Groundwater Fluctuations Research Articles

Hydrogeological characteristics of waterlogged areas in Natore District, Bangladesh

Waterlogging (WL) refers to the process by which water flow is resisted in vertical and horizontal directions and thus water stagnates for a short or long span of time; it is induced by a combination of human and natural factors. In the southwestern region of Bangladesh, including Natore District, WL is a significant issue that needs to be addressed if agricultural activity is to be successful. This study aimed to identify surface WL in Natore District and to characterise the WL scenario in the study area in terms of hydrogeology. Waterlogged areas were identified with a geographic information system using satellite images corresponding to the premonsoon and postmonsoon periods. Using groundwater level data (1990–2017), the pre- and postmonsoon scenarios of the waterlogged areas were indicated by seasonal and perennial types of WL. Groundwater recharge scenarios were classified as long and short lag times. Most of the study area was characterised by thick clay or silty clay surficial layers with low water penetration rates, resulting from low porosity and low hydraulic conductivity. The cross-correlation between rainfall and groundwater level revealed the response of groundwater to rainfall, with a lag time of 1–5 months. Long lag time areas exhibited slow groundwater recharge and significant groundwater level fluctuation, with lower hydraulic conductivity values of 49.37–76.24 m/day. In contrast, short lag time areas displayed rapid groundwater recharge and small groundwater fluctuation due to a good proportional relationship with rainfall and higher hydraulic conductivity values of 74.74–117.79 m/day.

Constructing a new irrigation model for desert riparian forests based on response of canopy EVI loss and tree rings growth to groundwater fluctuation

Vegetation in arid desert areas plays an extremely important role in maintaining biodiversity and inhibiting desertification. Quantitative understanding of vegetation response to groundwater is essential to priming drought prevention and mitigation, which is a topic that is attracting considerable attention. However, previous studies have rarely assessed the response of vegetation to groundwater from probabilistic or stoichiometric chemical perspective. To address this question, a highly sensitive copula joint distribution of the response of enhanced vegetation index (EVI) loss to groundwater was constructed and a stoichiometric chemistry indicator of the Nitrogen (N) and Phosphorus (P) concentrations in tree rings was innovatively put forward to verify its sensitivity to groundwater. The results obtained revealed that the correlation of EVI with groundwater was better than that with SPEI and TVDI; Furthermore, the critical groundwater thresholds of the EVI loss rate, described as “beginning”, “reaching the maximum”, and “the slowest” were 3.85 m, 6.18–6.75 m, and 7.89 m, respectively. At the inter-annual scale, by measuring the N and P contents of Populus euphratica tree rings, and constructing response model of element contents to groundwater/rainfall, the key thresholds were determined at 5.20–5.31 m and 60 mm, which challenges the traditional understanding that rainfall does not bring ecological benefits to desert riparian forests. To further promote vegetation restoration, based on the response rule of EVI loss and stoichiometric chemical elements of tree rings to groundwater and the intermediate overflow rotation irrigation method, a more advanced desert riparian forest irrigation mode, named “branch-infiltration-rotation-irrigation”, is here proposed.

Application of Geospatial Mapping in the Analyses of Pre-monsoon Groundwater Fluctuation: A Case Study of Piriyapatna Taluk of Karnataka State, India

The graphical representations of groundwater models play productive role in hydrological impacts like groundwater movement especially in rural areas. The demand of water for agriculture, domestic, industrial and other uses are increasing due to rise in population, over-withdrawal of groundwater and global warming (?). Periodic evaluation of groundwater levels are very much necessary for effective management due to rapidly changing climatic scenario. Geospatial technique have become the most significant tool for mapping and modeling of groundwater level resources using statistical data. An effort has been made to describe the groundwater level of Piriyapatna taluk of Karnataka State. Eight representative observation well points of pre-monsoon data had been collected over a period of 16 years (2003 - 2019) in order to analyze spatio-temporal variation. Groundwater levels are plotted on a base map with their respective amount of depths, and then the contours of equal values are drawn using Inverse Distance Weighted (IDW) method in ArcGIS. The final results are helpful in preparing for shortage and seeking alternatives if need arises from study report.

Groundwater Fluctuation of a Meliorated Forest Catchment in Connection with the Climate and the Growth of Forest Stands—30 Years of Monitoring

Hydromelioration networks aim to expand the vadose zones of waterlogged and peaty sites, which is expected to provide more soil space for trees’ roots, thus improving forest stand stability and production. However, the recent climate is manifested by increasing air temperatures, changed distribution of precipitation and frequent droughts. This raises the issue of the suitability of such measures. Additionally, the impacts on the ground water table (GWT) level, drainage, and forest health are disputed. This study deals with the behaviour of the shallow-aquifer GWT level in a formerly deforested headwater catchment named U Dvou louček (UDL) which had been monitored for 30 years and placed at a mountain site in north-eastern Bohemia, Czech Republic. GWT (84 m long transect with 22 probes), precipitation, throughfall, discharge, air temperatures and stand parameters were measured. Young Norway spruce stands now dominate within the UDL area. Average precipitation of the open area reached 1285 mm, and precipitation in years 2003, 2015 and 2018 was minimal (910 to 950 mm). Calibration of the GWT measurement took place in 1992–1995. After a 5-year stabilisation period in 1996–2001 with gradually falling GWT levels, following the digging of new ditches, the GWT no longer fluctuated significantly. The discharge and GWT change responses to stand growth were modest, and the impact of forest tending was limited. Lower GWTs in dry years were temporary. The inter-annual water levels in the immediate vicinity of the ditches fluctuated the least. The small-scale technical hydromelioration intervention neither had a negative impact on the GWT level, nor threatened the water supply of growing forest stands even in dry years. The results confirmed the long-term potential of such measures to improve the water regime of reforested clear cuts on waterlogged forest soils in mountains with a minimal risk of threat in warming environments.

Combing soil spatial variation and weakening of the groundwater fluctuation zone for the probabilistic stability analysis of a riverside landslide in the Three Gorges Reservoir area

Combing soil spatial variation and weakening of the groundwater fluctuation zone for the probabilistic stability analysis of a riverside landslide in the Three Gorges Reservoir area

Behaviour of Groundwater Table with Rainfall in North-West Region of Bangladesh

Groundwater is the major source of water to meet up the vast domestic and agricultural demand in Bangladesh. Additionally, reduction in reliable surface water resources resulting the increased reliance on groundwater day by day. Therefore, monitoring the groundwater fluctuation over time is crucial to ensure the sustainable use of groundwater resources in future. The present study analyzed historical groundwater data to know the behaviour of groundwater at four locations of two districts Pabna and Rangpur in the North-Eastern part of the country. Historical groundwater level data and monthly rainfall data from 1989 to 2017 were collected from Bangladesh Water Development Board and Bangladesh Meteorological Department, respectively. The annual maximum groundwater table depth (MaxGWT) and minimum groundwater table depth (MinGWT) and its trend was analyzed, and positive and negative recharge years were identified from these values. We found the maximum declining rate at 6.6 cm annually and the maximum 205 cm total depletion in the study area. The number of years of negative recharge is more than that of positive recharge for 32 years. As a result, a declining trend in groundwater table was found at three locations of the study area. The maximum groundwater table remains below suction limit at Ishwardi, causes no shallow tubewell (STW) works during that period. A declining trend in annual rainfall is observed in Pabna district. A linear relationship between rainfall and recharge was found at two locations of the study area. Bangladesh Rice J. 25 (2) : 85-95, 2021

Delineation of potential groundwater recharge zones using remote sensing, GIS, and AHP approaches

Groundwater resource plays a critical role in economic development, human health, and ecological diversity. Groundwater exploration has gained much prominence recently due to the rapid nature of geographic information systems and their ability to provide initial information on resources. Present study focuses on delination potential groundwater zones in Mulshi Taluka, Pune district, India, using remote sensing, GIS, and Analytic Hierarchical Process (AHP). Geomorphology, geology, slope, drainage density, rainfall, landuse/landcover, lineament density, soil, Normalized difference vegetation index (NDVI), curvature, and Topographic wetness index (TWI) were used for delineation of the groundwater recharge zones. All thematic maps were weighted using the AHP method according to their characteristics and water potential. The final groundwater potential zone (GWPZ) map was divided into five categories, viz., very low (4%), low (25%), moderate (45%), high (18%), and very high (8%) zones, respectively. The final map identifies 4% of area under a very high recharge zone with natural infiltration ability. The region's central, southern, and western regions account for 80% of the study area's recharge potential. Finally, groundwater fluctuation data was used to verify the accuracy of the GWPZ map through receiver operating characteristic curves (ROC). The AUC score for the AHP technique reveals 80.4% accuracy. Local and government authorities can use the study findings to effectively plan and manage groundwater development.

Soil water dynamics and groundwater evolutions of check dams under natural rainfall reduction in semi-arid areas

Stable regional water resource distribution is essential for ecosystems, yet soil water dynamics and groundwater evolutions of check dams remain many uncertainties under natural rainfall reduction in semi-arid areas. To explore these changeable hydrologic processes, continuous fixed-point observation and water balance models were introduced in nearly-four consecutive hydrological years (2018–2021). The results showed that soil water storage presented a downward fluctuation in each soil layer of all land uses. Moreover, the grassland profile moisture descended slowly and had deeper infiltration depths than others, which might be an ideal land-use type for the reservoir’s sustainable utilization in check dams. The results also indicated that surface soil moisture (<50 cm) could rapidly respond to a single rainfall event > 10 mm d−1, whereas deep soil moisture (>50 cm) and shallow groundwater fluctuations were mainly affected by annual cumulative precipitation. Furthermore, a conceptual hydrological model of rainwater falling to the ground, percolating through soil profiles, and reaching groundwater through different vegetation covers in check dams has been proposed. Soil infiltration rates varied under different land use types and depths, ranging from 0.82 to 3.47 cm h−1. The groundwater recharge time from accumulated annual rainfall was 69–250 days, whereas the discharge time due to vegetation water consumption and groundwater lateral movement was 66–774 days. With a decrease in annual rainfall, the recharge time gradually increased, whereas the discharge time gradually decreased. These results inaugurate new perspectives for a deeper understanding of ecohydrological equilibrium in check dams and provide theoretical insights into ecological restoration in semi-arid areas.

Fluctation moisture properties in the application of soil dielectric measurement in the North Bengkulu District, Indonesia

Information about soil moisture in the root layer is very important in evaluating water availability for plants, erosion rates and various other hydrological characteristics. Previous research has found a technology for measuring soil dielectric properties as a soil moisture estimator that can be carried out quickly in the field. The purpose of this study was to apply dielectricity technology in estimating the characteristics of soil moisture in situ in the field at the North Bengkulu in Bengkulu Province. Five land units in North Bengkulu Regency, Indonesia, have been selected as experimental sites. At each location, the soil profile was excavated to a depth of 100 cm, the basic characteristics of the soil in each layer were described in the field and analyzed in detail in the laboratory. The variables measured in the field are the measurement of the dielectric properties of the soil, the effective depth of the soil, the horizon and the characteristics of each horizon. The variables analyzed in the laboratory were texture, organic matter in each layer, aggregate stability at 0-10 cm layer, field soil moisture at the time of measurement, and groundwater characteristics. The relationship between the data on the basic characteristics of the soil with the soil moisture balance variable in the laboratory analysis and measurements of dielectric properties in the field, was then determined using regression analysis. The results showed that the five locations studied had different profile characteristics and groundwater fluctuations. Of the four independent variables tested (percentage of sand, silt, clay and organic carbon) then the content of sand and clay can be used as predictors of the water content of field capacity. Because the four independent variables have a very weak correlation with permanent wilting point water, the available water content can only be predicted from the sand and clay content.

Drought vulnerability assessment by employingtheGeographical Information Systemand Analytical Hierarchy Processfor the Kurnool district of Andhra Pradesh, India

Droughts are recurring events that adversely affect agricultural activities, population density, and irrigated land. The consequences vary from region to region and are called a 'creeping phenomenon'. It is necessary to map drought vulnerability comprehensively in order to develop and implement drought mitigation strategies. In this regard, remote sensing-based studies are most robust, effective, and efficient at monitoring and mapping droughts compared to conventional ground survey methods. The purpose of this study was to develop a comprehensive drought vulnerability map using geospatial techniques and remote sensing to assess the spatial extent of drought vulnerability in Kurnool district, Andhra Pradesh, India. A total of 13 drought-influencing parameters such as Slope, Elevation, Aspect, Soil texture, Geology/Lithology, Land Use &amp; Land Cover, Drainage density, Distance from water bodies, Groundwater fluctuation, Normalized Difference Vegetation Index, Rainfall, Land Surface Temperature, and Topographic Wetness Index were selected for the assessment of drought vulnerability. These indices were integrated to create drought maps of both spatial and temporal extent in ArcGIS. Using pairwise comparison matrices, the Analytical hierarchy process (AHP) calculates weights for each criterion. The Drought Vulnerability Assessment map is generated by analyzing the parameters through spatial analysis. The results revealed that the drought vulnerability index of Kurnool is 42.5. This finding has been successfully validated by historical drought records of the region. Decision-makers can use the results to develop and apply proactive drought mitigation strategies.

Assessment of hydrogeological parameters in a tropical region using GIS and AHP

Hydrogeological parameters have a significant impact on groundwater fluctuations in a tropical region. Malaysia is a tropical country experiencing rise in groundwater usage to meet the growing water demand. Therefore, an assessment of hydrogeological parameters is necessary for sustainable planning and management of groundwater. Geology, rainfall, drainage density, slope and soil are the hydrogeological parameters analysed for assessment in the region. The study aimed to assess hydrogeological parameters in the state of Selangor, Malaysia using Geographic Information System (GIS) and Analytic Hierarchy Process (AHP). The parameters were weighted based on the degree of impact on groundwater potential using AHP model. The weighted and ranked parameters were integrated through GIS to create groundwater potential zone map. The groundwater potential zones were divided into three categories low, moderate, and high potential zones. Moderate potential zones cover 73% of total area in the state of Selangor. The moderate potential zones cover most of the districts in the west such as Sabak Bernam, Klang, Kuala Langat and Sepang. As well as the majority of the area in districts like Hulu Selangor, Petaling, Gombak and Kuala Selangor. The findings of this study might be useful for policy makers and government organisations in formulating strategies for sustainable groundwater management and determining ideal locations for groundwater extraction.

Determining Aquifer Hydrogeological Parameters in Coastal Aquifers from Tidal Attenuation Analysis, Case Study: The Malta Mean Sea Level Aquifer System

The coastal and carbonate Mean Sea Level Aquifer (MSLA) of Malta is characterised by high anisotropy and heterogeneity, which together make evaluating the aquifer system parameters a challenging task. In this paper, we present an approach for the determination of the hydrogeological parameters of this coastal aquifer based on tidal-induced groundwater fluctuations that can be applied in other similar contexts. This work presents an analysis of data undertaken on monitoring boreholes located in the Malta MSLA exhibiting tidal-induced groundwater fluctuations. This allowed us to determine the values of three main hydrogeological parameters: hydraulic diffusivity, transmissivity and hydraulic conductivity. These will subsequently be used as an input for groundwater flow and reactive transport modelling purposes. In this study, a methodology based on the fast Fourier transform (FFT) is proposed to improve the applicability of the Jacob–Ferris method to the observed groundwater level and sea level fluctuations. The FFT reproduced signals allowed us to isolate the component induced by sea tides, thus eliminating short- and long-term variations of the water table induced by other disruptive factors. Results showed high variability of hydrogeological parameters within a short distance, reflecting the high anisotropy and heterogeneity of the aquifer system. The transmissivity values derived from the Jacob–Ferris method are complemented with results derived from the pumping tests with the aim of estimating the spatial distribution of the aquifer transmissivity for the study area. The spatial variability of transmissivity values is analysed by means of geostatistics tools for estimating uncertainty, correlation and variation in space through the use of semi-variograms.

MODELLING IMPACT OF CROPPING PATTERN AND URBAN AREAON GROUNDWATER RESOURSES OF NAGARJUNA SAGAR RIGHTCANAL COMMAND AREA USING VISUAL MODFLOW

Groundwater models can be used for the assessment of the impact of the different cropping pattern andchange in urban area on groundwater resource and modeling is the best tool to optimize the differentcombinations or scenarios and to select the best combination or scenario for management of sustainablegroundwater resources. In this study, three-dimensional finite-difference groundwater model VisualMODFLOW 2.8.1 was used to simulate the groundwater dynamics in Nagarjuna Sagar Right CanalCommand area. The net area irrigated under Nagarjuna Sagar Right Canal is 4.75 lakh ha. Calibration andvalidation of the model has been carried out and used to predict the static groundwater storage availabilityin the study area for different cropping pattern scenarios and change in the urban area. The validatedVisual MODFLOW 2.8.1 was used to simulate the groundwater dynamics in the study area for the years2030 and 2040 with different cropping pattern scenarios and change in the urban area. Global climatemodel MarkSim, which is developed by the International Centre for Tropical Agriculture (CIAT) was usedto generate future weather data for the years 2030 and 2040. The impact of change in cropping pattern onstorage of static groundwater resource in the study area for the years 2030 and 2040 was assessed with twoscenarios of change in rice cropped area decreased by 50 per cent and 100 per cent with this cropped areacultivated equally by the ID crops. These results showed that the lesser storage of static groundwaterresources in future lesser. The change in the cropping pattern affects the net recharge of the groundwaterwhich influences the groundwater levels. Increase in paddy area increases the recharge and rise ingroundwater level has been identified. In the study area, cropping pattern could be changed from rice cropto other irrigated dry crops to prevent the increase of groundwater resources which leads the water loggingcondition in the study area. The urbanization is one of the most significant factor considering for assessmentof the response on the groundwater levels and availability of static groundwater resources. The groundwaterrecharge is very less in case of increase in urban area and generates more runoff rather than the intake ofrainfall in the ground surface as having the impervious nature. In view of increase in urban area in thestudy area, the four scenarios are proposed with the combination of 10 per cent and 20 per cent decrease inrecharge and 50 per cent and 100 per cent increase in groundwater draft and simulated the groundwater fluctuations for the years 2030 and 2040. The impact of change in the urban area on storage of availablestatic groundwater resource in the study area for the years 2030 and 2040 was assessed with four scenarioscombination of groundwater recharge and groundwater pumping. The storage of static groundwaterresources would be expected in future lesser than the present storage of static groundwater resources in allscenarios due to increase in urban area as increased in impervious nature of the ground surface. The declinein available static groundwater resources would be expected 6.38 per cent and 7.08 per cent during 2030and 2040 respectively. The rapid expansion in the urban area and their settlements is also one of the reasonsfor the depletion of groundwater resources with low recharge and high groundwater draft.

Assessment of Bi-Decadal Groundwater Fluctuations in a Coastal Region Using Innovative Trends and Singular Spectrum Analysis

Abstract Coastal areas are among the densely populated regions in the world with growing population and subsequent increasing demands for water. Understanding the long-term variations in available water resources aids in efficient water conservation, management and allocation strategies. The present study investigated the longterm trends in groundwater depths (GWDs) for pre-monsoon and post-monsoon seasons in the coastal district of Kollam during the period 1996~2017, where groundwater is the primary source for domestic and agricultural uses during summer season. The trends examined using the modified Mann Kendall (mMK), innovative trend analysis (ITA) and Sen’s slope estimator indicated a decreasing pre-monsoon GWD trends at an average of -0.5m/ decade in 63% of the wells, while increasing post-monsoon GWD trends at an average rate of +0.43m/decade in 72% of the wells at 5% significance level. The singular spectrum analysis (SSA) captured monotonic as well as non-monotonic trend trajectories for the GWDs. About 41% wells exhibited a correlation below - 0.5 (p&amp;lt;0.05) between post-monsoon GWDs and JJASO (June, July, August, September and October) rainfall totals. The increasing post-monsoon GWDs could be related to recent changes in the southwest monsoon patterns over the peninsular India. Adequate planning and management of existing water resources could impart better control on water conservation strategies under the scenario of climate change.

Underground Water Level, Strain, and Tilt Changes Observed Around the Fault Near Tono Research Institute of Earthquake Science

Near the Tono Research Institute of Earthquake Science (TRIES), Mizunami City, Gifu, two 500 m- deep shafts with diameters of 4.5 m and 6.5 m were excavated by the Japan Atomic Energy Agency (JAEA). The 6.5 m shaft is crossed by an NNW-trending geological fault (NNW fault), which has a right-lateral strike-slip component and a dip-slip component. Since before the excavation TRIES has been performing observations by a comprehensive set of borehole crustal activity observation devices in deep boreholes and extensometers in a vault near the shafts to observe variations in, for example, strain, tilt, and groundwater level continuously. During the shaft excavation, groundwater inflow to the shafts was encountered. The water was twice pumped out. During the pumping and non-pumping periods, TRIES’s observation data such as the groundwater level, the strain, and the tilt showed anomalous variations. The analysis of them revealed relationships among the groundwater level, the fault, the strain and the tilt. Strain analysis of TGR350 borehole station showed that the direction of the maximum shear strain was parallel to strike of the NNW fault. In addition, when the water in the shafts was being pumped out, the groundwater level at TGR350 declined and the maximum shear strain showed a right-lateral strike-slip movement in the NNW direction. When pumping was paused, the groundwater level increased, and the maximum shear strain showed a left-lateral strike-slip movement in the NNW direction. On the other hand, strain analysis of TGR165 borehole station showed different behavior from that of TGR350 borehole station deeper than TGR165. Tilt analysis of TGR165 borehole station showed tilt changes nearly perpendicular to strike of the NNW fault corresponding to the pumping and the non-pumping periods. Tilt analysis of TGR350 borehole station showed tilt changes of E-W direction with much smaller amplitude than that of TGR165. Behavior of the strain and the tilt during the pumping and non-pumping periods can be attributed in part to differences in the response of the medium to groundwater fluctuations, due to differences in the number and distribution characteristics of the fractures in the medium where the observation instruments are installed. We also discussed the observation results from the viewpoint of poroelasticity.

Modeling and evaluation of NAPL-impacted soil vapor intrusion facilitated by vadose zone breathing

The water table fluctuations can cause a reciprocating advection of soil gas in the vertical direction, known as vadose zone breathing. In this study, we developed a vadose zone breathing-facilitated vapor intrusion (VI) model and applied it to evaluate the influence of NAPL (non-aqueous phase liquid)-impacted soils. The developed model was first validated with data from previously conducted sand tank experiments and then used to simulate VI scenarios involving different fluctuation amplitudes and periods of the water table, soil types, building structures, and source depths. Our results suggest that within one month of vadose zone breathing (amplitude of 0.5 m and period of 4 d), the indoor pollutant concentration varies by approximately seven orders of magnitude, and the averaged concentration is nearly nine times larger than the steady-state concentration. The results also show that with the increase of mean soil particle size, the indoor pollutant concentration tends to increase and becomes more sensitive to vadose zone breathing; compared to the basement foundation, buildings with a slab-on-grade foundation are less susceptible; when the source depth exceeds 10 m, the source depth plays an insignificant influence. Our findings highlight that vadose zone breathing can promote the VI risks of buildings with a basement foundation at sites with shallow water tables, significant groundwater fluctuations, and coarse-textural soils.

Assessment of shallow groundwater contamination on Pari Island, Indonesia.

Freshwater on small islands is generally limited and relies on rainwater and groundwater. This study aimed to assess changes in shallow groundwater quality on Pari Island, Indonesia. Pari Island is a small island with an area of 41.32 ha and belongs to a monsoon climate. Also, being a residential island, it attracts many tourists. The approach was to assess the shallow groundwater quality of ten wells during the dry and wet seasons. Changes in water quality were evaluated using traditional hydrochemical analysis methods (Schoeller, Piper, and Gibbs diagrams) and ion ratios. Shallow groundwater quality in the study area showed different responses depending on the season. Therefore, each well responded differently to changes represented by changes in water quality. The change is controlled by various factors: evaporation (or water balance), geology, aquifer characteristics, tides, wind direction, and wave height. These factors trigger the fluctuation of groundwater and seawater interface, affecting the amount of rainwater and seawater transported to the freshwater aquifer layer. This water volume transported affects the process of rock weathering, dissolution, and dilution of contaminants in shallow groundwater.

Interoperability of -Band Sentinel-1 SAR and GRACE Satellite Sensors on PSInSAR-Based Urban Surface Subsidence Mapping of Varanasi, India

The Sentinel-1 is an active synthetic aperture radar (SAR) satellite with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> -band SAR sensor operating at a center frequency of 5.405 GHz and a wavelength of 5.55 cm. With the availability of freely available SAR datasets from Sentinel-1, the persistent scatterer SAR interferometry (PSInSAR)-based urban surface subsidence mapping has become easy. However, apart from geological causes, the major cause of urban surface subsidence is the over-exploitation of groundwater that results in piezometric pressure loss in the aquifers resulting in net subsidence. With the Gravity Recovery and Climate Experiment (GRACE) satellite sensor, the groundwater level fluctuations can be very easily studied temporally. But the coarse spatial resolution of GRACE data makes the study of groundwater fluctuations difficult to study for smaller watersheds. This study aims to correlate the PSInSAR average surface line of sight (LOS) displacement from Sentinel-1, with the average groundwater fluctuations from the GRACE sensor temporally from May 2017 to February 2022. The study also compared the correlation between PSInSAR displacement in both VV and VH polarizations and observed the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R} ^{{2}}$ </tex-math></inline-formula> values to be 0.63 and 0.65 for VV and VH polarizations, respectively, with GRACE data. After that, using the displacement and groundwater level fluctuation data, an estimation of a gravimetric anomaly due to a decrease in groundwater level was carried out for Varanasi city. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R} ^{{2}}$ </tex-math></inline-formula> , mean absolute error (MAE), and root-mean-square error (RMSE) were observed to be 0.84, 1.23, and 2.4, respectively, in gravimetric anomaly estimation, thus giving sufficient acceptance for interoperability of the two sensors.

Groundwater dynamics of a lake-floodplain system: Role of groundwater flux in lake water storage subject to seasonal inundation

Groundwater behaviors in lake-floodplain systems are dynamic and complex; in particular, the role of groundwater flux in regulating lake water storage subject to strong seasonal variation is not well understood. This study addresses the contribution of groundwater flux in a large floodplain system (Poyang Lake, China), with focus on quantifying the groundwater-lake interactions at multiple time scales in high rainfall (2010) and low rainfall (2011) years using a groundwater flow model (MODFLOW). Simulated results revealed that the unconfined aquifer received approximately 8 % of the annual rainfall as groundwater recharge. Fluctuations in shallow groundwater and lake water level reflected hydraulic synchronization and hysteresis. Additionally, the diurnal variability in the groundwater-lake exchange fluxes was subject to dynamic and bidirectional patterns, and a time lag between the water exchange and rainfall was also found. For 2010 and 2011, the monthly net flux of lake infiltration into groundwater was 1.5–10.0 mm and 0.1–6.0 mm and groundwater exfiltration into lake was 1.3–9.5 mm and 0.4–2.2 mm, respectively, demonstrating a significant variation of the exchange magnitude and direction. In particular, we found that groundwater exfiltration contributed up to 55 % of lake storage change in February of 2011. The outcomes from this study indicate that groundwater can be a major component of the Poyang Lake's water balance, which suggests an important role of groundwater in regulating the lake water storage and perhaps other flood pulse systems.

Geo-statistical analysis of ground water fluctuations for sustainable management of groundwater resources within the chaliyar basin, southwest India

Ground water is the primary source for potable water and it forms the fundamental connecting link amongst the Climates, Society & Natural Ecosystem. Phenomenon like climate change has a marked influence on ground water recharge giving rise to spatial variation in ground water levels. Today, fluctuations in ground water level have become a major problem and their study is of prime importance from water security & sustainable development point of view. To meet such challenges, geospatial technologies have proven to be an effective enabler i.e. spatial interpolation mechanism using geo-statistical analysis has become very popular. The Kriging method is an example of such techniques. Hence, this paper attempts to study & analyze the spatio-temporal variations of ground water levels pertaining to 29 observation wells located in Chaliyar basin, Southwest India for which Geo-statistical analysis was performed using ordinary Kriging method in Arc GIS environment. Finally, the spatial maps showing the ground water level fluctuations were generated for the Chaliyar basin which could be used for sustainable management & planning of Ground water resources within the basin.