Li Wan

China University of Geosciences (Beijing) · School of Water Resources and Environment

Lithium (Li) isotopes have shown large potential in tracing weathering in various water bodies, but there is limited study on Li isotopes in subsurface conditions where CO2 has been largely consumed. In this study, we use a thick sandstone aquifer in the Ordos Basin, NW China, as a natural setting to investigate the behaviors of Li isotopes in hydr...

Causes and water sources of flowing artesian wells attracted the interest of many hydrogeologists throughout history, however, a quantitative model that satisfactorily considers the roles of topography, groundwater recharge/discharge and aquitards on hydraulics of flowing wells is still lacking. In this study, a three-layer river-valley basin with...

Freezing-induced water migration and groundwater level decline are widely observed in regions with shallow water table, but many existing studies trying to quantify freezing-induced groundwater migration do not account for water level fluctuations induced by freezing and thawing. Here, detailed field observations of liquid soil water content and gr...

Improved understanding of interactions among the atmosphere, soil water and groundwater can be achieved by observing time-series of soil-water content and water-table fluctuations in a soil profile. Field observations at a site in China show that from mid-June to mid-September, when evapotranspiration is strong, direct groundwater recharge does not...

The groundwater divide within a plane has long been delineated as a water table ridge composed of the local top points of a water table. This definition has not been examined well for river basins. We developed a fundamental model of a two-dimensional unsaturated-saturated flow in a profile between two rivers. The exact groundwater divide can be id...

Groundwater sampled at the outlets of uncased flowing wells in a thick unconfined aquifer, which has undergone mixing, has been found to have hydrochemistry similar to deep groundwater in discharge areas. To identify the hydrodynamic causes, transient models of groundwater flow and age in a three-dimensional homogeneous unit basin with flowing well...

The Ordos Basin is one of the most intensively studied groundwater basins in China. The Ordos Plateau, located in the north part of the Ordos Basin, is ideal to study the pattern of regional groundwater circulation induced by water-table undulations due to the wavy topography and the relatively simple aquifer systems with macroscopically homogeneou...

Soil saturation is thought to be an important control on plant zonation in intertidal wetlands, but quantitative studies linking saturation and plant zonation in real marsh systems are few. We conducted a combined field and modeling study to examine the potential links between groundwater flow and ecological zonation in a brackish marsh in the Yang...

Radium and radon mass balance models have been widely used to quantify submarine groundwater discharge (SGD) in the coastal areas. However, the losses of radium or radon in seawater caused by recirculated saline groundwater discharge (RSGD) are ignored in most of the previous studies for tracer-based models and this can lead to an underestimation o...

Nested groundwater flow systems have been revealed in Tóth's theory as the structural property of basin-scale groundwater circulation but were only well known with two-dimensional (2D) profile models. The method of searching special streamlines across stagnation points for partitioning flow systems, which has been successfully applied in the 2D mod...

As an indispensable component of groundwater circulation, groundwater evapotranspiration rate (ETG) estimation using water table fluctuations is a hot research topic in the past decades. However, most existing methods for estimating ETG using either diurnal or seasonal water table fluctuations are based on the assumptions that groundwater recharge...

Although it has been reported that flowing artesian wells could be topographically-controlled, there is no quantitative research on artesian flow conditions in unconfined aquifers. In this study, the water table, which has a lower amplitude than the land surface, is damped from the topography and used as the boundary condition to obtain the analyti...

This paper first visits uniqueness, scale, and resolution issues in groundwater flow forward modeling problems. It then makes the point that non-unique solutions to groundwater flow inverse problems arise from a lack of information necessary to make the problems well defined. Subsequently, it presents the necessary conditions for a well-defined inv...

Near- and off-shore fresh groundwater resources become increasingly important with the social and economic development in coastal areas. Although large scale (hundreds of km) submarine groundwater discharge (SGD) to the ocean has been shown to be of the same magnitude order as river discharge, submarine fresh groundwater discharge (SFGD) with magni...

The exchange rate between seawater and groundwater in a tidal flat was investigated at Laizhou Bay, China, where there are large-scale seepage faces with horizontal extension of several hundred meters developed during low tides. Taking into account the effects of seepage face and density, a simple and efficient method for estimating seawater–ground...

The theory of regional groundwater flow is critical for explaining heat transport by moving groundwater in basins. Domenico and Palciauskas’s (1973) pioneering study on convective heat transport in a simple basin assumed that convection has a small influence on redistributing groundwater temperature. Moreover, there has been no research focused on...

Analytical studies on release/capture zones are often limited to a uniform background groundwater flow. In fact, for basin-scale problems, the undulating water table would lead to the development of hierarchically nested flow systems, which are more complex than a uniform flow. Under the premise that the water table is a replica of undulating topog...

Deterioration of grottoes induced by the negative impacts of the variable temperature and moisture conditions has been an important issue in the conservation of heritage sites in China. In this case study, the spatial distributions and varying patterns of moisture and temperature in the caves of Yungang Grottoes, China, were investigated. The relat...

The source region of Yangtze River in China is a part of Tibet Plateau where the hydrological processes are sensitive to climatic change. The impacts of precipitation, air temperature and evapotranspiration on annual runoff in the source region of Yangtze River during 1957–2009 are investigated in the time-period domain using wavelet analysis metho...

Groundwater flow systems and stagnant zones in drainage basins are critical to a series of geologic processes. Unfortunately, the difficulty of mapping flow system boundaries and no field example of detected stagnant zones restrict the application of the concept of nested flow systems. By assuming the variation in bulk resistivity of an aquifer wit...

Groundwater evapotranspiration (GE) is an essential component for regional water balance in areas with shallow water table. When the depth to water table (DWT) falls due to pumping in a well field, GE will decrease, which also influence the redistribution of water table. A mathematical model of steady radial flow is developed to investigate the pro...

The change of groundwater level would drive air flow in the vadose zone and the air flow will interact with groundwater flow. This kind of coupling between groundwater level change and air flow will become more apparent when the unconfined aquifer is covered by a low-permeability layer. Intake and drainage experiments were carried out in a double-l...

Analytical solutions of groundwater travel time to a pumping well in an unconfined aquifer have been developed in previous studies, however, the change in evapotranspiration was not considered. Here, we develop a mathematical model of unconfined flow toward a discharge well with redistribution of groundwater evapotranspiration for travel time analy...

Current rates of urban development will result in water runoff becoming a major complication of urban water pollution. To address the worsening situation regarding water resource shortage and pollution, novel multilayer infiltration systems were designed and their effectiveness for removing pollutants in urban runoff tested experimentally. The mult...

In this study, we developed a stochastic estimator for characterizing the hydraulic heterogeneity in both unsaturated and saturated zones of unconfined aquifers using transient drawdown data from sequential pumping tests. This estimator was built upon the successive linear estimator by Yeh et al. (1996), the simultaneous successive linear estimator...

The catchment areas with the hydrological data in the southern region of the Cretaceous system are divided into seven categories according to the distribution characteristics of physical geographic conditions, watershed, lithology and geological structure. River baseflow of the Cretaceous system in the Ordos Basin is 1.143 billion m3/a. Baseflow of...

[1] Using a first-order cross-correlation analysis, this paper investigates the relationship between observed heads and hydraulic properties in the saturated and vadose zones at different times and locations of three-dimensional unconfined aquifers during pumping tests. Cross-correlation analysis is a weighted sensitivity analysis casted into a sto...

In arid and semi-arid regions, groundwater availability is one of the controls on vegetation distribution. This groundwater-dependent distribution of vegetation has been particularly observed in the Hailiutu River catchment, a semi-arid region in North China. We used remote sensing images of vegetation index (normalized difference vegetation index,...

A study on subsurface airflow plays a vital role in quantifying the effectiveness of natural attenuation of volatile organic compounds (VOCs) or in determining the need of engineering systems (e.g., soil vapor extraction of VOCs). Here, we present a new analytical solution for describing the subsurface airflow induced by barometric pressure and gro...

Water table variation will result in considerable variation of the weight of the pore water, which has loading effects on the groundwater flow in the underlying confined aquifer. Here we present an analytical solution on such a loading effect in a coastal aquifer system consisting of an unconfined aquifer, a confined aquifer, and an impermeable lay...

The Yinchuan plain is located in the arid climate zone of NW China. The western margin of the plain is the Helan mountain connecting a series of normal slip faults. The eastern margin of the plain connects with the Yellow River and adjacents with the Ordos platform. The south of the plain is bordered by the EN fault of the Niushou mountain. The bot...

Baseflow, which represents the drainage of groundwater aquifers, is an essential component of runoff in hydrological basins. In the source region of the Yangtze River, the change of baseflow typically reflects the interactions between groundwater system and climatic factors in cold and arid areas. With modified Kalinen separation method, annual bas...

From a subsurface physical point of view, this paper discusses the necessity and feasibility of considering two-phase heat and mass transfer process in land surface models (LSMs). The potential-based equations of coupled mass and heat transport under constant air pressure are adopted as the basis. The proposed model is developed on this basis by co...

Hydrological and ecological changes have been observed in past decades in the source region of the Yangtze and Yellow Rivers. We hypothesize that these changes are related to permafrost degradation in the region as a consequence of climate change. Ground temperature measurements show that at the maximum measurement depth of 3.2 m, the temperature h...

Analytical models are popular tools for analyzing pumping tests in unconfined aquifers. These models do not adequately describe the flow process in the vadose zone and the aquifer during the tests due to their simplified representations of the drainage process in the vadose zone and at the water table. Moreover, these models assume aquifer homogene...

Groundwater age determined by tracers is widely applied in studies on groundwater flow in large scale basins and calibration of groundwater flow and transport models using tracer age has attracted numerous hydrogeologists recently. Knowledge on groundwater age distribution in basins is the prerequisite of applying tracer ages. In this study, direct...

The concept of enhanced vapor transfer in unsaturated soils has been questioned for its reliance on soil temperature gradient, which leads to consideration of other mechanisms of vapor transfer, e.g., advective vapor transfer due to soil air pressure gradient. Although the advective flux is an important portion of evaporation, there is a lack of kn...

From a subsurface physical point of view, this paper discusses the necessity of considering the two-phase heat and mass transfer process in land surface models (LSMs). The potential-based equations of coupled mass and heat transport under constant air pressure form the basis of the proposed model. The model is developed considering dry air as a sin...

Theoretical analysis and field observations suggest that the depth-dependent trend of permeability anisotropy is a nature of the geological media accompanying the depth-decaying permeability. However, the effect of depth-dependent anisotropy has not been investigated in previous studies of regional groundwater flow. A more general analytical soluti...

Transition of the water release mechanismsSpatial variability of hydraulic parametersCross-correlation analysis

1] The unsteady state drainage of water from a vertical sand column with and without a finer layer on the top was studied theoretically and experimentally to investigate the airflow generated by the finer layer. The sand column, saturated at its lower portion and initially in the condition of hydrostatic equilibrium, is drained at its bottom at con...

The existence of stagnation points in nested flow systems is relevant to a range of geologic processes. There has been no analytical study on the characteristics and locations of stagnation points in nested flow systems. We derived analytical solutions for hydraulic head and stream function in basins with isotropic and depth-decaying hydraulic cond...

The eco-environment in the source region of the Yellow River in western China has been experiencing deterioration in the past decades. Vegetation affected by climate variables and anthropogenic activities is indicative of eco-environment well-being. To quantify temporal and spatial variations of vegetation coverage and analyse potential causes for...

This study contends that while groundwater inverse problems are inherently ill posed due to their unstable nature, uniqueness issues facing inverse modeling efforts mainly arise from ill definedness of the problems (the lack of information). Measurement noise, instability, and magnitude of sensitivity are issues related to solution techniques. We s...

The theory of regional groundwater flow is critical for understanding many geologic processes. It is known that heterogeneity and anisotropy in hydraulic conductivity caused by varying lithology and faults affect the pattern of nested flow systems in complex basin. In addition, depth-decaying hydraulic conductivity, a widely observed phenomenon in...

In this research, the S-shaped log drawdown vs. log time curve typical of pumping tests in unconfined aquifers is reinvestigated via numerical experiments. This study attributes the departure of the S shape from the drawdown-time behavior of the confined aquifer to presence of an “additional” source of water. To explain the additional source of wat...

Permeability loss with depth is a general trend in geological media and plays an essential role in subsurface fluid flow and solute transport. In the near surface zone where groundwater movement is active, the decrease in permeability with depth is dominated by the mechanical compaction of deformable media caused by the increase in lithostatic stre...

This paper considers the complexity in resolving the conflicts between mine drainage, water supply, and environmental protection for the coal basin of North China, and presents a management optimization framework that addresses these multiple conflicting issues simultaneously in the most cost effective manner. Due to the various unpredictable accid...

The age of groundwater is a manifestation of the temporal scale of groundwater flow in basins, whose pattern was recently found to be influenced by depth-dependent hydraulic conductivity (K). In this paper, we show through numerical simulations how well-documented depth-decaying K and porosity ($\theta$) influence groundwater age. In the unit basin...

The source region of the Yellow River, China, has experienced eco-environmental deterioration in recent decades. The Yellow River discharge has reduced to zero numerous times since 1960, which has left a devastating impact on water resources and ecosystems downstream. Seeking to understand the causes of drying up, we analyze the records of discharg...

Regional groundwater flow is critical for understanding a variety of geologic processes. Unfortunately, few studies have considered the impact of gradual decrease in hydraulic conductivity (K) with depth on groundwater flow. In this study, regional groundwater flow through a basin is analyzed under conditions of exponentially decaying K with depth....

Discontinuity normal stiffness and deformation modulus of large scale rock masses are very difficult to determine. A method for estimation of discontinuity normal stiffness based on the decrease in transmissivity with depth has been proposed by the authors in a former paper. In the current study, the method is further developed by accounting for th...

Both porosity and deformation properties of porous media are dependent on stress. For geological media, the stress-dependent porosity and deformation properties can be shown to be depth related. Unfortunately, both in situ porosity and in situ deformation properties are difficult to measure. In the current study, a method is developed to evaluate t...