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11.
L. L. Shoemaker W. L. Magette A. Shirmohammadi 《Ground Water Monitoring & Remediation》1990,10(1):109-115
The assessment of agricultural impacts on water quality are now being redirected to include both ground water and surface water. Mathematical models have enhanced the ability of scientists'to evaluate these impacts. A variety of public domain models are available that can aid in evaluating the effects of managerial activities on pesticide movement to ground water. However, the ideal non-point source (NPS) pollution management model does not exist. Current models fail to adequately describe the transport of chemicals to ground water and, simultaneously, the effect of managerial practices on transport mechanisms. Much more work is necessary to develop a model that can describe water quality impacts of agricultural practices in a holistic framework that includes ground water and surface water concerns. 相似文献
12.
Shoemaker WB 《Ground water》2004,42(6-7):829-840
Sensitivity analysis with a density-dependent ground water flow simulator can provide insight and understanding of salt water intrusion calibration problems far beyond what is possible through intuitive analysis alone. Five simple experimental simulations presented here demonstrate this point. Results show that dispersivity is a very important parameter for reproducing a steady-state distribution of hydraulic head, salinity, and flow in the transition zone between fresh water and salt water in a coastal aquifer system. When estimating dispersivity, the following conclusions can be drawn about the data types and locations considered. (1) The "toe" of the transition zone is the most effective location for hydraulic head and salinity observations. (2) Areas near the coastline where submarine ground water discharge occurs are the most effective locations for flow observations. (3) Salinity observations are more effective than hydraulic head observations. (4) The importance of flow observations aligned perpendicular to the shoreline varies dramatically depending on distance seaward from the shoreline. Extreme parameter correlation can prohibit unique estimation of permeability parameters such as hydraulic conductivity and flow parameters such as recharge in a density-dependent ground water flow model when using hydraulic head and salinity observations. Adding flow observations perpendicular to the shoreline in areas where ground water is exchanged with the ocean body can reduce the correlation, potentially resulting in unique estimates of these parameter values. Results are expected to be directly applicable to many complex situations, and have implications for model development whether or not formal optimization methods are used in model calibration. 相似文献
13.
This study develops a robust method for screening one-well hydraulic barrier design alternatives that can be easily computed without a numerical simulation model. The paper outlines the general method and shows its implementation with hydraulic barriers using a single pumping well. For such barriers, the method is easily computable with spreadsheets and/or charts depicted within the paper and posted online. The method applies the potential flow theory, which leads to using a curvilinear coordinate system for all types of calculations. For contaminant transport calculations, the method applies the boundary layer theory. For calculations of aquifer remediation, the method refers to bulk characteristics of the domain. As an example, the method has been applied to calculate the possible containment of a wide part of the coastal plain aquifer in Israel, which is contaminated by entrapped kerosene (a light nonaqueous phase liquid). 相似文献
14.
Watershed areal rainfall estimation, which is one of the most important and fundamental aspects in hydrological forecasting and various kinds of catchment‐scale hydrological models, is widely used in the analysis of hydrological regime change, and its precision has a direct influence on the accuracy of hydrological forecasting and hydrological simulation. In China, it is difficult to obtain the watershed areal rainfall estimate with reliable precision and avoid the phenomenon of ‘the same effect of different parameters’ because of the low density of the rain gauge network. Therefore, a watershed rainfall data recovery approach of improving the precision of watershed areal rainfall estimation is proposed here. This approach is to build new observatories, establish the time–space relations of rainfall between newly built observatories and previously built observatories in a relatively short interval and then recover the rainfall data of newly built observatories prior to their construction through simulating the relations over a longer time. As a result, watershed rainfall information could be elaborated to improve the precision of watershed areal rainfall estimate and avoid the phenomenon of ‘the same effect of different parameters’ to a certain degree in the process of hydrological simulation. The approach is used in the hydrological simulation of Hali River catchment. In combination with the Soil Water Assessment Tool model, a better result can be obtained in the hydrological simulation. Therefore, the approach can be used in other similar catchments. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
Estimation of urban subtropical bahiagrass (Paspalum notatum) evapotranspiration using crop coefficients and the eddy covariance method 
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下载免费PDF全文 Eddy covariance (EC) and micro‐meteorological data were collected from May 2010 to January 2013 from urban, non‐irrigated bahiagrass (Paspalum notatum) in subtropical south Florida. The objectives were to determine monthly crop coefficients (Kc) for non‐irrigated bahiagrass by using EC evapotranspiration (ET) data and the Food and Agriculture Organization 56 Penman–Monteith reference evapotranspiration equation; compare crop ET (ETc) calculated with new Kc values to ETc obtained using Kc values available in the literature; and compare results and methodologies for statistical differences. New Kc values ranged from 0.62 to 0.92 and were different from Kc values found in the scientific literature for bahiagrass. Resulting ETc calculated using literature Kc values were significantly different from EC ET data, whereas ETc using the new Kc values was not. Specifically, literature Kc values were temporally biased to miscalculate the timing of convergence between potential and actual ET, assuming that our new Kc values calculated with EC methods were most accurate. As a consequence, ETc calculated using the literature Kc values was either too large or too small. However, one set of literature Kc values from a similar climate and water table depth were closer to our new Kc values, indicating that climate should be considered when selecting urban non‐irrigated Kc from the literature to estimate ET. Results also indicated that more than 1 year of EC ET data was needed when establishing monthly Kc values because of annual variability in factors controlling ET, such as water availability. The new Kc values reported herein could be used as an estimate for urban non‐irrigated bahiagrass within similar climates. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
16.
At the beginning of a subglacial flood, storage of floodwater in bed depressions is very important. Storage delays the extension of a channel and forces the flood into a water sheet mode everywhere except upstream from the first depression encountered by the flood. In order for a grounded R-channel to evolve, it must extend its length continuously downstream by incorporating many subglacial ponds in its path. Simultaneous with R-channel extension, water sheet elimination works its way downstream. It is likely that limitations on the length of R-channels leading from the flood lake exist under ice sheets. In addition, volume discharge from a lake might be severely limited if a second lake exists downstream and close by.Bed depressions and humps are shown to delay the evacuation of water from the bed after a water sheet flood. Both channel and water-sheet flows are can exist beneath ice sheets. Ice displacement by uplift is important in creating cavities for water storage.Subglacial floods under ice sheets are likely to have a duration of years as compared to the 1972 Grimsvötn flood of 10 days. Any flood to the bed from a supraglacial lake has a duration of less than 3 days. Flood volumes are reduced for lakes located in the interior of ice sheets, particularly near ice divides. 相似文献
17.
G. Keller S.L. D'Hondt C.J. Orth J.S. Gilmore P.Q. Oliver E.M. Shoemaker E. Molina 《Meteoritics & planetary science》1987,22(1):25-60
Recent discoveries of microtektite and related crystal bearing microspherule layers in deep-sea sediments of the west equatorial Pacific DSDP Sites 292, 315A and 462, off-shore New Jersey in Site 612 and in southern Spain have confirmed the presence of at least three microspherule layers in Late Eocene sediments. Moreover, these discoveries have extended the North American strewn field from the Caribbean and Gulf of Mexico region to the northwest Atlantic, and have established a third strewn field in western equatorial Pacific and Indian Ocean which may extend to the Mediterranean. Stratigraphically the oldest microspherule layer occurs in the planktonic foraminifer Globigerapsis semiinvoluta Zone about 0.5 m.y. prior to the closely spaced crystal bearing microspherule layer and North American microtektite layer in the Globorotalia cerroazulensis Zone. Major element composition of the G. semiinvoluta Zone layer and the crystal bearing microspherule layer overlap, but there is a clear trend towards higher Al2O3 and FeO values in SiO2 equivalent microspherules of the latter layer. The G. semiinvoluta Zone microspherules also contain a higher percentage of non-crystalline spherules (microtektites) than the crystal bearing microspherule layer, but lower than the North American microtektite layer. Excess iridium due to an abrupt increase in supply is associated with the middle crystal bearing microspherule layer and to a lesser extent with the other two layers. But, Ir excess due to concentration as a result of carbonate loss was also observed at two sites (462, 612). The three late Eocene microspherule layers do not precisely coincide with planktonic foraminiferal species extinctions, but a major faunal assemblage change is associated with the G. semiinvoluta Zone layer. Abundant pyrite is present in the North American microtektite layer of DSDP Site 612 suggesting reducing conditions possibly due to a sudden influx of biologic matter (dead bodies) to the ocean floor, and the crystal bearing microspherule layer coincides with five radiolarian extinctions. All three microspherule layers are associated with decreased carbonate possibly due to sudden productivity changes, increased dissolution as a result of sea-level and climate fluctuations, or the impact events. 相似文献
18.
J. C. Brandt M. F. A'Hearn C. E. Randall D. G. Schleicher E. M. Shoemaker A. I. F. Stewart 《Earth, Moon, and Planets》1996,72(1-3):243-249
Arguments are presented for a substantial, unexplored population of comets with radii less than 1 km. Known examples confirm this population and extrapolation of any plausible size-distribution function indicates large numbers. However, their accurate numbers, orbital characteristics, and physical properties are unknown. Thus, even though the small comets may be the most frequent cometary bodies impacting the planets, a quantitative evaluation is not currently possible. We advocate an optimized, dedicated search program to characterize this population. 相似文献
19.
I. D. Benekos C. A. Shoemaker J. R. Stedinger 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):375-390
Groundwater contamination risk assessment for health-threatening compounds should benefit from a stochastic environmental
risk assessment which considers the effects of biological, chemical, human behavioral, and physiological processes that involve
elements of biotic and abiotic aquifer uncertainty, and human population variability. This paper couples a complex model of
chemical degradation and transformation with movement in an aquifer undergoing bioremediation to generate a health risk analysis
for different population cohorts in the community. A two-stage Monte Carlo simulation has separate stages for population variability
and aquifer uncertainty yielding a computationally efficient and conceptually attractive algorithm. A hypothetical example
illustrates how risk variance analysis can be conducted to determine the distribution of risk, and the relative impact of
uncertainty and variability in different sets of parameters upon the variation of risk values for adults, adolescents, and
children. The groundwater example considers a community water supply contaminated with chlorinated ethenes. Biodegradation
pathways are enhanced by addition of butyrate. The results showed that the contribution of uncertainty to the risk variance
is comparable to that of variability. Among the uncertain parameters considered, transmissivity accounted for the major part
of the output variance. Children were the most susceptible and vulnerable population cohort. 相似文献
20.
西藏丁青弧前蛇绿岩的地球化学特征 总被引：9，自引：4，他引：9
丁青蛇绿岩位于班化湖－丁青－怒江蛇绿岩带的东段，其地幔岩出露规模是该带中最大的。本文报道的丁青蛇绿岩主要由地幔橄榄岩、堆晶岩、辉长岩和斜长花岗岩组成。蛇绿岩剖面上覆硅岩中的放射虫化石是早株罗世和晚三叠世诺利克期的，中侏罗统砂岩和砾岩不整合覆盖在蛇绿岩之上，由此确定丁青蛇绿岩是晚三叠－早侏罗世的，在中株罗世之前侵位，丁青蛇绿岩属于玻安岩系，玻安岩的特点是富Si、Mg和大离子亲石元素（LILE），贫高场强元素（Ti、P、Zr、Y、Yb和Nb）。丁青蛇绿岩的堆晶岩、辉长岩和辉绿岩均具“U”型REE分布，暗示丁青玻安岩是由于亏损的地幔源岩和来自消减带的水和流体两组分的混合形成的。丁青玻安岩的地球化学特征类似西太平洋第三纪玻安岩，而明显不同于MORB的地球化学性质， 表明丁青玻安岩应当形成于洋内岛弧的弧前环境，属于弧前蛇绿岩。 相似文献