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51.
Subsurface flow measurements using passive flux meters in variably-saturated cold-regions landscapes
To date, passive flux meters have predominantly been applied in temperate environments for tracking the movement of contaminants in groundwater. This study applies these instruments to reduce uncertainty in (typically instantaneous) flux measurements made in a low-gradient, wetland dominated, discontinuous permafrost environment. This method supports improved estimation of unsaturated and over-winter subsurface flows which are very difficult to quantify using hydraulic gradient-based approaches. Improved subsurface flow estimates can play a key role in understanding the water budget of this landscape. 相似文献
52.
Previous “fraction of young water” (Fyw) estimates based on relative annual isotopic amplitudes in precipitation (Ap) and streamflow (As) produced low Fyw values in mountain catchments, which is contrary to extensive research that reports rapid water transmission in mountains. This study investigated this discrepancy by testing the effect of snow accumulation on the model that underpins the Fyw method. A Monte-Carlo analysis of simulations for 20,000 randomly-generated catchment model configurations used 10 years of precipitation inputs for the Upper Elbow River catchment in the Rocky Mountains (Alberta, Canada) to model discharge with and without snowpack storage of winter precipitation. Neither direct nor modified precipitation input produced a 1:1 relationship between As/Ap and Fyw, undermining the applicability of the original Fyw method in mountain watersheds with large seasonal snow accumulation. With snowpack-modified input a given As/Ap ratio corresponds to a range of Fyw values, which can still provide semi-quantitative information. In the small (435 km2) Elbow River catchment a Fyw range of 7–23% supports previous findings of rapid transmission in mountain catchments. Further analysis showed that the improved discharge prediction (Nash–Sutcliffe efficiency > 0.9) correlates with higher Fyw values and demonstrated that the interannual shifts in δ18O can be used to estimate of new water (<1 year) fraction in winter streamflow, and the estimate of 20% for the Elbow River further supports rapid transmission in mountain catchments. 相似文献
53.
John?G.?ManchukEmail author Ryan?M.?Barnett Clayton?V.?Deutsch 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(10):2585-2605
A challenge when working with multivariate data in a geostatistical context is that the data are rarely Gaussian. Multivariate distributions may include nonlinear features, clustering, long tails, functional boundaries, spikes, and heteroskedasticity. Multivariate transformations account for such features so that they are reproduced in geostatistical models. Projection pursuit as developed for high dimensional data exploration can also be used to transform a multivariate distribution into a multivariate Gaussian distribution with an identity covariance matrix. Its application within a geostatistical modeling context is called the projection pursuit multivariate transform (PPMT). An approach to incorporate exhaustive secondary variables in the PPMT is introduced. With this approach the PPMT can incorporate any number of secondary variables with any number of primary variables. A necessary alteration to the approach to make this numerically practical was the implementation of a continuous probability estimator that relies on Bernstein polynomials for the transformation that takes place in the projections. Stopping criteria were updated to incorporate a bootstrap t test that compares data sampled from a multivariate Gaussian distribution with the data undergoing transformation. 相似文献
54.
Effect of seasonal flushing on nutrient export characteristics of an urbanizing,remote, ungauged coastal catchment 总被引:1,自引:0,他引:1
Urbanization is a primary driver of nutrient export in coastal catchments; however, estimating the rate of export from urbanizing, remote and ungauged communities with episodic rainfall characteristics has rarely been reported in tropical and subtropical areas. In this study, the coastal catchment of Roebuck Bay near Broome, northwestern Australia, was instrumented to elucidate the effect of seasonal flushing on nutrient export. A cost-effective framework involving temporary gauging and community participation led to a quantitative estimate of surface hydrology and nutrient dynamics from this urbanizing, remote and ungauged catchment. The contribution of nutrient export was larger from the older Broome town site sub-catchments compared to sub-catchments that have been progressively urbanized since 2000. A distinctive seasonal first flush phenomenon, with an initial 30% of runoff volume containing 40–70% of the nutrient load was a key feature. This indicates there are opportunities for storm-water management to minimize impacts through adopting water-sensitive urban design principles. 相似文献
55.
We present a simple modelling method to estimate the volume of available groundwater in the freshwater lens of atoll islands under steady-state conditions. Model inputs include annual rainfall depth, island width for cross-sections along the length of the island, aquifer hydraulic conductivity, and depth to the contact between the upper sand aquifer and the lower limestone aquifer. The methodology is tested for nine islands of varying size in the Maldives and Micronesia. Sensitivity analysis indicates that lens volume on large islands typically is governed by the depth to the discontinuity, whereas lens volume for smaller islands is governed by rainfall rate and hydraulic conductivity. Volume curves, which relate lens volume to lens thickness, are developed for each of the nine islands and for three generic island shapes to allow rapid estimation of lens volume given field-estimated lens thickness. The methods presented in this study can be used for any small atoll island. 相似文献
56.
Dylan J. Irvine Martin A. Briggs Laura K. Lautz Ryan P. Gordon Jeffrey M. McKenzie Ian Cartwright 《Ground water》2017,55(1):10-26
Heat is a powerful tracer to quantify fluid exchange between surface water and groundwater. Temperature time series can be used to estimate pore water fluid flux, and techniques can be employed to extend these estimates to produce detailed plan‐view flux maps. Key advantages of heat tracing include cost‐effective sensors and ease of data collection and interpretation, without the need for expensive and time‐consuming laboratory analyses or induced tracers. While the collection of temperature data in saturated sediments is relatively straightforward, several factors influence the reliability of flux estimates that are based on time series analysis (diurnal signals) of recorded temperatures. Sensor resolution and deployment are particularly important in obtaining robust flux estimates in upwelling conditions. Also, processing temperature time series data involves a sequence of complex steps, including filtering temperature signals, selection of appropriate thermal parameters, and selection of the optimal analytical solution for modeling. This review provides a synthesis of heat tracing using diurnal temperature oscillations, including details on optimal sensor selection and deployment, data processing, model parameterization, and an overview of computing tools available. Recent advances in diurnal temperature methods also provide the opportunity to determine local saturated thermal diffusivity, which can improve the accuracy of fluid flux modeling and sensor spacing, which is related to streambed scour and deposition. These parameters can also be used to determine the reliability of flux estimates from the use of heat as a tracer. 相似文献
57.
Rethinking big data in digital humanitarianism: practices,epistemologies, and social relations 总被引:1,自引:0,他引:1
Ryan Burns 《GeoJournal》2015,80(4):477-490
58.
A modified DRASTIC model for Siting Confined Animal Feeding Operations in Williams County,Ohio, USA 总被引:1,自引:0,他引:1
Three of DRASTIC’s parameters (Depth to Water, Soil Media, and Topography) were modified and another parameter was added (land
use/land cover) to the model to determine the potential impact on groundwater from Confined Animal Feeding Operations (CAFO)
manure lagoon settings and manure application as fertilizer. Williams County is a mostly agricultural county located in northwest
Ohio, USA. It currently has three CAFOs, all dairy, with the possibility of the construction of a multi-million chicken egg
CAFO in the near future. A Geographic Information System (GIS) was utilized to modify the Ohio Department of Natural Resources
(ODNR) DRASTIC map for the county to fully assess the county-wide pollution potential of CAFOs. The CAFO DRASTIC map indicates
that almost half of Williams County has elevated groundwater pollution potential. The rest of the county, primarily the southeast
corner, has lower CAFO groundwater pollution potential. Future CAFO development within the county should focus on the southeastern
portion of the county where the groundwater table is deeper, and the aquifer is composed of shale substrate with low hydraulic
conductivity. The CAFO DRASTIC results are intended to be used as a screening tool and are not to replace site-specific hydrogeologic
investigations. 相似文献
59.
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