Evaluation of the hydraulic conductivity of aquitards

1993 ◽  
Vol 30 (5) ◽  
pp. 781-800 ◽  
Author(s):  
R. Kerry Rowe ◽  
Prebaharan Nadarajah
Keyword(s):  
Hydraulic Conductivity ◽  
Field Test ◽  
Diffusion Theory ◽  
Time Lag ◽  
Pumping Test ◽  
Biot’S Theory ◽  
Test Analysis ◽  
Biot's Theory ◽  
Vertical Hydraulic Conductivity ◽  
Different Types

The evaluation of the bulk vertical hydraulic conductivity of an aquitard based on its response to the pumping of an adjacent aquifer is examined using Biot's theory. Consideration is given to the errors in interpretation of the results of pumping tests which arise as a result of the time lag associated with different types of piezometers as well as the length of the piezometer. Factors to allow for correction of these errors are presented. Although these factors are originally developed for isotropic aquitards, they can be used for anisotropic aquitards with appropriate modifications described in the paper. A comparison is made between the results obtained from diffusion theory (as assumed in the development of techniques currently used in practice) and the more rigorous Biot's theory. The application of the technique is illustrated by two examples. Key words : hydraulic conductivity, field test, analysis, pumping test, piezometers, anisotropy.

Methods of interpretation of borehole falling-head tests performed in compacted clay liners

2005 ◽  
Vol 42 (1) ◽  
pp. 79-90 ◽  
Author(s):  
Paul Chiasson
Keyword(s):  
Hydraulic Conductivity ◽  
Time Lag ◽  
Past Research ◽  
Quality Assurance Program ◽  
Data Sets ◽  
Compacted Clay ◽  
Clay Liners ◽  
K Value ◽  
Considerable Uncertainty ◽  
Vertical Hydraulic Conductivity

The interpretation of falling-head tests in cased boreholes is discussed. These tests are commonly used to measure hydraulic conductivity of compacted clay liners and are often part of the construction quality assurance program. Three methods of interpretation are reviewed with data sets collected from real tests. Two of these methods have been the subject of past research by other authors: the Hvorslev, or time-lag, method and the velocity method. After the limitations of these two approaches have been underlined, a third method is proposed. It uses a best linear unbiased estimator to fit the theoretical head difference function in a plot of falling water column elevation as a function of time (Z–t method). The Hvorslev method is found unreliable and is not recommended. The velocity method is theoretically sound, but statistical uncertainty can become high when this method is used in testing materials with low hydraulic conductivity, such as clay liners. Materials with low hydraulic conductivity tend to produce scattered velocity plots, creating considerable uncertainty for the estimated k value. The proposed Z–t method is less sensitive to inaccuracies in measurements, yielding a more reproducible result. An interpretation method for stages I and II of two-stage borehole tests is also proposed. This method yields the anisotropy of the liner and the vertical hydraulic conductivity. As a result of inaccuracies in measurements and limited difference between the geometries of stages I and II, the computed anisotropy exhibits significant uncertainty.Key words: clay liners, clay covers, hydraulic conductivity, permeability, in situ test, anisotropy, interpretation.

Saturated Hydraulic Conductivity of Clayey Tills and the Role of Fractures

1990 ◽  
Vol 21 (2) ◽  
pp. 119-132 ◽  
Author(s):  
Johnny Fredericia
Keyword(s):  
Hydraulic Conductivity ◽  
American Studies ◽  
Field Measurements ◽  
Present Knowledge ◽  
Saturated Hydraulic Conductivity ◽  
Field Observations ◽  
Laboratory Measurements ◽  
Vertical Hydraulic Conductivity ◽  
Data Field

The background for the present knowledge about hydraulic conductivity of clayey till in Denmark is summarized. The data show a difference of 1-2 orders of magnitude in the vertical hydraulic conductivity between values from laboratory measurements and field measurements. This difference is discussed and based on new data, field observations and comparison with North American studies, it is concluded to be primarily due to fractures in the till.

Effect of temperature on streambed vertical hydraulic conductivity

2013 ◽  
Vol 45 (1) ◽  
pp. 89-98 ◽  
Author(s):  
Weihong Dong ◽  
Gengxin Ou ◽  
Xunhong Chen ◽  
Zhaowei Wang
Keyword(s):  
Hydraulic Conductivity ◽  
Water Temperature ◽  
Sediment Cores ◽  
Effect Of Temperature ◽  
In Situ Tests ◽  
Effect Of Water ◽  
Vertical Hydraulic Conductivity ◽  
Increasing Trend ◽  
Streambed Vertical Hydraulic Conductivity

In this study, in situ and on-site permeameter tests were conducted in Clear Creek, Nebraska, USA to evaluate the effect of water temperature on streambed vertical hydraulic conductivity Kv. Fifty-two sediment cores were tested. Five of them were transferred to the laboratory for a series of experiments to evaluate the effect of water temperature on Kv. Compared with in situ tests, 42 out of the 52 tests have higher Kv values for on-site tests. The distribution of water temperature at the approximately 50 cm depth of streambed along the sand bar was investigated in the field. These temperatures had values in the range 14–19 °C with an average of 16 °C and had an increasing trend along the stream flow. On average, Kv values of the streambed sediments in the laboratory tests increase by 1.8% per 1 °C increase in water temperature. The coarser sandy sediments show a greater increase extent of the Kv value per 1 °C increase in water temperature. However, there is no distinct increasing trend of Kv value for sediment containing silt and clay layers.

Biot’s theory and granular media

Poromechanics ◽  
2020 ◽  
pp. 191-196
Author(s):  
Nicholas P. Chotiros
Keyword(s):  
Granular Media ◽  
Biot’S Theory ◽  
Biot's Theory

scholarly journals New insights into the drainage of inundated ice-wedge polygons using fundamental hydrologic principles

2021 ◽  
Author(s):  
Dylan R. Harp ◽  
Vitaly Zlotnik ◽  
Charles J. Abolt ◽  
Brent D. Newman ◽  
Adam L. Atchley ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Aspect Ratio ◽  
Annular Region ◽  
Active Layer Thickness ◽  
Conductivity Anisotropy ◽  
Aspect Ratios ◽  
High Anisotropy ◽  
Vertical Hydraulic Conductivity ◽  
Depth Analysis ◽  
Ice Wedge

Abstract. The pathways and timing of drainage from inundated ice-wedge polygon centers in a warming climate have important implications for carbon flushing, advective heat transport, and transitions from carbon dioxide to methane dominated emissions. This research provides intuition on this process by presenting the first in-depth analysis of drainage from a single polygon based on fundamental hydrogeological principles. We use a recently developed analytical solution to provide a baseline for the effects of polygon aspect ratios (radius to thawed depth) and hydraulic conductivity anisotropy (horizontal to vertical hydraulic conductivity) on drainage pathways and temporal depletion of ponded water heights of inundated ice-wedge polygon centers. By varying the polygon aspect ratio, we evaluate the effect of polygon size (width), inter-annual increases in active layer thickness, and seasonal increases in thaw depth on drainage. One of the primary insights from the model is that most inundated ice-wedge polygon drainage occurs along an annular region of the polygon center near the rims. This implies that inundated polygons are most intensely flushed by drainage in an annular region along their horizontal periphery, with implications for transport of nutrients (such as dissolved organic carbon) and advection of heat towards ice wedge tops. The model indicates that polygons with large aspect ratios and high anisotropy will have the most distributed drainage. Polygons with large aspect ratio and low anisotropy will have their drainage most focused near the their periphery and will drain most slowly. Polygons with small aspect ratio and high anisotropy will drain most quickly. Our results, based on idealized scenarios, provide a baseline for further research considering geometric and hydraulic complexities of ice-wedge polygons.

scholarly journals Analysis of Differences in ECG Characteristics for Different Types of Drivers under Anxiety

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Yongqing Guo ◽  
Xiaoyuan Wang ◽  
Qing Xu ◽  
Quan Yuan ◽  
Chenglin Bai ◽  
...  
Keyword(s):  
Traffic Safety ◽  
Road Traffic ◽  
Warning System ◽  
Actual State ◽  
Ecg Signal ◽  
Test Analysis ◽  
Driving Experience ◽  
Road Traffic Safety ◽  
Different Types ◽  
Unpleasant Feeling

Anxiety is a complex emotion characterized by an unpleasant feeling of tension when people anticipate a threat or negative consequence. It is regarded as a comprehensive reflection of human thought processes, physiological arousal, and external stimuli. The actual state of emotion can be represented objectively by human physiological signals. This study aims to analyze the differences of ECG (electrocardiogram) characteristics for various types of drivers under anxiety. We used several methods to induce drivers’ mood states (calm and anxiety) and then conducted the real and virtual driving experiments to collect driver’s ECG signal data. Physiological changes in ECG during the experiments were recorded using the PSYLAB software. The independent sample t-test analysis was conducted to determine if there are significant differences in ECG characteristics for different types of drivers in anxious state during driving. The results show that there are significant differences in ECG signal characteristics of drivers by gender, age, and driving experience, in time domain, frequency domain, and waveform under anxiety. Our findings of this study contribute to the development of more intelligent and personalized driver warning system, which could improve road traffic safety.

scholarly journals The Effect of River Valleys and the Upper Cretaceous Aquitard on Regional Flow in the Dakota Aquifer in the Central Great Plains of Kansas and Southeastern Colorado

1995 ◽  
pp. 11-30
Author(s):  
P. Allen Macfarlane
Keyword(s):  
Hydraulic Conductivity ◽  
Great Plains ◽  
Upper Cretaceous ◽  
Flow System ◽  
Arkansas River ◽  
Local Flow ◽  
Discharge Area ◽  
Regional Flow ◽  
Regional Hydrogeology ◽  
Vertical Hydraulic Conductivity

In his reports on the regional hydrogeology of the central Great Plains, in particular southeastern Colorado and southwestern and central Kansas, Darton considered the Dakota aquifer to be a classic example of an artesian system. Computer simulations of the flow system in this study, however, suggest that the Dakota is not a regional artesian aquifer in the classic sense. Sensitivity analysis of a steady-state vertical profile flow model demonstrates that the flow system in the upper Dakota in western Kansas is heavily influenced by the Upper Cretaceous aquitard, the Arkansas River in southeastern Colorado, and rivers in central Kansas, such as the Saline, that have eroded through the aquitard and into the Dakota to the west of the main outcrop area of the aquifer. The model shows that local flow systems and the vertical hydraulic conductivity of the Upper Cretaceous aquitard heavily influence the water budget and the flow patterns. The aquitard restricts recharge from the overlying water table to underlying aquifers in western Kansas because of its considerable thickness and low vertical hydraulic conductivity. The Arkansas River intercepts ground-water flow moving toward western Kansas from recharge areas south of the river and further isolates the upper Dakota from sources of freshwater recharge. In central Kansas, the Saline River has reduced the distance between confined portions of the aquifer and its discharge area. In essence, this has improved the hydraulic connection between the confined aquifer and its discharge area, thus helping to generate subhydrostatic conditions in the upper Dakota upgradient of the river.

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