Drawdown Of Groundwater Level Research Articles

Development of a subsurface monitoring system for land subsidence hazard in the Bandung basin: a laboratory prototype

Abstract Land subsidence is a global environmental hazard posed by urban area worldwide, causing degradation in environmental quality and leads to further disasters such as increased flood risk, contamination risk, and infrastructure damages. Anthropogenic causes, such as groundwater extraction and building weight, cause high land subsidence rates. The behaviour of the subsurface under the influence of anthropogenic causes must be well understood to mitigate this problem. Conventional subsurface monitoring is robust and costly. In this case, we aim to first develop a versatile and low-cost subsurface monitoring prototype for land subsidence at a laboratory scale using a model box. Methods employed were constructing an experiment model box, developing the monitoring system, and trial experiments in the laboratory. The sensors are linear vertical displacement transducer, potentiometer, water level and pressure sensors. The monitoring system uses Arduino microcontroller to convert sensors inputs to desirable outputs and a logger to record the real-time data and transmit it to personal computer in the laboratory. Land subsidence in the Gedebage area in Bandung basin was taken as a model case. The model box was filled with soil from Gedebage, Bandung. A scenario of exploitation of confined groundwater and weight of building was applied for the model case. The results show that the laboratory prototype can monitor the subsurface changes due to the applied anthropogenic forces. In the case of Bandung soil, groundwater exploitation did not immediately cause subsidence instantaneously. There is a time delay between the drawdown of groundwater level and the subsequent vertical deformation. The rate of subsidence varies spatially inside the tank, the largest is close to the pump well and surface loads. A maximum of 2.88 mm subsidence over 663 days was recorded following 1 m groundwater drawdown. This information asserts the importance of long-time monitoring in subsidence areas.

Investigating Earth surface deformation with SAR interferometry and geomodeling in the transborder Meuse–Rhine region

Introduction: This study aims to differentiate local and regional ground uplift, as well as sub-regional subsidence induced by groundwater level drawdown, which are possibly enhanced across fault structures, as monitored by various synthetic aperture radar interferometry (InSAR) processing methods. A buoyant mantle plume under the Eifel may be responsible for the regional ground uplift, including the Weser–Geul (BE) and South Limburg regions (NL), which could negatively affect the area proposed for the future Einstein Telescope.Methods: Different InSAR processing techniques are compared to evaluate their limits in tracking fault structures on a time series of Copernicus Sentinel-1 images while detecting and measuring ground motion based on their phase signature. The results present an overall stable ground for the Euregio Meuse–Rhine region, especially at the Belgian–Dutch border, while tectonic activity is observed along the German side of the Rhine Graben.Results: As the current neotectonic activity in the target area was not well known, we performed a spatiotemporal analysis of ground deformation associated with the presence of NW–SE-trending normal faults where karst also develops, as well as along the Variscan NE–SW-trending thrust faults. This work demonstrates that the identification of deformation hazards using satellite remote sensing (and connected seismological) techniques is challenging mainly due to (very) small regional scale deformation, terrain conditions, and SAR properties.Discussion: Thus, the results mostly indicate ground stability over the area; however, also some agricultural activities were observed, as was deformation along some infrastructure such as railways. Displacements of millimetric order measured along the faults located near the Geul valley (BE) are probably related to old mining activities.

Role and impact of urban water prices on the management of groundwater consumption due to Covid-19 outbreaks

The main objective of this study is to investigate the environmental role and impact of urban water prices, and hence its consumption in Tehran on its groundwater level drawdown. The issue gets vital in times of drought when the scarcity value of water exceeds benefits of groundwater environmental flow. Hence, the argument is that urban water tariffs may play a role in managing groundwater flow.In this regard, the harmful impact of urban water consumption on the environmental flow of groundwater resources is distinguished. Then the objective would be to identify determinants of urban water consumption. To do so, an urban water's demand function, including important key regressors such as price, income, temperature, and rainfall is estimated. Moreover, the role of Covid-19 in urban water consumption is highlighted.Results show a demand elasticity of −0.29 ± 0.1 for urban water consumption, or that a 10 percent increase in average price results in a decline in urban water consumption of 1.9–3.9 percent. In addition, one percent lower urban water consumption causes 1.3 ± 0.1 percent less groundwater extraction, or that response of a 10 percent decrease in the consumption could cause a decline in groundwater extraction of 12–14 percent. Last but not least, a 1 percent decrease in underground extraction for urban water raises 13.2 ± 6.7 cm of GRACE water level after three months.The results show that groundwater exploitation for urban drinking water is a responsible contributor to the water level drawdown in Tehran. In addition, the significant elasticity of 0.29 shows that price mechanisms are useful to manage hydrological scarcity and the consequent disasters. Moreover, observing significant effects of covid-related determinants for calming down the upward trend of groundwater extraction, we alert for post-covid deterioration of subsidence areas due to regrowth of water consumption.

Identification of Aquifer and Pumped Well Parameters Using the Data Hidden in Non-Linear Losses

During the pumping of wells, the groundwater level drawdown, as measured in the pumped well, is increased by non-linear losses caused by the water flow velocity through the well screens. This undermines the adequacy of the direct use of the measured drawdown data in the well for the purpose of the realistic identification of the effective well radius and aquifer parameters. This anomaly is avoided by reshaping the drawdown function into a function of the specific drawdown sw/Q of the pumped well. This reshaping simplifies the exclusion of non-linear losses from the sequence of measured data of the water level in the well at the position of the effective radius of the pumped well. Combining the data of linear losses and the respective pumping rate of the pumped well, a function of the specific drawdown of the radial flow sw/Q was formed. This function describes the aquifer parameter relations during the respective test pumping. A consistent sequence of the function of the specific drawdown sw/Q of the pumped well reveals the actual value of the coefficient of nonlinear losses. Moreover, the specific drawdown function enables the reliable estimation of aquifer transmissivity using only the pumped well drawdown data.

Declining trees growth and vegetation productivity resulting from decreasing soil water contents induced by tunnels excavation in karst mountain areas

Tunnel construction in karst areas greatly impacts the local hydrological conditions. The drawdown of groundwater levels and the loss of soil water storage due to tunneling limit the available water resources on the karst land surface, and this may affect the function of plants. Here, we evaluated the responses of the radial growth rates of two major tree species (Masson pine and Camphor laurel) to a tunneling induced water stress event in a typical karst trough valley. Meanwhile, to discuss the overall influence of tunnel excavation on plant growth in all vegetation cover types, the dynamics of vegetation productivity around the tunnel were evaluated using remote sensing indices, the Normalized Difference Vegetation Index (NDVI), and Net Primary Productivity (NPP). Furthermore, we estimated the spatial–temporal variations of NDVI and NPP in other tunneling regions of Southwest China. The results showed that the soil moisture contents (SMC) around the Zhongliang Mountain Railway Line 6 (ZMRL6) tunnel had dramatically declined −5.06%∼−10.53% within the areas < 1500 m. After the excavation of ZMRL6 tunnel, the basal area increment (BAI) for the tree-ring widths of Masson pine and Camphor laurel within 1500 m of the tunnel central reduced by 94.8%∼135.8% and 116.6%∼139.9%, respectively, while the trees beyond this distance range were less influenced. Meanwhile, the remote sensing indices showed that tunnel excavation can reduce 3.3%∼7.6% of the NDVI and 15.7%∼17.4% of the NPP within 1500 m of the ZMRL6 tunnel. A similar distance range of such declines in NDVI and NPP was also found in other tunneling regions throughout the karst mountain areas of Southwest China. The findings in this study suggest that tunnel excavation may cause severe ecosystem degradation within 1500 m of the tunnel center, which should be considered in ecosystem management and conservation strategies in karst mountain areas.

Determination of Susceptibility to the Generation of Discontinuities Related to Land Subsidence Using the Frequency Ratio Method in the City of Aguascalientes, Mexico

Land subsidence in the Aguascalientes Valley, documented since the 1980s, has developed a large number of discontinuities that damage infrastructure. There is currently no methodology to accurately predict the site and time at which a discontinuity will occur, making it difficult to make decisions in urban planning or risk management. However, it is possible to determine the susceptibility of an area to the generation of fractures based on the factors associated with their formation. This study presents a zoning method based on the ground failure susceptibility index (GFSI) in the city of Aguascalientes, using the frequency ratio (FR) method and employing the depth of the basement, the subsidence rate, the subsidence gradient, and the groundwater level drawdown as variables. The zoning method included three categories of land subsidence susceptibility to fracturing, moderate, high, and very high, which were divided using the first (3.76) and second (4.24) quartiles of the GFSI. The zoning method was created with the discontinuities reported in 2010 and was validated with data from 2022. The results obtained show that 11.19% of the discontinuities developed between 2010 and 2022 were located in a zone of moderate susceptibility, 41.97% were located in a zone of high susceptibility, and 46.87% were located in a zone classified as having very high susceptibility.

Determination of critical aquifer subsidence points by DFFITS-COOK distance method using Importance sampling reliability analysis

The aim of this study is to investigate aquifer structure subsidence by groundwater level drawdown. In this study, a performance function matrix was developed in the first-order reliability method (FORM) by the importance sampling in order to investigate the regional resilience in a saturated aquifer. The study region is located in southwestern Iran. The changes in the layers of vertical structure destruction are an important factor affecting the plain's recharge capacity. Preparing the subsidence prediction layers due to the MODFLOW finite-difference model and criterion for its changes was related to five scenarios of recharge changes in the aquifer water level from 2008 to 2019 and also from 2019 to 2029. The results indicated that failure probability in Izeh aquifer varies from 0 to about 89 %. Considering structure type, most of the internal plain areas have high local resilience. For the aquifer boundary strips, the highest resilience is only in the southwestern part of aquifer. The high-risk border areas have a wide fitness on porous boundary strips as the main recharge sources. The reason for severe spatial changes in the failure probability of reliability was investigated by out-of-date analysis methods. The anomaly pattern was used in three methods of defining decision function to determine out-of-point under Robust Covariance, One-Class SVM and Isolation Forest. DFFITS and DFFITS methods (difference in fits) with COOK Distance were used to confirm the existence of 106 abnormal cells in the two-dimensional digit of baseline indices mean. Results showed that the most critical areas can be found in the central parts around the two lakes. The plain's permeable boundaries, the parts between the northwest and the center of the aquifer, and the northern aquifer's limited areas are other abnormal regions.

Evaluation of Groundwater Flow Changes Associated with Drainage within Multilayer Aquifers in a Semiarid Area

In order to evaluate the impact of groundwater drainage on groundwater flow, the Hetaoyu coal field was taken as a case study in the Longdong area, China, where the coal seam was covered with multilayer aquifers. A three-dimensional unsteady groundwater flow model and a one-dimensional fracture water flow model were calculated by joint equations for changing hydrogeological structures under coal mining. According to the results, mine construction had greatly affected groundwater reserves in the Quaternary phreatic aquifer, Cretaceous Huanhe confined aquifer, and Luohe confined aquifer. The groundwater drainage was mainly from the Cretaceous aquifer, in which the aquifer reserves of the Luohe Formation decreased by 30,861.8 m3/m, accounting for about 92% of the total changes in local groundwater reserves. A drop funnel with an area of about 2.3 km2 would be formed under the groundwater discharge of 187.6 m3/h for the main inclined shaft excavation of the Hetaoyu coal mine. With the continuation of mining activities, the mine water flow will reach 806.83 m3/h and would result in descending funnel area of about 4.5 km2, the groundwater level drawdown at least 16 m, which would exceed the limited value regulated by the government. Therefore, in order to ensure the safety of coal mining and protect groundwater resources, the Hetaoyu Coal Mine departments should take some water loss prevention and control projects to reduce the drawdown of groundwater.

Hidrogeologi daerah BRG berdasarkan kondisi hidrologi untuk mengetahui prediksi kesetimbangan Airtanah (Groundwater)

The rapid increase in groundwater exploitation in various sectors in Indonesia has caused preparations in the form of concrete steps that must be faced, especially reducing the impacts caused. The BRG area is an area known as an area in Geological Conditions the existence of intrusions that may result in retained groundwater flows and are productively small and even rare and in addition to that also in terms of environmental conditions of areas surrounded by large industries in the amount of very large groundwater use. Groundwater intake activities impacted the drawdown of groundwater levels. This study in cased the Water Balance conditions of the BRG area groundwater. This study employs hydrology variable to determine groundwater balance. Variables of Rainfall (CH in mm/yr), Evapotranspiration (ET in mm/yr), Infiltration (R in mm/yr) and Run Off (RO in mm/yr). Balance of Groundwater is based on a general formula of Capacity (S). Capacity (S) is directly proportional to Rainfall (CH) as Inflow and Total amount of Evapotranspiration (ET), Infiltration (R) and Run Off (RO) as Outflow. The study revealed that the inflow and outflow of water in BRG area are balanced. The results of the Hydrological Variables of the study area are as follows: Rainfall (CH) is of 8302 mm/yr average value, Evapotranspiration (ET) is of 2726,6 mm/yr average value, Infiltration (R) is of 2,02 x 107 mm/yr and Run off (Ro) 1316,3 mm/yr. The result of Groundwater Water balance is a negative value (Inflow &lt; Outflow). Hydrological calculations decreased in each year for the last 4 years the observation data showed the negative values were getting greater, as follows: (a) the first year -4.01 x 107, (b) the second year -5.63 x 107, (c) the third year -3.10 x 107, (d) the fourth year -4.72 x 107.

Assessing the impact of climate change on Ha Tu coal mine, Quang Ninh province

Climate change has been affecting the socio-economic life of Quang Ninh province in general, and the coal mining activities of many companies, including Ha Tu Coal Joint Stock Company in particular. By the methods of collection, synthesis, statistics, field survey, and public consultation, this study has evaluated the climate condition of the study region and the impact of climate change on the coal mines in the past. The environmental incident of landslides caused by heavy rain in 2015 has filled rivers and streams and destroyed infrastructure. According to the scenario of climate change for Quang Ninh province by 2100 (B2), the regional temperature will increase by 2.50C, and the rainfall will increase by 7.3% compared to the period 1980÷1999. The study predicted the potential impacts of climate change on mining operations in the future such as the increased risk of landslides, floods, geological hazards, the drawdown of groundwater levels, and subsidence of the ground surface at the mining site. By the forecast results, the larger the mining depth is, the higher the radius affected by the lowering of the groundwater level will become, which can be up to 2.4 km compared to the mining area. In addition, the increase in temperature will be one of the factors that cause difficulties for production activities, affect the health of workers, slow down the process of reclamation and restoration of the mine environment, and increase electricity and water costs, etc. The study also proposed several technical and management solutions to reduce the risk and respond to environmental incidents before the impact of climate change on the Ha Tu coal mine towards sustainable development.

Land surface deformation monitoring in the Al-Ain arid region (UAE) using microgravity and SAR interferometry surveys

The integration of geophysical and satellite-based monitoring techniques can yield new insights in land surface deformation (LSD) studies. In this study, we integrated the microgravity monitoring geophysical technique with Interferometry Synthetic Aperture Radar (InSAR) to reveal the possible sources of LSD changes. A microgravity survey was conducted over Al-Ain city for 1 year at one-month intervals, with time-lapse microgravity changes calculated based on the results. Over the same area of interest and time interval, InSAR analysis was performed using Sentinel-1 (C-band) data. The time-lapse microgravity changes for the whole studied period ranged from −36 to 365 μGal. The InSAR processing showed periodic land surface deformation over the area of interest varying with the season of the year. The InSAR technique detected land surface subsidence at the northeast and western parts of the study area (−7 mm/year and −8 mm/year, respectively) and land surface uplift in the central and southern parts of the study area (2 mm/year). The recorded subsidence may relate to water extraction in these areas. The integration of the two techniques showed a negative correlation, with coefficients of −0.43 and −0.39 for land surface subsidence and uplift, respectively. Furthermore, groundwater level drawdown zones were identified in the west and center of the study area. Overall, LSD is mainly stimulated by water volume exploitation in the Al-Ain region.

Land subsidence susceptibility mapping using PWRSTFAL framework and analytic hierarchy process: fuzzy method (case study: Damaneh-Daran Plain in the west of Isfahan Province, Iran).

Land subsidence susceptibility mapping is a necessary prerequisite for land subsidence management. Proper assessment of land subsidence requires determining parameters affecting subsidence to discover the spatial relationships with subsidence. For this purpose, two frameworks were prepared, according to the land site subsidence, eight parameters affecting the subsidence in the Damaneh-Daran plain. In the first framework, eight parameters including annual groundwater level drawdown, aquifer medium, land use, discharge, aquifer saturation thickness, net recharge, fault proximity and topography called PWRSTFAL based on weighting parameters and the second model based on optimization and compatibility of eight active layers on subsidence, were prepared by AHP-fuzzy method and the final map of subsidence vulnerability obtained. Radar images and the InSAR method validated the methods. The results show that both maps show a good correlation with radar data. Still, the map prepared by the AHP-fuzzy method offers the highest correlation with radar data and subsidence in the plain. It separates subsidence vulnerability in more detail on the whole surface of the plain. According to this model, most plain areas, especially the eastern part, are subject to subsidence, and management programs should control subsidence. The results ROC diagram obtained from the performance of the PWRSTFAL framework based on the AHP-fuzzy method was more promising than the ordinary PWRSTFAL framework.

Time series study for groundwater level evaluation in monitoring well

Climate and hydrogeological conditions of the Brazilian semi-arid demand sustainable and efficient water solutions. Groundwater monitoring programs are tools to subsidize the decision-making in this sense. In Ceará state, the monitoring of Araripe sedimentary basin aquifers is important for the development of the region. In this scenario, the present work aimed to study the groundwater level through an exploratory analysis of time series. The study area covered the eastern portion of the Araripe sedimentary basin, in the municipality of Milagres, in Ceará state. As the object of this study, it was obtained the time series of monthly average groundwater levels in a monitoring well of RIMAS/CPRM and installed in the Middle Aquifer System. Graphical and numerical methods were applied for the identification and description of time series main characteristics. Precipitation data in the study area were used to evaluate the system recharge. Results were discussed according to the environmental aspects of the study area. As a result, it was possible the identification and description of time series patterns such as trend and seasonality through the applied methods. It is also highlighted the sharp drawdown of groundwater levels in long term in the time series, reflecting the quantitative state of the aquifer system, as well as the groundwater recharge during the rainy season of the region, evidenced by the study of time series seasonality together with the precipitation data..

Ground settlement and fault deformation response to deep-buried tunnel excavation and groundwater drawdown

The groundwater drawdown caused by tunnel excavation may induce large-scale deformation, including uneven settlement deformation of rock mass and local deformation of faults, which poses a great risk to engineering safety, and requires the constraint of deformation stability. Based on the theory of deformation reinforcement and the effective stress principle, we study the nonuniform deformation and unbalanced force distribution of the rock mass and faults caused by the groundwater drawdown after the excavation and drainage of the deep tunnel. The results suggest that the groundwater level drawdown can increase the effective stress in a wide range, and significantly disturb the stress and deformation of the rock mass. It is noted that the fault crossing the tunnel is relatively dangerous under these disturbances, and deserves special attention. Moreover, the unbalanced force and the plastic zone can be transmitted to further distances along the fault, and reinforcement and support should be carried out in time. In addition, the greater the Biot coefficient can lead to the greater impact of groundwater drawdown on stress changes and deformation of the rock mass and faults.

Assessing rainfall spatial variability in the Brazilian savanna region with TMPA rainfall dataset

Rainfall is a major component of the hydrological cycle. The lack of basic information on rainfall spatial variability is a major source of uncertainty in many fields of studies, e.g., meteorology, hydrology, and agriculture. Satellite rainfall measurements are becoming increasingly popular for their extensive database and reliable estimates. The objective of this study was to use the Tropical Rainfall Measuring Mission (TRMM) dataset along with rain gauges to characterize aspects of rainfall spatial variability and discuss the possible impacts from recent trends in the Brazilian savannah biome (Cerrado). Gauge stations were used to assess TRMM bias error and calibrate data for further analyses. Rainfall rates and their spatial variability showed a strong relationship to the transition zones between different biomes. Rainfall showed a decreasing trend for the eastern region of the Cerrado biome, a region characterized by a recent and significant expansion of crop areas. These trends agree with results from different studies which highlight the current drawdown of groundwater levels and reduced discharge, and possible lengthening of the dry season in the long run. As many conflicts have already been documented for this region, these decreasing trends are alarming for urgent and consistent hydroclimatic monitoring, and improved water resources planning and management. Positive trends for rainfall in the central Cerrado are likely a momentary recovery of recent-period drought.

Modelling Shallow Groundwater Evaporation Rates from a Large Tank Experiment

A large tank (1.4 m x 4.0 m x 1.3 m) filled with medium-coarse sand was employed to measure evaporation rates from shallow groundwater at controlled laboratory conditions, to determine drivers and mechanisms. To monitor the groundwater level drawdown 12 piezometers were installed in a semi regular grid and equipped with high precision water level, temperature, and electrical conductivity (EC) probes. In each piezometer, 6 micro sampling ports were installed every 10 cm to capture vertical salinity gradients. Moreover, the soil water content, temperature and EC were measured in the unsaturated zone using TDR probes placed at 5, 20 and 40 cm depth. The monitoring started in February 2020 and lasted for 4 months until the groundwater drawdown became residual. To model the groundwater heads, temperature, and salinity variations SEAWAT 4.0 was employed. The calibrated model was then used to obtain the unknown parameters, such as: maximum evaporation rates (1.5-4.4 mm/d), extinction depth (0.90 m), mineral dissolution (5.0e-9 g/d) and evaporation concentration (0.35 g/L). Despite the drawdown was uniformly distributed, the increase of groundwater salinity was rather uneven, while the temperature increase mimicked the atmospheric temperature increase. The initial groundwater salinity and the small changes in the evaporation rate controlled the evapoconcentration process in groundwater, while the effective porosity was the most sensitive parameter. This study demonstrates that shallow groundwater evaporation from sandy soils can produce homogeneous water table drawdown but appreciable differences in the distribution of groundwater salinity.

1-Dimensional analysis of land subsidence in Semarang city due to anthropogenic forces

Anthropogenic factors play an important role in land subsidence. The northern part of Semarang City has long suffered from land subsidence since the 1980s. This paper aims to analyze the land subsidence process inthe northern part of the Semarang city due to anthropogenic factors of groundwater exploitation andbuilding loads. The analysis was carried out by using 1-dimensional numerical and analytical models. Results of modeling were subsequently compared to results from stable benchmark monitoring data in Madukoro and Kaligawe. Modeling results show that the contribution of groundwater level decrease accounts for 74-82% of the total subsidence, while the remaining 18-26% is attributed to the building load. The rate and magnitude of subsidence arehigher at thenortheastern part (Kaligawe) due to the thicker aquitard and more rapid groundwater level drop. Comparison of modeling and monitoring results signifies that the land subsidence in the northwestern part (Madukoro) approximately follows the model scenarios of groundwater level drawdown and surface loading;meanwhile the land subsidence rate in Kaligawe exceeds modeling results, most possibly due to the large discrepancy between the current conditions to modeling scenarios, presumably faster groundwater drawdown

Groundwater sustainability: Developing a non-cooperative optimal management scenario in shared groundwater resources under water bankruptcy conditions

Groundwater level drawdown changes the hydrological cycle and poses challenges such as land subsidence and reduction of the groundwater quality. In this study, a new approach using a simulation-optimization framework was developed for shared groundwater management under water bankruptcy conditions (where water demand is greater than the allowable discharge capacity of water resources). The novelty of this study lies in using bankruptcy rules and a game model to manage a bankrupted shared groundwater resource considering aquifer sustainability. Accordingly, groundwater flow in the aquifer was numerically simulated by a finite-differences model (MODFLOW). Then, the repeated performance code of the finite-differences model was run for different discharge scenarios, and the results were applied to develop an MLP-ANN meta-model. By coupling the meta-model with a non-dominated sorting genetic algorithm II (NSGA–II)–based multi-objective optimization model, an optimized cultivation pattern under water bankruptcy conditions was achieved. Then, six different bankruptcy methods were utilized to specify groundwater allocation between three stakeholders. To manage the water bankruptcy conditions, different scenarios considering various groundwater extraction rates and cultivation areas were defined, and the optimization model was recoded for each scenario to find the corresponding optimized cultivation pattern. To consider the competition between stakeholders for groundwater extraction, a non-cooperative 3-player game was applied to achieve a compromise for different combinations of management strategies, which maximizes the profit and yields the best cultivation scenario. Applicability of the proposed methodology was investigated in an aquifer system located in Golestan Province, Iran, including three regions (Minudasht, Azadshahr, and Gonbade-kavus). Results show that the proposed method is capable of managing the bankruptcy conditions by generating greater agricultural profit and reducing groundwater drawdowns.

Investigation of the impacts of tunnel excavation on karst groundwater and dependent geo-environment using hydrological observation and numerical simulation: a case from karst anticline mountains of southeastern Sichuan Basin, China.

Tunnel excavation has significant disturbance on groundwater system and related geo-environment, especially in karst regions like southwestern China. The present research was conducted to quantitatively understand the negative impacts posed by tunnel construction on the karst groundwater system and reveal the behavior of karst groundwater system under the tunnel disturbance, with the aid of field survey, hydrogeological analysis, and numerical simulation. The results suggested that negative impacts such as loss of surface and underground water, ground collapse, and house deformation would be posed directly and indirectly to the karst groundwater system and its dependent geo-environment as the result of groundwater level drawdown by tunnel excavation. The degree and range of groundwater drainage impact were determined by the lithological and hydrogeological characteristics of strata. These negative impacts were dominantly distributed in the karst depressions valleys, and the direct ones occurred at first and followed by the indirect ones. Simulation results showed groundwater level drawdown would not occur synchronously in spatial, but always occurred around the tunnel axis at first and gradually expanded towards far away over time. The maximum disturbance on groundwater system can reach to approximately 25 m vertically and 3000 m horizontally for present modeling tunnel. With the aid of numeral simulation, three response stages were identified for the karst groundwater system behavior to the tunnel disturbance. The impacts of tunnel practice on groundwater and surface water bodies can be gradually eliminated since the second stage, but would continue if existing failure of tunnel waterproof until a new balance state achieved. The present research can improve the understanding of the impacts of tunnel excavation on karst groundwater system and dependent geo-environment, and provide reference to the protection of water resources and geo-environment in karst regions like Chongqing worldwide.

Hydrochemical and Isotopic Characterization of the Waters of the Manglaralto River Basin (Ecuador) to Contribute to the Management of the Coastal Aquifer

Coastal aquifers are strategic and fundamental in the development of touristic areas. The coastal aquifer within the Manglaralto River Basin in Ecuador is essential, as it is the only source of water supply for a large part of the northern part of the Santa Elena province. It is a semi-arid region where high volumes of water are pumped from the aquifer, causing a significant drawdown of groundwater levels, thus affecting the water quality. This work aims to characterize the characteristics of groundwater in the coastal aquifer using hydrochemistry and stable isotopes to propose a hydrogeological conceptual model. The methodology for determining the chemical and isotopic characteristics of groundwater follows the following scheme: (i) studies of ionic concentrations using the Piper diagram, (ii) assessment of the origin of salinity through the Cl/Br ratio, the presence of seawater intrusion through the Hydrochemical Facies Evolution Diagram HFE-D, (iii) characterization of precipitation events using stable isotopes (18O and 2H), and, (iv) development of a hydrogeological conceptual model of the study area. The results indicate that in the basin there are mixing processes of the existing water in the aquifer with recharge water, direct cation exchange processes in the freshening process during recharge, and evaporation in the unsaturated zone. A conceptual model of the flow system in the basin is built, based on the mentioned processes. The main conclusions are: seawater intrusion is present in the areas of the wells located closest to the coast, urban activity through septic tanks is affecting the quality of the aquifer, and rainfall is highly relevant in the different hydrochemical and isotopic processes that operate in the basin.