Search

One of the major fault zones in the Semmering area runs along the Auebach Valley. In this fault zone a combination of soft fault rocks and water bearing hard rocks led to extremely challenging conditions in the design and execution of the tunnel. In difficult conditions, overlapping exploratory drillings in front of tunnel drive are essential to improve the geological‐hydrogeological model and to assess geotechnical risks. However, in the encountered geological‐hydrogeological conditions, the well‐established exploratory drilling methods reached their limits. Despite the ongoing risk analysis, a very large‐scale water and ground inflow with subsequent tunnel face collapse and development of a sinkhole on the surface occurred during the tunnelling. This paper describes the causes of the incident and the development of procedures to cope with the problem. In addition to the geological‐geotechnical analyses, the article also discusses the limitations of geotechnical surveillance in complex heterogeneous rock masses. [ABSTRACT FROM AUTHOR]

The improvement of surface‐groundwater interactions in land surface models are necessary to determine the evolution of hydrologic variables such as surface runoff, evapotranspiration, soil moisture, and streamflows, especially during dry conditions, when streamflows are largely derived from water releases from groundwater storage. Despite its importance, investigations of the effects of surface‐groundwater interactions on streamflows simulated by large‐scale land surface models are lacking. In this paper, we implement a new parameterization to represent groundwater dynamics in the Canadian Land Surface Scheme (CLASS), which is used for modelling the land surface component in the Canadian regional and global climate models. We compare offline simulations performed with the original and modified versions of CLASS to find the impact of these modifications on the regional hydrology. The offline simulations are driven by ERA‐Interim atmospheric forcing data from the European Centre for Medium‐Range Weather Forecasts reanalysis (for the 1980–2011 period), over a northeast Canadian domain. The original and modified versions of CLASS differ in the soil bottom boundary conditions, with free (gravitational) drainage in the former, while an unconfined aquifer at the depth of bedrock is considered in the latter. Results suggest higher soil moisture levels in the simulation with modified CLASS compared to the original version, particularly for regions with shallow water table. At these locations, summer surface runoff, evapotranspiration and streamflows are also higher in the simulation with modified CLASS, and the simulated low flow values are in better agreement to those observed. This study thus demonstrates the need to account for surface‐groundwater interactions in land surface models for realistic simulation of hydrological processes and streamflows. Difference between CLASS simulations, with and without surface water‐groundwater interactions, for soil moisture (left) and surface runoff (right), for JJA. Surface runoff is higher in the simulation with surface water‐groundwater interactions due to the higher soil moisture levels, which reduces infiltration and increases runoff. [ABSTRACT FROM AUTHOR]

1. This paper is a synthesis of a special issue on groundwater biodiversity with a focus on obligate subterranean species, the stygobionts. The series of papers constitutes a great leap forward in assessing and understanding biodiversity patterns because of the use of large quantitative data sets obtained over a broad geographic scale. They also represent a conceptual shift, away from a purely taxonomic and phylogenetic focus to the analysis of whole groundwater assemblages. 2. The general patterns emerging for groundwater fauna are: very high levels of endemism, low local diversity relative to regional diversity, a limited number of lineages, occurrence of many relicts, and truncated food webs with very few predators. 3. β-Diversity is at least as important as α-diversity in determining total richness at different scales (aquifer, basin and region) and overall taxa richness increases across spatial scales. 4. Advances in understanding groundwater biodiversity patterns further include identification of several important factors related to geology and hydrology that determine the composition of European stygobiotic assemblages. 5. Important challenges for future research include improving sampling strategies, filling gaps in sampling coverage, intensifying research on theoretical and statistical models, and including functional and genetic diversity components in biodiversity assessments. 6. Strategies are proposed for protecting groundwater biodiversity and an argument is made to integrate biodiversity in groundwater management. Applying principles such as complementarity and flexibility for groundwater biodiversity conservation is a major step toward delineating a reserve network that maximise species representation at the European scale. [ABSTRACT FROM AUTHOR]

Convolution is a form of superposition that efficiently deals with input varying arbitrarily in time or space. It works whenever superposition is applicable, that is, for linear systems. Even though convolution is well-known since the 19th century, this valuable method is still missing in most textbooks on ground water hydrology. This limits widespread application in this field. Perhaps most papers are too complex mathematically as they tend to focus on the derivation of analytical expressions rather than solving practical problems. However, convolution is straightforward with standard mathematical software or even a spreadsheet, as is demonstrated in the paper. The necessary system responses are not limited to analytic solutions; they may also be obtained by running an already existing ground water model for a single stress period until equilibrium is reached. With these responses, high-resolution time series of head or discharge may then be computed by convolution for arbitrary points and arbitrarily varying input, without further use of the model. There are probably thousands of applications in the field of ground water hydrology that may benefit from convolution. Therefore, its inclusion in ground water textbooks and courses is strongly needed. [ABSTRACT FROM AUTHOR]

In this paper we present a hydrologic application of a new statistical learning methodology called support vector machines (SVMs). SVMs are based on minimization of a bound on the generalized error (risk) model, rather than just the mean square error over a training set. Due to Mercer's conditions on the kernels, the corresponding optimization problems are convex and hence have no local minima. In this paper, SVMs are illustratively used to reproduce the behavior of Monte Carlo--based flow and transport models that are in turn used in the design of a ground water contamination detection monitoring system. The traditional approach, which is based on solving transient transport equations for each new configuration of a conductivity field, is too time consuming in practical applications. Thus, there is a need to capture the behavior of the transport phenomenon in random media in a relatively simple manner. The objective of the exercise is to maximize the probability of detecting contaminants that exceed some regulatory standard before they reach a compliance boundary, while minimizing cost (i.e., number of monitoring wells). Application of the method at a generic site showed a rather promising performance, which leads us to believe that SVMs could be successfully employed in other areas of hydrology. The SVM was trained using 510 monitoring configuration samples generated from 200 Monte Carlo flow and transport realizations. The best configurations of well networks selected by the SVM were identical with the ones obtained from the physical model, but the reliabilities provided by the respective networks differ slightly. [ABSTRACT FROM AUTHOR]

Conflicts between ecosystems and human needs for fresh water are increasing. The purpose of this paper is to raise awareness in the hydrogeologic community of environmental flows (EFs) and to address the major challenges involved in their protection. Ground water is a key component of EFs, and therefore hydrogeologists are called upon to get involved in the ongoing debates about maintaining healthy riverine ecosystems. Promising opportunities for achieving EFs in both underallocated and overallocated basins as well as new methods for protecting fresh water ecosystems developed in different countries are outlined. EF protection measures include private water trusts, “upside-down instream flow water rights,” the “public trust” doctrine, and water markets, among other measures. A number of knowledge gaps are identified, to which hydrogeologists could contribute, such as our rudimentary knowledge about ground water–dependent ecosystems, aspects of stream-aquifer interactions, and the impacts of land-use changes. The values that society places on the different uses of water ultimately determine where the water is allocated. EF requirements can be legitimately recognized and addressed by basing the environmental needs of hydrologic systems on robust science, focusing on increasing the productivity of water use, engaging society in understanding the benefits and costs of decisions that affect ecosystems, and taking advantage of various opportunities for achieving EF goals. [ABSTRACT FROM AUTHOR]

Studies at the intersection of cognitive science and linguistics have revealed the crucial role that metaphors play in shaping our thoughts about phenomena we cannot see. According to the domains interaction theory of cognition, a metaphoric expression sets up mappings between a target domain that we wish to understand and a familiar source domain. The source domain contains elements (“commonplaces”) that we manipulate mentally, like parts of an analogue model, to illuminate the target domain. This paper applies the structure of domains interaction theory to analyze the dynamics of a metaphor in hydrogeology: the so-called bubble formed by water injected into an aquifer during aquifer storage and recovery (ASR). Of the four commonplaces of bubbles—(1) they are discrete; (2) they are geometrically simple; (3) they rise; and (4) they burst—we focus on the first two using both displacement and dispersion (tracer) models for both homogeneous and heterogeneous storage zones patterned from geological studies of the Suwannee Limestone of Sarasota County, Florida. The displacement model easily shows that “bottle brush” better represents the geometric complexity predicted from the known and inferred heterogeneity. There is virtually no difference, however, in the prediction of recovery efficiency using the dispersion model for a bubble (homogeneous flow zone) vs. bottle brush (heterogeneous flow zone). On the other hand, only the bottle brush reveals that unrecovered tracer is located preferentially in the low-permeability layers that lie adjacent to high-permeability channels in the flow zones. [ABSTRACT FROM AUTHOR]

A precision scale landscape model designed for agricultural applications is described in this paper. The Precision Agricultural Landscape Modeling System (PALMS) is a combination of two process-based models: a diffusive wave runoff model with ponding (described in detail) and a biosphere model with a crops module (briefly reviewed). Several innovations, including numerical formulations for the hydrologic properties of the soil surface with crusting, slope/tillage angle interactions, and change of roughness and detention storage with cumulative precipitation have been included. The model is compared to observations on one 1.8 ha field planted with maize and soybeans during four growing seasons, and one 24 ha field planted with maize during one growing season. Daily average soil moisture is simulated well (within 5 percent volumetric), except in extended runoff/ponding episodes. Physical processes not simulated in the model suggest possible explanations for model errors. Planned improvements for PALMS are also presented. [ABSTRACT FROM AUTHOR]

The term flashiness reflects the frequency and rapidity of short term changes in streamflow, especially during runoff events. Flashiness is an important component of a stream's hydrologic regime. A variety of land use and land management changes may lead to increased or decreased flashiness, often to the detriment of aquatic life. This paper presents a newly developed flashiness index, which is based on mean daily flows. The index is calculated by dividing the pathlength of flow oscillations for a time interval (i.e., the sum of the absolute values of day-to-day changes in mean daily flow) by total discharge during that time interval. This index has low interannual variability, relative to most flow regime indicators, and thus greater power to detect trends. Index values were calculated for 515 Midwestern streams for the 27-year period from 1975 through 2001. Statistically significant increases were present in 22 percent of the streams, primarily in the eastern portion of the study area, while decreases were present in 9 percent, primarily in the western portion. Index values tend to decrease with increasing watershed area and with increasing unit area ground water inputs. Area compensated index values often shift at ecoregion boundaries. Potential index applications include evaluation of programs to restore more natural flow regimes. [ABSTRACT FROM AUTHOR]