scholarly journals Extensometer forensics: what can the data really tell us?

2019 ◽  
Vol 28 (2) ◽  
pp. 637-655
Author(s):  
Thomas J. Burbey
Keyword(s):  
Hydraulic Conductivity ◽  
Land Subsidence ◽  
Numerical Models ◽  
Water Levels ◽  
Depth Interval ◽  
Key Factors ◽  
Specific Storage ◽  
Las Vegas Valley ◽  
Multiple Frequencies ◽  
Parameter Values

AbstractExtensometer data have an advantage over satellite-based data for monitoring land subsidence in that extensometer data provide continuous measurements (hourly or better temporal resolution) at very high precision (several tens of microns) over a known depth interval; the latter is important for isolating groundwater pumping from other causes of land subsidence attributed to tectonics or eustatic adjustments in the Earth’s crust. This investigation aims to identify a semi-analytical procedure for quantifying aquifer and aquitard properties from a single extensometer record in lieu of the time-consuming development of more complex numerical models to quantify and constrain these parameter values. In spite of a limited 12-year record and the fact that water levels both decline and increase on an annual basis, this study successfully and reasonably estimated both aquifer and aquitard parameters at the Lorenzi extensometer site in Las Vegas Valley, Nevada (USA), when compared to the estimates developed numerically. The key factors that allow for estimates of elastic and inelastic skeletal-specific storage and hydraulic conductivity of the aquitards and elastic specific storage and hydraulic conductivity of the intervening aquifers is the presence of pumping cycles at multiple frequencies, and measured heads at all the aquifer units covered in the extensometer record. There is an inherent assumption that the aquitards possess the same hydrologic characteristics and are homogeneous and isotropic. This assumption is also a usual limitation in numerical modeling of these settings because of the complex temporal head relationships occurring within the aquitards that are rarely, if ever, measured.

scholarly journals Parameter estimation of a multiple aquifer-aquitard system from a single extensometer record: Las Vegas, Nevada, USA

2020 ◽  
Vol 382 ◽  
pp. 51-56
Author(s):  
Thomas J. Burbey
Keyword(s):  
Hydraulic Conductivity ◽  
Analytical Procedure ◽  
Las Vegas ◽  
Numerical Models ◽  
Water Levels ◽  
Key Factors ◽  
Specific Storage ◽  
Las Vegas Valley ◽  
Multiple Frequencies ◽  
Parameter Values

Abstract. The purpose of this investigation is to develop a semi-analytical procedure for quantifying aquifer and aquitard properties from a single extensometer record in lieu of the time-consuming development of more complex numerical models to quantify and constrain these parameter values. Despite a limited 12-year record and the fact that water levels both decline and increase on an annual basis, estimates of both aquifer and aquitard parameters have been reasonably estimated at the Lorenzi extensometer site in Las Vegas Valley, Nevada when compared to the estimates developed numerically. The key factors that allow for accurate estimates of elastic and inelastic skeletal specific storage and hydraulic conductivity of the aquitards and elastic specific storage and hydraulic conductivity of the intervening aquifers is the presence of pumping cycles at multiple frequencies, and measured heads at all the aquifer units covered in the extensometer record and the inherent assumption that the aquitards have identical hydrologic characteristics and are homogeneous and isotropic. This latter assumption is also a usual limitation in numerical modelling of these settings because of the complex temporal head relationships occurring within the aquitards that are rarely, if ever, measured.

scholarly journals Coupled Stress-Dependent Groundwater Flow-Deformation Model to Predict Land Subsidence in Basins with Highly Compressible Deposits

Hydrology ◽  
2019 ◽  
Vol 6 (3) ◽  
pp. 78
Author(s):  
Rashvand ◽  
Li ◽  
Liu
Keyword(s):  
Hydraulic Conductivity ◽  
Groundwater Flow ◽  
Land Subsidence ◽  
Three Dimensional ◽  
Deformation Model ◽  
Specific Storage ◽  
Aquifer System ◽  
Horizontal Strain ◽  
Stress Dependent ◽  
Coupled Stress

In this study, a stress-dependent groundwater model, MODFLOW-SD, has been developed and coupled with the nonlinear subsidence model, NDIS, to predict vertical deformation occurring in basins with highly compressible deposits. The MODFLOW-SD is a modified version of MODFLOW (the USGS Modular Three-Dimensional Groundwater Flow Model) with two new packages, NONK and NONS, to update hydraulic conductivity and skeletal specific storage due to change in effective stress. The NDIS package was developed based on Darcy–Gersevanov Law and bulk flux to model land subsidence. Results of sample simulations run for a conceptual model showed that hydraulic heads calculated by MODFLOW significantly overestimated for confining units and slightly underestimated for aquifer ones. Moreover, it showed that applied stress due to pumping changed initially homogeneous layers to be heterogeneous ones. Comparison of vertical deformations calculated by NDIS and MODFLOW-SUB showed that neglecting horizontal strain and stress-dependency of aquifer parameters can overestimate future subsidence. Furthermore, compared to the SUB (Subsidence and Aquifer-System Compaction) package, NDIS is more likely to provide a more accurate compaction model for a complex aquifer system with vertically variable compression (Cc), recompression (Cr), and hydraulic conductivity change (Ck) indices.

Direct Push Technology and Application to Vertical Profiling of Hydraulic Conductivity in Unconsolidated Formations

2003 ◽  
Author(s):  
Wesley McCall ◽  
Thomas M. Christy ◽  
James J. Butler
Keyword(s):  
Hydraulic Conductivity ◽  
Test Data ◽  
Small Diameter ◽  
Cost Effective ◽  
Depth Interval ◽  
Contaminant Migration ◽  
Slug Tests ◽  
Monitoring Wells ◽  
Direct Push ◽  
Vertical Profiling

Direct push (DP) methods provide a cost-effective alternative to conventional rotary drilling for investigations in unconsolidated formations. DP methods are commonly used for sampling soil gas, soil and groundwater; installing small-diameter monitoring wells; electrical logging; cone penetration testing; and standard penetration tests. Most recently, DP methods and equipment for vertical profiling of formation hydraulic conductivity (K) have been developed. Knowledge of the vertical and lateral variations in K is integral to understanding contaminant migration and, therefore, essential to designing an adequate and effective remediation system. DP-installed groundwater sampling tools may be used to access discrete intervals of the formation to conduct pneumatic slug tests. A small-diameter (38mm OD) single tube protected screen device allows the investigator to access one depth interval per advancement. Alternatively, a larger diameter (54mm OD) dual-tube groundwater profiling system may be used to access the formation at multiple depths during a single advancement. Once the appropriate tool is installed and developed, a pneumatic manifold is installed on the top of the DP rod string. The manifold includes the valving, regulator, and pressure gauge needed for pneumatic slug testing. A small-diameter pressure transducer is inserted via an airtight fitting in the pneumatic manifold, and a data-acquisition device connected to a laptop computer enables the slug test data to be acquired, displayed, and saved for analysis. Conventional data analysis methods can then be used to calculate the K value from the test data. A simple correction for tube diameter has been developed for slug tests in highly permeable aquifers. The pneumatic slug testing technique combined with DP-installed tools provides a cost-effective method for vertical profiling of K. Field comparison of this method to slug tests in conventional monitoring wells verified that this approach provides accurate K values. Use of this new approach can provide data on three-dimensional variations in hydraulic conductivity at a level of detail that has not previously been available. This will improve understanding of contaminant migration and the efficiency and quality of remedial system design, and ultimately, should lead to significant cost reductions.

scholarly journals Rates of consumption of atmospheric CO<sub>2</sub> through the weathering of loess during the next 100 yr of climate change

2013 ◽  
Vol 10 (1) ◽  
pp. 135-148 ◽  
Author(s):  
Y. Goddéris ◽  
S. L. Brantley ◽  
L. M. François ◽  
J. Schott ◽  
D. Pollard ◽  
...  
Keyword(s):  
Climate Change ◽  
Reaction Front ◽  
Numerical Models ◽  
Atmospheric Co2 ◽  
Co2 Production ◽  
Depth Interval ◽  
Mississippi Valley ◽  
The South ◽  
The North ◽  
The Future

Abstract. Quantifying how C fluxes will change in the future is a complex task for models because of the coupling between climate, hydrology, and biogeochemical reactions. Here we investigate how pedogenesis of the Peoria loess, which has been weathering for the last 13 kyr, will respond over the next 100 yr of climate change. Using a cascade of numerical models for climate (ARPEGE), vegetation (CARAIB) and weathering (WITCH), we explore the effect of an increase in CO2 of 315 ppmv (1950) to 700 ppmv (2100 projection). The increasing CO2 results in an increase in temperature along the entire transect. In contrast, drainage increases slightly for a focus pedon in the south but decreases strongly in the north. These two variables largely determine the behavior of weathering. In addition, although CO2 production rate increases in the soils in response to global warming, the rate of diffusion back to the atmosphere also increases, maintaining a roughly constant or even decreasing CO2 concentration in the soil gas phase. Our simulations predict that temperature increasing in the next 100 yr causes the weathering rates of the silicates to increase into the future. In contrast, the weathering rate of dolomite – which consumes most of the CO2 – decreases in both end members (south and north) of the transect due to its retrograde solubility. We thus infer slower rates of advance of the dolomite reaction front into the subsurface, and faster rates of advance of the silicate reaction front. However, additional simulations for 9 pedons located along the north–south transect show that the dolomite weathering advance rate will increase in the central part of the Mississippi Valley, owing to a maximum in the response of vertical drainage to the ongoing climate change. The carbonate reaction front can be likened to a terrestrial lysocline because it represents a depth interval over which carbonate dissolution rates increase drastically. However, in contrast to the lower pH and shallower lysocline expected in the oceans with increasing atmospheric CO2, we predict a deeper lysocline in future soils. Furthermore, in the central Mississippi Valley, soil lysocline deepening accelerates but in the south and north the deepening rate slows. This result illustrates the complex behavior of carbonate weathering facing short term global climate change. Predicting the global response of terrestrial weathering to increased atmospheric CO2 and temperature in the future will mostly depend upon our ability to make precise assessments of which areas of the globe increase or decrease in precipitation and soil drainage.

scholarly journals Uncertainty in geological and hydrogeological data

2006 ◽  
Vol 3 (4) ◽  
pp. 2675-2706 ◽  
Author(s):  
B. Nilsson ◽  
A. L. Højberg ◽  
J. C. Refsgaard ◽  
L. Troldborg
Keyword(s):  
Water Resources ◽  
Water Resources Management ◽  
Numerical Models ◽  
Effective Porosity ◽  
Environmental Data ◽  
Specific Yield ◽  
Model Structure ◽  
Specific Storage ◽  
Resources Management ◽  
Hydrogeological Data

Abstract. Uncertainty in conceptual model structure and in environmental data is of essential interest when dealing with uncertainty in water resources management. To make quantification of uncertainty possible it is necessary to identify and characterise the uncertainty in geological and hydrogeological data. This paper discusses a range of available techniques to describe the uncertainty related to geological model structure and scale of support. Literature examples on uncertainty in hydrogeological variables such as saturated hydraulic conductivity, specific yield, specific storage, effective porosity and dispersivity are given. Field data usually have a spatial and temporal scale of support that is different from the one on which numerical models for water resources management operate. Uncertainty in hydrogeological data variables is characterised and assessed within the methodological framework of the HarmoniRiB classification.

Renewed thinking on groundwater age

2021 ◽  
Author(s):  
Grant Ferguson ◽  
Mark Cuthbert ◽  
Kevin Befus ◽  
Tom Gleeson ◽  
Chandler Noyes ◽  
...  
Keyword(s):  
Environmental Flows ◽  
Numerical Models ◽  
Groundwater Age ◽  
Holistic Approach ◽  
Water Levels ◽  
Residence Times ◽  
Groundwater Sustainability ◽  
Long Time ◽  
Mean Residence Times ◽  
Recharge Rates

&lt;p&gt;Groundwater age and mean residence times have been invoked as measures of groundwater sustainability, with the idea that old or &quot;fossil&quot; groundwater is non-renewable. This idea appears to come from the link between groundwater age and background recharge rates, which are also of questionable use in assessing the sustainability of groundwater withdrawals. The use of groundwater age to assess renewability is further complicated by its relationship with flow system geometry. Young groundwaters near recharge areas are not inherently more renewable than older groundwaters down gradient. Similarly, there is no reason to preferentially use groundwater from smaller aquifers, which will have smaller mean residence times than larger aquifers for the same recharge rate. In some cases, groundwater ages may provide some information where groundwater recharge rates were much higher in the past and systems are no longer being recharged. However, there are few examples where the relationship between depletion and changes in recharge over long time periods has been rigorously explored. Groundwater age measurements can provide insights into the functioning of groundwater flow systems and calibration targets for numerical models and we advocate for their continued use, but they are not a metric of sustainable development. Simple metrics to assess groundwater sustainability remain elusive and a more holistic approach is warranted to maintain water levels and environmental flows.&lt;/p&gt;

scholarly journals Evaluating the Effectiveness of a Mine Tailing Cover

1992 ◽  
Vol 23 (3) ◽  
pp. 193-208 ◽  
Author(s):  
Roger B. Herbert
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Flow ◽  
Water Saturation ◽  
Pressure Head ◽  
Mine Tailing ◽  
Clay Layer ◽  
Cover Design ◽  
Water Saturated ◽  
Parameter Values ◽  
Maximal Reduction

This study presents a method for evaluating the effectiveness of a mine tailing cover. The cover is designed with a 0.5 m layer of clay covered by a 1.5 m layer of glacial till; full water saturation of the clay layer is assumed to be necessary for the maximal reduction of oxygen transport through the cover. The evaluation of cover effectiveness is based on: 1) the reduction of leachate production, and 2) the ability of the clay layer to remain water saturated and avoid cracking. Using 1990 precipitation data, the numerical model SUTRA simulates unsaturated flow in the cover, with results interpreted in terms of pressure head variations and vertical discharge from the cover. The modeling results indicate that this cover design would adequately reduce leachate production from a tailing deposit. In addition, the water saturation of the clay layer remains above its plastic limit during a simulated year of normal recharge conditions; it is therefore not likely that the clay layer would crack. A sensitivity analysis with different hydraulic parameter values is performed, and shows that leachate production is most sensitive to clay hydraulic conductivity, while the water saturation of the clay layer is sensitive to both clay hydraulic conductivity and till porosity.

scholarly journals Evaluation of LNAPL Behavior in Water Table Inter-Fluctuate Zone under Groundwater Drawdown Condition

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2337
Author(s):  
Reza Azimi ◽  
Abdorreza Vaezihir ◽  
Robert Lenhard ◽  
S. Hassanizadeh
Keyword(s):  
Numerical Models ◽  
Water Levels ◽  
Injection Point ◽  
Monitoring Wells ◽  
Water Pumping ◽  
Two Factors ◽  
Injection Water ◽  
Phase Liquid ◽  
Flow Through ◽  
Material Grain Size

We investigate the movement of LNAPL (light non-aqueous phase liquid) into and out of monitoring wells in an immediate-scale experimental cell. Aquifer material grain size and LNAPL viscosity are two factors that are varied in three experiments involving lowering and rising water levels. There are six monitoring wells at varying distances from a LNAPL injection point and a water pumping well. We established steady water flow through the aquifer materials prior to LNAPL injection. Water pumping lowered the water levels in the aquifer materials. Terminating water pumping raised the water levels in the aquifer materials. Our focus was to record the LNAPL thickness in the monitoring wells under transient conditions. Throughout the experiments, we measured the elevations of the air-LNAPL and LNAPL-water interfaces in the monitoring wells to obtain the LNAPL thicknesses in the wells. We analyze the results and give plausible explanations. The data presented can be employed to test multiphase flow numerical models.

scholarly journals A NEW HYBRID APPROACH IN THE CALIBRATION OF BOUSSINESQ-TYPE WAVE BREAKING MODELS

2018 ◽  
pp. 24
Author(s):  
Joaquín Moris ◽  
Patricio Catalán ◽  
Rodrigo Cienfuegos
Keyword(s):  
Wave Height ◽  
Wave Breaking ◽  
Numerical Models ◽  
Hybrid Approach ◽  
Boussinesq Equations ◽  
Water Levels ◽  
Statistical Parameters ◽  
Time Space ◽  
Forcing Mechanisms ◽  
Set Up

Wave breaking is one of the main forcing mechanisms in coastal hydrodynamics, driving mean water levels and currents. Understanding its behavior is key in the goal of improving our comprehension of coastal morphodynamics variations. One way to improve our understanding is through the use of numerical models, such as phase-resolving numerical models based on the Boussinesq equations (Kirby, 2016), which are modified to include breaking by the inclusion of a breaking criteria and a dissipation mechanism. Since there is not a universal law capable of characterizing the wave breaking, the existing models must be calibrated. Traditionally, this is done by adjusting wave height profiles and other free surface statistical parameters without explicitly considering the time-space location and duration of the breaking process. Consequently, it is possible to calibrate a model that accurately represents wave elevation statistics parameters, such as wave height and wave set-up; however, it might not necessarily represent the breaking location-duration and therefore, the forcing.

Sign in / Sign up

Export Citation Format

Share Document