瞬变电磁法在地下水勘查中的应用综述

水是地球上最重要的天然资源,供人类需要的淡水有95％以上取自地下水,地下水在人类经济活动中发挥着重要的作用．传统的地球物理方法在地下水勘查工作中得到应用的同时,新的更先进的物探方法不断涌现．近年来,瞬变电磁法在国内外的应用得到迅速发展,在地下水勘查领域的应用也得到拓展．与其它电探方法相比,利用瞬变电磁法进行地下水勘查具有明显优势。     

Assessing the restoration time of surface water and groundwater systems under groundwater pumping

Since surface water and groundwater systems are fully coupled and integrated, increased groundwater withdrawal during drought may reduce groundwater discharges into the stream, thereby prolonging both systems’ recovery from drought. To analyze watershed response to basin-level groundwater pumping, we propose a modelling framework to understand the resiliency of surface water and groundwater systems using an integrated hydrologic model under transient pumping. The proposed framework incorporates uncertainties in initial conditions to develop robust estimates of restoration times of both surface water and groundwater and quantifies how pumping impacts state variables such as soil moisture. Groundwater pumping impacts over a watershed were also analyzed under different pumping volumes and different potential climate scenarios. Our analyses show that groundwater restoration time is more sensitive to variability in climate forcings as opposed to changes in pumping volumes. After the cessation of pumping, streamflow recovers quickly in comparison to groundwater, which has higher persistence. Pumping impacts on various hydrologic variables were also discussed. Potential for developing optimal conjunctive management plans using seasonal-to-interannual climate forecasts is also discussed.     

Complexities in Hindcasting Models—When Should We Say Enough Is Enough?

Groundwater models are routinely used in hindcasting applications to predict the past concentration levels in contaminated aquifers. These predictions are used in risk assessment and epidemiological studies, which are often completed either for resolving a court case or for developing a public‐policy solution. Hindcast groundwater modeling studies utilize a variety of computer tools with complexity levels ranging from simple analytical models to detailed three‐dimensional, multiphase, multispecies, reactive transport models. The aim of this study is to explore the value of using complex reactive transport models in hindcasting studies that have limited historic data. I review a chlorinated solvent exposure problem that occurred at a U.S. Marine Corp Base in Camp Lejeune, North Carolina and use it as an example to discuss the limits of hindcasting modeling exercises. The lessons learned from the study are used to reflect upon the following questions related to model complexity: How should we decide how much is enough? Who should decide when enough is enough?     

Impact of watershed topography on hyporheic exchange

Among the interactions between surface water bodies and aquifers, hyporheic exchange has been recognized as a key process for nutrient cycling and contaminant transport. Even though hyporheic exchange is strongly controlled by groundwater discharge, our understanding of the impact of the regional groundwater flow on hyporheic fluxes is still limited because of the complexity arising from the multi-scale nature of these interactions. In this work, we investigate the role of watershed topography on river-aquifer interactions by way of a semi-analytical model, in which the landscape topography is used to approximate the groundwater head distribution. The analysis of a case study shows how the complex topographic structure is the direct cause of a substantial spatial variability of the aquifer-river exchange. Groundwater upwelling along the river corridor is estimated and its influence on the hyporheic zone is discussed. In particular, the fragmentation of the hyporeic corridor induced by groundwater discharge at the basin scale is highlighted.     

Groundwater use by vegetation in a tropical savanna riparian zone (Daly River, Australia)

Soil water matric potentials (Ψ_m) and the deuterium (δ²H) composition at natural abundance levels of xylem water, soil water, river water and groundwater were used to evaluate whether trees use groundwater during the dry season in the riparian zone of the Daly River (Northern Territory, Australia). Groundwater was a significant source of water for plant transpiration, probably accounting for more than 50% of the water transpired during the dry season. Groundwater use occurred either when trees used water from the capillary fringe or when low Ψ_m induced by soil water uptake lifted groundwater in the vadose zone. Several water use strategies were inferred within the riparian plant community. Melaleuca argentea W. Fitzg and Barringtonia acutangula (L.) Gaertn. appeared to be obligate phreatophytes as they used groundwater almost exclusively and were associated with riverbanks and lower terraces with shallow (<5 m) water tables. Several species appeared to be facultative phreatophytes (including Cathorium umbellatum (Vahl.) Kosterm. and Acacia auriculiformis A. Cunn. ex Benth.) and tended to rely more heavily on soil water with increased elevation in the riparian zone. The levee-bound Corymbia bella K.D. Hill and L.A.S. Johnson mostly used soil water and is either a facultative phreatophyte or a non-phreatophyte. The temporal variability in groundwater utilisation by the trees is unclear because the study focused on the end of the dry season only. A decline in the regional water table as a result of groundwater pumping may affect the health of riparian zone vegetation in the Daly River because groundwater use is significant during the dry season.     

Assessment of Groundwater Quality at Yuncheng Basin: Denotation for the Water Management in China

Dramatic decreases in groundwater quality have raised widespread concerns about water supplies and ecological crises in China. In this study, hydrochemistry, stable isotopes, and graphical and multivariate statistical methods are integrated to identify hydrogeochemical processes controlling groundwater quality in the Yuncheng Basin, China. Our results show that groundwater with 21 variables (pH, temperature-T, total dissolved solid, major-trace elements, and stable isotopes) is chemically classified into three distinct clusters: fresh water [C1], brackish-saline water [C2], and saline water [C3]. Groundwater salinization is identified as the prime process in controlling groundwater quality for shallow groundwater and deep groundwater in the lowland areas. Large-scale As, F, or B contaminations found in groundwater are closely related to groundwater salinization, agricultural activity, and the exploration of geothermal water in the area. With respect to the risk of contamination, groundwater in the basin is spatially divided into the following: shallow groundwater with a high risk located in the north side of the Salt Lake, shallow groundwater with a moderate risk, and deep groundwater with a low to moderate risk. Nationally, the increasing demand on groundwater is threatened by a range of environmental and health pressures, including salinization and contaminations of nitrate, As, F, or B. Our study indicates that natural water-rock interactions and hydrogeological conditions are significant factors controlling these contaminations. Systematic management and regulation of existing groundwater resources are required to prevent further deterioration of groundwater resources. Policies should be made and implemented to ensure “green” exploitation of geothermal water.     

Quantifying groundwater sensitivity and resilience over peninsular India

Groundwater in India plays an important role to support livelihoods and maintain ecosystems and the present rate of depletion of groundwater resources poses a serious threat to water security. Yet, the sensitivity of the hydrological processes governing groundwater recharge to climate variability remains unclear in the region. Here we assess the groundwater sensitivity (precipitation–recharge relationship) and its potential resilience towards climatic variability over peninsular India using a conceptual water balance model and a convex model, respectively in 54 catchments over peninsular India. Based on the model performance using a comprehensive approach (Nash Sutcliffe Efficiency [NSE], bias and variability), 24 out of 54 catchments are selected for assessment of groundwater sensitivity and its resilience. Further, a systematic approach is used to understand the changes in resilience on a temporal scale based upon the convex model and principle of critical slowing down theory. The results of the study indicate that the catchments with higher mean groundwater sensitivity (GWS) encompass high variability in GWS over the period (1988–2011), thus indicating the associated vulnerability towards hydroclimatic disturbances. Moreover, it was found that the catchments pertaining to a lower magnitude of mean resilience index incorporates a high variability in resilience index over the period (1993–2007), clearly illustrating the inherent vulnerability of these catchments. The resilience of groundwater towards climatic variability and hydroclimatic disturbances that is revealed by groundwater sensitivity is essential to understand the future impacts of changing climate on groundwater and can further facilitate effective adaptation strategies.     

A variable source area for groundwater evapotranspiration: impacts on modeling stream flow

Evapotranspiration (ET) plays a crucial role in catchment water budgets, typically accounting for more than 50% of annual precipitation falling within temperate deciduous forests. Groundwater ET is a portion of total ET that occurs where plant roots extend to the capillary fringe above the phreatic surface or induce upward movement of water from the water table by hydraulic redistribution. Groundwater ET is spatially restricted to riparian zones or other areas where the groundwater is accessible to plants. Due to the difficulty in measuring groundwater ET, it is rarely incorporated explicitly into hydrological models. In this study, we calibrated Topographic Model (TOPMODEL) using a 14‐year hydrograph record and added a groundwater ET pathway to derive a new model, Groundwater Evapotranspiration TOPMODEL (GETTOP). We inspected groundwater elevations and stream flow hydrographs for evidence of groundwater ET, examined the relationship between groundwater ET and topography, and delineated the area where groundwater ET is likely to take place. The total groundwater ET flux was estimated using a hydrological model. Groundwater ET was larger where the topography was flat and the groundwater table was shallow, occurring within about 10% of the area in a headwater catchment and accounting for 6 to 18% of total annual ET. The addition of groundwater ET to GETTOP improved the simulation of stream discharge and more closely balanced the watershed water budget. Copyright © 2013 John Wiley & Sons, Ltd.     

Formation conditions of useful reserves of Nizhnemzymtinskoe fresh groundwater deposit on Caucasian Black Sea coast and their space and time variations under intense anthropogenic load

The formation conditions of the useful reserves at the Nizhnemzymtinskoe Fresh Groundwater Deposit are considered. The deposit is confined to the lower part of the Mzymta R. valley on the Caucasian Black Sea coast. The main source of reserves formation is surface river water. In the previous years, the reserves depended on the development-induced channel deposits colmatage, whose characteristics were used in the evaluation of groundwater reserves since the 1980s using the method of analogy. The intense construction operation in the river valley in 2010–2011 appreciably increased the colmatage of channel deposits, resulting in a decrease in groundwater reserves. The developed space and time model of the deposit made it possible to take into account not only the spatial characteristic of all factors governing the formation of groundwater reserves, but their time variations as well.     

Assessment of groundwater resources of Quaternary aquifer system in concordance with avoidable negative impact on geoenvironment,south-eastern part of Lithuania

This paper focuses upon south-eastern Lithuanian Quaternary aquifer system groundwater resources formation modelling. Groundwater model calibration has been performed for a pre-development and transient flow conditions. The results demonstrate that there is an intense interaction between groundwater and surface water bodies which form groundwater resources and runoff. For Quaternary cover the majority of unconfined groundwater outflows to surface water streams, the remaining part discharges through the confined interglacial/interstadial aquifers and lateral outflows across the boundaries. Groundwater prognostic exploitable resources can be obtained without a significant negative impact on the geoenvironment. The main sources of exploitable resources formation are increase in groundwater recharge and lateral inflow (40.7%), decreased outflow via streams and lateral boundaries (41.2%) and drawing up additional flow from the hydraulically connected streams (14.5%).     

Underground Temperature Measurements as a Tool for Volcanic Activity Monitoring in the Island of Tenerife, Canary Islands

The spatial distribution of groundwater temperatures in the volcanic island of Tenerife, Canary Islands, has been inferred through measurements of water temperatures collected in the vast network of wells and subhorizontal tunnels, locally called “galleries,” which constitutes the main water supply of the island. The spatial coverage of the network of galleries allows us to reach from depth almost any geological feature of the island. The complex spatial distribution of temperatures in the interior of Tenerife is the result of the complex geological evolution of the island. Groundwater temperatures are greatly affected by groundwater flow and are considerably warmer in those galleries located in areas where water circulation is reduced due to the low permeability of materials and/or to the low infiltration rate of cooling meteoric water. In this sense, groundwater temperature should be characterized in quiescent conditions (background level), in order to facilitate monitoring changes in heat flow, such as those induced by ascending gases expected with an increase in volcanic activity.     

Re-Purposing Groundwater Flow Models for Age Assessments: Important Characteristics

Groundwater flow model construction is often time-consuming and costly, with development ideally focused on a specific purpose, such as quantifying well capture from water bodies or providing flow fields for simulating advective transport. As environmental challenges evolve, the incentive to re-purpose existing groundwater flow models may increase. However, few studies have evaluated which characteristics of groundwater flow models deserve greatest consideration when re-purposing models for groundwater age and advective transport simulations. In this paper, we compare simulated age metrics produced by three MODFLOW-MODPATH models of the same area but with differing levels of complexity (layering and heterogeneity). Comparisons are made at three watershed scales (HUC 8 to HUC 12). Groundwater age metrics, specifically the young fraction and median age of the young and old fractions, are used for evaluation because they relate to intrinsic susceptibility of aquifers and are simpler to interpret than full age distributions used for advective transport. Results indicate that: (1) the young fraction is less sensitive to model layering than the median age of young and old fractions, suggesting that simple models may suffice for basic intrinsic susceptibility assessments; (2) water table mounding and associated discharge into partially penetrating boundaries, such as head-water streams, is important for simulating both the young fraction and the median age of the young fraction; and (3) the influence of partially penetrating head-water streams is maintained regardless of the porosity distribution. Results of this work should aid modelers with evaluating the appropriateness of re-purposing existing groundwater flow models for age simulations.     

Modeling groundwater–surface water interactions using the Dupuit approximation

Global errors in head and/or discharge may be introduced when groundwater flow to a stream is modeled using the Dupuit approximation. We consider a simple case of steady groundwater flow in the vertical plane to a horizontal stream bed in direct connection with the aquifer, and compare solutions to the exact problem with Dupuit solutions where common representations of the stream are chosen. In all cases considered, adopting the Dupuit approximation introduces global errors into the mathematical model, and the magnitude of the errors depends on the regional flow conditions. This behavior makes calibration of a model difficult and limits the predictive abilities of the model under conditions of changed regional flow. The global errors and their dependence on flow conditions can be minimized, but not eliminated by treating the resistance of a fictitious leaky stream bed as an effective parameter.We propose an alternate Dupuit model of groundwater–surface water interaction and demonstrate, for the case considered, that adding a second effective parameter allows us to eliminate global errors in head and discharge, and eliminate the dependence of the effective values on the flow field. Explicit expressions are provided to evaluate the two effective properties. We propose that the results be used as a general guideline for modeling groundwater–surface water interaction at streams.     

Probabilistic risk and uncertainty analysis for bioremediation of four chlorinated ethenes in groundwater

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.     

Groundwater travel time in the freshwater lenses of Samborombón Bay,Argentina

Abstract

The Samborombón Bay area (Argentina) is a coastal plain environment that contains groundwater resources with high salinity. In addition, there are local freshwater lenses associated with shell ridges and sand sheets in the region. In this work, the groundwater travel time in these freshwater lenses is estimated based on their geological conditions, which include hydraulic conductivity, recharge, morphology and discharge to surface freshwater or to saline groundwater. Groundwater travel times in the freshwater lenses were calculated from the equations developed by Chesnaux and Allen. The travel times estimated for the different scenarios were relatively short. The results indicate that the groundwater flow tends to be strongly dependent on the recharge conditions, with an excess of water in the water balance. The results can be applied to help design sustainable management methods to exploit this water resource system and also to assess the impact of contaminant plumes on this groundwater resource.

Citation Carol, E., Kruse, E. & Roig, A. (2010) Groundwater travel time in the freshwater lenses of Samborombón Bay, Argentina. Hydrol. Sci. J. 55(5), 754–762.     

Groundwater Governance in the United States: Common Priorities and Challenges

Groundwater is a critical component of the water supply for agriculture, urban areas, industry, and ecosystems, but managing it is a challenge because groundwater is difficult to map, quantify, and evaluate. Until recently, study and assessment of governance of this water resource has been largely neglected. A survey was developed to query state agency officials about the extent and scope of groundwater use, groundwater laws and regulations, and groundwater tools and strategies. Survey responses revealed key findings: states' legal frameworks for groundwater differ widely in recognizing the hydrologic connection between surface water and groundwater, the needs of groundwater‐dependent ecosystems, and the protection of groundwater quality; states reported a range in capacity to enforce groundwater responsibilities; and states have also experienced substantial changes in groundwater governance in the past few decades. Overall, groundwater governance across the United States is fragmented. States nevertheless identified three common priorities for groundwater governance: water quality and contamination, conflicts between users, and declining groundwater levels. This survey represents an initial step in a broader, continuing effort to characterize groundwater governance practices in the United States.     

A multi‐tracer approach to quantifying groundwater inflows to an upland river; assessing the influence of variable groundwater chemistry

Understanding the behaviour and variability of environmental tracers is important for their use in estimating groundwater discharge to rivers. This study utilizes a multi‐tracer approach to quantify groundwater discharge into a 27 km upland reach of the Gellibrand River in southwest Victoria, Australia. Ten sampling campaigns were conducted between March 2011 and June 2012, and the distribution of ²²²Rn activities, Cl and ³H concentrations imply the river receives substantial groundwater inflows. Mass balances based on ²²²Rn, Cl and ³H yield estimates of groundwater inflows that agree to within ± 12%, with cumulative inflows in individual campaigns ranging from 24 346 to 88 467 m³/day along the studied river section. Groundwater discharge accounts for between 10 and 50% of river flow dependent on the time of year, with a high proportion (>40 %) of groundwater sustaining summer flows. Groundwater inflow is largely governed by regional groundwater flowpaths; between 50 and 90% of total groundwater inflows occur along a narrow 5–10 km section where the river intersects the Eastern View Formation, a major regional aquifer. Groundwater ²²²Rn activities over the 16 month period were spatially heterogeneous across the catchment, ranging between 2000 Bq/m³ and 16 175 Bq/m³. Although groundwater ²²²Rn activities display temporal variation, spatial variation in groundwater ²²²Rn is a key control on ²²²Rn mass balances in river catchments where groundwater and river ²²²Rn activities are within an order of magnitude of each other. Calculated groundwater discharges vary from 8.4 to 15 m³/m/day when groundwater ²²²Rn activities are varied by ± 1 σ. Copyright © 2013 John Wiley & Sons, Ltd.     

Energy considerations in groundwater‐ridging mechanism of streamflow generation

Groundwater ridging is the rapid rise of a shallow water table during a rainfall event, in an environment where, in the pre‐event period, the capillary fringe extends to the ground surface. Groundwater ridging is widely cited to account for the observed significant appearance of pre‐event water in a stream stormflow hydrograph. Various hypotheses have been advanced to explain the groundwater‐ridging mechanism; and most recently, from a field study site in South Africa, an energy hypothesis was proposed, which explains that groundwater‐ridging water‐table rise is a result of rapid introduction and transmission of additional pressure head into the capillary fringe from an intense rainfall at the ground surface. However, there is a need for further analysis and evidence from other field study sites to confirm and support this newly proposed energy hypothesis. The objectives of this paper are, therefore, as follows: to review previous observations on groundwater ridging, from other study sites, in order to deduce evidence of the newly proposed energy hypothesis; to present and evaluate a one‐dimensional diffusion mathematical model that can simulate groundwater‐ridging water‐table rise, based on the newly proposed energy hypothesis; and to evaluate the importance of a capillary fringe in streamflow generation. Analysis of previous observations from other study sites generally indicated that the rate of groundwater‐ridging water‐table rise is directly related to the rainfall intensity, hence confirming and agreeing with the newly proposed energy hypothesis. Additionally, theoretical results by the mathematical model agreed fairly well with the field results observed under natural rainfall, confirming that the rapidly rainfall‐induced energy is diffusively transmitted downwards through pore water, elevating the pressure head at every depth. The results in this study also support the concept of a three‐end‐member stream stormflow hydrograph and contribute to the explanation of how catchments can store water for long periods but then release it rapidly during storm events. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantifying aggregation and change in runoff source in accordance with catchment area increase in a forested headwater catchment

There has been a great deal of research interest regarding changes in flow path/runoff source with increases in catchment area. However, there have been very few quantitative studies taking subscale variability and convergence of flow path/runoff source into account, especially in relation to headwater catchments. This study was performed to elucidate how the contributions and discharge rates of subsurface water (water in the soil layer) and groundwater (water in fractured bedrock) aggregate and change with catchment area increase, and to elucidate whether the spatial variability of the discharge rate of groundwater determines the spatial variability of stream discharge or groundwater contribution. The study area was a 5‐km² forested headwater catchment in Japan. We measured stream discharge at 113 points and water chemistry at 159 points under base flow conditions. End‐member mixing analysis was used to separate stream water into subsurface water and groundwater. The contributions of both subsurface water and groundwater had large variability below 1 km². The contribution of subsurface water decreased markedly, while that of groundwater increased markedly, with increases in catchment area. The specific discharge of subsurface water showed a large degree of variability and decreased with catchment area below 0.1 km², becoming almost constant above 0.1 km². The specific discharge of groundwater showed large variability below 1 km² and increased with catchment area. These results indicated that the variabilities of stream discharge and groundwater contribution corresponded well with the variability of the discharge rate of groundwater. However, below 0.1 km², it was necessary to consider variations in the discharge rates of both subsurface water and groundwater. Copyright © 2016 John Wiley & Sons, Ltd.     

Joint Estimation of Gross Recharge,Groundwater Usage,and Hydraulic Properties within HydroSight

Groundwater management decisions are often founded upon estimates of aquifer hydraulic properties, recharge and the rate of groundwater usage. Too often hydraulic properties are unavailable, recharge estimates are very uncertain, and usage is unmetered or infrequently metered over only recent years or estimated using numerical groundwater models decoupled from the drivers of drawdown. This paper extends the HydroSight groundwater time-series package ( http://peterson-tim-j.github.io/HydroSight/ ) to allow the joint estimation of gross recharge, transmissivity, storativity, and daily usage at multiple production bores. A genetic evolutionary scheme was extended from estimating time-series model parameters to also estimating time series of usage that honor metered volumes at each production bore and produces (1) the best fit with the observed hydrograph and (2) plausible estimates of actual evapotranspiration and hence recharge. The reliability of the approach was rigorously tested. Repeated calibration of models for four bores produced estimates of transmissivity, storativity, and mean recharge that varied by a factor of 0.22-0.32, 0.13-0.2, and 0.03-0.48, respectively, when recharge boundary effects were low and the error in monthly, quarterly, and biannual metered usage was generally <10%. Application to the 30 observation bores within the Warrion groundwater management area (Australia), produced a coefficient of efficiency of ≥0.80 at 22 bores and ≥0.90 at 12 bores. The aquifer transmissivity and storativity were reasonably estimated, and were consistent with independent estimates, while mean gross recharge may be slightly overestimated. Overall, the approach allows greater insights from the available data and provides opportunity for the exploration of usage and climatic scenarios.