Showing papers on "Groundwater flow published in 2019"

Environmental flow limits to global groundwater pumping

Abstract: Groundwater is the world’s largest freshwater resource and is critically important for irrigation, and hence for global food security1–3. Already, unsustainable groundwater pumping exceeds recharge from precipitation and rivers4, leading to substantial drops in the levels of groundwater and losses of groundwater from its storage, especially in intensively irrigated regions5–7. When groundwater levels drop, discharges from groundwater to streams decline, reverse in direction or even stop completely, thereby decreasing streamflow, with potentially devastating effects on aquatic ecosystems. Here we link declines in the levels of groundwater that result from groundwater pumping to decreases in streamflow globally, and estimate where and when environmentally critical streamflows—which are required to maintain healthy ecosystems—will no longer be sustained. We estimate that, by 2050, environmental flow limits will be reached for approximately 42 to 79 per cent of the watersheds in which there is groundwater pumping worldwide, and that this will generally occur before substantial losses in groundwater storage are experienced. Only a small decline in groundwater level is needed to affect streamflow, making our estimates uncertain for streams near a transition to reversed groundwater discharge. However, for many areas, groundwater pumping rates are high and environmental flow limits are known to be severely exceeded. Compared to surface-water use, the effects of groundwater pumping are markedly delayed. Our results thus reveal the current and future environmental legacy of groundwater use. Estimates for when critical environmental streamflow limits will be reached—with potentially devastating economic and environmental effects—are obtained using a global model that links groundwater pumping with the groundwater flow to rivers.

Occurrence and Health Implication of Fluoride in Groundwater of Loess Aquifer in the Chinese Loess Plateau: A Case Study of Tongchuan, Northwest China

Abstract: This study was carried out to delineate the occurrence and spatial distribution of groundwater fluoride in a loess area of China and to determine the geochemical and anthropogenic factors that influence its concentration. Water quality was assessed for drinking purpose by comparing with the national and WHO drinking water guidelines, and the impacts of fluoride on human health were also quantified using the health risk assessment model recommended by the USEPA. The results demonstrate that groundwater in the study area is slightly alkaline in nature, and its quality is generally good except slightly excessive TDS, TH, Na+, F−, and nitrate at some local locations. High-fluoride groundwater is mainly distributed in the southeast part of the study area, which is in accordance with the groundwater flow direction in this area. Groundwater fluoride is mainly of natural origin and is dominantly controlled by natural factors such as pH, specific hydrochemical environment, ion exchange, and saturation state of minerals. Fluoride contributes the most to the total health risk in the present study. Children are at higher health risk than adults in this area. Establishing central water supply system and rainwater harvesting system are suggested to guarantee safe drinking water supply in this area.

The Importance of Interflow to Groundwater Recharge in a Snowmelt-Dominated Headwater Basin

Abstract: Author(s): Carroll, RWH; Deems, JS; Niswonger, R; Schumer, R; Williams, KH | Abstract: Understanding the sensitivity of groundwater generation to climate in a mountain system is complicated by the tight coupling of snow dynamics to vegetation and topography. To address these feedbacks, we combine light detection and ranging (LiDAR)-derived snow observations with an integrated hydrologic model to quantify spatially and temporally distributed water fluxes across varying climate conditions in a Colorado River headwater basin. Results indicate that annual groundwater flow is an important and stable source of stream water. However, interflow decreases during drought as a function increased plant water use and the relative fraction of groundwater to streams increases. Seasonal snowmelt and vegetation water use regulate small recharge rates in the lower portions of the basin, but snowmelt transported via interflow from high mountain ridges toward convergent topographic zones defines preferential recharge in the upper subalpine. Recharge in this zone appears decoupled from annual climate variability and resilient to drought.

Comprehensive simulation of nitrate transport in coupled surface-subsurface hydrologic systems using the linked SWAT-MODFLOW-RT3D model

Abstract: This paper presents SWAT-MODFLOW-RT3D, a model that couples the semi-distributed watershed model SWAT (Soil and Water Assessment Tool) with the groundwater flow model MODFLOW and the groundwater solute reactive transport model RT3D to simulate nitrate (NO3) fate and transport in a watershed system. The model is based on a recently developed SWAT-MODFLOW model, with RT3D now called as a subroutine within the MODFLOW code to provide a single, stand-alone model code. RT3D uses NO3 concentration of deep percolation water from SWAT and groundwater heads and flows from MODFLOW to simulate spatially-varying groundwater NO3 concentration and NO3 loading to/from streams, with the latter used by SWAT to route NO3 mass through the network. Model use is demonstrated through an application to the Sprague River Watershed (4100 km2) in Oregon. Other chemical species of interest can be included in the RT3D reaction module in applications of the model to other watersheds.

Large Earthquake Reshapes the Groundwater Flow System: Insight From the Water‐Level Response to Earth Tides and Atmospheric Pressure in a Deep Well

Abstract: Quantitative evaluation of earthquake‐induced permeability changes is important for understanding key geological processes, such as advective transport of heat and solute and the generation of elevated fluid pressure. Many studies have independently documented permeability changes in either an aquifer or an aquitard, but the effects of an earthquake on both the aquifer and aquitard of the same aquifer system are still poorly understood. In this study, we use the well water‐level response to earth tides and atmospheric pressure to study the changes in hydraulic properties in an aquifer and an overlying confining layer in Beijing, China, following the 11 March 2011 Tohoku earthquake in Japan. Our results show that both the tidal response amplitude and the phase shift increased and that the phase shift changed from negative to positive after the earthquake. We identified increased permeability in both the aquifer and aquitard by the barometric response function method. The horizontal transmissivity of the aquifer increased by a factor of 6, and the vertical diffusivity of the aquitard doubled.

Applied Mathematics in Hydrogeology

Abstract: Conservation Equations Source Functions and Convolution Laplace and Hankel Transforms Drawdown in Confined Aquifers Drawdown in Unconfined Aquifers Heat Transfer and Groundwater Flow Solute Transport Solving Ax=b Finite Element Analysis Inverse Problems Appendix: Notes on Equation Solving

Biogeochemical Regimes in Shallow Aquifers Reflect the Metabolic Coupling of the Elements Nitrogen, Sulfur, and Carbon.

Abstract: Near-surface groundwaters are prone to receive (in)organic matter input from their recharge areas and are known to harbor autotrophic microbial communities linked to nitrogen and sulfur metabolism. Here, we use multi-omic profiling to gain holistic insights into the turnover of inorganic nitrogen compounds, carbon fixation processes, and organic matter processing in groundwater. We sampled microbial biomass from two superimposed aquifers via monitoring wells that follow groundwater flow from its recharge area through differences in hydrogeochemical settings and land use. Functional profiling revealed that groundwater microbiomes are mainly driven by nitrogen (nitrification, denitrification, and ammonium oxidation [anammox]) and to a lesser extent sulfur cycling (sulfur oxidation and sulfate reduction), depending on local hydrochemical differences. Surprisingly, the differentiation potential of the groundwater microbiome surpasses that of hydrochemistry for individual monitoring wells. Being dominated by a few phyla (Bacteroidetes, Proteobacteria, Planctomycetes, and Thaumarchaeota), the taxonomic profiling of groundwater metagenomes and metatranscriptomes revealed pronounced differences between merely present microbiome members and those actively participating in community gene expression and biogeochemical cycling. Unexpectedly, we observed a constitutive expression of carbohydrate-active enzymes encoded by different microbiome members, along with the groundwater flow path. The turnover of organic carbon apparently complements for lithoautotrophic carbon assimilation pathways mainly used by the groundwater microbiome depending on the availability of oxygen and inorganic electron donors, like ammonium.IMPORTANCE Groundwater is a key resource for drinking water production and irrigation. The interplay between geological setting, hydrochemistry, carbon storage, and groundwater microbiome ecosystem functioning is crucial for our understanding of these important ecosystem services. We targeted the encoded and expressed metabolic potential of groundwater microbiomes along an aquifer transect that diversifies in terms of hydrochemistry and land use. Our results showed that the groundwater microbiome has a higher spatial differentiation potential than does hydrochemistry.

Hydrogeochemical, seawater intrusion and oxygen isotope studies on a coastal region in the Puri District of Odisha, India

Abstract: Groundwater is the major source of freshwater in coastal areas, and gradual declining of water quality is a major cause of concern. The present study is focused on a coastal aquifer, to study the groundwater chemistry, hydrogeochemical characteristics, and salinization processes in a coastal area of the Puri District of Odisha, southeastern coast of India. Groundwater chemistry reveals, water compositions are generally near neutral to slightly alkaline nature in pH, and the total dissolved solids (TDS) concentrations varies from 150 mg/l in the inland area to 4006 mg/l towards the shorelines. Piper plot shows four principal hydrochemical water types prevailed in the groundwater zones with water composition changes from fresh water to the saline water mixing. The oxygen isotope (δ18O) values are found between −5.3‰ to and −2.96‰, which indicates groundwater compositions were influenced by the evaporation process. Based on Cl− concentrations (0.4–35 meq/l), the saline end-member is mixing of seawater with the groundwater. Calculations of ionic deltas in groundwater show deficiency of Na+, Ca2+, Mg2+, SO42− ions and significantly mixed with seawater and subsequent reactions governed by ion exchange processes in the aquifer. Saturation index shows groundwater were subsaturated to near equilibrium conditions with mineral phases such as dolomite, gypsum, halite and under-saturated with calcite, aragonite and anhydrite. Sulphate depletion observed in groundwater indicates the seawater mixing. Groundwater flow path shows, there is a gradual increasing of TDS concentrations from inland recharge areas to towards the discharge areas of shoreline and groundwater facies changes from Na-K-HCO3 to Na-Mg-Cl type. The coastal aquifers are subjected to the continuous influence of seawater mixing, dissolution of carbonate phase minerals, aided with rock-water interaction, and ion exchange processes are the significant governing factors, which controls the groundwater evolution.

Solving Groundwater Flow Problems with Time Series Analysis: You May Not Even Need Another Model.

Abstract: Time series analysis is a data-driven approach to analyze time series of heads measured in an observation well. Time series models are commonly much simpler and give much better fits than regular groundwater models. Time series analysis with response functions gives insight into why heads vary, while such insight is difficult to gain with black box models out of the artificial intelligence world. An important application is to quantify the contributions to the head variation of different stresses on the aquifer, such as rainfall and evaporation, pumping, and surface water levels. Time series analysis may be applied to answer many groundwater questions without the need for a regular groundwater model, such as what is the drawdown caused by a pumping station? Or, how long will it take before groundwater levels recover after a period of drought? Even when a regular groundwater model is needed to solve a groundwater problem, time series analysis can be of great value. It can be used to clean up the data, identify the major stresses on the aquifer, determine the most important processes that affect flow in the aquifer, and give an indication of the fit that can be expected. In addition, it can be used to determine calibration targets for steady-state models, and it can provide several alternative calibration methods for transient models. In summary, the overarching message of this paper is that it would be wise to do time series analysis for any application that uses measured groundwater heads.

Prediction of groundwater levels from lake levels and climate data using ANN approach

Abstract: There are many environmental concerns relating to the quality and quantity of surface and groundwater It is very important to estimate the quantity of water by using readily available climate data for managing water resources of the natural environment As a case study an artificial neural network (ANN) methodology is developed for estimating the groundwater levels (upper Floridan aquifer levels) as a function of monthly averaged precipitation, evaporation, and measured levels of Magnolia and Brooklyn Lakes in north-central Florida Groundwater and surface water are highly interactive in the region due to the characteristics of the geological structure, which consists of a sandy surficial aquifer, and a highly transmissive limestone confined aquifer known as the Floridan aquifer system (FAS), which are separated by a leaky clayey confining unit In a lake groundwater system that is typical of many karst lakes in Florida, a large part of the groundwater outflow occurs by means of vertical leakage through the underlying confining unit to a deeper highly transmissive upper Floridan aquifer This provides a direct hydraulic connection between the lakes and the aquifer, which creates fast and dynamic surface water / groundwater interaction Relationships among lake levels, groundwater levels, rainfall, and evapotranspiration were determined using ANN-based models and multiple-linear regression (MLR) and multiple-nonlinear regression (MNLR) models All the models were fitted to the monthly data series and their performances were compared ANN-based models performed better than MLR and MNLR models in predicting groundwater levels

Analysis of spatio-temporal variability of surface–groundwater interactions in the Gharehsoo river basin, Iran, using a coupled SWAT-MODFLOW model

Abstract: Although groundwater and surface water are often treated as individual water compartments in hydrological cycle studies, they essentially originate from one source. Such a split approach restricts the optimal usages of these water resources in several water management applications. The present study aims to shed light on the complex interaction of surface–groundwater interactions in terms of groundwater recharge from drainage network towards the adjacent aquafer and conversely, groundwater discharge from the aquifer towards the drainage network in the Gharehsoo River Basin (GRB), with the enclosed Ardabil aquifer, located in northwest Iran. To that end, the Soil and Water Assessment Tool (SWAT), as the surface hydrological model was fully coupled with the latest version of the Modular Three-Dimensional Finite-Difference Groundwater Flow (MODFLOW-NWT) (Newton–Raphson Technique to improve the solutions of unconfined groundwater-flow problems). The total study period, i.e. 1978–2012 was split into two intervals for calibration (1988–2012) and validation (1978–1987). To facilitate and expedite the calibration of the coupled model, first we calibrated SWAT and MODFLOW-NWT independently against the observed streamflow and groundwater head time series, respectively. Afterwards, we recalibrated the coupled model SWAT-MODFLOW. To link these two models, the surface and sub-surface water flow components are exchanged between the Disaggregated Hydrological Response Units (DHRUs) of SWAT with the MODFLOW-NWT’ grid cells. In addition, three more flow components are sequentially exchanged: the deep percolation from SWAT to MODFLOW-NWT, baseflow/groundwater discharge from MODFLOW-NWT to SWAT, and the river heads from SWAT to MODFLOW-NWT. The results of the application show that the coupled model satisfactorily, quantified by R2 ≥ 0.5, simulates streamflow and particularly, groundwater heads. In fact, both observations and simulations indicate that, owing to an ongoing overexploitation of the aquifer, heads have been decreased steadily over the studied period which has led to a parallel decline of the groundwater storage. Moreover, the analysis of the stream–aquifer exchange flows indicates that groundwater discharge towards the stream-network (effluent conditions) is orders of magnitude higher than the opposite process (influent conditions). In addition, findings reveal that many of the tributaries across the GRB have shifted from a perennial regime to ephemeral/intermittent system over the past decades. The provided and well-tested coupled model would be a viable asset to assess a wide range of plausible scenarios to identify most effective and practical water resource management schemes to recover the severely depleted surface water and groundwater resources of the GRB.

SUTRA, a model for saturated-unsaturated, variable-density groundwater flow with solute or energy transport—Documentation of generalized boundary conditions, a modified implementation of specified pressures and concentrations or temperatures, and the lake capability

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