Land Subsidence Measurements Research Articles

Linked Data-Driven, Physics-Based Modeling of Pumping-Induced Subsidence with Application to Bangkok, Thailand.

Research into land subsidence caused by groundwater withdrawal is hindered by the availability of measured heads, subsidence, and forcings. In this paper, a parsimonious, linked data-driven and physics-based approach is introduced to simulate pumping-induced subsidence; the approach is intended to be applied at observation well nests. Time series analysis using response functions is applied to simulate heads in aquifers. The heads in the clay layers are simulated with a one-dimensional diffusion model, using the heads in the aquifers as boundary conditions. Finally, simulated heads in the layers are used to model land subsidence. The developed approach is applied to the city of Bangkok, Thailand, where relatively short time series of head and subsidence measurements are available at or near 23 well nests; an estimate of basin-wide pumping is available for a longer period. Despite the data scarcity, data-driven time series models at observation wells successfully simulate groundwater dynamics in aquifers with an average root mean square error (RMSE) of 2.8 m, relative to an average total range of 21 m. Simulated subsidence matches sparse (and sometimes very noisy) land subsidence measurements reasonably well with an average RMSE of 1.6 cm/year, relative to an average total range of 5.4 cm/year. Performance is not good at eight out of 23 locations, most likely because basin-wide pumping is not representative of localized pumping. Overall, this study demonstrates the potential of a parsimonious, linked data-driven, and physics-based approach to model pumping-induced subsidence in areas with limited data.

Analysis Of Presumed Land Subsidence In The Cities Of Lampung Province Using InSAR And GNSS Data

Land subsidence is a naturally occurring phenomenon that has become a growing concern in various regions, including Lampung Province. In this study, we investigate land subsidence in various cities within Lampung Province, Indonesia, utilizing Sentinel-1A using Sentinel-1A satellite image data from the period 2014 to 2022. The cities of Lampung Province analyzed in this study were Liwa, Kota Agung, Kalianda, Sukadana, Bandar Lampung and Krui. The method used is Interferometric Synthetic Aperture Radar (InSAR) with the Small Baseline Area Subset (SBAS) technique. Furthermore, to validate and improve the accuracy of land subsidence measurements, the Global Navigation Satellite System (GNSS) velocities were utilized. The land subsidence result obtained in this study is presumed land subsidence. The cities that experienced land subsidence was Kalianda, Sukadana, Bandar Lampung and Krui ranging from ~3 mm/yr to ~15 mm/yr. Meanwhile, the areas that experienced an uplift were the Liwa and Kota Agung cities.

Analisis Laju Erosi Berdasarkan Kemiringan Lereng Pada Area Pasca Spreading PT Angsana Jaya Energi Tanah Bumbu Kalimantan Selatan

The implementation of mining requires employment of protection and management of the affected environment, such as reclamation. The initial stage of reclamation in the form of spreading topsoil serves to prevent land subsidence/erosion. Post spreading area will be left empty for 1 month which causes erosion. This study aims to determine the amount of erosion rate that occurs in the spreading area based on the slope of gentle and sloped slopes and the direction of flow that occurs. The determination of the sampling point was carried out using the purposive sampling method and the measurement of the erosion rate was carried out using the stick method by sticking a stick with a depth of 30 cm with a plot size of 10x10 meters with division of 3 points on the slope of the slope and 3 points on the slope of the gentle slope. Soil sampling is carried out to measure the weight of the volume. Land subsidence measurements were carried out for 19 days for 30 days in each rain event. The calculation of the largest erosion rate on the slope of the gentle slope and the slope was 7,531.29 tons/ha/year and 7,746.44 tons/ha/year respectively which occurred on December 03, 2022., while the smallest erosion rate value on the slope of the gentle slope was on December 15, 2022 of 1,551.6 tons/ha/year and on the slope of the gentle slope was on December 1, 2023 of 1,647.1 tons/ha/year.

Investigation of groundwater induced land subsidence in Ludhiana City using InSAR and Sentinel-1 data

Land Subsidence (LS) is a vertically downward motion of land surface due to various reasons such as natural processes and anthropogenic activities especially excessive exploitation of groundwater. LS has adverse effects on substantial infrastructural damage, severe environmental problems, extensive economic losses, and significant societal impacts. In this study, we investigated the LS of Ludhiana city, a densely populated, largest and major industrial city of Punjab state, India. We presented a comprehensive methodology of Short BAseline Subset Interferometric Synthetic Aperture Radar (SBASInSAR) for LS measurement using an open-source computational environment. We generated 197 interferograms from 65 Sentinel-1A images acquired in descending pass between September 2019–July 2022 for deriving radar line of sight (LOS) displacement time-series and mean LOS velocity. Deformation results showed that the southern, and south-eastern parts of the city had been consistently moving downward with a mean subsidence rate of 24.7 mm/yr, while in western, few small patches in eastern and northern regions it ranges from 2 to 21 mm/yr, 3–20 mm/yr and 4–16 mm/yr respectively. The standard deviation of mean LOS velocity was observed between 0.7 and 3.3 mm/yr with majority values < 2 mm/yr. SBASInSAR results were compared with six Groundwater Level (GWL) wells observations, and both measurements generally agreed well at GWL locations (W1–W6) except W1–W2. For assessing the influence of groundwater change on LS, a correlation analysis was performed, and correlation of 0.50, 0.47, 0.81, 0.77, 0.84, and 0.64 was observed at GWL stations (W1–W6) respectively. Overall comparison of InSAR and GWL measurements are found in good agreement and significantly correlated, which can provide sufficiently detailed information about LS.

Analysis Of Land Subsidence Relationship With Groundwater Table Depletion In South Jakarta

Increased development activities and urbanization in South Jakarta have increased groundwater extraction. Continuous withdrawal of groundwater with poor management can cause a decrease in the groundwater level and trigger a subsidence. Therefore, a study is needed regarding the relationship of land subsidence with the decrease in groundwater levels that occur in South Jakarta. This research was conducted using secondary data in the form of drill log data to determine subsurface lithology, land subsidence measurement data using the GPS geodetic method, and groundwater level data in monitoring wells in Jakarta. The results of the study show that surface sediment deposits are dominated by a layer of clay which is still unconsolidated and relatively thickened to the north with a thickness of more than 300 m. This condition shows that the sediment layers in Jakarta are still undergoing a compaction process so that naturally subsidence occurs in the soil surface. Subsidence in the land surface in South Jakarta has a fairly strong correlation with the decline in the groundwater level, which is equal to 0.504, which means it has a fairly strong degree of correlation of 50.4%.&#x0D;

Tri-decadal evolution of land subsidence in the Beijing Plain revealed by multi-epoch satellite InSAR observations

The persistent land subsidence in the Beijing Plain induced by the massive exploitation of groundwater caused significant decreases in ground elevation and damages to buildings and civil infrastructures. Although various satellite SAR datasets have been analyzed to monitor subsidence in the Beijing Plain, no multi-decadal scale deformation measurement has been derived from multi-sensor InSAR results, and the recent deceleration of land subsidence or even uplift remains unclear. This study retrieved land subsidence measurements over the past three decades (1992–2022) by integrating multi-sensor C-band InSAR measurements into a logistic model. The cumulative subsidence presented three major subsidence funnels surrounding downtown in the North, Northeast, and East, with the maximum vertical displacement as high as 1.98 m in the Chaoyang District. The land subsidence positively responded to the changes in groundwater depth, showing a clear deceleration since 2016. After five and half years, it became almost stagnated within the context of continuous groundwater recovery, which implied the delayed compaction of lowly draining aquitards. Only slight residual subsidence persisted in Chaoyang, Shunyi, and Daxing Districts. Meanwhile, land uplift happened in Shunyi, Huairou, and Pinggu Districts. Remarkably, a portion of the land subsidence in the Chaobai Plain reversed to uplift due to multiple artificial recharges using diverted water. Although groundwater storage could recover significantly in the next decade, most severely sunken lands and inelastically compacted aquitards are irrecoverable, leading to a permanent loss of storage capacity in the Beijing Plain. This study provides scientific data support for the local government decision-maker to better manage groundwater resources and mitigate land subsidence, which presents a typical example of monitoring long-term land subsidence in similar global megacities.

Use of InSAR data for measuring land subsidence induced by groundwater withdrawal and climate change in Ardabil Plain, Iran

The Ardabil plain, with an approximate area of 1097.2 km2 in northwestern Iran, has experienced land subsidence due to intensive groundwater withdrawal and long seasons of drought in recent years. Different techniques have been used to investigate and evaluate subsidence in this region including: Global Positioning Systems (GPS), Levelling, and Geotechnical methods. These methods are typically expensive, time-consuming, and identify only a small fraction of the areas prone to subsidence. This study employs an Interferometric Synthetic Aperture Radar (InSAR) technique to measure the long-term subsidence of the plain. An open-source SAR interferometry time series analysis package, LiCSBAS, that integrates with the automated Sentinel-1 InSAR processor (COMET-LiCSAR) is used to analyze Sentinel-1 satellite images from October 2014 to January 2021. Processing of Sentinel-1 images shows that the Ardabil plain has been facing rapid subsidence due to groundwater pumping and reduced rainfall, especially between May 2018 to January 2019. The maximum subsidence rate was 45 mm/yr, measured at the southeastern part of the plain. While providing significant advantages (less processing time and disk space) over other InSAR processing packages, implementation of the LiCSBAS processing package and its accuracy for land subsidence measurements at different scales needs further evaluation. This study provides a procedure for evaluating its efficiency and accuracy for land subsidence measurements by comparing its measurements with the results of the GMTSAR and geotechnical numerical modeling. The results of geotechnical numerical modeling showed land subsidence with an average annual rate of 38 mm between 2006 and 2020, which was close to measurements using the InSAR technique. Comparison of the subsidence measurements of the Ardabil plain using the LiCSBAS package with results obtained from other techniques shows that LiCSBAS is able to accurately detect land deformation at large scales (~ km). However, they may not be optimized for more local deformations such as infrastructure monitoring.

Results of land subsidence measurement using GPS method in the Jakarta groundwater basin in 2015-2019

The development of population and development activities in big cities in Indonesia, especially in the city of Jakarta and surrounding areas is very rapid. From several land subsidence studies, several factors have been identified that cause land subsidence, namely: excessive groundwater extraction, reduction due to building/infrastructure loads, subsidence due to natural consolidation of soft soil layers, and subsidence due to tectonic forces. At present the exploitation of ground water for industrial and residential needs is at a level that needs attention. Excessive pumping of groundwater will cause a decrease in the quantity of ground water, entry of seawater into the land (sea water intrusion) and land subsidence. Symptoms of the negative impact of land subsidence have been felt in several areas, especially in industrial areas located in the northern part of Jakarta. This land subsidence can be measured by GPS or satellite geodetic method, which have begun to develop in Indonesia in the past two decades. Measurements were made using the radial method at 53 GPS points in 2015 up to 100 measurement points in 2019 in Jakarta Groundwater Basin. The result of these campaign GPS surveys that is northern part of Jakarta relatively had higher subsidence rate than the southern. The largest subsidence almost reached 6.2 cm/year in Muara Baru in northern area which is southern area only suffered an average rate of 1.16 cm/year.

Land Subsidence Measurement in Reclaimed Coastal Land: Noksan Using C-Band Sentinel-1 Radar Interferometry

Nur, A.-S.; Achmad, A.-R., and Lee, C.-W., 2020. Land subsidence measurement in reclaimed coastal land: Noksan using C-Band Sentinel-1 radar interferometry. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 218-223. Coconut Creek (Florida), ISSN 0749-0208.It has been 27 years since the beginning of the Noksan national industrial complex construction at downstream of the Nakdong River in Busan. The complex was built by landfilling a coastal area over one of Korea's deepest soft ground areas. Land subsidence occurred since the start of construction due to primary consolidation and secondary consolidation after the creation finished. Since secondary consolidation directly affects the structure over Noksan, it is crucial to monitor the subsidence rate. This study found that land subsidence happened in four areas of Noksan National Industrial Complex from 2017 to 2020 by applying Stamford Methods for Persistent Scatterer (StaMPS) time-series method using C-band Sentinel-1 SAR datasets from descending and ascending track. The results show land subsidence with a maximum velocity of 20.98 mm/year from descending track datasets and 20.92 mm/year from ascending track datasets. The highest rate area of land subsidence occurred in the south part of Noksan. Mean vertical deformation maps between descending and ascending track have been compared and show a good relationship with 0.93 of coefficient correlation. These approach methods in this study that using StaMPS could be used to monitor slow rate of land subsidence in reclaimed coastal land.

Land Subsidence Measurement of Jakarta Coastal Area Using Time Series Interferometry with Sentinel-1 SAR Data

Hakim, W.L.; Achmad, A.R.; Eom, J., and Lee, C.-W., 2020. Land subsidence measurement in Jakarta coastal area using time series interferometry with Sentinel-1 SAR data. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 75-81. Coconut Creek (Florida), ISSN 0749-0208.Jakarta coastal area is a part of North Jakarta which has a boundary to the Java Sea. Coastal flood from the Java Sea was not a new case in North Jakarta, the situations occurred due to sea-level rise. The conditions of coastal flood in Jakarta can be worsening by land subsidence in Jakarta coastal area. The land subsidence in Jakarta coastal area was occurred in many years and detected by geodetic measurement methods such as GPS and leveling surveys. The study about land subsidence in Jakarta coastal area needed to be updated because it could affect the urban development. This study presents the mean vertical deformation map using Stanford Methods for Persistent Scatterer (StaMPS) for time-series analysis on the Sentinel-1 data archives in the period of March 2017 through April 2020 in both ascending and descending track. The comparison of mean vertical deformation map between two tracks shows a good correlation in terms of displacement patterns with slightly different in 4 individual chosen points that show a high deformation at rates between 30 mm/year and 40 mm/year. The area chosen in this study known as a reclaimed area and the subsidence occurred due to young alluvium consolidation that not supported the maximum compression from a lot of buildings. These approach methods in this study that using StaMPS could be used to monitor land subsidence from all-terrain.

Effects of Water Diversion Project on groundwater system and land subsidence in Beijing, China

South-to-North Water Diversion Project Central Route (SNWDP-CR) is one of the largest human engineering projects aimed at redistributing water resources, receiving a worldwide attention. It conveys water from southern China to the Beijing Plain northward through a 1300-km long canal system and operated since December 2014. Before this date, water supply to Beijing was mainly provided by means of aquifer over-exploitation, causing a significant lowering of the piezometric levels and a huge land subsidence. After 3 years of SNWDP-CR activity, it results of general interest to investigate if the implemented managed aquifer recharge and the supposedly reduced aquifer exploitation have been already accompanied by a piezometric recovery and a decrease of the subsidence rates. This is evaluated for the first time in this contribution, by integrating and statistically analyzing a large dataset consisting of hydrogeologic information, piezometric records, and land subsidence measurements carried out by Persistent Scatterer Interferometry and levelling. The results show that a small (~3 m) to large (~10 m) raise of the piezometric levels has been recorded in the central portion of the north Beijing plain with a certain decrease (up to 10 mm/yr) of the subsidence rates. Conversely, piezometric drawdown and land subsidence has continued to increase in the remaining parts of the study area. Managed aquifer recharge (MAR) carried out through infiltration ponds has produced a positive feedback, but at a local scale only. Therefore, it will be necessary to wait a longer period to assess whether the SNWDP-CR will be able to mitigate the hydrogeological hazards connected to groundwater overuse or only to counterbalance in part the growing water demand of the Chinese capital.

Remotes sensing capabilities on land subsidence and coastal water hazard and disaster studies

Lowering on land surface which is commonly known as land subsidence is quite an issue in Indonesia today especially for coastal low elevation young sediment area, including cities or urban area lies on top of it. Jakarta is one of the city with most famous for land subsidence at the moment. If we go along northern coast of Java, many cities are experiencing the same situation as Jakarta and even more. As the impact from land subsidence, those coastal areas may experience water disaster such as sea water inundation and intrusion, wider expansion of flood and aquifer damage. Investigation of such areas in large and even regional scale with limited research budget is a problem. Nevertheless we found way for at least reducing the problem by using the capabilities of remote sensing product, geological and geostatistic data. We can identify land subsidence, coastal effected by subsidence like mentioned above by only time series of satellite image archive such as Google earth or Landsat free distributed, geological map and published geostatistic data like water consumption and population growth, with sample validated by land subsidence measurement and groundwater monitoring points. This paper will highlight our finding.

Application of D-InSAR technology in urban land subsidence measurement: A case study on Beihai city

Land subsidence monitoring is of great significance for the city safety and development. D-InSAR technology is widely used in city ground subsidence monitoring as the development of synthetic aperture radar satellite applications, because of the surface deformation information in all-weather conditions with merits of large coverage, fast reaction and high accuracy. This paper studied and analyzed the land subsidence in Beihai by the track method of differential radar interferometry; the information of land subsidence was obtained. The distribution of land subsidence in Beihai city is widespread; the maximum land subsidence was 0.1567m in the studying area from 2001 to 2011, with the maximum annual average subsidence rate of 0.0157m/a, the most serious land subsidence point is located in E109°16′49.443″, N21°37′45.243″. Combined with the field investigation, ascertain the main influencing factors of land subsidence in Beihai city is the exploitation of groundwater resources. The result implies that the D-InSAR technology is remarkably effective on ground subsidence monitoring in Beihai, which can accurately extract the information of ground deformation area.

Model-based estimation of land subsidence in Kathmandu Valley, Nepal

ABSTRACTThis study is the first to assess land subsidence in the Kathmandu Valley, Nepal. Land subsidence simulations were based on a fully calibrated groundwater (GW) flow model developed using a coupled surface–subsurface modelling system. Subsidence is predicted to occur as a result of deep aquifer compaction due to excessive GW abstraction. The north and north-east areas at the periphery of the GW basin are hotspots for this subsidence. The estimated subsidence is most sensitive to changes in land cover within the recharge areas. The model shows the Melamchi water supply project assists in the control of subsidence to some extent. In the absence of land subsidence measurements, this paper highlights the location and the potential levels of the subsidence hazard which will be useful for hazard prevention management. Additionally, this work provides a basis to design field investigations, monitoring networks for land subsidence and upgrading the present GW monitoring network. Although the study has presented a preliminary analysis, a more comprehensive model inclusive of clay subsidence is required to address the subsidence vulnerability of the central densely populated core of the valley, which reflects the need for a comprehensive database of the hydrogeology in the valley.

The present status of subsiding land vulnerable to roof collapse in the Jharia Coalfield, India, as obtained from shorter temporal baseline C-band DInSAR by smaller spatial subset unwrapped phase profiling

ABSTRACTIn this paper, we identified recently subsiding areas in Jharia Coalfield, Jharkhand, India from the shorter temporal baseline Radarsat-2 C-band interferometric synthetic aperture radar (InSAR) data pairs of 2012. Although shorter wavelength C-band differential InSAR (DInSAR) is more sensitive to slow deformation and better suited for higher precision land subsidence measurement, the dynamic and adverse land cover in mining areas and resulting temporal decorrelation problem poses a serious problem for DInSAR observation in mining areas. We used smaller temporal baseline data pairs and adopted InSAR coherence-guided incremental filtering with smaller moving windows to highlight the deformation fringes over temporal decorrelation noise. We identified the deformation fringes and validated them based on ground information to prepare the land subsidence map of the coalfield in 2012. Several new, previously unreported subsidence areas were detected in the present study with a total subsiding area of 6.9 km2. The recent incidence of roof collapse on 15 November 2014 at Angar Patra village in Katras region of the coalfield where 45 houses collapsed and 10 people were injured is situated in a highly subsiding vulnerable area as obtained from the present study. Due to spatial discontinuities of InSAR coherence, DInSAR phase unwrapping for the entire study area in one go did not appear feasible. To avoid this problem, we performed DInSAR processing in smaller spatial subsets and unwrapping of the subset interferograms by a ‘minimum cost flow’ algorithm. Subsequently, we plotted unwrapped phase profiles across the deformation fringes and retrieved the maximum deformation phase with respect to background phase and translated them into radar line of sight (LOS) displacement rates. For obtaining the average subsidence rates, we adopted InSAR coherence-weighted LOS displacement rates taking into account the contribution of each data pair as a function of DInSAR phase quality of the fringe areas. Ground-based subsidence measurements by precision levelling were conducted in four test sites that had been undergoing active underground mining during the observation period. We compared space-borne DInSAR-based subsidence rates obtained by the adopted technique with precision levelling measurements. Overall, the results are found to agree well. In the four test sites with gentle to flat topography, land subsidence occurs at slow to moderate rates due to compression of in-filled material (resulting from sand stowing in underground mining), without any evidence of roof collapse. In such cases, the horizontal displacement component is less significant, and overall surface displacement occurs essentially in the vertical direction. However, we assessed the nature of subtle horizontal strain to infer relative shrinkage or dilation of the land surface which could be additive or subtractive to vertical displacement in DInSAR-based LOS displacement.

Influence of Groundwater Management on Land Subsidence in Deltas

This paper examines effects of groundwater management on land subsidence taking into consideration visco-plastic creep and delayed compaction. The method used in this paper decomposes total strain into a direct elastic contribution and a transient viscous contribution. It is applied to a conceptual model that is partially based on real data of geology, land subsidence measurements, and hydrogeology of northern Jakarta, Indonesia. The developed model is conditioned on land subsidence measurements (from 1974 to 2010) using the Maximum a Posteriori method. The calibrated model is used to evaluate effects of four groundwater management scenarios (from 2010 to 2100) on land subsidence. Maintaining piezometric heads at their values of 2010 has not stopped land subsidence while continuous drawdown has led to larger amount of land subsidence. Furthermore, although piezometric heads recovery decreases effective stresses along the subsurface profile, land subsidence continued (at a lower rate) over time due to creep and slow dissipation of excess pore water pressure. The paper also showed that contribution of creep compaction to total land subsidence could be significant. In addition, coupled processes of consolidation and creep compaction leads to a favorable condition where slow dissipation of excess pore water pressure reduces contribution of the creep compaction to total land subsidence at early times at which degrees of consolidation are small and creep rate is large.

Key technology of D-InSAR at X-band for monitoring land subsidence in mining area and its application

In theory, land subsidence measurement results with high accuracy can be obtained by using the Differential Interferometry Synthetic Aperture Radar (D-InSAR) at X-band. In practice, however, the measuring accuracy of D-InSAR at X-band has been seriously affected by some factors, e.g., decorrelation and high deformation gradient. In this work, the monitoring capability of D-InSAR for coal-mining subsidence is evaluated by using SAR data acquired by TerrraSAR-X system. The SAR image registration method for low coherence image pairs, the denoising phase filter for high noise level interferogram and atmospheric effects mitigation method are the key technical aspects which directly influence the measurement results of D-InSAR at X-band. Thus, a robust image registration method, an improved phase filter method and an atmospheric effects mitigation method are proposed in this paper. The proposed image registration method successfully achieves InSAR coregistration, while the amplitude cross-correlation cannot properly coregister low coherence SAR image pairs. Moreover, the time complexity of the proposed image registration method is obviously slighter than that of the Singular Value Decomposition (SVD) method. The comparing experiment results and the unwrapping phase results show that the improved Goldstein filter is more effective than the original Goldstein filter in noise elimination. The atmospheric influence correction experiment results show that the land subsidence areas with atmospheric influence correction are more clarified than that of without atmospheric influence correction. In summary, the presented methods directly improved the measurement results of D-InSAR at X-band.

Land subsidence characteristics of Bandung Basin as revealed by ENVISAT ASAR and ALOS PALSAR interferometry

In this work, land subsidence in Bandung Basin, Indonesia between 2002 and 2011 was mapped using the C-band ENVISAT ASAR and L-band ALOS PALSAR data. Twenty four ALOS PALSAR and thirty ENVISAT ASAR images acquired between 2002–2008 and 2007 – 2011, respectively, were analysed. Several locations that were experiencing land displacement were identified including Cimahi, Dayeuh Kolot, Rancaekek, Solokan Jeruk and Gedebage. The subsidence rates in the basin range from −240mm/year to 40mm/year. The comparison between the ALOS PALSAR and ENVISAT ASAR measurements, which showed good agreement, suggested the subsidence in many areas of the basin were steady between 2002 and 2011, except south Bandung. Acceleration of subsidence in south Bandung was observed between the measurements from the two datasets, likely as a result of increasing population and industries. The subsidence in the basin was expected mainly as a result of excessive groundwater extraction and soil consolidation caused by surficial loading. GPS survey data collected between 2002 and 2010 were used to validate the ALOS PALSAR and ENVISAT ASAR measurements. Good correlations were observed between InSAR and GPS measurements. The comparison between the land subsidence measurements and the groundwater level information showed there were some correlations between them. For every 1m reduction in groundwater level per annum, ground subsidence of 20-23mm per annum has been observed. The comparison results suggested that there was no evidence showing the aquifer in the basin is being recovered.

Ensemble smoothing of land subsidence measurements for reservoir geomechanical characterization

SummaryGeomechanical models are often used to predict the impact on land surface of fluid withdrawal from deep reservoirs, as well as investigating measures for mitigation. The ability to accurately simulate surface displacements, however, is often impaired by limited information on the geomechanical parameters characterizing the geological formations of interest. In this study, we employ an ensemble smoother, a data assimilation algorithm, to provide improved estimates of reservoir parameters through assimilation of measurements of both horizontal and vertical surface displacement into geomechanical model results. The method leverages the demonstrated potential of remote sensing techniques developed in the last decade to provide accurate displacement data for large areas of the land surface.For evaluation purposes, the methodology is applied to the case of a disk‐shaped reservoir embedded in a homogeneous, isotropic, and linearly elastic half space, subject to a uniform change in fluid pressure. Multiple sources of uncertainty are investigated, including the radius, R, the thickness, h, and the depth, c, of the reservoir; the pore pressure change, Δp; porous medium's vertical uniaxial compressibility, cM, and Poisson's ratio, ν, and the ratio, s, between the compressibilities of the medium during loading and unloading cycles. Results from all simulations show that the ensemble smoother has the capability to effectively reduce the uncertainty associated with those parameters to which the variability and the spatial distribution of land surface displacements are most sensitive, namely, R, c, cM, and s. These analyses demonstrate that the estimation of these parameters values depends on the number of measurements assimilated and the error assigned to the measurement values. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Monitoring Land Subsidence in Sacramento Valley, California, Using GPS

Land subsidence measurement is usually based on a comparison of bench‐mark elevations surveyed at different times. These bench marks, established for mapping or the national vertical control network, are not necessarily suitable for measuring land subsidence. Also, many bench marks have been destroyed or are unstable. Conventional releveling of the study area would be costly and would require several years to complete. Differences of as much as 3.9 ft between recent leveling and published bench‐mark elevations have been documented at seven locations in the Sacramento Valley. Estimates of land subsidence less than about 0.3 ft are questionable because elevation data are based on leveling and adjustment procedures that occurred over many years. A new vertical control network based on the Global Positioning System (GPS) provides highly accurate vertical control data at relatively low costs, and the survey points can be placed where needed to obtain adequate areal coverage of the area affected by land subsidence.