Groundwater最新文献

As readers of Groundwater, you have all faced a quizzical look when you told someone that you are a hydrogeologist. You have discovered that simply repeating the word—although, after all, it describes itself—is rarely sufficient. So, you have developed your own short explanation for what a hydrogeologist does and why our work is critical to society (one of my favorite is, “You know that water you drank yesterday? You're welcome.”). If you are in a position to hire an entry-level professional hydrogeologist, you are likely to share something else: a growing concern that there are not enough graduates to fill current demand, let alone future needs for our profession.

In summary, the future of hydrogeology is bright, but we are not producing enough MS-level trained students even to meet the current demand. In addition, universities are moving away from their role as the principal source of master's graduates and are unlikely to fill the future needs of industry or academia.

The good news is that there are several efforts in progress to address this problem. Some programs (e.g., the University of Neuchatel) have strong enrollment and continue to produce graduates. Other programs are coming together to offer multi-university degrees (e.g., the European ERASMUS+ cooperation project iNUX). In addition, there are efforts to redesign the university-based MS to deliver accessible in-person (e.g., the University of Arizona) or hybrid in-person/online programs (e.g., the University of Kansas and the University of Waterloo). There are also extra-university programs that focus on advanced topics (e.g., the Italian SYMPL School of Hydrogeologic Modeling). Finally, there are efforts to make videos and textbooks available for free to support educational programs (e.g., the micro-video project, the Groundwater Modeling for Decision Support Initiative, and the Groundwater Project).

We need all of these efforts to succeed if we hope to produce the workforce that will be needed in the future. However, there is a crucial first step that we need to complete as a community to ensure that future students are receiving the training that they need to enter the profession.

This is where we need your help as groundwater professionals.

Thank you for being part of the Groundwater community and I hope to work with you to advance our profession into the future!

Many sedimentary aquifers consist of small layers of coarser and finer material. When groundwater flow in these aquifers is modeled, the hydraulic conductivity may be simulated as homogeneous but anisotropic throughout the aquifer. In practice, the anisotropy factor, the ratio of the horizontal divided by the vertical hydraulic conductivity, is often set to 10. Here, numerical experiments are conducted to determine the effective anisotropy of an aquifer consisting of 400 horizontal layers of which the homogeneous and isotropic hydraulic conductivity varies over two orders of magnitude. Groundwater flow is simulated to a partially penetrating canal and a partially penetrating well. Numerical experiments are conducted for 1000 random realizations of the 400 layers, by varying the sequence of the layers, not their conductivity. It is demonstrated that the effective anisotropy of the homogeneous model is a model parameter that depends on the flow field. For example, the effective anisotropy for flow to a partially penetrating canal differs from the effective anisotropy for flow to a partially penetrating well in an aquifer consisting of the exact same 400 layers. The effective anisotropy also depends on the sequence of the layers. The effective anisotropy values of the 1000 realizations range from roughly 5 to 50 for the considered situations. A factor of 10 represents a median value (a reasonable value to start model calibration for the conductivity variations considered here). The median is similar to the equivalent anisotropy, defined as the arithmetic mean of the hydraulic conductivities divided by the harmonic mean.

Streamflow records are biased toward large streams and rivers, yet small headwater streams are often the focus of ecological research in response to climate change. Conventional flow measurement instruments such as acoustic Doppler velocimeters (ADVs) do not perform well during low-flow conditions in small streams, truncating the development of rating curves during critical baseflow conditions dominated by groundwater inflow. We revisited an instantaneous solute tracer injection method as an alternative to ADVs based on paired measurements to compare their precision, efficiency, and feasibility within headwater streams across a range of flow conditions. We show that the precision of discharge measurements using salt dilution by slug injection and ADV methods were comparable overall, but salt dilution was more precise during the lowest flows and required less time to implement. Often, headwater streams were at or below the depth threshold where ADV measurements could even be attempted and transects were complicated by coarse bed material and cobbles. We discuss the methodological benefits and limitations of salt dilution by slug injection and conclude that the method could facilitate a proliferation of streamflow observation across headwater stream networks that are highly undersampled compared to larger streams.

Miami-Dade County (MDC) has over 112,000 septic systems, some of which are at risk of compromise due to water table rise associated with sea level rise. MDC is surrounded by protected water bodies, including Biscayne Bay, with environmentally sensitive ecosystems and is underlain by highly transmissive karstic limestone. The main objective of the study is to provide first estimates of the locations and magnitudes of septic return flows to discharge endpoints. This is accomplished by leveraging MDC's county-scale surface-groundwater model using pathline analysis to estimate the transport and discharge fate of septic system flows under the complex time history of groundwater flow response to pumping, canal management, storms, and other environmental factors. The model covers an area of 4772 km² in Southeast Florida. Outputs from the model were used to create a 30-year (2010 to 2040) simulation of the spatial–temporal pathlines from septic input locations to their termination points, allowing us to map flow paths and the spatial distribution of the septic flow discharge endpoints under the simulated conditions. Most septic return flows were discharged to surface water, primarily canals 52,830 m³/d and Biscayne Bay (5696 m³/d), and well fields (14,066 m³/d). Results allow us to identify “hotspots” to guide water quality sampling efforts and to provide recommendations for septic-to-sewer conversion areas that should provide most benefit by reducing nutrient loading to water bodies.

Numerical modeling of the recovery of moisture by injecting warm air in the unsaturated zone in a 100 m × 100 m plot of agricultural land in Kuwait, a country located in an arid environment, was conducted to provide “proof of concept” of the technique. If technically and economically feasible, it will be a potential additional source of water that could be exploited for farming activities and other uses. The COMSOL software was used to develop the model and, based on the results of the scenario runs, the effects of different hydraulic and operational parameters, including that of well spacing, on moisture recovery were assessed. In general, the results suggested that the recovery should increase with the increase in the hydraulic conductivity of the unsaturated zone, the amount of heat input, and the pressure differential between the unsaturated zone and the well head. Within the period examined (0 to 11 days), the recovery decreases with the increase in the soil moisture content, possibly due to the fall in relative permeability to moisture-rich air with the increased water contents in the pore spaces, although the effects may change over a longer period as water contents decrease with moisture recovery. The moisture recovery from the unsaturated zone through the injection of warm air appears to be a feasible proposition from this study that should be demonstrated through a pilot scale experiment in the field.

Supercritical CO₂ (sCO₂) removes water from brine held in pumice stone at levels well above the solubility of water in sCO₂. The higher water removal results from a combination of passive emulsification of water in sCO₂ and viscous fingering of sCO₂ through the saturated pumice. This leads to higher levels of salt deposition than that expected from solubility considerations alone. These deposits could impact the injectivity of sCO₂ as well as its movement in the subsurface. The finding that the water concentration in sCO₂ is not necessarily capped at the solubility limit should influence the parametrization of injection models.

In this paper, we review the derivation of the Gauss–Levenberg–Marquardt (GLM) algorithm and its extension to ensemble parameter estimation. We explore the use of graphical methods to provide insights into how the algorithm works in practice and discuss the implications of both algorithm tuning parameters and objective function construction in performance. Some insights include understanding the control of both parameter trajectory and step size for GLM as a function of tuning parameters. Furthermore, for the iterative Ensemble Smoother (iES), we discuss the importance of noise on observations and show how iES can cope with non-unique outcomes based on objective function construction. These insights are valuable for modelers using PEST, PEST++, or similar parameter estimation tools.