Calibration of the pass-through magnetometer—II. Application     

Robert L. Parker  Jeffrey S. Gee 《Geophysical Journal International》2002,150(1):140-152

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Novel Well Completions in Small Diameter Coreholes Created Using Portable Rock Drills          下载免费PDF全文

Amanda A. Pierce  Beth L. Parker  Robert Ingleton  John A. Cherry 《Ground Water Monitoring & Remediation》2018,38(1):42-55

Difficult access conditions have limited techniques for groundwater system characterization and monitoring in bedrock exposed landscapes. This condition is common in the mining industry and resulted in the development of lightweight portable drills. This paper describes how these drills were used at a contaminated site to understand the groundwater flow system by adapting piezometer designs, ensuring effective seals to obtain reliable hydraulic head, hydrochemistry, and contaminant concentrations. Two drilling machines were evaluated: the Shaw Portable Core Drill? fits in a backpack and can advance continuously cored rock holes, nominal 51 millimeters (mm) diameter, to depths up to approximately 15 meters (m); and the larger Winkie Drill? requires a two or more people to mobilize and can advance continuously cored holes, nominal 48 mm diameter, to depths of approximately 45 m. The resulting small diameter coreholes were accommodated in the design of each well using a seal created by injecting grout into a semipermeable fabric sleeve. This “fabric sleeve” serves as a means to contain the grout and ensures that the entire annulus above the screen is sealed without loss of grout into the formation, allowing the well to perform as a piezometer. To develop and demonstrate this methodology for groundwater monitoring in bedrock, the two drills were used in drainages located along the slopes of an elevated sandstone outcrop near Los Angeles, California. Unique insights into the groundwater flow system of this bedrock environment, which would otherwise be unattainable, were achieved. This methodology overcomes the accessibility limitations of conventional drilling methods that prevent installation of wells in remote and rugged mountainous terrains.  相似文献   

Modelling surface‐water depression storage in a Prairie Pothole Region          下载免费PDF全文

Lauren Hay  Parker Norton  Roland Viger  Steven Markstrom  R. Steven Regan  Melanie Vanderhoof 《水文研究》2018,32(4):462-479

In this study, the Precipitation‐Runoff Modelling System (PRMS) was used to simulate changes in surface‐water depression storage in the 1,126‐km² Upper Pipestem Creek basin located within the Prairie Pothole Region of North Dakota, USA. The Prairie Pothole Region is characterized by millions of small water bodies (or surface‐water depressions) that provide numerous ecosystem services and are considered an important contribution to the hydrologic cycle. The Upper Pipestem PRMS model was extracted from the U.S. Geological Survey's (USGS) National Hydrologic Model (NHM), developed to support consistent hydrologic modelling across the conterminous United States. The Geospatial Fabric database, created for the USGS NHM, contains hydrologic model parameter values derived from datasets that characterize the physical features of the entire conterminous United States for 109,951 hydrologic response units. Each hydrologic response unit in the Geospatial Fabric was parameterized using aggregated surface‐water depression area derived from the National Hydrography Dataset Plus, an integrated suite of application‐ready geospatial datasets. This paper presents a calibration strategy for the Upper Pipestem PRMS model that uses normalized lake elevation measurements to calibrate the parameters influencing simulated fractional surface‐water depression storage. Results indicate that inclusion of measurements that give an indication of the change in surface‐water depression storage in the calibration procedure resulted in accurate changes in surface‐water depression storage in the water balance. Regionalized parameterization of the USGS NHM will require a proxy for change in surface‐storage to accurately parameterize surface‐water depression storage within the USGS NHM.  相似文献   

Reintroduced large wood modifies fine sediment transport and storage in a lowland river channel          下载免费PDF全文

Chris Parker  Alexander J. Henshaw  Gemma L. Harvey  Carl D. Sayer 《地球表面变化过程与地形》2017,42(11):1693-1703

This paper explores changes in suspended sediment transport and fine sediment storage at the reach and patch scale associated with the reintroduction of partial large wood (LW) jams in an artificially over‐widened lowland river. The field site incorporates two adjacent reaches: a downstream section where LW jams were reintroduced in 2010 and a reach immediately upstream where no LW was introduced. LW pieces were organized into ‘partial’ jams incorporating several ‘key pieces’ which were later colonized by substantial stands of aquatic and wetland plants. Reach‐scale suspended sediment transport was investigated using arrays of time‐integrated suspended sediment samplers. Patch‐scale suspended sediment transport was explored experimentally using turbidity sensors to track the magnitude and velocity of artificially generated sediment plumes. Fine sediment storage was quantified at both reach and patch scales by repeat surveys of fine sediment depth. The results show that partial LW jams influence fine sediment dynamics at both the patch and reach scale. At the patch‐scale, introduction of LW led to a reduction in the concentration and increase in the time lag of released sediment plumes within the LW, indicating increased diffusion of plumes. This contrasted with higher concentrations and lower time lags in areas adjacent to the LW; indicating more effective advection processes. This led to increased fine sediment storage within the LW compared with areas adjacent to the LW. At the reach‐scale there was a greater increase in fine sediment storage through time within the restored reach relative to the unrestored reach, although the changes in sediment transport responsible for this were not evident from time‐integrated suspended sediment data. The results of the study have been used to develop a conceptual model which may inform restoration design. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Gravel‐bed river evolution in earthquake‐prone regions subject to cycled hydrographs and repeated sediment pulses          下载免费PDF全文

Chenge An  Yantao Cui  Xudong Fu  Gary Parker 《地球表面变化过程与地形》2017,42(14):2426-2438

Sediment often enters rivers in the form of sediment pulses associated with landslides and debris flows. This is particularly so in gravel‐bed rivers in earthquake‐prone mountain regions, such as Southwest China. Under such circumstances, sediment pulses can rapidly change river topography and leave the river in repeated states of gradual recovery. In this paper, we implement a one‐dimensional morphodynamic model of river response to pulsed sediment supply. The model is validated using data from flume experiments, so demonstrating that it can successfully reproduce the overall morphodynamics of experimental pulses. The model is then used to explore the evolution of a gravel‐bed river subject to cycled hydrographs and repeated sediment pulses. These pulses are fed into the channel in a fixed region centered at a point halfway down the calculational domain. The pulsed sediment supply is in addition to a constant sediment supply at the upstream end. Results indicate that the river can reach a mobile‐bed equilibrium in which two regions exist within which bed elevation and surface grain size distribution vary periodically in time. One of these is at the upstream end, where a periodic discharge hydrograph and constant sediment supply are imposed, and the other is in a region about halfway down the channel where periodic sediment pulses are introduced. Outside these two regions, bed elevation and surface grain size distribution reach a mobile‐bed equilibrium that is invariant in time. The zone of fluctuation‐free mobile‐bed equilibrium upstream of the pulse region is not affected by repeated sediment pulses under the scenarios tested, but downstream of the pulse region, the channel reaches different fluctuation‐free mobile‐bed equilibriums under different sediment pulse scenarios. The vertical bed structure predicted by the simulations indicates that the cyclic variation associated with the hydrograph and sediment pulses can affect the substrate stratigraphy to some depth. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Multidimensional Investigation of Bedrock Heterogeneity/Unconformities at a DNAPL‐Impacted Site          下载免费PDF全文

Colby M. Steelman  Jessica R. Meyer  Beth L. Parker 《Ground water》2017,55(4):532-549

Organic solvent (i.e., dense nonaqueous phase liquid, DNAPL) migration in the subsurface is known to be extremely sensitive to geologic heterogeneity. There is often a focus on heterogeneity that results from changing depositional conditions over short spatial scales. Similar or even more extreme spatial heterogeneity can result postdeposition due to erosional processes. This study applies a synergistic approach based on a combination of high‐resolution lithologic logs of continuous cores, borehole geophysical logs, surface electrical resistivity, and seismic refraction tomography models to assess spatial heterogeneity in a shallow bedrock sequence subject to multiple unconformities and contaminated with a mixture of organic chemicals. The persistence of DNAPL in the source zone and an associated dissolved‐phase plume led to variable impacts on formation resistivity across the study site. Seismic refraction in combination with electrical resistivity tomography improved interpretation of highly irregular erosional boundaries by delineating sharp lateral transitions in lithologic composition near the source zone and across the dissolved‐phase plume. Electrical resistivity was effective at differentiating between clean and mud‐rich sandstones and their unconformable contact with an underlying dolostone. Geophysical measurements revealed eroded dolostone mounds encased by a network of younger mud‐rich sandstones channelized by clean semi‐lithified sand, all of which was buried beneath variable glacial drift. Our synergistic multidimensional approach resulted in the development of a detailed three‐dimensional shallow bedrock geospatial model, which has led to an improved understanding of DNAPL migration and contaminant plume heterogeneity.  相似文献   

Mapping Shakespeare: An Exploration of Shakespeare’s World Through Maps     

Philip Parker 《The Cartographic journal》2019,56(1):93-94

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Spatial considerations when monitoring reef fishes     

D Parker  H Winker  ATF Bernard  MKS Smith  A Götz 《African Journal of Marine Science》2019,41(1):93-101

Spatial dependence can obscure relationships between response and explanatory variables because of structuring within the residuals reducing variance and biasing coefficient estimates. Here, we highlight the influence of the spatial component, in the presence of spatial dependence, on abundance trends. This is illustrated using abundance data for a Critically Endangered reef fish, dageraad Chrysoblephus cristiceps, which were obtained from a long-term monitoring programme in the Tsitsikamma National Park marine protected area, South Africa. Correlograms illustrate distinct spatial structuring in the abundance data, and spatial variables were determined as more important than temporal variables when ranked according to predictive power using a random forest analysis. A generalised additive model (GAM) that did not account for spatial dependencies was compared to a generalised additive mixed model (GAMM) that incorporated a spatial residual correlation structure. Results derived from the spatially explicit GAMM differed considerably from the GAM lacking a spatial component, with the latter deemed to produce over-precise and partially biased abundance trends. The study emphasises the importance of space in accurately modelling abundance estimates, particularly temporal trends, and provides an introduction to the minimal statistical requirements necessary to address the violations associated with spatial autocorrelation.  相似文献   

Citation analysis for the 1995 FAO Code of Conduct for Responsible Fisheries     

Joan Parker  David Doulman  Jean Collins 《Marine Policy》2010

This paper presents the results of a 2008 citation-analysis study that was undertaken for the 1995 FAO Code of Conduct for Responsible Fisheries and its associated instruments. The overall objective of this study was to contribute towards a strategy for improved dissemination, awareness raising and communication about the Code and its implementation. For each citation, additional information was collected to identify patterns by year, topic, author affiliation or type of literature. Results support previously suggested anecdotal patterns, in particular related to the diversity of publishing outlets and the high proportion of fisheries information published as grey literature. The results also point to areas of concern for long-term preservation and dissemination of fisheries information.  相似文献   

Richtmyer–Meshkov Instability Reshock Experiments Using Laser-Driven Double-Cylinder Implosions     

J. M. Taccetti  S. H. Batha  J. R. Fincke  N. D. Delamater  N. E. Lanier  G. R. Magelssen  R. M. Hueckstaedt  S. D. Rothman  C. J. Horsfield  K. W. Parker 《Astrophysics and Space Science》2005,298(1-2):327-331

As a shock travels through the interface between substances of different densities, existing perturbations can grow via the Richtmyer–Meshkov (RM) instability. The study of the RM instability in a convergent geometry leads to a better understanding of implosions applicable to inertial confinement fusion and various astrophysical events, such as core-collapse supernovae. We present results of laser-driven double-cylinder implosions performed at the Omega laser facility with an emphasis on sending a second shock through an already shocked RM unstable interface. The uniform reshock of a cylindrical interface is achieved by inserting a second cylinder inside the first that reflects the inwardly traveling shock and causes it to interact a second time with the unstable interface. We present an analysis of the instability growth as a function of shock strength and zero-order perturbation behavior during reshock.  相似文献