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This paper presents the numerical simulation results of cluster pumping test in a heterogeneous aquifer with transmissivity variability described by the model of a stationary random field of its logarithm with a given scale of correlation in the plan. The case of a comparable planar distance to observation wells and correlation scale is considered. The parameters of the model of transmissivity heterogeneity of the simulated aquifer have been obtained from the data of experimental tests carried out within the Yuzhno-Voronezhskoye groundwater field. The simulation has shown that the average results of interpretation of the cluster pumping data correspond to the geometric value of the transmissivity, which confirms the previously obtained approximate theoretical result for the model of small-scale heterogeneity and extends it to an important case of the similarity of cluster well test planar sizes and the spatial scale of heterogeneity. This study confirmed the possibility of applying standard methods in processing cluster pumping data under horizontal heterogeneity conditions to estimate the equivalent aquifer transmissivity in the well cluster location area.

We developed a method to estimate aquifer transmissivity from the hydraulic-head data associated with the normal cyclic operation of a water supply well thus avoiding the need for interrupting the water supply associated with a traditional aquifer test. The method is based on an analytical solution that relates the aquifer's transmissivity to the standard deviation of the hydraulic-head fluctuations in one or more observation wells that are due to the periodic pumping of the production well. We analyzed the resulting analytical solution and demonstrated that when the observation wells are located near the pumping well, the solution has a simple, Dupuit like form. Numerical analysis demonstrates that the analytical solution can also be used for a quasi-periodic pumping of the supply well. Simulation of cyclic pumping in a statistically heterogeneous medium confirms that the method is suitable for analyzing the transmissivity of weakly or moderately heterogeneous aquifers. If only one observation well is available, and the shift in the phase of hydraulic-head oscillations between the pumping well and the observation well is not identifiable. Prior knowledge of aquifer's hydraulic diffusivity is required to obtain the value of the aquifer transmissivity.

Information on recharge value is necessary for solving different classes of hydrogeological problems. One of the methods of recharge estimation is simulation of flow in vadose zone. Soil hydraulic parameters are used to estimate recharge by flow in vadose zone. One of the hydraulic parameters is the pore connectivity parameter l. The sensitivity of estimated recharge to the value of pore connectivity parameter, especially under humid climate conditions, is studied insufficiently. In present study, the experimental values of soil hydraulic parameters of samples from two different sites with various landscape conditions and vadose zone structure (forest landscape on sand and field landscape on loam) were used to estimate recharge.Recharge estimation was also carried for the value of l=0,5 and for reported values of l parameter for certain type of sediment. Analysis of calculation results demonstrated that using fixed value of l=0,5 leads to significant overestimation of calculated recharge both for forest and filed landscapes, which emphasizes the importance of experimental definitions of soil hydraulic parameters for recharge estimation. The analysis of the water balance components showed that the increase of estimated recharge with enhancement of l value is mainly associatedwith the decrease of evaporation from the upper soil layer.

Sanitary protection zones (SPZ) of water intakes allocate on the time of movement from the outer boundary of the zone to the water intakes. For example, for zone II it is the time of microbial contamination transport, accepted for target aquifers insufficiently protected from the surface, which is equal to 400 days. For zone III, this is the time of chemical pollution transport equal to the estimated lifetime of the water intake. To calculate the spatial position of the boundaries of these zones, analytical and numerical methods are used based on the integration of equations for the velocities of neutral particles in the groundwater flow, the flow field of which formed by the superposition of the natural flow velocities and the disturbances imposed on it by groundwater abstraction. When these methods are used, the only configuration of the sanitary protection zone that corresponds to some homogeneous or heterogeneous spatial field of hydraulic parameters obtained from field materials and (or) from the solution of the inverse problem is obtained as a result of calculations. At the same time, possible variations of SPZ boundaries are not considered due to local hydraulic heterogeneity, which is not taken into account in the water intake model. The article analyzes the influence of vertical hydraulic heterogeneity on the formation of sanitary protection zones in the layered heterogeneous aquifer. Random stationary fields of normally distributed logarithms of hydraulic conductivity were used as a basis for the model of hydraulic heterogeneity. As a result, the sizes of the first and second zones of sanitary protection were estimated and the comparative analysis of the received values with the sizes of SPZ was carried out, which were determined without taking into account model hydraulic heterogeneity. The analysis showed that the consideration of model hydraulic heterogeneity leads to a significant increase in the sanitary protection zones.

The relationship between groundwater recharge in a small river basin to the current and expected climatic changes in the European area of Russia has been analyzed using the catchment basin of the Zhizdra River (Kaluga Region) as an example. The analysis is based on modeling of moisture transformation processes on the earth’s surface and moisture transfer in the unsaturated zone. The global climate predictions of five CMI5 Coupled Atmosphere–Ocean General Circulation Models (GCM) have been applied to forecast the groundwater recharge in the second half of the 21st century using the LARSWG5 forecast weather conditions generator. Despite the fact that all used GCMs predict a warming by 2–6°C in the studied region, the difference in the predicted recharge values is still considerable due to the difference in the predicted dryness index.

Estimating streambed hydraulic conductivity is particularly important in arid and semi-arid regions, where surface water infiltration from ephemeral dryland streams helps maintain riparian ecosystems. In situ permeameter tests are widely used to estimate the hydraulic conductivity of streambed sediments. Previous studies have demonstrated that one of the major factors controlling spatiotemporal variations in streambed hydraulic conductivity in such areas is streambed clogging by suspended sediments. Recently, a modified Hvorslev (1951) formula was theoretically proposed to account for the effect of streambed clogging on streambed hydraulic properties due to suspended particle sedimentation during falling-head tests. To validate the modified formula, fieldwork was conducted at five sites in the lower Heihe River, a typical intermittent river of north-western China, in September 2017. A simple PVC pipe with an inner diameter of 4 cm was used as a permeameter for the field tests. Both muddy river water and clean water were used to fill the permeameter to conduct comparative tests. To differentiate the interpretation of the field testing data obtained with clean water, the data obtained with muddy river water were analysed with an equation considering an iteratively increasing total hydraulic resistance of riverbed sediments due to the effects of riverbed clogging. The estimated vertical hydraulic conductivity for the top 0.3 m of riverbed sediments varied from 1 to 41 m/day. The proposed model was shown to accurately estimate the hydraulic conductivity of riverbed sediments using both clean and muddy water during slug tests.

International audience; Global climate warming disproportionately affects high-latitude and mountainous terrestrial ecosystems. Warming is accompanied by permafrost thaw, shorter winters, earlier snowmelt, more intense soil freeze-thaw cycles, drier summers, and longer fire seasons. These environmental changes in turn impact surface water and groundwater flow regimes, water quality, greenhouse gas emissions, soil stability, vegetation cover, and soil (micro)biological communities. Warming also facilitates agricultural expansion, urban growth, and natural resource development, adding growing anthropogenic pressures to cold regions" landscapes, soil health, and biodiversity. Further advances in the predictive understanding of how cold regions" critical zone processes, functions, and ecosystem services will continue to respond to climate warming and land use changes require multiscale monitoring technologies coupled with integrated observational and modeling tools. We highlight some of the major challenges, knowledge gaps, and opportunities in cold region critical zone research, with an emphasis on subsurface processes and responses in both natural and agricultural ecosystems.

Despite the significance of river leakage to riparian ecosystems in arid/semi-arid regions, a true understanding and the accurate quantification of the leakage processes of ephemeral rivers in these regions remain elusive. In this study, the patterns of river infiltration and the associated controlling factors in an approximately 150-km section of the Donghe River (lower Heihe River, China) were revealed using a combination of field investigations and modelling techniques. The results showed that from 21 April 2010 to 7 September 2012, river water leakage accounted for 33% of the total river runoff in the simulated segments. A sensitivity analysis showed that the simulated infiltration rates were most sensitive to the aquifer hydraulic conductivity and the maximum evapotranspiration (ET) rate. However, the river leakage rate, i.e., the ratio of the leakage volume to the total runoff volume, of a single runoff event relies heavily on the total runoff volume and river flow rate. In addition to the hydraulic parameters of riverbeds, the characteristics of ET parameters are equally important for quantifying the flux exchange between arid ephemeral streams and underlying aquifers. Coupled surface/groundwater models, which aim to estimate river leakage, should consider riparian zones because these areas play a dominant role in the formation of leakage from the river for recharging via ET. The results of this paper can be used as a reference for water resource planning and management in regulated river basins to help maintain riparian ecosystems in arid regions.

Groundwater pumping and changes in climate-induced recharge lead to lower groundwater levels and significant changes in the water balance of a catchment. Water previously discharged as evapotranspiration can become a source of pumpage. Neglecting this effect leads to overestimated streamflow depletion. A small river basin (Sudogda River Basin, Russia) with a boreal climate and with long-term records of groundwater head and streamflow rate (showing that the measured stream depletion is less than the pumping rate) was investigated. The role of evapotranspiration in the water balance was analyzed by a hydrogeological model using MODFLOW-2005 with the STR package; the annual variation in recharge was obtained with the codes Surfbal and HYDRUS. The Sudogda River Basin was classified according to landscape and unsaturated-zone texture classes, and for each classified zone, the unsaturated-zone flow simulation was used to calculate the annual recharge dynamics for the observation period. Calibration of the regional flow model was conducted using flow and head observations jointly for two steady-state flow conditions—natural (before pumping started) and stressed (pumping). The simulations showed that pumped water originates from three sources: intercepted baseflow (75% of the annual total pumping rate), the capture of groundwater evapotranspiration discharge plus increased groundwater recharge (17%), and induced stream infiltration (8%). Additionally, multi-year precipitation records were analyzed to detect any long-term recharge and pumping water-budget changes. The results showed that increasing groundwater recharge by natural precipitation leads to (1) decreased intercepted baseflow and induced streamflow infiltration and (2) increased intercepted evapotranspiration discharge, thereby reducing stream depletion.

Widely distributed in arid and semiarid regions, phreatophytic roots extend into the saturated zone and extract water directly from groundwater. In this paper, we implemented a vegetation optimality model of root dynamics (VOM-ROOT) in the Noah land surface model with multi parameterization options (Noah-MP LSM) to model the extraction of groundwater through phreatophytic roots at a riparian site with a hyperarid climate (with precipitation of 35 mm/yr) in northwestern China. VOM-ROOT numerically describes the natural optimization of the root profile in response to changes in subsurface water conditions. The coupled Noah-MP/VOM-ROOT model substantially improves the simulation of surface energy and water fluxes, particularly during the growing season, compared to the prescribed static root profile in the default Noah-MP. In the coupled model, more roots are required to grow into the saturated zone to meet transpiration demand when the groundwater level declines over the growing season. The modeling results indicate that at the study site, the modeled annual transpiration is 472 mm, accounting for 92.3% of the total evapo- transpiration. Direct root water uptake from the capillary fringe and groundwater, which is supplied by lateral groundwater flow, accounts for approximately 84% of the total transpiration. This study demonstrates the importance of implementing a dynamic root scheme in a land surface model for adequately simulating phreatophytic root water uptake and the associated latent heat flux.

Increased attention to precipitation changes in permafrost-dominated Siberia is promoted by intensified flooding under climate warming. The observed daily precipitation spanning 60 years (1959–2018) from 129 meteorological stations across the Siberian lowlands with elevations less than 500 m (50°N–70°N, 60°E–140°E) captures significant changes in both annual and extreme precipitation. For 1959–2018, the average annual precipitation over the Siberian lowlands was 428 ± 110 mm. The average annual precipitation in non-permafrost zones was approximately 458 ± 114 mm, larger than that in permafrost zones (407 ± 102 mm). Additionally, non-permafrost zones experienced greater intensities and frequencies of precipitation extremes than permafrost zones according to four extreme precipitation indices (i.e., R99p, R95p, R×5d, and R10mm). However, the rate of increase in precipitation and precipitation extremes was greater in permafrost zones than in non-permafrost zones. These results obtained from in situ observations are generally consistent with ERA5 precipitation reanalysis data. Given faster warming in permafrost than in non-permafrost zones, the rate of increase in precipitation and precipitation extremes in permafrost zones also respond more than those in non-permafrost zones. In particular, summer precipitation in permafrost zones accelerates permafrost degradation, and the release of carbon dioxide and methane from permafrost sediments is very likely to have positive feedback effects on regional temperature and precipitation increases. Our results indicate that Siberia will face risks attributable to increased precipitation and precipitation extremes in the context of climate warming, and such risks will be greater in the permafrost zones than in the non-permafrost zones.

Diffusion coefficients for Na + was measured in low-permeability samples (diameter of 3 cm and average length of 7 cm) from the deep disposal site of the Siberian Chemical Combine (SCC) using the end-diffusion technique. The direction of diffusion was perpendicular to the direction of bedding. Special equipment was designed and constructed for the experiment. Two types of concentration observations were used. For non-sorbing Na+, EC sensors and the length distribution of sorbed elements were used. The synthetic solution used in the experiments was a model of the low-activity contaminant of the SCC and consisted of NaNO3 (25 g/L) and nitrate compounds of Cs+, Ni2+, Co2+, and Sr2+ (100 mg/L each). The measured values of the effective diffusion coefficients De for Na+ from 1.92 × 10−11 to 1.70 × 10−10 m2/s. The microstructure was studied with X-ray microtomography for the same cores. Image shooting was performed on undisturbed microsamples with a size of 0.913 mm (7003 vox). Spatial correlation analysis was performed after the binarization of each obtained 3-D structure. This analysis showed that the spatial correlation scale of the indicator variogram is considerably smaller than the microsample length. Then, a numerical simulation of the Laplace equation with binary coefficients for each microsample was performed. The results were analysed in the form of a plot of the tortuosity versus the porosity. Pore-scale simulations show a nonlinear decrease in the tortuosity with decreasing porosity. Exponential values in the range between 1.8 and 2.4 were found by fitting this graph with Archie's model. Anisotropic tortuosity is also detected in the horizontal and vertical directions. The diffusion coefficients of non-sorbing Na + measured in this study agree with those of the pore-scale diffusion simulation of the microtomography data.

Surface water infiltration from ephemeral dryland streams is particularly important in hyporheic exchange and biogeochemical processes in arid and semi-arid regions. However, streamflow transmission losses can vary significantly, partly due to spatiotemporal variations in streambed permeability. To extend our understanding of changes in streambed hydraulic properties, field investigations of streambed hydraulic conductivity were conducted in an ephemeral dryland stream in north-western China during high and low streamflow periods. Additionally, streamflow transmission losses were numerically estimated using combined stream and groundwater hydraulic head data and stream and streambed temperature data. An analysis of slug test data at two different river flow stages (one test was performed at a low river stage with clean water and the other at a high river stage with muddy water) suggested that sedimentation from fine-grained particles, i.e., physical clogging processes, likely led to a reduction in streambed hydraulic properties. To account for the effects of streambed clogging on changes in hydraulic properties, an iteratively increasing total hydraulic resistance during the slug test was considered to correct the estimation of streambed hydraulic conductivity. The stream and streambed temperature can also greatly influence the hydraulic properties of the streambed. One-dimensional coupled water and heat flux modelling with HYDRUS-1D was used to quantify the effects of seasonal changes in stream and streambed temperature on streamflow losses. During the period from 6 August 2014 to 4 June 2015, the total infiltration estimated using temperature-dependent hydraulic conductivity accounted for approximately 88% of that using temperature-independent hydraulic conductivity. Streambed clogging processes associated with fine particle settling/wash up cycles during flow events, and seasonal changes in streamflow temperature are two considerable factors that affect water infiltration in ephemeral dryland streams. Our results show that time series measurements of stream and sediment temperature and surface and groundwater head can be used to effectively determine the seasonal dynamics of streambed water exchange. Such combined heat and head monitoring at field sites is useful for calibrating regional surface-groundwater models. The results of this study may provide insights into hyporheic exchange in ephemeral dryland streams.

Based on the actual meteorological data that characterize statistically significant changes in the air temperature and the amount of precipitation in the southwest of the Moscow artesian basin, the conditions that form the water balance and groundwater recharge are modeled. The comparison of the calculated longterm average values for the previous (1965–1988) and recent (1989–2012) periods made it possible to estimate the climate changes in the elements of water balance and groundwater recharge. Based on the maps of longterm average groundwater recharge for these periods, which were constructed using the results of modeling, the estimation of the change in natural resources of groundwater in the territory was performed, showing an increase of 9% (780000 m3/day).

The well-known White method (A method of estimating ground-water supplies based on discharge by plants and evaporation from soil: Results of investigation in Escalante Valley, Utah. Washington D.C, US Geological Survey. Water Supply Paper 659-A United States Department of the Interior, 1932) based on diurnal water table observations has been widely applied to estimate groundwater evapotranspiration (ETG) from phreatophyte vegetation. One of the limitations of this method is its large uncertainties in quantifying the daily groundwater recovery rate (r), which is assumed to be equal to the average rate of groundwater level rise between midnight (i.e., 00:00 h) and 04:00 h. Recent studies pointed out that ETG is highly dependent on the shape and duration of the diurnal clear-sky solar radiation curve and that using the groundwater recovery rate over a short interval of nighttime hours to represent the daily r may lead to large uncertainties in ETG estimates. In this study, we analysed the dependence of the estimated daily r on the sunset and sunrise timings. Numerical experiment results showed that the estimated r is highly sensitive to the duration between sunset and sunrise, which varies seasonally. Instead of using fixed time spans (TSs), e.g., from midnight to 04:00 h, we recommend a more universal method for determining the TS, which is associated with the sunset and/or sunrise timings and used to estimate the daily r. This dynamic TS approach was tested at a Tamarix ramosissima-dominated riparian site with a hyper-arid climate (precipitation of 35 mm a−1) in northwestern China. Compared with the observed evapotranspiration (ET), our approach showed better performance and less subjectivity in estimating ETG than the traditional White approach.

Despite the increasing Siberian river discharge, the sensitivity of streamflow to climate forcing/permafrost thawing is poorly quantified. Based on the Budyko framework and superposition principles, we detected and attributed the changes in streamflow regimes for the three great Siberian rivers (Ob, Yenisei, and Lena) during 1936–2019. Over the past 84 years, streamflow of Ob, Yenisei and Lena has increased by ∼7.7%, 7.4% and 22.0%, respectively. Intensified precipitation induced by a warming climate is a major contributor to increased annual streamflow. However, winter streamflow appears to be particularly sensitive to temperature. Whilst rising temperature can reduce streamflow via evapotranspiration, it can enhance groundwater discharge to rivers due to permafrost thawing. Currently, every 1 °C rise in temperature likely leads to 6.1%–10.5% increase in groundwater discharge, depending on the permafrost condition. For permafrost-developed basins, the contribution to increased streamflow from thawing permafrost will continue to increase in the context of global warming.

Groundwater recharge by precipitation is the main source of groundwater resources, which are widely used in the European part of Russia (ER). The main goal of the presented studies is to analyze the effect of observed climate changes on the processes of groundwater recharge. For this purpose analysis of long-term meteorological data as well as water budget and groundwater recharge simulation were used. First, meteorological data of 22 weather stations, located from south (Lat 46°) to north (Lat 66°) of ER for historical (1965–1988) and modern (1989–2018) periods were compared to investigate the observed latitudinal changes in annual and seasonal averages of precipitation, wind speed, air temperature, and humidity. Second, water budget in critical zone was simulated, using codes SURFBAL and HYDRUS-1D. SURFBAL generates upper boundary conditions for unsaturated flow modelling with HYDRUS-1D, taking into account snow accumulation and melting as well as topsoil freezing, which are important processes that affect runoff generation and the infiltration of meltwater. Water budget and groundwater recharge simulations based on long-term meteorological data and soil and vegetation parameters, typical for the investigated region. The simulation results for the historical and modern periods were compared to find out the impact of climate change on the average annual and seasonal averages of surface runoff, evapotranspiration, and groundwater recharge, as well as to assess latitudinal differences in water budget changes. The results of the simulation showed, that despite a significant increase in air temperature, groundwater recharge in the southern regions did not change, but even increased up to 50–60 mm/year in the central and northern regions of ER. There are two main reasons for this. First, the observed increase in air temperature is compensated by a decrease in wind speed, so there was no significant increase in evapotranspiration in the modern period. Also, the observed increase in air temperature and precipitation in winter is the main reason for the increase in groundwater recharge, since these climate changes lead to an increase in water infiltration into the soil in the cold period, when there is no evapotranspiration.

Water supply in Voronezh city, Russian Federation with the population more than 1,1 million people are based only on the groundwater of alluvial the Neogene-Quaternary (N-Q). Due to the riverbank filtration (RBF), the contaminated groundwater provinces with iron pollution formed in the alluvial aquifer. The high iron content in groundwater interferes its use for the Voronezh city's water supply. It may even bring about the inevitable water intakes abandonment due to problems with well clogging. We performed the series of field experiments (chemical tests of groundwater, spring, rain, reservoir and pore water, aquifer and bottom sediments) and numerical simulation to detect the potential iron source in pumped groundwater by riverbank water wells. We found that during the RBF, two contrary processes of Fe behaviour take place. On the one hand, the iron accumulation and transformation due to the iron hydroxides reduction by dissolved organic matter, occur in the bottom sediment. On the other hand, we observe the iron removal process from the bottom sediment due to Fe migration with attracted surface water along hydraulic pathways "surface water – bottom sediments – aquifer – pumping wells". Finally, the mix of the attracted water with dissolved iron with natural Fe-free groundwater coming from the watershed forms the iron concentration pattern in pumping groundwater. The simulation results show that in the 3rd year of the RBF, the iron content reaches a maximum value in pumping groundwater and does not change for the operation time (25 years). Moreover, we have shown that during the long RBF, the iron pollution area will extend and even the northern and southern aquifer parts of the water intake facility will be contaminated by iron.

The well-known Hvorslev (1951) formula was developed to estimate soil permeability using single-well slug tests and has been widely applied to determine riverbed hydraulic conductivity using in situ standpipe permeameter tests. Here, we further develop a general solution of the Hvorslev (1951) formula that accounts for flow in a bounded medium and assumes that the bottom of the river is a prescribed head boundary. The superposition of real and imaginary disk sources is used to obtain a semi-analytical expression of the total hydraulic resistance of the flow in and out of the pipe. As a result, we obtained a simple semi-analytical expression for the resistance, which represents a generalization of the Hvorslev (1951). The obtained expression is benchmarked against a finite-element numerical model of 2-D flow (in r-z coordinates) in an anisotropic medium. The results exhibit good agreement between the simulated and estimated riverbed hydraulic conductivity values. Furthermore, a set of simulations for layered, stochastically heterogeneous riverbed sediments was conducted and processed using the proposed expression to demonstrate the potential associated with measuring vertical heterogeneity in bottom sediments using a series of standpipe permeameter tests with different lengths of pipe inserted into the riverbed sediments.

The main purpose of this work is to evaluate diffuse groundwater recharge and its temporal dynamics at sites with different landscapes and soil profiles under observed and projected climate variability. Three typical sites with different landscapes and topsoil profiles were chosen for the field study. Field work consisted of pit development and soil sample collection for laboratory study using the centrifuge method. Soil hydraulic parameters were obtained by the RETC code using the observed values of volumetric water content vs. pressure head. HYDRUS-1D code was used to estimate groundwater recharge based on a 70-year (1945–2015) meteorological dataset with daily resolution (including values of precipitation, air temperature, wind speed, and humidity). This dataset was preprocessed using our SURFBAL code to calculate the surface and topsoil water and energy balance. Retrospective historical simulation results showed that there was a considerable variation in the mean annual groundwater recharge values (49–104 mm/year) for the three studied profiles. The temporal change in groundwater recharge occurred relatively synchronously at all sites and was governed by the change in the current annual aridity index. The results of this historical simulation did not reveal any traces of climate change in the groundwater recharge of the studied region in the last 30–40 years. To predict the recharge variations in the second half of the 21st century, the LARSWG forecast weather generator with the climate projections of the 5th General Circulation Models (GCMs) from the Coupled Model Intercomparison Project 5 (CMIP5) family was used. On average in the case of climate development under the maximum greenhouse gas emissions RCP8.5 scenario, there will be a reduction in groundwater recharge in the studied region in 2060–2080, caused by two factors: change of aridity index, which determines evapotranspiration during a warm season and the accumulation of snow and subsequent meltwater infiltration during the snowmelt periods.

A steady-state flow regime in riverbank well fields is often violated by fluctuations in river stages and variations in groundwater extraction. In this study, a criterion of quasi-steady flow during filtration processes at riverbank well fields was introduced. Under the assumption of steady-state flow, an analytical approach for determining the key hydraulic parameters (aquifer transmissivity and riverbed filtration resistance) between a stream and a hydraulically connected aquifer during riverbank filtration was presented. An optimal regular observation network (consisting of the locations of monitoring wells and the observation regime), which is based on the model-oriented approach using an example of a riverbank well field near the Kuybyshev Reservoir, Russia, was designed to minimise the uncertainty in the estimates of hydraulic parameters. The analyses showed that the initial recession in the surface water levels for the simplest constant groundwater withdrawal patterns can be used to determine the key hydraulic parameters; the error in these estimated parameters was less than 7% or 12%, depending on the designed monitoring network. When comparing the two typical monitoring networks, observation line A-A that passes midway through the water supply wells performed better than observation line B-B that passes through the water supply wells when estimating the hydraulic parameters. The results of this study can be used as a reference for designing and optimising a monitoring network that aims to determine the key hydraulic parameters at riverbank well fields. (C) 2015 Elsevier B.V. All rights reserved.

Since 1963, radioactive waste has been injected in deep artesian aquifers of Cretaceous terrigenous deposits in western Siberia. It is well known that geologic heterogeneity strongly affects contaminant transport in unconsolidated formations. To predict the long-term migration of this radioactive waste the effective hydraulic and macrodispersion parameters are estimated by using a three-dimensional high-resolution hydraulic heterogeneity model. The heterogeneous model of the injection area is developed by applying transition probability geostatistics. This model is used to simulate local steady-state groundwater flow and advective transport, leading to numerical estimates of effective hydraulic conductivity and macrodispersion parameters. Mean seepage velocities and effective longitudinal macrodispersion are calculated from observed breakthrough curves for a conservative tracer. Results show that mean horizontal lengths exceed vertical lengths by a factor of more than 30. As a result, vertical effective hydraulic conductivity is two orders of magnitude less than the horizontal effective conductivity. Observed breakthrough curves exhibit long tails and appear to be non-Fickian. Estimated effective longitudinal macrodispersivity in the vertical direction is one order of magnitude less than that in the horizontal direction. Under a Fickian framework, this implies that dispersion modeling for regional transport simulations requires an anisotropic-media dispersion model.

Shallow groundwater is primarily discharged via evapotranspiration (ETg) in arid and semi-arid riparian systems; however, the quantification of ETg remains a challenge in regional water resource assessments of such systems. In this study, the diagnostic indicators of groundwater evapotranspiration processes and the principles of applying the water table fluctuation (WTF) method to estimate ETg based on seasonal groundwater level changes were presented. These techniques were then used to investigate groundwater evapotranspiration processes at two sites dominated by phreatophytes (Tamarix ramosissima and Populus euphratica) within hyper-arid desert environments in northwestern China for the period 2010-2012. The results indicate that steady declines in the water table, which are commonly attributed to groundwater evapotranspiration, occurred at both sites during the growing season. Based on the proposed WTF method, the estimated ETg was 0.63-0.73 mm/d at the Tamarix ramosissima site and 1.89-2.33 mm/d at the Populus euphratica site during the summer months (June-August). Numerical simulations using a one-dimensional root water uptake model indicate that the seasonal variations in ETg at both sites were primarily dependent on the potential evaporation rates. Comparisons with previous studies on plant transpiration at similar sites in this area show that these results are reasonable. It is apparent that the WTF method can provide a simple and relatively inexpensive method of estimating ETg on a large scale in arid/semi-arid regions. However, there are significant uncertainties associated with time-dependent lateral flow rates, which creates a challenge when applying this method. In addition, the selection of calculation periods that show steady declines in the groundwater level can be somewhat subjective. To enhance the performance of the WTF method based on seasonal water table declines, further research on the estimation of lateral flow rates should be performed using an effective network of groundwater monitoring. (C) 2014 Elsevier B.V. All rights reserved.

Regional groundwater flow and transport models were substantiated for the site of underground disposal of liquid radioactive waste from the Siberian Chemical Combine. The migration of a neutral component and two radionuclides (90Sr and U) in groundwaters was predicted for the long-(1000 years) and super-long-term (10 000 years) periods using the microdispersion and macrodispersion approaches. A local model-insert of the lithological and hydraulic heterogeneity was developed for substantiating the macrodispersion parameters. The simulation results show that, during the long-term period, the contaminated waters will be mainly localized within the injection zone (below buffer horizon IV), and during the super-long-term period about 90% of the total amount of neutral wastes will be discharged into the drainage network, whereas uranium will be fully retained within the disposal site.

Over the last few decades, automatic sensors that record groundwater levels at high-frequency intervals have become widely used in groundwater monitoring practice. These sensors provide large amounts of data regarding diurnal groundwater fluctuations, which can be treated as stochastic periodic time series. In this study, a simple relationship between the average standard deviation of diurnal groundwater level fluctuations and the daily evapotranspiration over relatively short periods (days or weeks) was developed for estimating groundwater consumption by phreatophytes in arid/semiarid areas. Our approach allows estimating groundwater evapotranspiration (ETg) using stable statistical characteristics of diurnal groundwater fluctuations, and it is useful for analyzing large amounts of data obtained from digital groundwater level monitoring sensors. A comparison of the ETg results from a synthetic set of groundwater level fluctuations with predefined values shows that this technique behaves consistently and is robust. A numerical analysis of one-dimensional saturated-unsaturated water flow to a root system using Richards' equation indicates that this method provides a reliable estimate of ETg when the basic assumptions of the White method are met. The method was also applied to two phreatophyte-dominated riparian sites in New Mexico to demonstrate its usefulness, which provides better results than the commonly used White method. Key Points A new approach to estimating groundwater evapotranspiration is proposed Diurnal groundwater fluctuation has relative stable statistical characteristics The approach is useful for analysis of large amount of data 2014. American Geophysical Union. All Rights Reserved.

Shallow groundwater is an important source of water for the maintenance and restoration of ecosystems in arid environments, which necessitates a deeper understanding of its complex spatial and temporal dynamics driven by hydrological processes. This study explores the dominant hydrological processes that control the shallow groundwater dynamics in the Gobi Desert-riparian-oasis system of the lower Heihe River, a typical arid inland river basin located in northwestern China. The groundwater level and temperature were monitored in 14 shallow wells at 30-min intervals during the 2010-2012 period. After combining this information with meteorological and hydrological data, a comprehensive analysis was conducted to understand the dynamic behaviour of the shallow groundwater system and to determine the dominant factors that control the groundwater flow processes. The results of the study indicate notably large temporal and spatial variations in both the groundwater level and temperature. Noticeable fluctuations in the groundwater level (0.5-1 m) and temperature (4-8 C) were observed in the riparian zone, evidencing a clear river influence. In comparison, the groundwater fluctuations in the Gobi Desert were more stable (the annual variations of the water table were less than 0.5 m, and the water temperature varied by no more than 2 C). Strong variations in the groundwater table (1.5-5.0 m/year) and temperature (1.5-6.5 C), mainly caused by surface flood irrigation and groundwater pumping, were observed in the oasis area. The investigated sites were categorized into three types that reflect the dominant hydrological processes: (1) the riparian zone, dominated by riverbank filtration and groundwater evapotranspiration; (2) the Gobi Desert area, controlled by groundwater evaporation and lateral recharge; and (3) the oasis area, dominated by groundwater evapotranspiration as well as surface-groundwater interactions caused by human activities. 2012 John Wiley Sons, Ltd.

Development of heterogeneity model of layered sandy-clay formation and impact of this model on transport is considered. The lithological data of more than 250 wells that captured 300 meters formation at the investigated area of 40 km2 are used for model of heterogeneity construction. Two models of heterogeneity were developed with using these well data: TP/MC model based on 3D Markov chain simulation for four hydrofacies and 2D kriging interpolation of thicknesses of elementary lithological layers. Simulation of conservative transport by particle tracking algorithm shows that horizontal transport along layers is similar for both models. The main difference is in vertical transport cross formation bedding. The kriging interpolation model gives more conservative results than TP/MC model due to larger characteristic horizontal length of layers in the kriging model. As the result vertical effective hydraulic conductivity of formation is in two times larger and the first particle arriving time is in four times faster in TP/MC model.

The results of 3D numerical simulation of coupled flow and transport processes of light-waste migration in heterogeneous aquifer with brine are described. The study is based on the geological data and monitoring of deep-well injection of liquid waste at Chepetsk Mechanical Plant (ChMZ, Glazov). The buoyancy of light waste is simulated for the post-injection period of 300 years using different conceptual models of heterogeneity. The procedure of 3D geostatistical simulation based on transition probability analysis with TSIM code of the reservoir heterogeneity is presented. The results of the ascending waste migration simulation using SEAWAT2000 code indicate that both the variable fluid density and the hydraulic heterogeneity must be considered in the forecast models for determining the possible waste distribution during the injection and the post injection periods.

The focus of our investigation was simulating pre-injection and post-injection subsurface conditions at the waste disposal site of liquid radioactive wastes at the Siberian Chemical Complex (SCC). The main environmental and human safety concern posed by this site is related to the potential radionuclide discharge into the nearby Tom River and into the existing public-water-supply well fields located 10–13 km away. Even though (within the site) the two lower injection aquifers are isolated from the upper aquifers by a relatively continuous aquitard, in terms of regional flow they represent one hydrogeologic system that is affected by injection as well as by groundwater withdrawal from the upper aquifers and groundwater discharge into the river. Groundwater flow and transport models were developed to simulate regional flow and waste migration. Even after 1,000 years, none of the simulations indicated that there is any serious potential of high-concentration contamination of water supply wells and the discharge zone. In that time frame, simulation indicated a potential for upward movement of some amounts of contaminants through the heterogeneous sandy-clay aquitard. That is why a conceptual model incorporating heterogeneity of the clay aquitard with the possibility of preferential flow via sandy windows needs to be developed. Additional field characterization of the aquitard properties should be performed along the potential contaminant migration pathways that lead to the groundwater discharge zone.

Numerical models of groundwater flow require hydraulic conductivity values for the gridblocks covering the flow domain. However, field conductivity data are usually measured at a different scale (usually smaller) than that of the gridblocks. The present paper describes an approach for upscaling to block-scale, which combines the rigorous result of small-value perturbation analysis with a plausible generalization of the first-order results to large variance. Steady-state flow through a block of stochastically heterogeneous medium, with constant values of the hydraulic head at the two opposite sides, is analysed. An upscaling rule and relationship is obtained between the local-scale hydraulic conductivity and the expected mean and variance of blockscale conductivity, where the block size is comparable with the correlation scale of the local conductivity field. The rather simple expressions that are obtained are validated using data from numerical experiments. Further, a generalized spatial power-averaging method to calculate the block-scale conductivity from values of local-scale conductivity is developed, in which the exponent value is given as a function of the ratios of flow domain dimensions to the respective correlation length.

Publisher Summary This chapter describes the development of a 3D high-resolution model of Injection Area 18, a disposal site at the Siberian Chemical Complex, to study the impact of heterogeneity on the subsurface spreading of waste. The new feature of this model is the ability to describe in detail the site formation's internal 3D architecture, using a Markov's chain for modeling binary lithological heterogeneity. Numerical studies of transport at this site show that the problem of selecting the best model for predicting long-term regional-scale waste transport at this site still exists. The effective macro-dispersion model and dual-porosity model are competitive approaches for such predications. The simulation of 40 years of injection history, up to the present, to obtain 3D distributions of injected wastes within the studied formation, shows that today, the main mass of waste is predominantly distributed within the sand. The modeling results did not show any significant upward waste movement during 40 years of injection through preferential flow paths that could be formed in such a heterogeneous system. This fact indicates that the anisotropy of effective correlation scales, which leads to the hydraulic anisotropy of the system, prevents vertical migration of injected waste.

Publisher Summary This chapter explains the experimental study measuring the temporal pressure responses in Aquifer IV, overlying Aquitard D, on temporal termination of injection in Aquifer III from overlying formation at the disposal site of the Siberian chemical complex. Specially designed high-resolution hydraulic sensors, connected to digital recording hardware, were used. During all measurement periods, water levels fluctuate synchronously in both monitoring wells with amplitude of 1 cm. Monitoring well A-44, which was closest to the sensor wells, captured an injection interval where the maximum observed drawdown of groundwater head was 6.5 m. After the elimination of atmospheric pressure and Earth tidal responses, residual water level fluctuations in both observation wells do not show a downward trend. This result is additional proof of good isolation of the injected interval from the overlying formation at the disposal site. Processing of measurement results included decomposition of hydrographs in the wells by estimating water-level response to atmospheric pressure time-variation and periodic response to Earth tides.

In this paper, we consider an approach for estimating the effective hydraulic conductivity of a 3D medium with a binary distribution of local hydraulic conductivities. The medium heterogeneity is represented by a combination of matrix medium conductivity with spatially distributed sets of inclusions. Estimation of effective conductivity is based on a self-consistent approach introduced by Shvidler (1985). The tensor of effective hydraulic conductivity is calculated numerically by using a simple system of equations for the main diagonal elements. Verification of the method is done by comparison with theoretical results for special cases and numerical results of Desbarats (1987) and our own numerical modeling. The method was applied to estimating the effective hydraulic conductivity of a 2D and 3D fractured porous medium. The medium heterogeneity is represented by a combination of matrix conductivity and a spatially distributed set of highly conductive fractures. The tensor of effective hydraulic conductivity is calculated for parallel- and random-oriented sets of fractures. The obtained effective conductivity values coincide with Romm's (1966) and Snow's (1969) theories for infinite fracture length. These values are also physically acceptable for the sparsely-fractured-medium case with low fracture spatial density and finite fracture length. Verification of the effective hydraulic conductivity obtained for a fractured porous medium is done by comparison with our own numerical modeling for a 3D case and with Malkovsky and Pek's (1995) results for a 2D case.

The focus of our investigation is simulating local thermal and solute concentration effects on liquid nuclear waste spreading in natural groundwater flow. To study these effects 3-D non-isothermal non-constant density flow and transport model simulated conditions of the radioactive waste injection into a multiple layer system at Siberian Chemical Combine was developed. The used mathematical model includes: equation of continuity, general form of Darcy's law, equation of heat generation and transfer, transport equation for neutral species affected by liquid density and transport equation for radioactive species. The simulation scenario includes 50 years waste injection into a sand aquifer that isolated from top and bottom by semipermeable clay units and after long-term wastes migration in groundwater. Modeling results show that thermal and density effects influence vertical waste spreading. The thermal effect is more significant for radioactive species, while the density effect is more significant for neutral species.

The goal of this work was to develop the methodology and to improve understanding of subsurface radionuclide transport for application to the Lake Karachai Site and to identify the influence of the processes and interactions involved into transport and fate of the radionuclides. The report is focused on two sets of problems, which have to do both with, hydrodynamic and hydrogeochemical aspects of the contaminant transport.

Numerical models of groundwater flow require hydraulic conductivity values to be assigned to the grid blocks covering the flow domain. However, field-measured conductivities tend to be measured at a different scale (usually smaller) than that of the grid blocks. The present paper describes a novel approach for upscaling field values to block-scale, which combines the rigorous result of small-value perturbation analysis with a plausible generalization of the first-order results to large variance. Also the correlation lengths are assumed to be comparable to block size. Steady-state flow through a block of stochastically heterogeneous medium with constant hydraulic head values at the two opposite sides is analyzed. An upscaling rule and relationship is obtained between the local-scale hydraulic conductivity and the expected mean and variance of block-scale conductivity, where the block size is comparable with the correlation scale of the local conductivity field. The rather simple expressions obtained are validated using data from numerical experiments. Furthermore, a generalized spatial power-averaging method to calculate the block-scale conductivity from values of local-scale conductivity is developed, in which the exponent value is given as a function of the ratios of flow domain dimensions to the respective correlation lengths.