Aquifer Hydraulic Properties Research Articles

GROUNDWATER CONDITION AND VULNERABILITY IN THE ATHABASCA AND COLD LAKE OIL SANDS REGIONS: GAPS, OPPORTUNTIES AND CHALLENGES

Oil sands development in the Athabasca and Cold Lake oil sands regions of Alberta has raised concerns about potential impacts to groundwater and groundwater dependent ecosystems. This review summarizes the current state of understanding as to how oil sands mining and in situ activities can affect groundwater systems using a stressor-mechanism-response framework. Specific oil sands activities and practices are reviewed, and where possible, described in terms of how they can impact hydraulic head, the hydraulic properties of aquifers, recharge and transport of constituents of concern and linked to observed or potential impacts to groundwater quantity and quality. Groundwater is an important component of the water balance in boreal ecosystems, and specific vulnerabilities related to development are reviewed, including water use, landscape disturbance, groundwater withdrawals, tailings pond seepage, deep well disposal and thermal impacts. Knowledge gaps include lack of baseline data and monitoring of the quantity and quality of groundwater discharge to rivers, lakes and wetlands. One key monitoring challenge is attribution of hydrogeologic responses to specific oil sands stressors given the range of other natural and anthropogenic factors contributing to their variability. Quantitative groundwater exchange mapping, regional-scale isotope mass balance assessment, and broader incorporation of isotopic and geochemical tracers for fingerprinting water sources and incorporation of Indigenous Knowledge appear promising for improved effectiveness of monitoring.

Determination of Aquifer Hydraulic Properties, Aquifer Potential and Vulnerability Characteristics Using Pumping Test and Surface Geophysical Data: A Case Study of Udi and Ezeagu Areas, Southeastern Nigeria

Determination of Aquifer Hydraulic Properties, Aquifer Potential and Vulnerability Characteristics Using Pumping Test and Surface Geophysical Data: A Case Study of Udi and Ezeagu Areas, Southeastern Nigeria

Short high-accuracy tritium data time series for assessing groundwater mean transit times in the vadose and saturated zones of the Luxembourg Sandstone aquifer

Abstract. Among the manifold of environmental tracers at hand, tritium is the only one that can give information on groundwater age within the timescale of 100 years for the entire flow system, i.e., unsaturated and saturated. However, while in the Southern Hemisphere, a single water sample is sufficient for tritium-based young groundwater dating, several tritium measurements spanning multiple years are still needed in the Northern Hemisphere to disentangle the natural cosmogenic tritium input from that caused by the atmospheric thermonuclear weapons tests mainly carried out in the early 1960s. Although it is advised to focus tritium dating on sites where long chronicles of tritium data are available, in this study we tested the potential for short high-accuracy tritium data series (∼4 years) to date groundwater from 35 springs draining the Luxembourg Sandstone aquifer (central western Europe). We determined groundwater mean transit times using the lumped-parameter model approach in a Monte Carlo uncertainty estimation framework to provide uncertainty ranges inherent to the low number of tritium data at hand and their related analytical errors. Our results show that unambiguous groundwater mean transit time assessments cannot be determined solely based on such recent short tritium time series, given that several ranges of mean transit times appeared theoretically possible. Nonetheless we succeeded in discriminating groundwater mean transit times in the vadose and saturated zones of the aquifer through a stepwise decision process guided with several supplementary data. The mean transit time required for water to cross the vadose zone was estimated to be between 0.5±0.5 and 8.1±1.2 years depending on the spring, while for water to flow through the saturated zone, it varied from 5.7±2.4 to 18.9±4.6 years (median ± half of the 5–95 percentile range). Our findings are consistent with both the tritium measurements of individual springs and the hydrogeological context of the study area. We specifically corroborated the dating results using the known hydrogeological properties of the Luxembourg Sandstone aquifer, the hydrochemistry of the studied springs, and their discharge dynamics. When translated into water velocities (which average ∼12 and ∼170 m yr−1 for the vadose and the saturated zones, respectively), the tritium dating results mirrored the horizontal–vertical anisotropy of the aquifer's hydraulic properties caused by the bedded character of the Luxembourg Sandstone. In addition to improving our understanding of water transit times in the Luxembourg Sandstone aquifer, this study demonstrates how it is currently possible to use short tritium time series to date young groundwater bodies at new sites in central Europe.

Groundwater potential assessment in parts of Nnewi Industrial Zone: Implications for sustainable development and conservation

Integrated field geological and geophysical (Vertical Electrical Sounding VES and 2D Electrical Resistivity Tomography ERT) investigations were carried out in the Nnewi Industrial Zone, SE Nigeria to identify and characterize productive aquifer, aquifer hydraulic properties, and aquifer vulnerability. Data acquired from 17 VES points and across a profile line of about 800 m for the 2D ERT were processed, interpreted, and modeled. Results from the geologic mapping showed that the outcropping units are mainly the sandstone, shaly-sandstone, and less commonly shale of the Nanka and Ogwashi-Asaba Formations which are relatively permeable and offer poor protective cover to the underlying aquifer. Models from the resistivity data showed that the depth-to and thickness of the aquifer vary from 38.60 to 98.80 m and 30.10–177 m, respectively. Aquifer properties estimated from the geophysical data gave values ranging from 0.611127 m2/day to 246.6576 m2/day and 0.1609 m/day to 5.6325 m/day for transmissivity and hydraulic conductivity, respectively, and suggestive of low – moderate aquifer potential. Aquifer Protective Capacity APC distribution modeled from the longitudinal conductivity values, and the aquifer vulnerability modeled using the DRASTIC method indicate that the study area is characterized by poor – moderate APC and low – moderate – high aquifer vulnerability, respectively. Analysis shows that the modeled aquifer parameters, APC, and aquifer vulnerability have similar trend which tends to improve towards the southern and more specifically southeastern parts of the study area, suggesting that even though aquifer units were identified all through the study area, the southeastern parts are best suited for the development of groundwater exploitation schemes. Also, aquifer vulnerability model results recommend that proper and efficient waste disposal schemes are put in place to conserve groundwater quality from pollution from industrial waste since the aquifer in the area is relatively vulnerable.

Hydrogeological trends in an alluvial valley in the Brazilian semiarid: Impacts of observed climate variables change and exploitation on groundwater availability and salinity

Study regionMimoso Alluvial Valley, Semiarid Brazil. Study focusThis study aims to assess the influence of climate variability and exploitation on groundwater accessibility, quantity and quality, based on a spatiotemporal data analysis from long-term monitoring field campaigns, conducted monthly from 2000 to 2019. This study successfully identified representative stable monitoring points, piezometers and wells, for piezometric and salinity levels employing the technique of relative differences, taking into account aquifer hydraulic properties. Trend analysis was then carried out adopting the Mann-Kendall Method, Sen's Slope test, Pettitt test, and the Seasonal Trend decomposition through the Loess (STL) method. Principal Component Multivariate Analysis (PCA) was also employed to validate long-term analysis of annual groundwater levels, rainfall, evapotranspiration, and pumping rates. New hydrological insights for the regionThe spatial-temporal variability of salinity is closely linked to the salt balance in regions with low hydraulic permeability and groundwater use for irrigation. Groundwater salinity presented a strong link between rainfall and groundwater levels. A temporal rise in evapotranspiration alongside declines in rainfall and groundwater levels was observed, potentially exacerbating groundwater scarcity alongside intensified aquifer exploitation. Furthermore, groundwater salinity presented a decreasing trend for the pumping wells and no trends for piezometers. This could potentially disrupt future irrigation plans and cause long-term water shortages in a region already under severe water scarcity. Hence, groundwater pumping constitutes a positive management alternative for controlling groundwater salinity in the domain.

Evaluation of aquifer parameters through integrated approach of geophysical investigations, pumping test analysis and Dar-Zarrouk parameters in the central part of Bari Doab, Punjab, Pakistan.

In the central part of Bari Doab in Punjab Province of Pakistan, the factors such as sporadic rainfall pattern, decrement of water in rivers, subsurface salinity and excessive mining of groundwater have badly affected the hydrogeology and recharge system of aquifer. The present research work is an endeavour to evaluate the characteristics and potential of aquifer for its future sustainable availability within the study area of central part of Bari Doab. The geophysical studies, pumping tests data, borehole logs and Dar-Zarrouk parameters were used integrally to evaluate the aquifer hydraulic and hydrologic parameters in the study area. VES technique of geophysical investigations using Schlumberger electrodes configuration was carried out at sparsely distributed 435 locations. Litho-logs and VES results altogether decipher that the subsurface alluvial succession is primarily composed of intermixed layers of sand, gravel, clay, silt and some kankar inclusions. The VES data allied with pumping test analysis of test wells in the study area were used to evaluate the aquifer hydraulic properties. Comparatively low values of discharge rate, hydraulic conductivity and transmissivity were evaluated in two wells whilst relatively higher values of these parameters were evaluated in rest of six wells. The results of hydrologic parameters also confirm the results of hydraulic parameters in the wells. Finally, the Dar-Zarrouk parameters were used for the estimation of hydraulic parameters for whole study area and the aquifer zones of relatively high and low potential were delineated.

Hydrogeologic and magmatic controls on phreatomagmatism at the La Garrotxa monogenetic volcanic field (NE of Iberian Peninsula)

Phreatomagmatism caused by direct interaction of erupting magma and groundwater is a common phenomenon accompanying monogenetic volcanism. The controls on the type of phreatomagmatic phases and deposits that can be observed in such eruptions have been attributed to magma ascent rate, magma rheology, magma discharge, magma vesiculation, water availability, and the properties of the interacting aquifer (i.e., permeability, pore water pressure, recharge rate, etc.). The La Garrotxa monogenetic volcanic field displays a wide variety of eruption sequences and deposits among its 50 volcanoes, half of them including phreatomagmatic phases with very distinct characteristics. Using the characteristics of the phreatomagmatic deposits, including the lithology and content of the accidental lithic fragments, and the substrate stratigraphy and its hydrogeology through the analysis of available information on the water wells and boreholes of the area, it is evident that several aquifers with very different lithologic and hydraulic properties have interacted with the erupting magmas. Moreover, these same data show that all the phreatomagmatic explosions nucleated at a maximum depth of 200 m. These results suggest that pressure variations inside the eruptive conduit, caused by changes in the recharge rate from the magmatic plumbing system, have played a major role in controlling phreatomagmatism, rather than due to variation of the lithological and hydraulic properties of aquifers.

Statistical Analysis of Aquifer Hydraulic Properties by a Continuous Pumping Tomography Test: Application to the Boise Hydrogeophysical Research Site

AbstractCharacterizing aquifer heterogeneity is paramount for accurate flow and transport modeling. In this work, we present a new approach for statistical analysis of hydraulic properties in continuous pumping tomography tests of a phreatic aquifer. The method entails determining equivalent hydraulic conductivity (Keq), specific storage (Ss,eq), and specific yield (Sy,eq) at many locations in the field and then calculating statistical moments of the equivalent properties, assuming they are random space variables. Equivalent properties are defined as the ones pertinent to a homogeneous aquifer for which the head time dependent signal fits the one observed in the pumping test. Calculation is carried out in a novel approach, by matching measured head data to two separate semianalytical solutions considering two time periods, early and late. We apply this approach to the Boise Hydrogeophysical Research Site and find that the equivalent property spatial averages decrease with horizontal distance from the pumping well and appear to stabilize at sufficiently large distances, in line with existing theory for Keq. The squared coefficient of variation shows similar behavior, with values indicating a weakly heterogeneous aquifer. Furthermore, estimated values for Keq, Ss,eq, and Sy,eq are in agreement with literature values for the site.

Time- and frequency-domain determination of aquifer hydraulic properties using water-level responses to natural perturbations: A case study of the Rongchang Well, Chongqing, southwestern China

Effective management of groundwater resources requires accurate estimates of aquifer hydraulic parameters. One approach for estimating these parameters is to use aquifer water-level responses to natural perturbations, such as barometric pressure and earth tides. In this study, the time- and frequency-domain methods of barometric pressure and earth tide response are used to estimate aquifer hydraulic properties (transmissivity and specific storage), and taking the Rongchang well in Southwest China as an example in application. The results show that the specific storage and transmissivity estimated by the four different methods vary widely, with specific storage ranging from 8.43×10−7 − 4.68×10−5/m and transmissivity ranging from 6.90×10−7 − 3.40×10−6 m2/s. However, the differences in aquifer transmissivity are smaller than the aquifer specific storage. The transmissivity obtained by the slug test is one order lager than those from Barometric (frequency), Barometric (time) and Tidal-Turnadge methods, and two orders of magnitude greater than those of Tidal-Merrit method. The Ss value obtained by the Barometric (time) method is closer to the results of the slug test, while the Ss values obtained by the other three methods are one or two orders of magnitude smaller than the slug test results. In the Tidal-Turnadge method, the uncertainty in the effective porosity introduces an additional uncertainty in the results. The errors in the calculation process are minor in comparing to the uncertainties caused by the model assumptions. For the Rongchang well, the tidal response method averages the hydraulic properties on a larger area than that of CBP model.

Statistical analysis of aquifer hydraulic properties by a continuous pumping tomography test: Application to the Boise Hydrogeophysical Research Site

Statistical analysis of aquifer hydraulic properties by a continuous pumping tomography test: Application to the Boise Hydrogeophysical Research Site

Estimating Hydraulic Conductivity, Transmissibility and Specific Yield of Aquifer in Barind Area, Bangladesh Using Pumping Test

Reliable hydraulic parameters values are essential and crucial basic data for potential groundwater withdrawal (aquifer yield) and also for sustainable groundwater management. They are also essential for simulation model study for different management scenario analyses. The laboratory test has limitations, while in situ tests produce representative aquifer parameters. The pumping test method is the only method that provides simultaneous information on the hydraulic behavior of the well, the aquifer, and the aquifer boundaries. Pumping tests were performed to determine aquifer hydraulic properties such as hydraulic conductivity (K), transmissibility (T), and specific yield (Sy) at two Upazilas of the Barind area, namely Nachol and Niamatpur. The aquifer formation is composed of layers: upper fine sand, medium sand, a conductive sand layer, and lower fine sand at the bottom, below which the impervious clay layer exists. The K was determined through Dupit’s steady radial flow equation, T through Theis’s and Copper-Jacob approach, and Sy through Copper-Jacob and gravity drainage of aquifer materials. The mean K, T, and Sy were found as 30.3 m3/m2/day, 756.7 m3/m/day, and 4.6%, respectively for the Nachol location; and 52.7 m3/m2/day, 1027.3 m3/m/day and 6.6%, respectively for Niamatpur location. The values obtained are supported by regional values reported earlier, and also by other locations’ values situated elsewhere having similar aquifer materials. To achieve long-term sustainability in the studied locations, withdrawal of groundwater resources should be optimized considering the aquifer hydraulic properties values.

Mapping of aquifer hydraulic properties in Ogbeje and Umeghe in Abraka, Delta State Nigeria: insights from geophysical and hydrogeological methods

Vertical Electrical Sounding (VES), Pumping test, well logging and grain size analysis were conducted with the aim of studying the subsurface geophysical formation in order to determine aquifer characteristics such as hydraulic conductivity, transmissivity and other parameters for groundwater exploration purposes around Ogbeje and Umeghe, Abraka Delta State. Nine (9) VES stations were occupied and the results obtained from the computer iterations suggest 4 to 5 geoelectric layers. The aquiferous layers wwerefound at a depth ranging from 20.0 m – 38.3 m with resistivity ranging from 2200 ?m to 8500 ?m and thickness varying between 6.7 and 20.0 m. The VES study reveals the possibility of having a maximum drill depth the o water table of about 38 m. The results obtained from the pumping test and well logginwereas used to estimate the transmissivity value of T = 0.0722 m2/min, storativity S = 0.00063, specific capacity of the well = 0.39 m2/min and hydraulic conductivity, K= 8.5 m/day while the result from the grain size analysis gave hydraulic conductivity as Kmin= 12.96 m/d to Kmax = 26.96 m/d respectively. Thus, these results indicate that the aquifer is capable of proda ucing sufficient amount of water for both domestic and industrial purposes for the people in the area. 

Experimental Study of Artificial Recharge of Unconfined Groundwater Aquifer for Elected Sites in Salahaddin, Iraq

The study aims to assess the efficiency and susceptibility of aquifers and geological formations in Salahaddin to store excess surface water in rainy and flood seasons, to be alternatives for surface aquifers and to achieve an increase in groundwater levels. Five sites that represent several hydrological basins have been selected for artificial recharge experiments, in which two types of experiments were conducted. In the first, the water was injected into the recharge well with monitoring the level in the same recharge well. In the second, water was injected into the recharge well and the water level was monitored in a close well to the recharge one. Test infusion experiments have been conducted in some locations, and data of water level drawdown was drawn in against time in the form of hydrographs, by using Excel program with attempting to analyze groundwater behavior and movement within the unsaturated layers of the aquifer. Then, the hydraulic properties have also been calculated in some locations from pumping tests or artificial recharge experiments and drawing the hydrograph curve using (Aquifer win32). The study concluded that all the aquifers, in which the artificial recharge experiments were carried out, were very efficient in their response to injections, with minor variations due to heterogeneity of porous media and the thickness of unsaturated zones, which cause different permeability between layers, and different hydraulic properties of aquifers.

Groundwater flow near a recirculation well with mixed-type boundary condition along wellbore in confined, unconfined, leaky, or reservoir-covered aquifers

Vertical recirculation wells used for remediation or heat recovery induce drawdown distribution that varies for confined, unconfined, leaky, and reservoir-covered aquifers. A recirculation well with arbitrary arrangement of extraction and injection screen intervals is simulated with the general well function of Perina and Lee (2006) and Perina (2014) after a minor modification. Distribution of radial flux along the screen intervals is determined as part of the solution for the mixed boundary condition along the well-aquifer interface. Drawdown distribution reaches steady state, with the transient period lasting over one year for unconfined aquifer and less than one hour for the other three aquifer types in the example considered. The drawdown distribution varies by aquifer type and shows sensitivity to aquifer hydraulic properties and well construction, suggesting that a recirculation well offers an effective and economical alternative to pumping tests for characterization of aquifer hydraulic properties.

Denitrification in heterogeneous aquifers: Relevance of spatial variability and performance of homogenized parameters

Nitrate contamination of aquifers is threatening the sustainability of water resource production around the globe. Denitrification is an ubiquitous process in groundwater systems and needs to be represented in managerial and predictive efforts. Yet, fully understanding the temporal and spatial dynamics of all biogeochemical and physical properties controlling nitrate reduction at the basin scale remains a challenging task. Conceptual simplifications such as homogenization are used, but their implications on model performance are often not well assessed. This paper (1) analyzes the importance of denitrification spatial variability on the fate of non-point source nitrate contamination, and (2) assesses the performance of upscaled denitrification rate coefficient values. Heterogeneity in the hydraulic conductivity of a typical unconsolidated alluvial aquifer system and its associated uncertainty is systematically represented in our 3D numerical simulations of flow and transport. The spatial variability in the nitrate reduction capacities of the aquifer is accounted for by 3 different conceptual models: a positive and a negative correlation with the aquifer hydraulic properties and a uniform random distribution. Our results indicate that heterogeneity in the denitrification rate coefficient – as well as the model describing spatial variability – has a significant impact on concentration statistics observed at a series of extraction wells. However, we also show that, under the modeling setting used in this study (e.g., stationarity of reactivity), upscaled values of denitrification rate coefficients allow a virtually perfect reproduction of nitrate concentration statistics, a promising outcome for employing parameter estimation (calibration) of effective rate coefficients of denitrification: A detailed description of the spatial variability of the nitrate reduction capacity of the alluvial aquifer is not necessary. Yet, these homogeneous, upscaled denitrification rate coefficients result from a complex interaction between the biochemistry and the physics of the aquifer, which makes their direct estimation a challenging task.

Delineation of discrete conduit networks in karst aquifers via combined analysis of tracer tests and geophysical data

Abstract. Assessment of the karst network geometry based on field data is an important challenge in the accurate modeling of karst aquifers. In this study, we propose an integrated approach for the identification of effective three-dimensional (3D) discrete karst conduit networks conditioned on tracer tests and geophysical data. The procedure is threefold: (i) tracer breakthrough curves (BTCs) are processed via a regularized inversion procedure to determine the minimum number of distinct tracer flow paths between injection and monitoring points, (ii) available surface-based geophysical data and borehole-logging measurements are aggregated into a 3D proxy model of aquifer hydraulic properties, and (iii) single or multiple tracer flow paths are identified through the application of an alternative shortest path (SP) algorithm to the 3D proxy model. The capability of the proposed approach to adequately capture the geometrical structure of actual karst conduit systems mainly depends on the sensitivity of geophysical signals to karst features, whereas the relative completeness of the identified conduit network depends on the number and spatial configuration of tracer tests. The applicability of the proposed approach is illustrated through a case study at the Hydrogeological Experimental Site (HES) in Poitiers, France.

A new modified chloride mass balance approach based on aquifer hydraulic properties and other sources of chloride to assess rainfall recharge in brackish aquifers

AbstractA reasonable estimation of aquifer recharge can assist in the sustainable management of groundwater resources. The methodology to calculate aquifer recharge presents many challenges due to geological complexity and the existence of different water qualities in the aquifer. The classic chloride mass balance (CMB) method has been used widely for aquifer recharge estimation but the assumptions in the equations neglect other sources of chloride than rainfall; chloride accumulation due to evaporation and the hydraulic properties of the recharged aquifer. This research aims to introduce modifications and derive a new CMB equation that covers the shortcomings in the earlier classic CMB approach. The newly developed approach was verified mathematically to identify the sensitive parameters that affect the results of aquifer recharge. Also, it was verified by independent data and method (groundwater modelling) and showed that it is approaching reality about recharge estimation than the earlier classic method which underestimates aquifer recharge especially for brackish aquifers. This article applies the new modified method to sedimentary aquifers of brackish nature and carbonate aquifers predominantly with fresh water and brackish water. In particular, numerical modelling showed that the optimum percentage of aquifer recharge from rainfall for brackish aquifers is between 10% and 20%. Application of the classic method in brackish aquifers in Kuwait estimates the aquifer recharge to be 0.5%–3% due to rainfall, while the modified method yields aquifer recharge of 9.3%–20% from total rainfall which agrees with the results of numerical modelling approach. The application of the classic CMB method for the carbonate aquifers containing fresh to brackish groundwater in the West Bank, gave recharge percentage of 25% from rainfall while the modified method indicated the recharge percentage is 32% from rainfall. The results of the study obtained by the modified CMB technique are proved promising.

Sensitivity of an integrated groundwater flow model to model parameters—application to vulnerability assessment of karst aquifers

The sustainable use and management of groundwater can benefit from improvements to both qualitative and quantitative groundwater vulnerability methods for a variety of hydrogeologic systems. Vulnerability methods in karst aquifers rely on key factors assigned different weights according to their estimated influence on groundwater resilience to contamination. Because of the duality of infiltration and flow in karst aquifers, the assessment of vulnerability may be best validated by a process-based approach involving a selection of key parameters and their coefficients. In this study, an integrated validated numerical groundwater model of a karst catchment area (Lebanon) is used to evaluate the impact of model parameters on recharge and spring discharge and identify important parameters that control the intrinsic system vulnerability. The model sensitivity is evaluated using an automatic calibration tool for local sensitivity analysis in addition to a variance-based local sensitivity assessment of model output time-series to various model parameters for two consecutive years (2016–2017). The influence of each parameter was normalized to estimate standardized weights for each of the process-based key-controlling parameters. Findings indicate greatest model sensitivity to 1) soil (moisture content), 2) fast infiltration through dolines (simulated using a bypass function), 3) climatic parameters (precipitation, melting temperature, and degree-day coefficient), and 4) aquifer hydraulic properties (conduit, matrix), which have been assigned weights according to their impacts on spring hydrographs and recession. Other parameters play less important roles. Based on the results, this method proposes to reevaluate the weighting coefficients of key vulnerability factors in the conventional methods based on a numerical model for the proper delineation of protection zones and the establishment of water protection guidelines. The conclusions and methods from this study can be upscaled to different karst systems and climatic settings and can assist decision makers toward sustainable groundwater development and protection policies based on scientific evidence.

Macrodispersion and Recovery of Solutes and Heat in Heterogeneous Aquifers

AbstractThe recovery efficiency of aquifer storage systems with radial flow fields are studied for heterogeneous aquifers. Macrodispersion, arising from spatially heterogeneous hydraulic conductivity, is modeled as a scale‐dependent mechanical dispersion process. Approximate solutions for the recovery efficiency as a function of local dispersion and macrodispersion parameters, the injection‐extraction rate and duration , and storage cycle count, are derived and validated against numerical simulations. If macrodispersion dominates and the macrodispersion coefficient scales linearly with distance, the recovery efficiency is independent of both . For sublinear and superlinear scalings, recovery increases and decreases respectively if increases. However, if local dispersion dominates, increasing always increases recovery. As macrodispersion becomes increasingly dominant with scale, the recovery efficiency may be a nonmonotonic function of , with a maximum. In homogeneous aquifers, nonmonotonicity does not occur for 1D and 2D radial flow, but occurs for 3D radial flow fields only as a function of , not . These methods may also be used for fitting local dispersion and macrodispersion parameters with push‐pull tests using recovery data, with advantages in scope of applicability and ease of data acquisition and interpretation, compared to existing push‐pull test methods, which fit to breakthrough curves and do not consider macrodispersion. Furthermore, characterizing macrodispersion with push‐pull tests may be advantageous over methods that use observation wells, as observation well placement may be challenging in highly heterogeneous aquifers. The results show that the macrodispersion parameters are not innate aquifer hydraulic properties, as their values vary with flow field geometry.

An improved method to estimate the rate of change of streamflow recession and basin synthetic recession parameters from hydrographs

Recession analysis of -dQ/dt ∼ Q is popularly used for determining catchment storage-discharge relationship, estimating the aquifer hydraulic properties, and predicting low flow processes. However, there are uncertainties arising from the numerical approximation of -dQ⁄dt by the finite difference (ΔQ/Δt) for individual recession and the fitting cloud-like data of -dQ⁄dt ∼ Q for many recession events in a catchment. In this study, we proposed an improved variable time step increment method (IVTS) to minimize the effects of the noisy observations on estimating -dQ⁄dt, and a fitting method in terms of the binning-average of -dQ⁄dt ∼ Q data points to determine the basin synthetic recession parameters. The proposed methods are validated by using numerical generation of recessions with different noises and recession behaviors and the observed hydrographs from twenty catchments in Huai River Basin in China. The results from our proposed method are compared with those from the other popularly used methods. The IVTS method is proven to be robust for approximation of -dQ⁄dt, which can significantly reduce errors of the estimated -dQ⁄dt and the recession slope (b). Combining with the IVTS method, the fitting method in terms of the binning average by splitting range of -dQ⁄dt, instead of Q, could overcome the shortage of traditional recession analysis methods that underestimate the recession slope. Our study indicates that the more accurate and reliable calculation of -dQ⁄dt ∼ Q data and estimation of basin synthetic recession parameters could increase the objectivity in interpretation of recession behaviors and accuracy in perdition of low flow processes.