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.

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

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

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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.

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.

Galveston Bay is the second largest estuary in the Gulf of Mexico. The bay’s watershed and shoreline contains one of the largest concentrations of petroleum and chemical industries in the world, with the greatest concentration within the lower 15 km of the San Jacinto River/Houston Ship Channel (SJR/HSC). Extensive groundwater has been withdrawn to support these industries and an expanding population has resulted elevated land subsidence, with the highest land subsidence in the lower SJR/HSC, of over 3 m (3 cm yr^-1) and has decreased seaward throughout the bay to 0.6 cm yr^-1 near Galveston Island. Mercury (Hg) contamination is well documented throughout the bay’s sediments. Sediment vibra-cores were collected throughout the bay systems. 210Pb and 137Cs geochronologies from these cores was used to determine sedimentation rates and correlated to Hg profiles to estimate input histories. Relative Sea Level Rise (RSLR) is the sum of eustatic sea level rise and land subsidence. The results show sedimentation rates are high in areas with high rates of RSLR and the rates are of the same order of magnitude, however, in general, sedimentation rates are as much as 50% of RSLR, indicating that sedimentation has not kept pace with land subsidence, although they have the same relative order. Hg core profiles were correlated with radioisotope geochronologies and show significant input of Hg beginning around 1940, with a peak around 1971, and a dramatic drop off in concentration afterwards, demonstrating it to be a valuable geochronology tool. Hg concentrations were found to be dramatically higher proximal to the SJR/HSC and progressively decreasing seaward and to distal parts of the bay.