Rates Of Land Subsidence Research Articles

The three-dimensional groundwater salinity distribution and fresh groundwater volumes in the Mekong Delta, Vietnam, inferred from geostatistical analyses

Abstract. Over the last decades, economic developments in the Vietnamese Mekong Delta have led to a sharp increase in groundwater pumping for domestic, agricultural and industrial use. This has resulted in alarming rates of land subsidence and groundwater salinization. Effective groundwater management, including strategies to work towards sustainable groundwater use, requires knowledge about the current groundwater salinity distribution, in particular the available volumes of fresh groundwater. At the moment, no comprehensive dataset of the spatial distribution of fresh groundwater is available. To create a 3D model of total dissolved solids (TDS), an existing geological model of the spatial distribution and thickness of the aquifers and aquitards is updated. Next, maps of drainable porosity for each aquifer are interpolated based on the sedimentological description of the borehole data. Measured TDS in groundwater, inferred TDS from resistivity measurements in boreholes and soft incomplete data (derived from measurements in boreholes and data from domestic wells) are combined in an indicator kriging routine to obtain the full probability distribution of TDS for each (x,y,z) location. This statistical distribution of TDS combined with drainable porosity yields estimates of the volume of fresh groundwater (TDS < 1 g L−1) in each aquifer. Uncertainty estimates of these volumes follow from a Monte Carlo analysis (sequential indicator simulation). Results yield an estimated fresh groundwater volume for the Mekong Delta of 867 billion cubic metres with an uncertainty range of 830–900 billion cubic metres, which is somewhat higher than previous assessments of fresh groundwater volumes. The resulting dataset can for instance be used in groundwater flow and salt transport modelling as well as aquifer storage and recovery projects to support informed groundwater management decisions, e.g. to prevent further salinization of the Mekong Delta groundwater system and land subsidence, and is available at https://doi.org/10.5281/zenodo.4441776 (Gunnink et al., 2021).

Integration of InSAR and LiDAR Technologies for a Detailed Urban Subsidence and Hazard Assessment in Shenzhen, China

Spaceborne interferometric synthetic aperture radar (InSAR) methodology has been widely successfully applied to measure urban surface micro slow subsidence. However, the accuracy is still limited by the spatial resolution of currently operating SAR systems and the lacking precision of geolocation of the respective scatters. In this context, high-precision urban models, as provided by the active laser point cloud methodology through light detection and ranging (LiDAR) techniques, can assist in improving the geolocation quality of InSAR-derived permanent scatters (PS) and provide the precise contour of buildings for hazard analysis. This paper proposes to integrate InSAR and LiDAR technologies for an improved detailed analysis of subsidence levels and a hazard assessment for buildings in the urban environment. By the use of LiDAR data, most building contours in the main subsidence area were extracted and SAR positioning of buildings via PS points was refined more precisely. The workflow for the proposed method includes the monitoring of land subsidence by the TS-InSAR technique, the geolocation improvement of InSAR-derived PS, and building contour extraction by LiDAR data. Furthermore, a reasonable hazard assessment system of land subsidence was developed. Significant vertical subsidence of −40 to 12 mm per year was detected by the analysis of multisensor SAR images. The land subsidence rates in the Shenzhen District obviously follow certain spatial patterns. Most stable areas are located in the middle and northeast of Shenzhen except for some areas in Houhai, the Qianhai Bay, and the Wankeyuncheng. An additional hazard assessment of land subsidence reveals that the subsidence of buildings is mainly caused by the construction of new buildings and some by underground activities. The research results of this paper can provide a useful synoptic reference for urban planning and help reducing land subsidence in Shenzhen.

Variation in the rate of land subsidence induced by groundwater extraction and its effect on the response pattern of soil microbial communities

AbstractExcessive extraction of groundwater leads to (irreversible) changes in the physical soil properties, causing land subsidence associated with soil compaction to occur. Using a combined image processing and field approach, we examined: (1) how variation in the land subsidence rate induces different soil compaction degrees; and (2) the response patterns of microbial communities to such variations. By using Sentinel Synthetic Aperture Radar image processing, we selected three locations that exhibited different land subsidence rates, including high (HSR), moderate (MSR), and low (LSR). Then, soil sampling was undertaken within these representative locations. Indicators of soil compaction, including total porosity, air‐filled porosity, water‐filled porosity, and bulk density, were measured. The soil microbial community was determined using qPCR and sequencing. The highest and lowest values for bulk density were observed in the HSR–MSR and LSR zones, respectively. The greatest values of total porosity and macropore volume were displayed in the LSR zone compared to other zones. Bacterial abundance in the LSR zone was significantly greater than that in the HSR and MSR zones. The relative abundances of bacterial taxa indirectly demonstrated that the anaerobic phyla were significantly increased (by 10–13%), and the aerobic phyla decreased (by 30–40%) in the HSR zone compared to the LSR zone. This result demonstrates that the aerobes declined as larger volumes of the soil became more anaerobic. Indeed, the increased abundance of anaerobes was not able to compensate for the larger decrease in the abundance of aerobes. Our work showed that at the increased rates of land subsidence, the abundance distribution of the microbial community critically declined. These findings highlight the critical impacts of increasing the land subsidence rate on the emergence of high soil compaction degrees, which can significantly affect the resilience thresholds of the microbial communities in dryland soils.

Assessing the Accuracy of ALOS/PALSAR-2 and Sentinel-1 Radar Images in Estimating the Land Subsidence of Coastal Areas: A Case Study in Alexandria City, Egypt

Recently, the Differential Interferometric Synthetic Aperture Radar (DInSAR) technique is widely used for quantifying the land surface deformation, which is very important to assess the potential impact on social and economic activities. Radar satellites operate in different wavelengths and each provides different levels of vertical displacement accuracy. In this study, the accuracies of Sentinel-1 (C-band) and ALOS/PALSAR-2 (L-band) were investigated in terms of estimating the land subsidence rate along the study area of Alexandria City, Egypt. A total of nine Sentinel-1 and 11 ALOS/PALSAR-2 scenes were used for such assessment. The small baseline subset (SBAS) processing scheme, which detects the land deformation with a high spatial and temporal coverage, was performed. The results show that the threshold coherence values of the generated interferograms from ALOS-2 data are highly concentrated between 0.2 and 0.3, while a higher threshold value of 0.4 shows no coherent pixels for about 80% of Alexandria’s urban area. However, the coherence values of Sentinel-1 interferograms ranged between 0.3 and 1, with most of the urban area in Alexandria showing coherent pixels at a 0.4 value. In addition, both data types produced different residual topography values of almost 0 m with a standard deviation of 13.5 m for Sentinel-1 and −20.5 m with a standard deviation of 33.24 m for ALOS-2 using the same digital elevation model (DEM) and wavelet number. Consequently, the final deformation was estimated using high coherent pixels with a threshold of 0.4 for Sentinel-1, which is comparable to a threshold of about 0.8 when using ALOS-2 data. The cumulative vertical displacement along the study area from 2017 to 2020 reached −60 mm with an average of −12.5 mm and mean displacement rate of −1.73 mm/year. Accordingly, the Alexandrian coastal plain and city center are found to be relatively stable, with land subsidence rates ranging from 0 to −5 mm/year. The maximum subsidence rate reached −20 mm/year and was found along the boundary of Mariout Lakes and former Abu Qir Lagoon. Finally, the affected buildings recorded during the field survey were plotted on the final land subsidence maps and show high consistency with the DInSAR results. For future developmental urban plans in Alexandria City, it is recommended to expand towards the western desert fringes instead of the south where the present-day ground lies on top of the former wetland areas.

The Change in Elevation, Land Subsidence and Local Sea Level Rise Using Coastal Response Model in Jakarta

The rapid urban development activities on the coast of Jakarta has a major impact on the risk of land subsidence. This land subsidence causes significant changes in land elevation. Especially, the coastal areas of Jakarta receive the risk of inundation. The primary purpose of this research was to examine the responses of Jakarta coastal areas based on land subsidence rates of a 24-day baseline data of SAR Sentinel 1A, and local sea-level rise prediction from MOTIWALI data. The methods used in this research were an interferometric SAR (InSAR) and Coastal Response Models. The results of this study indicate that the coastal model response using adjusted elevation based on interferogram elevation and land subsidence rates of SAR Sentinel A1 in a relatively short time (monthly) escalates the evaluation of areas with potential undergoing inundation impacts. Jakarta coastal area receives a greater response with changes in the elevation adjustment based on the local sea-level rise of 0.54 m and land subsidence rates of 0.02. The model demonstrates that the coastal landscape of Jakarta was not possessing the capacity to respond to sea-level rise. Coastal dikes are quite effective as an initial defense in the event of extreme sea waves. The coastal response model using SAR Sentinel 1A data can respond to resource management decisions in coastal areas, and improve assessments quickly that consider the impacts of future land subsidence and local sea-level rise.

Land Subsidence Induced by Rapid Urbanization in Arid Environments: A Remote Sensing-Based Investigation

The rapid increase in the population of many of the older major cities within the countries of the Saharan-Arabian Desert is steering vast and disorganized urban expansion and in many cases introducing adverse environmental impacts such as soil erosion, rise in groundwater levels, and contamination of shallow aquifers, as well as development of deformational features including land subsidence. Using the rapidly growing city of Riyadh (1992: 467 km2; 2018: 980 km2), the capital of the Kingdom of Saudi Arabia as a test site, we utilized Small Baseline Subset (SBAS) interferometric analyses of 2016 to 2018 Sentinel-1 images together with multi-temporal high-resolution images viewable on Google Earth, GPS, field, land use land cover (LULC), and geological data to assess the distribution and rates of land subsidence and their causal effects. Three main causes of subsidence were identified and assessed: (1) discharge of wastewater effluents from septic systems in newly urbanized areas that lead to an increase in soil moisture, rise in groundwater levels, waterlogging, and wetting and hydrocompaction of dry alluvium loose sediments causing land subsidence (up to −20 mm/y) in wadis and lowlands; (2) the subsurface dissolution of karst formation by wastewater effluents and the collapse of voids and cavities at depth under stresses introduced by heavy construction machinery, causing sagging and land subsidence (up to −5 mm/y); and (3) leveling, compaction, and degradation of municipal and building waste materials in organized landfills and disorganized dump sites that resulted in significant land subsidence (up to −21 mm/y) and differential settling that could jeopardize the stability of structures erected over these sites. Our findings highlight the potential use of the advocated integrated approach to assess the nature and extent of land deformation associated with rapid urban growth in arid lands, and to identify areas most impacted for the purpose of directing and prioritizing remediation efforts.

Land subsidence: A global challenge.

This study presents a comprehensive review of the Land subsidence (LS) cases, as a worldwide environmental, geological, and global geohazard concern. Here, 290 case studies around the world mostly conducted in large metropolitan cities (e.g. Bangkok, Beijing, California, Houston, Mexico City, Shanghai, Jakarta, and Tokyo) in 41 countries were collected. The spatial distribution of LS characteristics (e.g. intensity, magnitude, and affected area), impacts, and influential factors are scrutinized. Worldwide attempts to remedy the crisis of LS were also investigated in this review. It is shown that the coastal plains and river deltaic regions are of high-frequent subsided areas around the world (~47% of 290 study areas). The spaceborne monitoring of LS is the more prevalent technique (~ 38% of total cases) compared to the ground-investigation (e.g. geological surveying, leveling, GPS, and modeling). Human-induced LS cases are 76.92% of all the LS cases around the world and groundwater extraction contributes 59.75% of these cases. Strong direct correlations with the exponential trend are observed between the average LS rate (LSavg) with groundwater withdrawal (R2=0.950) and groundwater level decline (R2=0.888). To understand the influential factors on LS occurrences, the relationship of LS rate with climate factors, hydrogeological characteristics of the aquifer, human-induced factors are investigated. Finally, we provide future research guidelines and implications that need to be expanded in order to better monitor and reduce the impact of the LS phenomenon. The outcomes of this study can be used to derive a framework helpful for interpreting the observed LS phenomena and for forecasting future situations to mitigate or control this geohazard.

Spatial Variability of Relative Sea-Level Rise in Tianjin, China: Insight From InSAR, GPS, and Tide-Gauge Observations

The Tianjin coastal region in Bohai Bay, Northern China, is increasingly affected by storm-surge flooding which is exacerbated by anthropogenic land subsidence and global sea-level rise (SLR). We use a combination of synthetic aperture radar interferometry (InSAR), continuous GPS (CGPS), and tide-gauge observations to evaluate the spatial variability of relative SLR (RSLR) along the coastline of Tianjin. Land motion obtained by integration of 2 tracks of Sentinel-1 SAR images and 19 CGPS stations shows that the recent land subsidence in Tianjin downtown is less than 8 mm/yr, which has significantly decreased with respect to the last 50 years (up to 110 mm/yr in the 1980s). This might benefit from the South-to-North Water Transfer Project which has provided more than 1.8 billion cubic meters of water for Tianjin city since 2014 and reduced groundwater consumption. However, subsidence centers have shifted to suburbs, especially along the coastline dominated by reclaimed harbors and aquaculture industry, with localized subsidence up to 170 mm/yr. Combining InSAR observations with sea level records from tide-gauge stations reveals spatial variability of RSLR along the coastline. We find that, in the aquaculture zones along the coastline, the rates of land subsidence are as high as 82 mm/yr due to groundwater extraction for fisheries, which subsequently cause local sea levels to rise nearly 30 times faster than the global average. New insights into land subsidence and local SLR could help the country's regulators to make decisions on ensuring the sustainable development of the coastal aquaculture industry.

The Comparison of Land Subsidence between East and West Side of Bangkok, Thailand

The land deformation in line of sight (LOS) direction can be measured using time series InSAR. InSAR can successfully measure land subsidence based on LOS in many big cities, including the eastern and western regions of Bangkok which is separated by Chao Phraya River. There are differences in prosperity between both sides due to human activities, land use, and land cover. This study focuses on the land subsidence difference between the western and eastern regions of Bangkok and the most possible cause affecting the land subsidence rates. The Radarsat-2 single look complex (SLC) was used to set up the time series data for long term monitoring. To generate interferograms, StaMPS for Time Series InSAR processing was applied by using the PSI algorithm in DORIS software. It was found that the subsidence was more to the eastern regions of Bangkok where the vertical displacements were +0.461 millimetres and -0.919 millimetres on the western and the eastern side respectively. The districts of Nong Chok, Lat Krabang, and Khlong Samwa have the most extensive farming area in eastern Bangkok. Besides, there were also three major industrial estates located in eastern Bangkok like Lat Krabang, Anya Thani and Bang Chan Industrial Estate. By the assumption of water demand, there were forty-eight wells and three wells found in the eastern and western part respectively. The number of groundwater wells shows that eastern Bangkok has the demand for water over the west, and the pumping of groundwater is a significant factor that causes land subsidence in the area.Keywords: Subsidence, InSAR, Radarsat-2, Bangkok

Present-day land subsidence rates, surface faulting hazard and risk in Mexico City with 2014–2020 Sentinel-1 IW InSAR

Among the fastest sinking cities globally, the metropolitan area of Mexico City is the target of an unprecedented satellite investigation based on over 300 Sentinel-1 Synthetic Aperture Radar (SAR) Interferometric Wide swath mode scenes acquired in 2014–2020. Two-pass differential Interferometric SAR (InSAR) and the parallelized Small BAseline Subset (SBAS) repeat-pass InSAR approach provide a complete account of spatial patterns, long-term trend and present-day settlement rates affecting the city. The 3D deformation field reveals that foremost is the role of the vertical velocity VU, with peaks of −38.7 cm/year in Nezahualcóyotl, −32.0 cm/year in Gustavo A. Madero and Venustiano Carranza, and −39.1 cm/year in Iztapalapa. Settlement at the metropolitan Cathedral in Cuauhtémoc is ongoing at up to −8.8 cm/year, consistently with the last six decades. Volcanic edifices mark ground stability “islets” inside the main subsidence bowls. East-west rates are limited, except for some horizontal strain (up to ±5 cm/year) within the subsidence bowls. Comparison with surface geology and geotechnical zoning confirms that aquitard compaction is the predominant process. The power relationship between VU [cm/year] and the thickness of lacustrine clay deposits HC [m] is: VU=176∗HC1.8. The 2019–2020 deformation scenario shows that subsidence still involves most of Nezahualcóyotl, with −3.0 cm/month VU. A well-defined long-term deformation behaviour comes out from 2014–2019 InSAR time series and comparison with 2008–2020 GPS data. RMSE of 0.9 cm is found at MMX1 station deployed within the lacustrine unit, and 0.6 cm at TNGF station onto hard volcanic rocks. The sharpest subsidence gradients and angular distortions β in 2017–2019 (up to over 1/400, i.e. 0.14°) – thus the greatest vulnerability to surface faulting and cracking as a consequence of large tensile stress in the soil caused by differential settlement – are found at the foothills of Sierra de Santa Catarina, Peñón del Marqués, Cerro Chimalhuachi, Peñón de los Baños and Sierra de Chichinautzin, where the transition unit is narrower (or absent). Faults and cracks develop where β > 1/3000, i.e. 0.03%, in 2017–2019. The observed width of the influence zone (i.e. damage band), where β is still significant to induce damage, is 250 m. Differential settlement and surface faulting could compromise the serviceability of housing and utility infrastructure. It is estimated that over 457,000 properties and 1.5 million inhabitants of the Valley of Mexico Metropolitan Area (ZMVM) are in zones at high to very high surface faulting risk, mainly in Iztapalapa, Tláhuac, Chimalhuacán and Chalco. Increased flood exposure due to formation of topographic depressions involves over 751,000 properties and ~2.7 million inhabitants of the ZMVM, mainly in Nezahualcóyotl, Tláhuac, Venustiano Carranza, Iztapalapa, Gustavo A. Madero and Ecatepec de Morelos. These municipalities are often hit by catastrophic floods.

Extreme subsidence in a populated city (Mashhad) detected by PSInSAR considering groundwater withdrawal and geotechnical properties

Ground deformation can cause serious environmental issues such as infrastructure damage, ground compaction, and reducing the ground capacity to store water. Mashhad, as one of the largest and most populated cities in the Middle East, has been suffering from extreme subsidence. In the last decade, some researchers have been interested in measuring land subsidence rates in the Mashhad valley by InSAR techniques. However, most of those studies were based on inaccurate measurements introducing uncertainties in the resulting subsidence rates. These researches used a small number of EnviSat data with long perpendicular and inhomogeneous temporal baseline. This paper seeks to determine the subsidence rate in urban areas of Mashhad in recent years, the threat that was neglected by the city managers and decision-makers. For this purpose, the Persistent Scatterer InSAR technique was applied in the study area using two time-series of descending and ascending Sentinel-1A acquisitions between 2014 and 2017. The results demonstrated the maximum line-of-sight deformation rate of 14.6 cm/year and maximum vertical deformation (subsidence) rate about 19.1 cm/year which could have irreversible consequences. The results were assessed and validated using piezometric data, GPS stations, and geotechnical properties. This assessment confirms that the main reason for subsidence in the interested area is groundwater over-extraction. Also, investigation of geotechnical properties shows that thick fine-grained layers in the northwest of the city could strongly affect the results. At the end of this paper, a new simplified method was proposed to estimate specific storage in special cases to predict the subsidence rate.

Gaining or losing ground? Tracking Asia's hunger for ‘new’ coastal land in the era of sea level rise

Many coastal cities are short of land for development and, coupled with the need to mitigate the impact of extreme events against a background of ongoing sea-level rise, coastal land reclamation (CLR) has emerged as a frequently applied solution, most especially in Asia. However, the sustainability of these newly reclaimed lands under the combined onslaught of increasing population pressure, SRL, greater frequency of extreme events, and land subsidence is largely unknown. In order to assess the spatial extent and temporal trends in recent CLR projects, we mapped and tabulated the annual magnitude of change in coastal land gain from 1988 to 2018 for eight major Asian coastal cities. Across these cities, both the spatial extent and rate of CLR is remarkable; some 700 km2 has been reclaimed in just three decades. >35% of this new coastal land has been constructed in Shanghai alone (562 km2), while Singapore and Incheon have also experienced substantial land gains. These three cities alone account for almost 10% of all the land gained globally over the last three decades. An analysis of the spatio-temporal patterns reveals that, since recently reclaimed areas are predominantly characterized by construction, including ports, airports, commercial and residential uses, economic development is the most prominent driver. Shanghai, however, represents a significant departure from this trend, whereby >50% of the new coastal land gained during the recent past has not been devoted to construction projects and is vegetated, suggesting a different policy context. Commercial or otherwise, subsidence is widely reported as a major characteristic of recently reclaimed coastal land and is a major environmental challenge. Mapping recent rates of land subsidence over these newly reclaimed lands reveal that most are subject to significant levels of deformation, in the case of the international airport at Incheon, Republic of Korea, exceeding 25 cm annually.

Geostatistical evaluation of spatial variability of land subsidence rates in Lagos, Nigeria

Accurate land subsidence prediction is fundamental for effective management of land subsidence and other associated geohazards. Lagos, the most densely populated city in Nigeria, has been adversely affected by widespread land subsidence. Previous studies have largely been restricted to analyzing space geodetic technique data. Unfortunately, this technique imposes spatial limitations resulting in incomplete coverage of the study areas due to atmospheric effects, orbital satellite characteristics, or surface characteristics. The application of geostatistics to georeferenced data obtained from space-based measurements can reliably provide complete information on spatial variability. The objective of this study is to provide an overview of current subsidence rates and to assess the spatial variability of land subsidence in the study area by using geostatistics that integrate semivariogram and ordinary kriging. The study area was partitioned into eight subregions; for each subregion, the experimental variogram was determined from the observed data and fitted to the optimal models. Seven subregions were fitted to exponential models and one was fitted to the spherical model. The model semivariograms were used in the kriging analysis to estimate the spatial variability of subsidence rates. The results showed that the nugget-to-sill ratio lies between 44 and 70%, indicating that the spatial variation of subsidence rates at the scale under study is moderately distributed and the mechanism of deformation is similar. The nugget effect of the subsidence rate is between 0.25 and 0.75, indicating that subsidence rates are influenced by various contributions. The predicted spatial variability of subsidence rates by Ordinary Kriging presents reliable values of R-squared (0.32–0.42) and RMSE (0.21–0.30). Critical subsidence rates characterised the areas around the Atlantic Ocean coastal alluvium deposit, the Lagos lagoon, and the Ogun River flood alluvium. This study successfully demonstrates the suitability of the geostatistical tools to evaluate spatial variability of subsidence rates.

Detection of silent subsidence over extensive area by SBAS DInSAR: a case study of Southern Bali, Indonesia

Numerous cities around the world are facing the problem of land subsidence. In many cases, it is the excessive groundwater extraction to meet human needs that leads to this subsidence. Since land subsidence rates are very slow (a few centimeters per year), the subsidence usually remains unnoticed until it has progressed to the point of causing severe damage to buildings, houses, and/or other infrastructures. Therefore, it is very important to detect the presence of subsidence in advance. In this study, screening for the presence of land subsidence in the city of Denpasar, Bali, Indonesia is conducted. The Sentinel-1A/B SAR dataset, taken from October 2014 to June 2019, is processed using the SBAS DInSAR method. Subsidence is found in the districts of Denpasar Selatan, Denpasar Barat, and Kuta, which falls in the range of -100 mm to -200 mm in an area of about 93.03 ha. All the extracted points of interest show the subsidence having linear behavior. The spatio-temporal behavior of the subsidence in Denpasar is presented clearly. However, the mechanism and the deriving factors of the subsidence remain unclear. Therefore, further studies are needed.

Do we care enough? revisiting land subsidence and coastal spatial planning policy in Semarang, Indonesia

Land subsidence is a common unsustainable pattern of land use on young sediment coasts worldwide, such as Semarang coastal area. The impact had already transformed its northeast area become permanently tidal flooded, damage in houses and streets, and economic loss. However, local government efforts are noticeably as band-aid measures, which can lead to further mismanagement in halting land subsidence. Given that, this research aimed to evaluate how the latest coastal spatial planning policy in Semarang responds to its geological hazards. This type of research is a content analysis of various spatial planning policy documents, coastal zoning plans, regional spatial planning, and strategic environmental assessment. The results show that, although land subsidence is already mentioned, no specific zoning plan or development programs were applied. Also, rather than creating more in-depth law in groundwater management or other activities that exaggerate land subsidence rates, the northeast shorelines’ structural measures are preferable. A key point of the result concluded that the local government should develop more strict laws in land subsidence to prevent more intense activities on land, together with vigorous law enforcement. Any structural measures should be planned and built effectively to avert more threatening problems to the regions.

A Rapid Assessment Method to Identify Potential Groundwater Flooding Hotspots as Sea Levels Rise in Coastal Cities

Sea level rise (SLR) will cause shallow unconfined coastal aquifers to rise. Rising groundwater can emerge as surface flooding and impact buried infrastructure, soil behavior, human health, and nearshore ecosystems. Higher groundwater can also reduce infiltration rates for stormwater, adding to surface flooding problems. Levees and seawalls may not prevent these impacts. Pumping may accelerate land subsidence rates, thereby exacerbating flooding problems associated with SLR. Public agencies at all jurisdiction levels will need information regarding where groundwater impacts are likely to occur for development and infrastructure planning, as extreme precipitation events combine with SLR to drive more frequent flooding. We used empirical depth-to-water data and a digital elevation model of the San Francisco Bay Area to construct an interpolated surface of estimated minimum depth-to-water for 489 square kilometers along the San Francisco Bay shoreline. This rapid assessment approach identified key locations where more rigorous data collection and dynamic modeling is needed to identify risks and prevent impacts to health, buildings, and infrastructure, and develop adaptation strategies for SLR.

ESTIMATING THE IMPACT OF URBAN EXPANSION ON LAND SUBSIDENCE USING TIME SERIES OF DMSP NIGHT-TIME LIGHT SATELLITE IMAGERY

Abstract. In recent decades, urbanization has resulted a massive increase in the amount of infrastructure especially large buildings in large cities worldwide. There has been a noticeable expansion of entire cities both horizontally and vertically. One of the common consequences of urban expansion is the increase of ground loads, which may trigger land subsidence and can be a potential threat of public safety. Monitoring trends of urban expansion and land subsidence using remote sensing technology is needed to ensure safety along with urban planning and development. The Defense Meteorological Satellite Program Operational Line scan System (DMSP/OLS) Night-Time Light (NTL) images have been used to study urbanization at a regional scale, proving the capability of recognizing urban expansion patterns. In the current study, a normalized illuminated urban area dome volume (IUADV) based on inter-calibrated DMSP/OLS NTL images is shown as a practical approach for estimating urban expansion of Beijing at a single period in time and over subsequent years. To estimate the impact of urban expansion on land subsidence, IUADV was correlated with land subsidence rates obtained using the Stanford Method for Persistent Scatterers (StaMPS) approach within the Persistent Scatterers InSAR (PSInSAR) methodology. Moderate correlations are observed between the urban expansion based on the DMSP/OLS NTL images and land subsidence. The correlation coefficients between the urban expansion of each year and land subsidence tends to gradually decrease over time (Coefficient of determination R = 0.80 – 0.64 from year 2005 to year 2010), while the urban expansion of two sequential years exhibit an opposite trend (R = 0.29 – 0.57 from year 2005 to year 2010) except for the two sequential years between 2007 and 2008 (R = 0.14).

On the margins of the hydrosocial: Quasi-events along a stagnant river

This article investigates stagnation as a product of hydrosocial relations in light of ethnographic research conducted in the port city of Semarang, Indonesia. In Semarang’s coastal north, river water spills daily into neighbourhoods during high tide, and often stagnates in houses and streets. While recent studies have shown that water governance is a form of social control, reproducing (infra)structures of subjugation and social inequality, little attention has been paid to the margins of water infrastructure, especially in cities. By focusing on stagnation, this article examines hydrosocial arrangements in the margins of postcolonial drainage infrastructure. When the peripheral and densely populated neighbourhoods in Semarang’s north are flooded during high tide, residents resort to private or semi-public pumps to get rid of stagnant water. Residents deplore insufficient state attention to their area, reflected in collapsing or seeping riverbanks. A relatively reliable flood prevention is the timely and regular raising of house floors and streets. The municipality responds to dramatic rates of land subsidence (10–15 cm/year) by raising roads and riverbanks. Yet, many dwellings along the Banger River have been destroyed by intruding sea water and left behind in ruins, suggesting a permanent failure of the city’s drainage system. Residents bear the brunt of supplementary infrastructural labour, their efforts of infrastructural repair and maintenance sustaining a bare minimum of safety. The article mobilizes Elizabeth Povinelli’s concept of quasi-events to understand the hydrosocial relations that shape peoples’ precarious relation with drainage infrastructure as unequal yet generalized. Quasi-events, that is, efforts to hold water at bay, suck energy and resources from marginalized residents. As such, the article argues that the margin of the hydrosocial is integral to the political configuration of land and water.

The relation between land use and subsidence in the Vietnamese Mekong delta

The Vietnamese Mekong delta is subsiding due to a combination of natural and human-induced causes. Over the past several decades, large-scale anthropogenic land-use changes have taken place as a result of increased agricultural production, population growth and urbanization in the delta. Land-use changes can alter the hydrological system or increase loading of the delta surface, amplifying natural subsidence processes or creating new anthropogenic subsidence. The relationships between land use histories and current rates of land subsidence have so far not been studied in the Mekong delta.We quantified InSAR-derived subsidence rates for the various land-use classes and past land-use changes using a new, optical remote sensing-based, 20-year time series of land use. Lowest mean subsidence rates were found for undeveloped land-use classes, like marshland and wetland forest (~6–7mmyr−1), and highest rates for areas with mixed-crop agriculture and cities (~18–20mmyr−1). We assessed the relationship strength between current land use, land-use history and subsidence by predicting subsidence rates during the measurement period solely based on land-use history. After initial training of all land-use sequences with InSAR-derived subsidence rates, the land-use-based approach predicted 65–92% of the spatially varying subsidence rates within the measurement error range of the InSAR observations (RMSE=5.8mm). As a result, the spatial patterns visible in the observed subsidence can largely be explained by land use. We discuss in detail the dominant land-use change pathways and their indirect, causal relationships with subsidence. Our spatially explicit evaluation of these pathways provides valuable insights for policymakers concerned with land-use planning in both subsiding and currently stable areas of the Mekong delta and similar systems.

Groundwater-pumping optimization for land-subsidence control in Beijing plain, China

Beijing, in the North China plain, is one of the few megacities that uses groundwater as its main source of water supply. Groundwater accounts for about two-thirds of the city’s water supply, and during the past 50 years the storage depletion from the unconsolidated aquifers underlying the city has been >10.4 billion m3. By 2010, groundwater pumping in the city had resulted in a cumulative subsidence of greater than 100 mm in an area of about 3,900 km2, with a maximum cumulative subsidence of >1,200 mm. This subsidence has caused significant social and economic losses in Beijing, including significant damage to underground utilities. This study was undertaken to evaluate various future pumping scenarios to assist in selecting an optimal pumping scenario to minimize overall subsidence, meet the requirements of the Beijing Land Subsidence Prevention Plan (BLSPP 2013–2020), and be consistent with continued sustainable economic development. A numerical groundwater and land-subsidence model was developed for the aquifer system of the Beijing plain to evaluate land subsidence rates under the possible future pumping scenarios. The optimal pumping scenario consistent with the evaluation constraints is a reduction in groundwater pumping from three major pumping centers by 100, 50 and 20%, respectively, while maintaining an annual pumping rate of 1.9 billion m3. This scenario’s land-subsidence rates satisfy the BLSPP 2013–2020 and the pumping scenario is consistent with continued economic development. It is recommended that this pumping scenario be adopted for future land-subsidence management in Beijing.