Impact of water table on hierarchically nested groundwater flow system

Water table configuration gives rise to hierarchically nested groundwater flow systems.However,there remains a lack of comprehensive understanding regarding the controlling factors of water table and its impact on flow systems.Moreover,it remains challenging to identify characteristics of water table space variation through limited groundwater observations at the regional scale.Based on two ideal two-dimensional cross-section analytical models,this study presents a simplified approach to preliminarily assess the nonlinear interactions between water table variation and three driving factors:Topography,geol-ogy and climate.Two criteria,C1 and C2,are utilized to address issues at different scales ranging from basin to local:(i)the influence of various factors on water table configuration;and(ii)the influence of water table on groundwater flow pattern.Then,the Ordos Plateau is taken as an example to explore the role of the water table in nested groundwater systems using the provided approach and criterion.The applica-tion of this approach in the Ordos Plateau demonstrates its appropriateness as a practical method for prelim-inarily determining the characteristics of water table configuration and its impact on flow systems.The study explores the mechanism influencing spatial variation in the water table and improves understanding of the interaction between topography,geology,and climate on groundwater flow patterns.

Seasonal Effect on Weather Elements on Water Table Fluctuation in Potable Wells in Kono District, Eastern Sierra Leone

The study investigated the seasonal effects of weather elements on water table fluctuations in drinking wells in Nimikoro and Tankoro Chiefdoms in Kono District, Eastern Sierra Leone. The study specifically determined the trends in precipitation, air temperature and relative humidity relative to water table depth and water volume in both manually dug and mechanically drilled water wells in the chiefdoms. The key objective was to provide a clear guide on sustainable well development and operation in the study area and beyond. To do so, the depth of each well was taken and the water table measured. Also, data on key weather elements such as precipitation, air temperature and relative humidity were collected on the 15th of every month for a period of one year. The data were analyzed on Excel, SPSS and ArcGIS platforms for monthly and seasonal trends in the time-space fabric. The results showed that the depth to water table was high in the dries (small well water volume) and low in the rains (large well water volume) for both manually dug and mechanically drilled wells. Well water temperature increased as temperature increased during the dry season but decreased as temperature decreased during the rainy season. The study showed that weather elements such as precipitation and temperature had direct impact on groundwater availability. This is critical for groundwater development and management in the study area and in Sierra Leone at large.

Displaying Water Table Levels, Flow Direction for Predicting Construction Techniques Using Geographic Information: Case Study of Kumba (South West, Cameroon)

The rapid economic growth of the town present the matter of water issue as a problem to human life human life, construction life, agriculture, etc. This study is to predict techniques of foundation construction through the displaying of the water table at the flow direction in the town of Kumba and GIS. It is characterized by a significant research question which is the level of fall and rise in groundwater levels within the town of Kumba and this influence on choice of types of foundation in construction. This study is directed to decision makers, and technicians of the construction field to develop policies facilitating the supervision when building construction foundation by informing about water level depth and its flow direction in the town. To achieve this, depths of static water levels were measured in over 200 randomly selected hand-dug wells in Kumba, after their geolocation and data were collected during the dry season (November and March 2017) and during the rainy season (between April and October 2017). Data were analyzed and treated using Microsoft Excel and GIS software us as Golden Surfer, Global Mapper, and ArcGIS. The results show variations of water level and those areas that may threaten foundation construction. Quarter as Kumba Station, Mile 1, Bulletin Street (Fongong Quarter), and parts of Fiango show that water table is to deep water and proper for the shallow foundation but very hard for water supply through borehole. Groundwater flow direction was revealed to be towards the south and southeastern parts of Kumba. The significant of the study is to propose to the technician the direct application on the field of chosen types of foundations according to the quarter and proposed groundwater supply possibilities.

Irrigation and Nitrogen Requirements of Wheat under Shallow Water Table Conditions of Asmara, Eritrea

Wheat (Triticum astivum L.) is traditionally rainfed in Eritrea. Yields are low because of poor soil management and low water and nutrient inputs. A field experiment was conducted in Akria farm, located in the outskirts of Asmara. The soil was clay loam associated with non-saline shallow water tables fluctuating from 0.4 to 1.2 m depths during the crop season. Wheat variety Wedel Nile was planted in split plot design with four levels of supplementary irrigations (SI) viz. I1 (rainfed, 0 SI), I2 (1/3 of full SI), I3 (2/3 of full SI), and I4 (full SI) in main plots and three levels of nitrogen viz. N1 (18 kg N haǃ), N2 (50 kg N haǃ), and N3 (100 kg N haǃ) as sub-plots in three replications. Full SI refers to amount of water necessary to replenish soil moisture deficit in the root zone from field capacity to 50% depletion of the available soil moisture. Groundwater table was constant around 0.4 m depth for 32 days from planting and declined slowly thereafter. Wetness around 0.3 m depth was thus near field capacity until second week of December and reduced thereafter with declining water table. Average soil moisture depletion was 94 mm under rainfed and 64 mm under full irrigation. No symptoms of wilting were observed in any of the treatments due to shallow water tables. Upward flux from the water table was 4.6 mm·d-1 until 30 days from planting, which declined to 0.2 mm·d-1 when the water table declined below 0.9 m depth. Optimum yield of wheat (5603 kg·ha-1) was obtained by application of 58 mm irrigation (I3) and 100 kg·ha-1 nitrogen (N3). Total water use for optimum yield of wheat was 382 mm and water use efficiency was 14.7 kg·ha-1·mm-1. Contribution from water table to the evapotranspiration requirements of wheat was highest (61%) under rainfed (I1) and lowest (52%) under full SI (I4).

Exploring Soil Layers and Water Tables with Ground-Penetrating Radar

Ground-penetrating radar (GPR) has been used predominantly for environments with low electrical conductivity like freshwater aquifers, glaciers, or dry sandy soils. The objective of the present study was to explore its application for mapping in subsurface agricultural soils to a depth of several meters. For a loamy sand and a clayey site on the North China Plain, clay inclusions in the sand were detected; the thickness, inclination, and continuity of the confining clay and silt layers was assessed; and a local water table was mapped. Direct sampling (soil coring and profiling) in the top meter and independent measurement of the water table were utilized to confirm the findings. Also, effective estimates of the dielectric number for the site with the dielectric number of moist clayey soils depending strongly on frequency were obtained. Thus, important properties of soils, like the arrangement and type of layers and in particular their continuity and inclination, could be explored with moderate efforts for rather large areas to help find optimal locations for the time-consuming and expensive measurements which would be necessary to detail a model of the subsurface.

EFFECTS OF WATER TABLE AND NITROGEN ADDITION ON CO_2 EMISSION FROM WETLAND SOIL

Soil respiration is a main dynamic process of carbon cycle in wetland. It is important to contribute to global climate changes. Water table and nutritious availability are significant impact factors to influence responses of CO2 emission from wetland soil to climate changes. Twenty-four wetland soil monoliths at 4 water-table positions and in 3 nitrogen status have been incubated to measure rates of CO2 emission from wetland soils in this study. Three static water-table controls and a fluctuant water-table control, with 3 nitrogen additions in every water-table control, were carried out. In no nitrogen addition treatment, high CO2 emissions were found at a static low water table (Ⅰ) and a fluctuant water table (Ⅳ), averaging 306.7mg/(m2·h) and 307.89mg/(m2·h), respectively, which were 51%-57% higher than that at static high water table (Ⅱ and Ⅲ). After nitrogen addition, however, highest CO2 emission was found at Ⅱ and lowest emission at Ⅲ. The results suggested that nutritious availability of wetland soil might be important to influence the effect of water table on the CO2 emission from the wetland soil. Nitrogen addition led to enhancing CO2 emissions from wetland soil, while the highest emission was found in 1N treatments other than in 2N treatments. In 3 nutritious treatments, low CO2 emissions at high water tables and high CO2 emissions at low water tables were also observed when water table fluctuated. Our results suggested that both water table changes and nutritious imports would effect the CO2 emission from wetland.

Effect of Perched Water Tables on Aluminosilicate Stability and Soil Genesis

The mineral stability and solute activities of soil solution extracted from selected horizons of seven studied pedons of Alfisols in Kentucky, USA, and the relationship between distribution of iron-manganese concretions and the restrictive layers were investigated. The results showed that the genesis and development of these soils and mineral weathering trends were strongly influenced by the depth of bedrock and the presence of perched water tables at lithic (limestone) interfaces due to the dissolution and buffering effect of limestone bedrock. The extractable Mg/Ca ratio as depth function and soil depth above bedrock could be used as indices of weathering and degree of soil development. Maximum iron-manganese concretion accumulation was found to occur in the horizon overlying clay horizon (>40% clay) with a sharp increase in clay content (>10%), which suggested that zones of Fe-Mn concretion accumulation in soils of the Inner Bluegrass Region appeared to be a sensitive genetic indicator of argillic horizons with restrictive permeability.

Response of Coastal Groundwater Table to Offshore Storms

Large groundwater table fluctuations were observed in a coastal aquifer during an offshore storm. The storm induced significant changes of the mean shoreline elevation, characterized by a pulse like oscillation. This pulse propagated in the aquifer, resulting in the water table fluctuations. A general analytical solution is derived to quantify this new mechanism of water table fluctuation. The solution is applied to field observations and is found to be able to predict reasonably well the observed storm induced water table fluctuations. Based on the analytical solution, the damping characteristics and phase shift of the oscillation as it propagates inland are examined.

Rise of Urban Water Table as a Cause of Flooding: Improving Knowledge in the City of Niamey (Niger Republic)

Niamey, the capital of Niger, has experienced continuous demographic growth (+4%), accompanied by rapid urban expansion that is insufficiently controlled. This growth, combined with the effects of climate change as well as a drastic change in land use (urbanization of cultivated fields, deforestation of plateaus and erosion of slopes) disrupts the water cycle, thus leading to the superposition of three types of floods: 1) rain floods (monsoon period);2) river floods (Niger river);and 3) flooding caused by rising water table. In several neighbourhoods, the water table is now out in a sustainable manner and degrades already fragile sanitary conditions. This study aims to clarify the functioning of aquifers in the city of Niamey due to the combination of geological, geophysical and hydrogeological data. Hydrogeological investigations make it possible to identify, in areas flooded by the water table, a shallow aquifer with low capacitance (effective porosity of a few %) and low permeability (2 × 10-6 to 1 × 10-4 m/s), overlying at a level shallow clay (~10 m) and lying on the Precambrian base (schists, granites). This configuration limits flows and has led to the appearance of permanent pools created by the water table in the valley thalweg in and around the city. Thus, in Niamey, an increase of up to twenty to forty meters was observed between 1961 and 2021 with seasonal piezometric fluctuations of a pluri-metric order following the rainy season. Beyond the health impacts, this trajectory negatively impacts land and locally causes degradation or displacement of traffic axes. Containing the level of the water table appears to be essential in the long term for sustainable sanitation in the city of Niamey.

Quantification of groundwater recharge and evapotranspiration along a semi-arid wetland transect using diurnal water table fluctuations

Groundwater is a vital water resource in arid and semi-arid areas.Diurnal groundwater table fluctuations are widely used to quantify rainfall recharge and groundwater evapotranspiration(ET_(g)).To assess groundwater resources for sustainable use,we estimated groundwater recharge and ET_(g) using the diurnal water table fluctuations at three sites along a section with different depths to water table(DWT)within a wetland of the Mukai Lake in the Ordos Plateau,Northwest China.The water table level was monitored at an hourly resolution using a Keller DCX-22 A data logger that measured both the total pressure and barometric pressure,so that the effect of barometric pressure could be removed.At this study site,a rapid water table response to rainfall was observed in two shallow wells(i.e.,Obs1 and Obs2),at which diurnal water table fluctuations were also observed over the study period during rainless days,indicating that the main factors influencing water table variation are rainfall and ET_(g).However,at the deep-water table site(Obs3),the groundwater level only reacted to the heaviest rainfalls and showed no diurnal variations.Groundwater recharge and ET_(g) were quantified for the entire hydrological year(June 2017–June 2018)using the water table fluctuation method and the Loheide method,respectively,with depth-dependent specific yields.The results show that the total annual groundwater recharge was approximately 207 mm,accounting for 52%of rainfall at Obs1,while groundwater recharge was approximately 250 and 21 mm at Obs2 and Obs3,accounting for 63%and 5%of rainfall,respectively.In addition,the rates of groundwater recharge were mainly determined by rainfall intensity and DWT.The daily mean ET_(g) at Obs1 and Obs2 over the study period was 4.3 and 2.5 mm,respectively,and the main determining factors were DWT and net radiation.

Responses of phreatophyte transpiration to falling water table in hyper-arid and arid regions,Northwest China

Quantitative assessment of the impact of groundwater depletion on phreatophytes in(hyper-)arid regions is key to sustainable groundwater management.However,a parsimonious model for predicting the response of phreatophytes to a decrease of the water table is lacking.A variable saturated flow model,HYDRUS-1D,was used to numerically assess the influences of depth to the water table(DWT)and mean annual precipitation(MAP)on transpiration of groundwater-dependent vegetation in(hyper-)arid regions of northwest China.An exponential relationship is found for the normalized transpiration(a ratio of transpiration at a certain DWT to transpiration at 1 m depth,T_(a)^(*))with increasing DWT,while a positive linear relationship is identified between T_(a)^(*)and annual precipitation.Sensitivity analysis shows that the model is insensitive to parameters,such as saturated soil hydraulic conductivity and water stress parameters,indicated by an insignificant variation(less than 20%in most cases)under±50%changes of these parameters.Based on these two relationships,a universal model has been developed to predict the response of phreatophyte transpiration to groundwater drawdown for(hyper-)arid regions using MAP only.The estimated T_(a)^(*)from the model is reasonable by comparing with published measured values.

The response of Caragana microphylla seedlings to water table changes in Horqin Sandy Land,China

This paper focuses on the growth response of Caragana microphylla seedlings to changes of artificially controlled water table in Horqin Sandy Land, China. Monitoring results of soil water content shows that soil moisture is closely correlated to groundwater depths. Soil volumetric water increased rapidly when close to water sources and finally stabilized in a saturated state. The soil moisture trend of CK （control） increased gradually at 0-50 cm of soil depth then decreased to 4% below 50 cm soil depth. C. microphylla can adapt to different soil environments by changes in ecological and physiological characteristics. By comparing the ecological characteristics of C. microphylla seedlings at various water tables, we found that a shallow water table of 40 cm depth inhibited seedling groundwater depth of 120 em was more advantageous for plant growth because of weak ecological characteristics. A height and canopy growth of C. microphylla seedlings. During the first two years, the most suitable water depth for root biomass was 120 cm, and 180 cm for root length. The growth of vertical roots is positively correlated with groundwater depth, and root thickness is the determinate factor for root biomass while the fine root is the determinate factor for root length. A thick root would grow much more in a natural drought environment while access to ground water promotes the growth of fine roots.

Numerical Modeling of Shallow Water Table Behavior with Lisse Effect

Air entrapment is an important consideration in environments with shallow water tables and sandy soil, like the condition of highly conductive sandy soils and flat topography in Florida, USA. It causes water table rises in soils, which are significantly faster and higher than those in soils without air entrapment. Two numerical models, Integrated Hydrologic Model (IHM) and HYDRUS-1D (a single-phase, one-dimensional Richards′ equation model) were tested at an area of west central Florida to help further understanding the shallow water table behavior during a long term air entrapment. This investigation employed field data with two modeling approaches to quantify the variation of air pressurization values. It was found that the air pressurization effect was responsible at time up to 40 cm of water table rise being recorded by the observation well for these two models. The values of air pressurization calculated from IHM and HYDRUS-1D match the previously published values. Results also indicated that the two numerical models did not consider air entrapment effect (as the predictive parameters remain uncertain) and thus results of depth to water table from these models did not compare to the observations for these selected periods. Incorporating air entrapment in prediction models is critical to reproduce shallow water table observations.

Comparing phreatic evaporation at zero water table depth with water surface evaporation

Salt-affected soils are mostly found in irrigated areas within arid and semi-arid regions where the groundwater table is shallow.Soils of this type have become an increasingly severe problem because they threaten both the environment and the sustainable development of irrigated agriculture.A tool to estimate phreatic evaporation is therefore urgently required to minimize the salinization potential of salt-affected areas.In this context,phreatic evaporation at zero water table depth(E0)is a key parameter for establishing a model for calculating phreatic evaporation.The aim of this study was to explore the law of phreatic evaporation and to develop structurally rational empirical models for calculating phreatic evaporation,based on E0data of six types of soil(i.e.,gravel,fine sand,sandy loam,light loam,medium loam,and heavy loam)observed using the non-weighing lysimeter and water surface evaporation(E601)data observed using a E601 evaporator of same evaporation area with a lysimeter-tube at the groundwater balance station of the Weigan River Management Office in Xinjiang Uygur Autonomous Region,China,during the non-freezing period(April to October)between 1990 and 1994.The relationship between E0and E601was analyzed,the relationship between the ratio of E0to E601and the mechanical compositions of different soils was presented,and the factors influencing E0were discussed.The results of this study reveal that E0is not equal to E601.In fact,only values of the former for fine sand are close to those of the latter.Data also show that E0values are related to soil texture as well as to potential atmospheric evaporation,the ratio of E0to E601and the silt-clay particle content(grain diameter less than 0.02 mm)is negatively exponentially correlated,and that soil thermal capacity plays a key role in phreatic evaporation at E0.The results of this analysis therefore imply that the treatment of zero phreatic depth is an essential requirement when constructing groundwater balance stations to study the law of phreatic evaporation.

Mapping of the Water Table Levels of Unconfined Aquifers Using Two Interpolation Methods

The spatial prediction of the water table can be used for many applications related to civil works (foundations, excavations) and other urban and environmental management activities. Deterministic and geostatistical interpolation methods were used to predict the spatial distribution of water table levels (unconfined aquifers) of important geological formations of the Joao Pessoa City (capital of Paraiba State, Brazil) with dense urban occupation and high demand for new civil works. The deterministic (topo to raster) and geostatistical (ordinary kriging) interpolation methods were evaluated using a Geographic Information System (GIS)-based investigation. The water table levels were obtained from 276 boring logs of Standard Penetration Test (SPT) in situ investigation distributed over the geological formations studied (an area of 59.8 km2, covering 40 districts of the Joao Pessoa City). The Nspt values and textural characterization data are stored for levels of 1 m depth. Some boreholes located in the area investigated were not included in the interpolation processes in order to be compared with estimated values (validation of the results). Maps of the water table depths were also produced to further analyze the quality of the water table surfaces interpolated by both methods. The phreatic surface interpolations provided satisfactory results for both methods (RMSE = 1.8 m). The topo to raster method showed a slight general tendency to be less affected by local values in relation to the kriging method and also has the advantage of integrating the drainage flow system, which is a relevant aspect for spatial models of the water table levels of unconfined aquifers. The ordinary kriging (geostatistical method) provides a prediction surface and some measure of the certainty or accuracy of the predictions.

Recharge Estimation of Hard Rock Aquifers under Sahelian Climate Conditions Using Water Table Fluctuation:Case Study of Tougou Catchment,Burkina Faso

This study aims to characterize water table fluctuations and estimate groundwater recharge in the Tougou catchment located in the Sahel zone of Burkina Faso. Water table fluctuation and groundwater budget approaches are developed on an experimental site equipped with observation wells. The trends of water fluctuations in the different layers of the weathering profile are similar. There is a time-lag response of groundwater recharge to the daily precipitation occurrences. The interaction between the upper (clayey alteration) and lower (transition zone-fractured schist complex) parts of the weathering profile shows that generally the hydraulic head in the upper part is higher than that of the lower part due to difference in drainage porosity. The latter varies at the catchment scale between 0.006 and 0.009 and is inversely proportional to the saturated thickness of the clayey alteration layer. The groundwater recharge is annually estimated between 36 and 49 mm, which correspond to 6% and 9% of mean annual rainfall in the catchment. Annual evapotranspiration was estimated to be about 223 to 443 mm.

Effects of water tables and nitrogen application on soil bacterial community diversity, network structure, and function in an alpine wetland, China

Nitrogen deposition and water tables are important factors to control soil microbial community structure.However,the specific effects and mechanisms of nitrogen deposition and water tables coupling on bacterial diversity,abundance,and community structure in arid alpine wetlands remain unclear.The nitrogen deposition(0,10,and 20 kg N/(hm^(2)•a))experiments were conducted in the Bayinbulak alpine wetland with different water tables(perennial flooding,seasonal waterlogging,and perennial drying).The 16S rRNA(ribosomal ribonucleic acid)gene sequencing technology was employed to analyze the changes in bacterial community diversity,network structure,and function in the soil.Results indicated that bacterial diversity was the highest under seasonal waterlogging condition.However,nitrogen deposition only affected the bacterial Chao1 and beta diversity indices under seasonal waterlogging condition.The abundance of bacterial communities under different water tables showed significant differences at the phylum and genus levels.The dominant phylum,Proteobacteria,was sensitive to soil moisture and its abundance decreased with decreasing water tables.Although nitrogen deposition led to changes in bacterial abundance,such changes were small compared with the effects of water tables.Nitrogen deposition with 10 kg N/(hm^(2)•a)decreased bacterial edge number,average path length,and robustness.However,perennial flooding and drying conditions could simply resist environmental changes caused by 20 kg N/(hm^(2)•a)nitrogen deposition and their network structure remain unchanged.The sulfur cycle function was dominant under perennial flooding condition,and carbon and nitrogen cycle functions were dominant under seasonal waterlogging and perennial drying conditions.Nitrogen application increased the potential function of part of nitrogen cycle and decreased the potential function of sulfur cycle in bacterial community.In summary,composition of bacterial community in the arid alpine wetland was determined by water tables,and diversity of bacterial community was inhibited by a lower water table.Effect of nitrogen deposition on bacterial community structure and function depended on water tables.

Exploring the groundwater response to rainfall in a translational landslide using the master recession curve method and cross-correlation function

Rainfall is a common trigger for landslide reactivation,as it raises groundwater levels and reduces bedrock or soil shear resistance.This study focuses on the Kualiangzi landslide in the southern region of Sichuan Province,China.Real-time monitoring of groundwater levels and rainfall from July 2013 to September 2016 is analyzed.Groundwater table increments,considering groundwater drainage rate,were calculated using the water-table fluctuation and master recession curve method and the response time of the groundwater table to rainfall events was estimated using the cross-correlation function.Results reveal that groundwater level declines from tension troughs to landslide fronts in the rainy season,with a significant positive correlation between the groundwater level in the tension trough and landslide surface displacement.Evaluated spring elevations for groundwater discharge range from 410 m to 440 m,which is in agreement with the actual spring elevations(390-423 m).Lag times of groundwater response to rainfall decreases with cumulative rainfall of the rainy periods.In the middle part of the landslide,two responses between rainfall and groundwater levels indicate two water movement pathways:Vertical cracks or fractures resulting from the slow landslide movement,and matrix pore space in unconsolidated sediment.Variations in peak values of the cross-correlation function suggest early dominance of the uniform matrix flow and later dominance of preferential flow during the rainy period.

Temperature Responses to Infrared-Loading and Water Table Manipulations in Peatland Mesocosms

We initiated a multi-factor global change experiment to explore the effects of infrared heat loading （HT） and water table level （WL） treatment on soil temperature （T） in bog and fen peatland mesocosms. We found that the temperature varied highly by year, month, peatland type, soil depth, HT and WL manipulations. The highest effect of HT on the temperature at 25 cm depth was found in June for the bog mesocosms （3.34-4.27 ℃） but in May for the fen mesocosms （2.32-4.33 ℃） over the 2-year study period. The effects of WL in the bog mesocosms were only found between August and January, with the wet mesocosms warmer than the dry mesocosms by 0.48-2.03 ℃ over the 2-year study period. In contrast, wetter fen mesocosms were generally cooler by 0.16-3.87℃. Seasonal changes of temperatures elevated by the HT also varied by depth and ecosystem type, with temperature differences at 5 cm and 10 cm depth showing smaller seasonal fluctuations than those at 25 cm and 40 cm in the bog mesocosms. However, increased HT did not always lead to warmer soil, especially in the fen mesocosms. Both HT and WL manipulations have also changed the length of the non-frozen season.