Intensive Groundwater Extraction Research Articles

Current land subsidence in Jakarta: a multi-track SBAS InSAR analysis during 2017–2022 using C-band SAR data

In Jakarta, Indonesia, rapid urbanization and intensive groundwater extraction have led to significant land subsidence, posing challenges for sustainable urban management. This study utilized Interferometry Synthetic Aperture Radar (InSAR) integrated with multi-track data analysis to generate refined time-series and velocities of 2D displacement across Greater Jakarta. This study reveals notable variation in subsidence rates across different areas, with the most significant subsidence observed in Cikarang and the coastal regions of North Jakarta, which remains linear to this day. Notably, while the 2D approach improved accuracy by up to 53% at some locations, discrepancies at others indicated that simpler descending projections might sometimes yield better results. This underscores the necessity for a nuanced application of geodetic methods based on specific site conditions to effectively monitor and manage land subsidence in complex urban environments. Our findings highlight the critical importance of integrating multiple monitoring approaches to comprehensively address both vertical and horizontal displacement.

Analysis of Deformation Dynamics in Guatemala City Metropolitan Area Using Persistent Scatterer Interferometry

The analysis of deformation dynamics in Guatemala city and its surrounding region presented in this paper holds significant relevance due to the high vulnerability of this area to natural disasters, combined with its rapid urbanization, similar to most Central American cities, contrasting with a lack of InSAR and deformation studies in the region. A total of 226 SAR images from Sentinel-1 A and B satellites in both ascending and descending geometries were processed with the Persistent Scatterer Interferometry (PSI) technique employing the SNAP-StaMPS integrated processing chain. The study area encompasses the Metropolitan Region of Guatemala, which is characterized by a diverse and active geological framework, with a historical record of earthquakes, intense groundwater extraction, and local subsidence phenomena, causing fissures and sinkholes. Four active areas were identified in the study area, each covering more than 50 hectares, with subsidence velocities greater than 10 mm/yr. This study provides valuable insights into fostering the sustainable development of this region by identifying deformation patterns, characterizing main active areas, and evaluating associated risks for disaster management and prevention. The results can also aid informed decision-making processes and guide urban planning and resource management strategies in other Central American countries. The application of InSAR studies is crucial for improving safety and sustainability in urban environments and natural resource management in vulnerable regions.

An Assessment of Geospatial Analysis Combined with AHP Techniques to Identify Groundwater Potential Zones in the Pudukkottai District, Tamil Nadu, India

Groundwater is critical to the socioeconomic development of any region. Infiltration of surface water into the ground is influenced by a variety of factors such as soil pores, folds, fractures, faults, and joints, all of which contribute to groundwater recharge. Groundwater is an important source of freshwater in the drought-prone Pudukkottai district of Tamil Nadu, India. Therefore, the search for groundwater potential zones (GWPZs) is critical. The present study focuses on the investigation of potential groundwater zones using geospatial techniques. Geology, land use and land cover, geomorphology, soil, drainage density, lineament, and groundwater levels were obtained from state and non-state associations. ArcGIS version 10.8 was used to create all thematic layers and classified grids. The intensive use of groundwater in arid and semiarid regions is becoming a problem for the public to meet their freshwater needs. The condition of arid and semi-arid regions due to intensive groundwater extraction has become one of the most important environmental problems for the public. In this study, a powerful groundwater potential mapping technique was developed using integrated remote sensing data from GIS-AHP. Using AHP techniques, thematic layers for geology, geomorphology, and soil followed by drainage, drainage density and lineament, lineament density, slope, water level, and lithological parameters were created, classified, weighted, and integrated into a GIS environment. According to the results of the study, it is estimated that 14% of the groundwater potential in the study area is good, 49% is moderate and 36% is poor. A groundwater level map was used to verify the groundwater potential. In addition, the model was validated with a single-layer sensitivity analysis, which showed that geology was the most influential layer and water level was the least influential thematic layer. The low-potential areas identified on the groundwater potential map can be used for further study to identify ideal locations for artificial recharge. In low potential areas, the groundwater potential map can be used to find ideal locations for artificial recharge. The water table in the area must be raised by artificial recharge structures such as infiltration basins, recharge pits, and agricultural ponds. Artificial recharge structures such as infiltration basins, recharge pits, and agricultural ponds can be used for groundwater development in the low potential zones. The GWPZ map was successfully validated with three proxy data, such as the number of wells, groundwater level, and well density, obtained from well inventory information. The results of this study will improve our understanding of the geographic analysis of groundwater potential and help policy makers in this drought-prone area to create more sustainable water supply systems.

SAR-based Subsidence Monitoring and Assessment of the Factors Involved in the Occurrence of Subsidence, Lahore City

The judicious use and management of natural resources is vital to achieve sustainable development. Land and water are prime natural resources, and their depletion and degradation can lead to serious threats like land subsidence. Land subsidence is a phenomenon of the alteration of elevation at a point on the earth through the sinking of the surface. It occurs when the earth's surface loses its support. The major causes of land subsidence include groundwater extraction, mining, construction overload, and other similar factors that increase pressure on the surface and eventually subsidize the land. Urban centers with excessive groundwater extraction and infrastructure development are at a high risk of subsidence. Lahore, the second-largest city in Pakistan, is undergoing an enormous increase in population density, uncontrolled urbanization with very large-scale construction projects, and intensive groundwater extraction which are responsible for subsidence directly or indirectly. Therefore, studies on groundwater status and unplanned urban appraisals have seriously urged monitoring of the subsidence in Lahore. Herein, we used freely available Sentinel-1 data for one year (from August 2018 to August 2019), with a high spatial and temporal resolution, to monitor subsidence in Lahore. The data were processed using the SNAP/StaMPS approach for Persistent Scatterer Interferometric Synthetic Aperture Radar (PSI) analysis, which is an advanced InSAR technique. The displacement velocity map from InSAR processing shows a significant land deformation in the area with values ranging from –114 to 15 mm yr–1. Along with the Sentinel-1 data, we also used supplementary data obtained from various government agencies of Pakistan to study the land cover map, transportation network and waterways of Lahore, soil types, population density, and field points for assessing the results and understanding the roles of various factors in the occurrence of uplift or subsidence. A strong correlation was established between subsidence and various parameters such as groundwater extraction and lowering of the water table, soil type variations, land cover changes, surface water channels, and population density. The deformation map confirms the greatest subsidence in the central part of Lahore, while the uplift is observed in the less populated and rural areas situated near Ravi River. The land subsidence and uplift could be attributed to groundwater extraction and recharge through the canal system and the river, respectively.

Assessing social vulnerability to riverbank erosion across the Vietnamese Mekong Delta

ABSTRACT Climate change and trans-boundary development in the major deltas of the world, including the Vietnamese Mekong Delta have exacerbated environmental risks. Land subsidence, riverbed sand mining, and intensive groundwater extraction have all contributed to lower channel bed levels, resulting in riverbank erosion and the loss of assets and livelihoods for local residents. This study investigated the drivers, and classified the social vulnerability of local communities affected by riverbank erosion along two main branches in the Vietnamese Mekong. Direct interviews were conducted with 218 erosion-affected households along the Mekong and Bassac rivers in Dong Thap and An Giang provinces in order to create a social vulnerability index. More than 70% of the total surveyed households belonged to the highly, moderately, or low vulnerability groups, suggesting a range of affected communities within the sample, some of whom had the ability to cope with its short-term impacts. However, the estimated social vulnerability index revealed significant geographical heterogeneity, with communities along the Mekong branch being more vulnerable than those along the Bassac. The recommendations from our investigations include the establishment of community awareness programmes, as well as policy changes that ensure and support local residents’ livelihoods adaptation. Stakeholder participation and enhanced community engagement was found to be the most important tools available in terms of aiding local people cope with the complex impacts of riverbank erosion.

Manganese pollution of drinking water extracted from the terrace of Vacha River

The presented study is aimed towards determining the reasons for manganese pollution of drinking water extracted from the terrace of Vacha River. The results show that this is due to the seepage of from the artificial lake, formed after the construction of a small hydropower plant. Another possible reason is the natural accumulation in the upper parts of the river terrace of poorly soluble in water manganese compounds that turn into soluble ones as a result of changes in the redox environment, which take place in the conditions of very intensive groundwater extraction.

Controls on distributions of sulphate, fluoride, and salinity in aquitard porewater from the North China Plain: Long-term implications for groundwater quality

Groundwater interacts with porewater within clay-rich sequences. However, the effects of aquitard porewater on groundwater quality are generally poorly understood. This study explores potential links between porewater chemistry in a thick clay-rich sequence of Quaternary sediments, and groundwater quality in the North China Plain (NCP), one of China’s most important water supply aquifers. Previous studies have hypothesised the release of salinity, fluoride, and sulphate from aquitards in response to intensive pumping, without explicitly analysing the chemistry of aquitard porewaters. This study further investigated this hypothesis through targeted analysis of porewater chemistry profiles through the NCP sedimentary sequence. Two cores were analysed – one in the central plain (Hengshui, HS) and the other in the coastal plain (Cangzhou, CZ). Both areas have experienced significant groundwater extraction over recent decades from confined aquifers inter-layered with clays. Aqueous extraction (AE) and squeezing (SE) methods were both used to assess porewater chemistry. The hydrochemical characteristics of groundwater are closer to those of the squeezed porewater, which can be regarded as more closely corresponding to in-situ porewater compositions than AE profiles. Chloride was generally consistent between the two methods, while sulphate and fluoride concentrations were greater using AE, ranging from 340 to 48,700 mg/L and 8.8 to 144 mg/L, compared to 350 to 8860 mg/L and 0.2 to 4.3 mg/L using SE, respectively. The much greater concentrations of fluoride derived from the AE method indicates a high susceptibility to release during changes to the ambient geochemical environment. While the primary fluoride sources in groundwater and porewater are likely minerals from weathering of volcanic rocks in the sedimentary sequence, release into groundwater appears linked to common geochemical influences such as high Na/Ca ratio (increased during cation exchange) and the presence of iron and aluminium oxides (providing sorption sites). The primary source of solutes is interpreted to be different in each profile, with evapotranspiration important in the central plain and marine solutes important in the coastal profile, indicating significant storage of salinity, fluoride, and sulphate within low permeability sediments. Our data supports the hypothesis that release of these ions is driving degradation of groundwater quality, in response to decades of intensive groundwater extraction, which is an ongoing threat to the quality of groundwater in the NCP.

Numerical groundwater flow modeling of the Kombolcha catchment northern Ethiopia

Intensive groundwater extraction is a changing groundwater system. It is also the main challenge for future groundwater availability. In this study, numerical groundwater flow model was developed in Kombolcha catchment, Ethiopia by using MODFLOW-OWHM. To address this concern, the conceptual model was built by analyzing the hydrogeological data. The groundwater model was calibrated under the steady-state condition to produce the best match between the simulated and observed hydraulic head. The simulated outflow of the MODFLOW model was 358,221.09 m3/day which is nearly equal to 358,221.08 m3/day of groundwater inflow with a difference 0.01 m3/day and zero discrepancies. The subsurface inflow covers the most percentage (76%) in the budget and surface outflow contributes about 66% of the total groundwater outflow. The model result shows that the Kombolcha aquifer system is highly sensitive to change of hydraulic conductivity. Prediction of this aquifer behavior for increasing well withdrawal and decreasing recharge scenarios has been carried out. The effect of increasing withdrawal by 25, 50 and 100% results in a decline of groundwater level by 6.77, 12.15 and 24.37 m, respectively, whereas the effect of decreasing groundwater recharge by the same percentage of withdrawal results in a decline of groundwater level by 4.27, 6.34 and 11.25 m, respectively. This model can be as a tool to understand the aquifer system and sustainable utilization of groundwater resources.

Modelling the effects of climate change and population growth in four intensively exploited Mediterranean aquifers. The Mijas range, southern Spain

Groundwater is key to economic growth in the Mediterranean region. This is particularly true of areas such as southern Spain, where aquifers underpin social development by supplying water to a booming tourist industry. Intensive groundwater use raises sustainability concerns, as pumping often exceeds the long-term recharge rate. Climate change and population growth are likely to exacerbate the water supply challenge in the coming years, due to the expected decrease in rainfall and to increasing competition among users. This paper examines some of the main aquifers in the Costa del Sol region, one of Spain's leading tourist destinations, where intensive groundwater extraction has led to water table drawdowns and the desiccation of all major springs. A numerical model was developed and calibrated for the purpose of evaluating the likely evolution of the system in the future. Downscaled scenarios from global circulation models were coupled with population growth forecasts to establish a range of plausible water management scenarios. Given the relatively small size of the aquifers and the limited recharge rate, the current pumping patterns appear unsustainable. Results suggest that drawdowns in excess of 150 m could take place within the next decade, thus compromising domestic supplies.

Land Subsidence Vulnerability Assessment of Rural Settlements in Fars Province

Purpose- Land subsidence is caused by natural factors and human activities around the world. Fars Province, located in the south of Iran, is subject to land subsidence due to the uncontrolled exploitation of groundwater, causing damages to the population and human settlements and also environmental, social and economic areas. Design/methodology/approach- The present research is descriptive in terms of describing land subsidence in the case study region, whereas it is also analytical as time series analysis techniques based on Radar Interferometry (InSAR) is applied to monitor temporal changes in subsidence in Darab and Fasa Plains, including 470 rural points. Using 8 ENVISAT ASAR images spanning between 2005 and 2010, nine Interferograms were processed. In the study area. Geographic Information System (GIS) is then used to study groundwater level decline at the well locations in a 24-year period (from 1991 to 2015). Findings- The results of the research confirm that there is a significant correlation between groundwater water level decline and land surface subsidence. Time series analysis of the processed Interferograms indicate the mean displacement velocity map, demonstrating the maximum subsidence rate of 25 cm/yr. The InSAR analysis reveal within the study area subsidence rate of 25 cm/year in 24 years period and locally exceeding 30 cm/yr in the last decade. This area of significant subsidence is limited in its spatial extent to the agricultural land and is partly influenced by the large-scale over-exploitation of groundwater resources in the region study. The temporal and areal relationships of subsidence and groundwater level data suggest that a significant part of the observed subsidence in the Darab region is caused by intense groundwater extraction which has led to widespread compaction within the upper parts of the up to 300m. Socioeconomic analysis and the subsidence hazard map show that 105523 people are generally at risk of subsidence, of 65068 who are at high risk. In addition, there are 2679 socioeconomic infrastructures such as public service at risk of damage by land subsidence. Research limitations/implications- Limitation in In SAR data access, especially for long-term data was one of the main limitations in land subsidence research and also in this research. Practical implications- Integrated water resource management and the observed extraction of groundwater could influence the subsidence rate in the regions exposed to land subsidence. Originality/value- This research will be important to provide vulnerability in regions with groundwater overexploitation.

Land subsidence in Beijing and its relationship with geological faults revealed by Sentinel-1 InSAR observations

Beijing, the capital city of China, has been affected by land subsidence due to intensive groundwater extraction since 1935. Recent studies reported that the maximum subsidence occurred in the east of Beijing, reaching more than 11 cm/year till 2017. To investigate the subsidence (2015˜2017) in Beijing, in this paper, time series interferometric synthetic aperture radar (TS-InSAR) analysis was performed with 22 Sentinel-1 Terrain Observation by Progressive Scans (TOPS) mode SAR data. Results show that wide areas in the east of Beijing are subsiding with a maximum rate of 14 cm/year, which is consistent with GPS data. Detailed analysis of the obtained subsidence map reveals the existence of several characteristic near-linear boundaries within the subsiding areas. As a result of our previous three-year project, we generated the exact location, direction, and late Quaternary activity of the main potential active faults in the Beijing area. The relationship between the trace of these existing geological faults and the mentioned subsidence boundaries was investigated in detail. It is suggested that land subsidence in Beijing was mainly caused by the over-extraction of groundwater, with its spatial pattern being controlled by geological faults.

Groundwater Pumping Is a Significant Unrecognized Contributor to Global Anthropogenic Element Cycles.

Quantifying anthropogenic contributions to elemental cycles provides useful information regarding the flow of elements important to industrial and agricultural development and is key to understanding the environmental impacts of human activity. In particular, when anthropogenic fluxes reach levels large enough to influence an element's overall cycle the risk of adverse environmental impacts rises. While intensive groundwater pumping has been observed to affect a wide-range of environmental processes, the role of intensive groundwater extraction on global anthropogenic element cycles has not yet been characterized. Relying on comprehensive datasets of groundwater and produced water (groundwater pumped during oil/gas extraction) chemistry from the U.S. Geological Survey along with estimates of global groundwater usage, I estimate elemental fluxes from global pumping, consumptive use, and depletion of groundwater. I find that groundwater fluxes appreciably contribute to a number of elements overall cycles and thus these cycles were underestimated in prior studies, which did not recognize groundwater pumping's role. I also estimate elemental loadings to agricultural soils in the United States and find that in some regions, groundwater may provide a significant portion (more than 10%) of crop requirements of key nutrients (K, N). With nearly 40% of globally irrigated land under groundwater irrigation, characterizing nutrient and toxic element fluxes to these soils, which ultimately influence crop yields, is important to our understanding of agricultural production. Thus, this study improves our basic understanding of anthropogenic elemental cycles and demonstrates that quantification of groundwater pumping elemental fluxes provides valuable information about the potential for environmental impacts from groundwater pumping.

Groundwater Overexploitation and Seawater Intrusion in Coastal Areas of Arid and Semi-Arid Regions

The exploitation of groundwater resources is of high importance and has become very crucial in the last decades, especially in coastal areas of arid and semi-arid regions. The coastal aquifers in these regions are particularly at risk due to intrusion of salty marine water. One example is the case of Tripoli city at the Mediterranean coast of Jifarah Plain, North West Libya. Libya has experienced progressive seawater intrusion in the coastal aquifers since the 1930s because of its ever increasing water demand from underground water resources. Tripoli city is a typical area where the contamination of the aquifer in the form of saltwater intrusion is very developed. Sixty-four groundwater samples were collected from the study area and analyzed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters Electrical Conductivity, Na+, K+, Mg2+, Cl− and SO42−, which can be attributed to seawater intrusion, where Cl− is the major pollutant of the aquifer. The water types according to the Stuyfzand groundwater classification are mostly CaCl, NaCl and Ca/MgMix. These water types indicate that groundwater chemistry is changed by cation exchange reactions during the mixing process between freshwater and seawater. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 25 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high NO3− concentration in the region.

Influence the condition land subsidence and groundwater impact of Jakarta coastal area

Jakarta has been experiencing land subsidence for ten years due toerecting weight building and intensive extraction of groundwater for society drink water through ground water wells. Many groundwater extraction for drinkingwater has caused intensive scouring of land rock and further triggering land subsidence developed widely in coastal area of Jakarta. Measurement of the land subsidence has been performed by various experts and institutes. Between 1974 to 2010 subsidence has happened between 3 to 4.1 meters especially in Jakarta coastal area. Two major causes of the subsidence are identified. The first major cause is a result of erecting weight building such as hotels, appartments, and various human activities buildings. The second major cause is extracting ground water from aquifers bellow Jakarta land due to water deep wells down to the aquifer and traditional shallow water well of shallow or subsurface uncovered ground water. Weighter building and higher debit of water flow from deep water wells has fastened and deepened the land subsidence. Continuous measurement of land subsidence by means of geodetic as well as geophysical earth behaviour measurements need to be performed to monitor the rate, location as well as mapping of the land subsidence.

Degradation of groundwater quality in coastal aquifer of Sabratah area, NW Libya

Overextraction of groundwater is widely occurring along the coast where good quality groundwater is at risk, due to urbanization, tourist development and intensive agriculture. The Sabratah area at the northern central part of Jifarah Plain, Northwest Libya, is a typical area where the contamination of the aquifer in the form of saltwater intrusion, gypsum/anhydrite dissolution and high nitrate concentrations is very developed. Fifty groundwater samples were collected from the study area and analysed for certain parameters that indicate salinization and pollution of the aquifer. The results demonstrate high values of the parameters electrical conductivity, sodium, potassium, magnesium, chloride and sulphate which can be attributed to seawater intrusion. The intensive extraction of groundwater from the aquifer reduces freshwater outflow to the sea, creates drawdown cones and lowering of the water table to as much as 30 m below mean sea level. Irrigation with nitrogen fertilizers and domestic sewage and movement of contaminants in areas of high hydraulic gradients within the drawdown cones probably are responsible for the high nitrate concentration towards the south of the region. Seawater intrusion and deep salt water upconing result in general high SO4 2− concentrations in groundwater near the shoreline, where localized SO4 2− anomalies are also due to the dissolution of sebkha deposits for few wells in the nearby sebkhas. Upstream, the increase in SO4 2− concentrations in the south is ascribed to the dissolution of gypsum at depth in the upper aquifer.

Quantifying groundwater exploitation induced subsidence in the Rafsanjan plain, southeastern Iran, using InSAR time-series and in situ measurements

Decades of groundwater overexploitation for agriculture and industrial development have resulted in substantial land subsidence in the Rafsanjan plain of southeastern Iran. This work presents the results of an InSAR time series analysis obtained by the exploitation of Envisat, ALOS and Sentinel-1 (S1) SAR data archives between June 2004, and May 2016, to investigate land subsidence in the plain. The InSAR analysis revealed an area of approximately 1000km2 within the study area showing subsidence of >5cm/year and locally exceeding 30cm/yr in the last decade. This area of significant subsidence is limited in its spatial extent to the agricultural land and is partly influenced by Quaternary faults. The temporal and areal relationships of subsidence and groundwater level data suggest that a significant part of the observed subsidence in the Rafsanjan region is caused by intense groundwater extraction that has led to widespread compaction within the upper parts of the up to 300m thick unconsolidated sediments, causing irreversible and inelastic deformation of the aquifer. The average volume storage loss of the aquifer system due to overexploitation is estimated to have been approximately 300millioncubicmetre (mcm)/yr over the last decade.

Basin and local scale detection of ground subsidence through persistent scatterer interferometry: The Anthemountas Basin (Northern Greece) case study.

In the framework of the Terrafirma Extension project, a study has been established for ground motion detection and mapping in the Anthemountas basin (Central Macedonia). Terrafirma promotes the exploitation of Persistent Scatterer Interferometry (PSI) techniques, a remote sensing technology based on multi-temporal satellite Synthetic Aperture Radar (SAR) imagery. The potential of SAR interferometry has been exploited through the innovative Wide Area Mapping approach, recently implemented by the German Space Agency (DLR) and aimed at measuring land deformation over large areas. Interferometric results from 1995-2001 by ERS1/2 satellites has been analyzed at a basin scale to investigate spatial patterns of land motion in the wider Anthemountas plain, where subsidence phenomena related to intense groundwater extraction is clearly manifested. The WAP results turned out to be a valuable tool for the characterization at local scale of the land subsidence in the runaways area of the Macedonia airport and in the village of Perea, affected in 2005-2006 by a series of tensile ground ruptures due to excessive groundwater withdrawal. Besides the study of the phenomenon, this work confirmed the suitability of PSI techniques to detect and measure surface displacements with millimetre accuracy and also to reconstruct the deformations history of the investigated areas through displacement time series analysis.

InSAR time-series investigation of long-term ground displacement at Beijing Capital International Airport, China

Interferometric synthetic aperture radar (InSAR) time-series analysis provides high spatial resolution and continuous temporal coverage for investigations of long-term ground displacement. Beijing, the capital city of China, has suffered from land subsidence since the 1950s, and extreme groundwater extraction has led to subsidence rates of >100mm/year. In this study, InSAR time-series analysis is performed on different data subsets to investigate the ground displacement at Capital International Airport, Beijing, between June 2003 and November 2013. The results show that the ground surface in the airport has deformed at different rates ranging from −66.2mm/year (sinking) to 8.2mm/year (uplift) relative to the reference point. The projected vertical displacement rates agreed with measurements estimated from ground-leveling surveys, and the correlation coefficient of the fitting result is 0.96, with a standard deviation of 0.9mm/year and a mean different of 2.0mm/year. The runways and terminals have been affected by land subsidence to various degrees. Previous studies has indicated that long-term intense groundwater extraction is the main reason leading to land subsidence in this area. Other triggering factors, such as active faults, the quaternary compressible layers and urbanization, also have different degrees of contribution or impact on land subsidence in Beijing Plain. Furthermore, some interesting behaviors from groundwater (such as inter- and semi-annual variations) and subsidence, the relationship between them are also found in this study.

Characteristics of land subsidence, earth fissures and related disaster chain effects with respect to urban hazards in Xi’an, China

The ancient capital of Xi’an is a typical city in China with a shortage of water resources. With an urban population of 7 million, its domestic and industrial use of water depends almost entirely on groundwater. Large-scale long-term extraction of groundwater has caused severe land subsidence and triggered the reactivation of active normal faults in the Quaternary under-consolidated sediments underlying the city. This has further led to ground ruptures that have gradually evolved into earth fissure zones. During this process, there has been a close spatiotemporal relationship between land subsidence and the formation of earth fissures. From field monitoring data, the subsidence bowls are typically located in loess depressions between earth fissure zones within structural blocks of sediment cut by active Quaternary faults and preexisting fault planes. The subsidence bowls are generally elliptical in shape, with the long axes consistent with the preferred orientation of the earth fissures. The underlying Quaternary active faults and preexisting fault planes predispose the intervening sediment blocks to formation of earth fissures, and intense groundwater extraction has led to accelerated subsidence and earth fissuring during the past 50 years. Mining groundwater, land subsidence and earth fissures occur in a sequence and constitute a disaster chain with respect to urban hazards in Xi’an. Thus, it is important to understand the relationships between these events. This paper summarizes the characteristics of land subsidence and earth fissures in Xi’an and discusses the chain of relationships that connects them.

Evaluating karst geotechnical risk in the urbanized area of Sete Lagoas, Minas Gerais, Brazil

An increase in groundwater consumption in the municipality of Sete Lagoas (Minas Gerais, Brazil) has induced subsidence and collapse in the last three decades. The area is associated with natural karst conditions. The primary objective of this research was to evaluate and identify the potential subsidence or collapse risk zones. Aerial photographs, lithologic well profiles, optical well logs, and geologic mapping were utilized to categorize risk factors influencing karst subsidence and collapse, which were then applied to an index system. The study showed that the majority of the urbanized area overlies mantled limestone from the Sete Lagoas Formation covered with unconsolidated sediments, contained within a graben, resulting in barrier boundaries for groundwater flow. This structure, together with natural karst processes, explains the location of solutionally enlarged bedding-plane conduits and high hydraulic conductivity in the limestone. Five risks zones in the municipality were identified (negligible, low, moderate, considerable, and high risks) related to geologic and hydrologic risk factors. The urbanized area is located largely in the high risk zone where the majority of the collapse features are located. Additional intensive groundwater extraction in that area will likely generate additional events.