m; Ts=7.13s). Similar conditions were exhibited during the winter deployment (Hs=0.95m; Ts=6.79s). Observed relationships between wind direction and near-bed current direction, combined with calculated sediment entrainment rates, enabled predictions of the frequency of shoreward sediment transport by bottom currents to be made. Onshore currents, associated with winds from the southwest, prevailed during the deployment period. However, observed current velocities alone were generally incapable of inducing sediment motion. Analysis suggests that wave properties are likely to govern the frequency of sediment transport in the nearshore, as their presence is required to lift sediment into suspension for dispersal by ambient background currents. Onshore movement of sediment was estimated to be ~11,800 m3/year or 2.6 m3/m. Monochromatic wave statistics measured during the field study were used to calibrate a numerical wave refraction model. The wave refraction influence of Mayor Island was found to be the major feature influencing the distribution of wave energy along the shoreline, which is likely to contribute to localised accelerated beach erosion and dune setback. Wave energy focusing at northern Waihi Beach is maximised by swell waves, resulting in greater wave heights along eroding sectors of the beach. Potential sediment transport rates were investigated. Results suggest the littoral drift direction was bi-directional at northern Waihi Beach, although net littoral drift was southeasterly during the study period. An estimated net loss of 46,200 m3/year or 10.3 m3/m was predicted for northern Waihi Beach during the present study. Longer-term drift patterns were examined using a five year record of wave data collected offshore Pukehina by Environment Bay or Plenty from 2003-2008. Similar patterns but with lower magnitudes of sediment transport were obtained, with net annual drift rates estimated to range from 1,300-58,000 m3/year. A conceptual model of nearshore sediment dynamics is proposed for Waihi Beach to identify the major factors contributing to long-term erosion in the northern sector. Approximately 115,000 m3 of sediment was estimated to be moving within the defined northern Waihi Beach littoral cell during the study period. The derived sediment budget produced a net deficit of sediment of approximately 36,000 m3/year or -8 m3/year during the year commencing November 2007. The net southeasterly littoral drift was determined the major contributor to the net erosion rate during the study period, with alongshore transport rates exceeding available supply to the beach from diabathic movement of sediment onshore. Several aspects of the erosion problem at northern Waihi Beach are recommended to be researched further to identify what coastal management options are required.

Thesis (M.C.E.)--University of Delaware, 2007. / Principal faculty advisor: Nobuhisa Kobayashi, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

The increasing world demand for oil has pushed oil companies to extract it from the ocean at extreme depths. With the increase in depth comes an increase in operation costs, especially the deep-sea equipment changeover cost. To be able to push the oil to the ocean surface, Electrical Submersible Pumps (ESPs) are commonly used as artificial lift. The changeover cost of these pumps in deep-water has been estimated to sometimes be as much as forty times the cost of a new pump. One common reason for the failure of ESPs is the erosion and abrasion created by the fine sands that seep through the gravel pack mesh in the well hole. These fine sand particles are most destructive to the bearings and bushings due to their capability to enter the clearances lubricated by the pumped fluid. Over time, the sustained abrasion and erosion in the different components of the ESP will affect the performance of the pump and could lead to its damage. This work describes the design, construction and evaluation of an erosion test rig built at the facilities of the Turbomachinery Laboratory in Texas A&M University. The test rig is capable of introducing 100 mesh (6 mil) sand into the flow loop, measure its concentration and separate it at the exit with minimal water loss. The pump under study is a Baker Hughes 10.25" WJE1000. The performance of the pump is described by measuring the head, flow rate, power and efficiency. The pump is equipped with accelerometers to detect the casing vibration as well as proximity probes in five locations along the pump to detect the internal vibrations of the shaft near the bearings as well as impeller radial movement. The baseline data, to be used for comparison with the worn out pump, has been shown and recommendations for the study method and operation of the rig are given.

A research program was undertaken to quantify the effect of flow induced erosion on the stability of natural river banks along the Red River in Winnipeg, Manitoba. The study correlated the percent decrease in factor of safety to intensity of river flow and duration. Two methods to quantify flow induced erosion were assessed, the first method based on observed erosion and the second on theoretically calculated erosion. The first method involved aligning annual historical river bank cross-sections and measuring the distance between cross-sections to represent the erosion induced from the flow year between successive cross-sections. Due to the fact there are no sites along the Red River regularly surveyed, the analysis did not provide for a correlation between erosion from a specific flow event to percent decrease in factor of safety. The second part involved the use of theoretical equations to quantify erosion given the river elevation of a specific flow year. The study showed a 1% to 8% decrease in factor of safety from low to high intensity flows and as high as 14.5% for high intensity flows of long duration. Additionally, the evolutionary stability of the riverbank was generated showing the percent decrease each year in factor of safety due to erosion and the years during which failure occurs. The results correlated well to the previous analysis showing a 1% to 5% decrease for low to high intensity flows respectively and as high as 10% for high intensities of long duration. / October 2007