Land subsidence is a common phenomenon worldwide. When mitigation has approached a limitation, adaptation becomes an important strategy for sustainable development. Specially, climate variability and changes can make more serious impacts on coastal areas. This study focused on adaptation to land subsidence in Chiangyuan area consisting of several coastal villages, Pingtung county, Taiwan. Little research about the adaptations had been done in this area, except there was some studies for its awareness. Using a case study approach with questionnaires, in-depth interview, direct observation, this study explored past and existed adaptation behaviour in different categories of stakeholders. Moreover, we also tried to analyze the capacity of these adaptation for future impacts from land subsidence and flood made by climate change, and could increase the capacity. The results have revealed local people in Chiangyuan area had abundant experiences on adaptations to land subsidence and flood. They used different kinds of adaptation at same time to cope with flooding, land loss, and salted land problems. The followings have summarized the adaptation of four categories of stakeholders. 1. for local citizen, the major adaptation is house-elevating, who didn¡¦t adopt house elevating were without budget or planning to move out. 2. for farmer, planting economic fruits with higher tolerance to salt-water. 3. for aquaculture, fish-pond elevating, harvesting earlier, or building fish-pond on higher land. 4. for school, using water-proof gates or no classes during flooding. Some suggestion focused on adaptation to land subsidence was also given in this study, specially for government.

Land subsidence is the gradual settling or sudden sinking of the earth's surface. According to the United States Geological Survey more than 80% of identified subsidence in the United States is a result of groundwater removal. Due to the hydrologic structure and reliance on the Potomac Aquifer, the Southern Chesapeake Bay region of Virginia has suffered from land subsidence since the 1940s. In coastal regions, land subsidence can increase the risk of flooding. This paper presents a mathematical simulation that predicts land subsidence from groundwater pumping. This simulation is used to see how the location of groundwater pumping, as well as the amount of amount of groundwater pumped would differ from two different groundwater pumping policies. The first policy is aimed at limiting land subsidence in the region, while the second policy aims at limiting the damages from land subsidence. These two policies are used to show that a spatially heterogeneous groundwater pumping policy is necessary to minimize the damages from groundwater pumping when land subsidence is present. / Master of Science

Measurement and analysis of aquifer-system compaction have been used to characterize aquifer and confining unit properties when other techniques such as flow modeling have been ineffective at adequately quantifying storage properties or matching historical water levels in environments experiencing land subsidence. In the southeastern Coastal Plain of Virginia, high-sensitivity borehole pipe extensometers were used to measure 24.2 mm of total compaction at Franklin from 1979 to 1995 (an average of 1.5 mm/yr) and 50.2 mm of total compaction at Suffolk from 1982 to 1995 (an average of 3.7 mm/yr). Analysis of the extensometer data reveals that the small rates of aquifer-system compaction appear to be correlated with withdrawals of water from confined aquifers. One-dimensional vertical compaction modeling indicates that the measured compaction is the result of nonrecoverable hydrodynamic consolidation of the fine-grained confining units and interbeds as well as recoverable compaction and expansion of coarse-grained aquifer units. The modeling results also provide useful information about specific storage and vertical hydraulic conductivity of individual hydrogeologic units. The results of this study enhance the understanding of the complex Coastal Plain aquifer system and will be useful in future modeling and management of ground water in this region. / Master of Science

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This dissertation describes the occurrence of pumping-induced earth fissures associated with quaternary faulting using numerical simulations. The Eglington Fault located in Las Vegas valley has been selected as the prototype fault described herein. The finite-element software program ABAQUS is used for the numerical simulations. The Eglington fault area is chosen because it represents one of the best examples displaying the complex relationship between fissuring, faulting and pumping-induced stress. This fault is known to influence both the vertical and horizontal deformation patterns through the accumulation of stress in its vicinity. The result is that fissures are observed on both sides of the fault and in close proximity to the fault plane. In addition to the complex fault-fissure connection, a thick caliche-rich vadose zone with weak mechanical strength allows for the initiation and propagation of fissures. The numerical analysis a) investigates the geometrical and hydromechanical features of the zone of influence surrounding the Eglington Fault; b) identifies the zones of accumulated stress on the surface and at depth that can lead to fissuring; and c) simulates the onset and propagation of tensile-induced fissures. Three-dimensional numerical simulations of this fault indicate that a 100-meter wide fault-zone composed by sand-like material best reproduces the conditions of stress that may lead to fissuring in the vicinity of the fault. Additionally, two-dimensional models reveal that two main mechanisms promote the accumulation of stress in the vicinity of the fault zone: one is the counterclockwise rotation of the unsaturated portion of the fault zone; the other is the differential compaction caused by the difference in the accumulated thickness of compressible layers. Tensile stress is concentrated on the surface in the hanging wall, but maximum shear stress zones are simulated to occur on both sides of the fault at the contact between the saturated aquifer and the vadose zone. A final analysis of the initiation and propagation of tensile-induced fissures demonstrates that fissures commence and propagate only within the vadose zone, and that the propagation path is influenced by the mechanical properties of the medium and the location of the main load, which in this case is pumping. / Ph. D.

Coastal zones are hotspots of global environmental changes. Worldwide, coastal environments face multiple, interactive stressors caused by both natural and anthropogenic impacts on climatic, oceanographic, ecological, and socio-economic processes such as sea level rise, storm surges, hurricanes, land subsidence, and population growth. The coastal U.S. is highly vulnerable to many of these climate and human-induced stressors. Over the past three decades, sea levels have risen by about 0.1 m along the U.S. coasts, with an additional projected increase of 0.2 to 0.3 m by 2050, and up to 2.0 m by the end of the century. The rise in sea levels will cause tides and storm surges to reach further inland, significantly altering flood regimes in coastal cities. By 2050, potentially damaging coastal flooding is expected to occur ten times as often compared to a baseline for the start of the 21st century. Moreover, these changes along the U.S. coastlines vary regionally and locally due to either positive or negative changes in land elevation over time (i.e., vertical land motion (VLM)). Lowering of land elevation (i.e., land subsidence) exacerbates sea level rise and the risk of inundation along coastal zones, presenting significant security challenges to coastal ecosystems, infrastructure, and populations. These dynamic and interacting stressors necessitate continuous monitoring to inform effective mitigation and adaptation strategies. Earth observation data allows for accurate, high-resolution, and continuous measurements of changing coastline. Despite the increasing availability of Earth observation data, current methods for monitoring VLM along coastlines lack the necessary spatial resolution and continuous coverage to accurately assess localized surface elevation changes. In this dissertation, I introduce a framework to jointly invert interferometric synthetic aperture radar (InSAR) and global navigation satellite systems (GNSS) data to provide semi-continuous measurement (50 m spatial resolution) of VLM for the contiguous U.S. coasts from 2007 – 2020. Combining the VLM dataset with projected sea level rise using different scenarios, I estimate flood hazards exposure for 32 major U.S. coastal cities by 2050, demonstrating that current measurements and frameworks underestimate flood vulnerability in several cities by not accounting for local and regional high-resolution VLM data. Next, I evaluate the possible drivers of land subsidence, exploring the relationship between spatio-temporal dynamic VLM and groundwater withdrawal from aquifers in major U.S. cities. Additionally, I assess the hazards and risks of land subsidence to infrastructure and wetlands along U.S. coasts. Finally, I extend this analysis beyond the U.S. coastline, investigating how land subsidence is linked to the incessant occurrence of building collapses in Lagos, Africa's most populous coastal city. / Doctor of Philosophy / Coastal areas worldwide are under significant stress from both natural and human-made changes, including rising sea levels, flooding, storms, hurricanes, land sinking, and population growth. The U.S. coasts are particularly affected by these issues. Sea levels have risen significantly over the past few years, with further increases expected in the near future. As sea levels rise, tides and storm patterns will change; thereby altering the flood frequency and magnitude in coastal cities. Land sinking exacerbates the impact of sea-level rise and flooding, affecting people, buildings, and the natural environment in coastal cities. These factors change over time, so they must be constantly monitored to develop effective strategies for adaptation and mitigation. Here, I used satellite-based tools to monitor land changes over time, identifying areas where the land is sinking. I combined this information of where land is sinking with sea-level rise data to estimate the areas that will be vulnerable to flooding by 2050 in 32 U.S. coastal cities, including Boston (MA), New York (NY), Virginia Beach (VA), Charleston (SC), Miami (FL), New Orleans (LA), Galveston (TX), and San Diego (CA). I also examined the causes of land sinking, particularly how groundwater extraction can lead to land sinking and the risks this poses to buildings and the natural environment along the U.S. coasts. This research highlights the impact of climate change and human activities on the U.S. coasts and the importance of continuous monitoring to enhance coastal resilience against current and future challenges.

In this research, the fundamental mechanics for the changes in stresses and strains states due to groundwater pumping is formulated. This was accomplished by developing a 3D closed form solution. The results from this research are compared with results of finite element (FE) analyses and data obtained from interferometric synthetic aperture radar (InSAR). Land subsidence (LS) due to groundwater pumping from a single well for different geological profiles and the reason why LS continues after groundwater pumping cessation were investigated. FE analyses for four different scenarios were used to investigate the effects of cemented layers and non-cemented layers above the aquifer on EF initiation. A practical method which is based on the stiffness and cementation strength of the cemented layer and the gradient of the slope of the subsidence bowl (ɑ) was proposed to determine earth fissure (EF) initiation. Three-point bending beam test was conducted in the lab to determine the mode of failure and the modulus of rupture of a local cemented soil that occurs in areas where EFs were observed. The major findings are as follows. LS due to groundwater pumping consists of i) isotropic compression and ii) simple shear on vertical planes with rotation. For a parabolic distribution of groundwater level in a homogenous aquifer, simple shear on vertical planes will be dominant when the characteristic length of the aquifer is larger than √2 times the aquifer thickness. Fine-grained soils are responsible for LS occurring after the cessation of pumping and for sagging in LS profiles. Regardless of the stiffness and cementation strength of the top layer above the aquifer, EF will not initiate if ɑ is less than 8x10⁻⁵. When the stiffness of the top cemented layer increases, it becomes more prone to EF initiation. However if the layer is stiff enough to be classified as "rock" then a higher value of ɑ is needed to initiate an EF. The experiments show that the preferred mode of failure of a cemented soil is shear rather than bending and existing cracks significantly influence the results of EF formation.

Coastal zone become the object which is used to develop when the economy developed quickly and population increase. As a result of coastal zone is a region which involves economy, environment, ecology, and engineering. We must integrated many factors and coordinated related groups. Then we can achieve the goal of sustainable development. The research involved the knowledge and experiences from Europe, American, and Japan. Except they used a construct of Integrated Coastal Zone Management (ICZM) to think the questions, they combined ecology, water conservancy engineering, social economic activities, and environmental protection. Then they used DSR framework as the foundation to establish the system which evaluated sustainable development of the coastal zone, and they can develop the system dynamic model analyzing the coastal management in many conditions. Land subsidence is a potential crisis, it grows obviously with the time and has the impact to the environment., When typhoon occurs in the west part of Taiwan coastal area, draining which is unable to operate may cause flood, mole avalanche, seawater intrusion and soil salinization. First we must understand the origin and the management of land subsidence, then we can make the effective strategies by researching different background and geography characteristic of the region. As a result of land subsidence involves economy, environment, ecology and engineering, the process of land subsidence is a complex problem which has multiple causes. This problem usually involves time-delay and long-term effect. System dynamics is an approach that is used to describe, explore and analyze the procedure, information and the boundary of organizations in complex systems. Such model is good for solving dynamic complex problems with non-linearity, causal circulation, information feedback and time-delay as long as the estimative parameter fall in its confidence level. The object of the research is to inspect land subsidence in the Pingtung plain. Therefore, this study proposes to find strategies which is suitable to solve interested problems according to integrate social-economic and ecologic-environment development. The framework of the research is based on the DSR (Driving forces-State-Response) index, and it makes evaluated factor from collecting domestic and foreign literature. Then we selected the important factors and its weight value by using the method of AHP (Analytic Hierarchy Process) to visit the expert and the scholar. According to above, we developed the model of system dynamics and build confidence in the model. In addition, the result of the simulation can provide good supporting information for decision makers by using the model for several strategies simulation and making the index to represent the performance of simulation analysis.