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 Extensive groundwater has been withdrawn to support these industries and an expanding population has resulted elevated land subsidence, with the highest land subsidence in the lower SJR/HSC, of over 3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.

A mathematical model is developed for quantification of aquifer deformation due to ground-water withdrawal and, with some modifications, is potentially applicable to petroleum reservoirs. A porous medium saturated with water is conceptually treated in the model as a nonlinearly viscous fluid continuum. The model employs a new three-dimensional extension, made in this thesis, of Helm's poroviscosity as a constitutive law governing the stress-strain relation of material deformation and Gersevanov's generalization of Darcy's law for fluid flow in porous media. Relative to the classical linear poroelasticity, the proposed model provides a more realistic tool, yet with greater simplicity, in modeling and prediction of aquifer movement. Based on laboratory consolidation tests conducted on clastic sedimentary materials, three phases of skeletal compaction are recognized. They are referred to as "instantaneous compression", "primary consolidation" and "secondary compression" according to Terzaghi and Biot's theory of poroelasticity. Among the three modes of consolidation, material behavior during the secondary compression phase has a nonlinear stress-strain relationship and is strongly time-dependent, exhibiting a phenomenon often known as "creep". In poroelasticity, the primary and secondary compressions have been conceptually considered as two separate physical processes that require two sets of material parameters to be evaluated. In contrast, the proposed poroviscosity model is a unified theory of time-dependent skeletal compression that realistically describes the physical phenomena of sediment compression as one single transient process. As a general model, two sets of governing equations are formulated for Cartesian and cylindrical coordinates, respectively, and allow for mechanical anisotropy and the assumption of principal hydraulic directions. Further simplifications of the governing equations are formulated by assuming mechanical isotropy, irrotational deformation and mechanical axisymmetry, which are more suitable for field applications. Incremental forms of the governing equations are also provided. / Ph. D.

The use of delayed drainage in land subsidence modeling greatly complicates model calibration, particularly when the thickness of the fine-grained interbeds varies throughout the modeled region. This thesis documents two separate projects (chapters) related to the use of delayed drainage in groundwater flow and subsidence modeling with parameter estimation. The overall goal of these projects was to better understand how delayed drainage affects accurate parameter estimation and how it is currently affecting the subsidence processes occurring in Las Vegas Valley. Chapter 1 describes an investigation on the value of subsidence data for groundwater model calibration considering delayed drainage. The calibration results of 13 hydraulic parameters of a synthetic conceptual model evaluated for 24 test cases indicate that (1) the inverse of the square of the observation values is a reasonable method to weight the observations, (2) spatially abundant subsidence data typically produce superior parameter estimates even with observation error under constant and cyclical pumping, (3) when subsidence data are limited and combined with drawdown data, outstanding results are obtained for constant pumping conditions. However, for cyclical pumping with observation errors, the best parameter estimates are achieved when multiple years of seasonal subsidence data are provided. The results provide useful suggestions for real-world calibration problems. Chapter 2 outlines the development of an updated flow and subsidence model for Las Vegas Valley covering the entire period of development of the basin. The new model includes a subsidence package that takes into account delayed drainage of fine-grained interbeds. Previous models used subsidence packages that assumed instantaneous equilibration of heads across all hydrogeologic units. The new model resulted in an agreement with measured water-level and improved the simulation of land subsidence. The analysis shows that the typical residual subsidence in Las Vegas Valley can be accurately simulated by incorporating delayed drainage in a long-term model. The study also indicates the need for more sophisticated modeling practices that use delayed drainage with parameter estimation processes to accurately calibrate flow and subsidence models. / Master of Science

The Coastal Plain in the southern Chesapeake Bay area is becoming increasingly susceptible to nuisance flooding as a result of the combination of sea-level rise and land subsidence associated with aquifer compaction from excessive groundwater pumping. Detailed time-series of cumulative compaction data (land subsidence) from the three U.S. Geological Survey deployed extensometers in the regions, along with cyclical piezometer data, reflect the nature of the complex multi-aquifer/aquitard system in the Coastal Plain. Franklin, Virginia and Suffolk, Virginia extensometers were deactivated in 1995 and were reactivated in 2016 along with the addition of a high-sensitivity borehole extensometer in Nansemond, Virginia in collaboration with the Hampton Roads Sanitation District as a part of the Sustainable Water Initiative for Tomorrow (SWIFT). Yearly compaction rates estimated from the reactivated extensometers are -3.3 mm/year, 15.6 mm/year, and -20.7 mm/year in Franklin, Suffolk, and Nansemond, Virginia respectively. One-dimensional vertical compaction modeling is utilized to estimate the total compaction and differentiate which fine-grained confining units or aquifer interbeds are contributing most to total compaction historically and presently. Additionally, properties of the system can be estimated including the elastic specific storage of the aquitards and aquifers and the inelastic storage of the aquitards. The total cumulative change in aquifer system thickness estimated by the MODFLOW subsidence package can be compared to the observed total cumulative change in aquifer system thickness at each site for validation of hypothesis about the dynamics of the aquifer system to known changes in stress. Subsidence rates and aquifer/aquitard properties can be useful for managing and modeling the groundwater in the Coastal Plain of Virginia. / Master of Science / The Coastal Plain in the southern Chesapeake Bay area is becoming increasingly susceptible to flooding at high tides in low lying areas as a result of the combination of sea-level rise and sinking of the land surface (land subsidence) associated with aquifer compaction from excessive groundwater pumping from buried aquifers. Detailed time-series of land subsidence data from the three U.S. Geological Survey deployed extensometers in the region, along with water level data from nearby wells, reflect the nature of the complex multi-aquifer/aquitard system in the Coastal Plain. Franklin, Virginia and Suffolk, Virginia extensometers were deactivated in 1995 and were reactivated in 2016 along with the addition of a high-sensitivity borehole extensometer in Nansemond, Virginia in collaboration with the Hampton Roads Sanitation District as a part of the Sustainable Water Initiative for Tomorrow (SWIFT). Yearly land subsidence rates estimated from the reactivated extensometers are -3.3 mm/year, 15.6 mm/year, and -20.7 mm/year in Franklin, Suffolk, and Nansemond, Virginia respectively. One-dimensional vertical compaction modeling is utilized to estimate the total sinking of the land surface as well as to differentiate which fine-grained confining units or aquifer interbeds are contributing most to total subsidence historically and presently. Additionally, properties of the system can be estimated including the elastic specific storage of the aquitards and aquifers and the inelastic storage of the aquitards. The total cumulative change in aquifer system thickness estimated by the MODFLOW subsidence package can be compared to the observed total cumulative change in aquifer system thickness at each site for validation of hypothesis about the dynamic changes of the aquifer system with known changes in stress. Subsidence rates, understanding the dynamics of the aquifer system, and aquifer/aquitard properties can be useful for managing groundwater and modeling the aquifer system in the Coastal Plain of Virginia.

Subsurface constructions, such as tunnels, create hydrogeological challenges in mitigating risk of subsidence due to groundwater drawdown. Presenting readily made precautionary mitigation plans, such as strategically planned artificial recharge applications, can help effectivise the mitigation process. The Bypass Stockholm project comprises of several subsurface constructions which may lower the surrounding groundwater level through tunnel leakage. Risk of land subsidence persists in the nearby urban area of Vinsta, Stockholm, where a groundwater drawdown may cause the clays in the area to experience land subsidence. A hydrogeological modelling approach was used in the area to create strategic artificial infiltration plans that could be employed as a mitigative response to the drop in groundwater head. In order to simulate the potential tunnel drainage, a steady state hydrogeological model was built using MODFLOW. A 220 l/s tunnel leakage was then simulated. Four different artificial groundwater infiltration scenarios were then conceptualized and simulated to observe effects on groundwater heads. The groundwater levels of the baseline model of the area fit the calibration targets with average absolute deviation of 0.18 m. The tunnel drainage scenario lowered the groundwater level in the till aquifer and bedrock by 0 - 1.5 m and 0.5 - 5 m respectively, with higher drawdowns observed closer to the tunnel. The infiltration scenarios mitigate the groundwater drawdown with different efficacies; proximity to the recharge point, and discharge into the till aquifer were observed to have the highest effect on groundwater recharge in the model. The model could have been improved by improving the data quality surrounding the hydraulic conductivity of the bedrock, as it had the highest effect according to the parameter sensitivity analysis. / Konstruktioner under mark kan skapa hydrogeologiska utmaningar, såsom sättningsrisk orsakade av grundvattenavsänkning. Ett sätt att effektivisera åtgärdsprocessen är att förbereda för eventuell artificiell grundvatteninfiltration. Vägprojektet Förbifart Stockholm innefattar konstruktioner under mark och riskerar, genom inläckage, att sänka grundvattennivån i omgivningen. Ett potentiellt problemområde är stadsdelen Vinsta, delar av vars är byggd på sättningskänslig lera som kan påverkas av en grundvattenavsänkning. För att kunna motverka en grundvattensänkning i Vinsta har hydrogeologisk modellering utförts för att strategiskt planera artificiell grundvatteninfiltration. Ett tunnelläckage på 220 l/s har simulerats genom en hydrogeologisk steady state-modell i MODFLOW. Fyra olika scenarier för grundvatteninfiltration har konceptualiserats och simulerats för att observera påverkan på grundvattennivån. Den spatialt variabla grundvattennivån i grundmodellen nådde kalibreringsmålen med en genomsnittlig absolutavvikelse på 0,18 m. Modellen för tunnelläckage resulterade i att grundvattennivån i moränakvifären och berget sjönk med 0 – 1,5 resp. 0,5 – 5 m, med större grundvattensänkning närmare tunneln. Scenarierna för infiltration motverkade grundvattensänkningen i olika grad. Närhet tilltunneln, eller platsen för inläckage, samt den hydrauliska konduktiviteten mellan infiltrationen och akvifären visade störst påverkan på resultatet för att motverka grundvattensänkningen. Känslighetsanalysen för parametrarna i modellen visade att berget och dess hydrauliska konduktivitet hade störst påverkan på resultatet. Tillgång till bättre data för berget möjliggör förbättrat modelleringsresultat.

The overall goal of this dissertation is to determine and develop optimal strategies for inversely calibrating transmissivities (T), elastic and inelastic skeletal storage coefficients (Ske and Skv) of the developed-zone aquifer and conductance (CR) of the basin-fill faults for the entire Las Vegas basin, and to investigate future trends of land subsidence in Las Vegas Valley. This dissertation consists of three separate stand-alone chapters. Chapter 2 presents a discrete adjoint parameter estimation (APE) algorithm for automatically identifying suitable hydraulic parameter zonations from hydraulic head and subsidence measurements. Chapter 3 compares three different inversion strategies to determine the most accurate and computationally efficient method for estimating T and Ske and Skv at the basin scale: the zonation method (ZM), the adaptive multi-scale method and the Differential Evolution Adaptive Metropolis Markov chain Monte Carlo scheme (DREAM MCMC). Chapter 4 outlines a fine-scale numerical model capable of capturing far more hydrologic detail than any previously developed model of Las Vegas Valley The new model is calibrated using high-resolution InSAR data and hydraulic head data from 1912 to 2010. The calibrated model is used to investigate the influence of faults and their potential role on influencing clay thicknesses and land subsidence distributions, and to investigate future trends of land subsidence in Las Vegas Valley. / Ph. D.

台灣地區地層下陷問題肇始於六十年代迄今已逾三十餘載，持續下陷面積已達1,194平方公里，最大累積下陷量達到三公尺以上。而目前地層下陷地表監測所採用的傳統水準測量耗費人力、時間較多，且不易獲得連續和全面性之地層下陷資料，目前國內水利單位限於人力時間，無法針對所有監測區域每年皆施測一次。近年來由於空載光達測量技術興起，其具有短時間內獲取大區域高密度、高精度高程資料的特性，因此本研究之目的在探討如何利用空載光達測量技術快速獲取高精度之三維點雲資訊，進行大區域的地層下陷監測及其成效。 研究方法係首先將監測區內掃瞄的光達點雲資料進行網格化分群；接著，計算網格區域內所有光達點擬合平面的中心高程；然後，以人工或自動方法萃取出平坦、穩固的網格區域做為監測面；最後，進行不同時期網格監測面高程差異之統計測試分析，以求出地層下陷量。 實驗結果顯示改善點雲高程精度至5公分以內後，經由網格監測面的精度、坡度、坡向、反射強度、道路範圍等為門檻值，可萃取出80%以上正確率的穩固監測面，且其高差成果與長期監測成果的平均值差異在1.3公分至2.9公分之間，由此成果可以說明本研究成果對建立一套省時省力的監測模式，進而達到地層下陷監測自動化的目的有相當幫助。 / The issue of land subsidence in Taiwan has been concerned for over 30 years since 1970. Land subsidence area has been already over 1194 km2, the maximum amount of accumulative subsidence is more than 3 meters. The conventional leveling for the land subsidence monitoring is labor-intensive and time-consuming, so that the Water Resources Agency could not monitor all the subsidence area every year. Airborne LIDAR technology was developed in recent years, it has the characteristics of collecting 3-D point data at the high density and high elevation accuracy in short time. The purpose of this study, therefore, is to discuss how to utilize the airborne LIDAR technology to monitor the land subsidence. The proposed approach, therefore, is first to divide the collecting DSM points in the monitor area into regular grids. Secondly, all the points in the regular grids are fitted to one set planar parameters by least squares principle and the centric elevation of each grid is calculated. Third, the flatness and well-defined planar grids are selected as the monitoring surfaces with the manual or automatic method. Finally, the difference of centric elevation in each monitoring surfaces at different period is calculated and analyzed with statistical approach. This study shows that after refining the elevation accuracy of point clouds within 5 cm, our approach can extract stable monitoring surfaces by limiting planar fitting accuracy, flatness, slope, intensity, or by using road information. The extracted correct rate can be more than 80%. The discrepancy of elevation difference between this study and long-term monitoring result is between 1.3 cm and 2.9 cm. It proves the proposed approach is helpful on constructing the monitoring model in timesaving and efficient way, and our proposed approach has the potential for developing automatic land subsidence monitoring method.

Under the consideration of ¡§avoiding the overusing the ground water¡¨, ¡§proper planning for the utilization of the land in the land-subsidence areas¡¨, and ¡§facilitating the exploitation of surface water and substitute water¡¨, we take eight counties included in the ground-water-constrained areas in Kaohsiung as illustrations to discuss the issue of optimal planning for matching the land-use and the demand of water resource. Compared with the traditional Linear Programming, Fuzzy Linear Programming has received a great deal of attention in the recent years for its strength on working out results more fitting in with the uncertainty faced while making decisions in practice, and we adopt this model to solve the problem in this study. By separately following the Zimmermann¡¦s Symmetric Model, Werners¡¦s Symmetric Model and combining model of Delgado¡¦s Model and Flexible Programming, we show that setting 2006 as the target year, our models can properly describe linguistic objective and vague constraints after taking the uncertainty of the result into account and work out the optimal-alterative-based planning.

台灣養殖漁業自1970年代起，進入快速成長時期，而在1980年代為台灣養殖漁業全盛時期，造就台灣成為「養蝦王國」、「養殖王國」揚名國際之美名，也為台灣沿海農漁村地區開拓新的漁業契機，而讓農漁民累積不少財富，故當時養殖漁業儼然成為台灣農業結構上重要之一環，對繁榮沿海農村經濟，安定農村社會，極具貢獻。 然而，諷刺的是，1980年代卻也是台灣耕地轉供養殖池之情況快速蔓延的時代，形成台灣沿海逐漸形成養殖區域性發展，卻也因為養殖漁業對於水土資源超限使用下，而超抽地下水而引起地層下陷及地下水體汙染等永世災難及耕地轉供養殖池諸多問題產生，導致環境不永續之後果，值得謀求解決之道。 本研究以質化研究中之個案研究法，以永續發展理念為基礎，運用文獻分析法及深度訪談法交互分析。先探討台灣養殖漁業管理及養殖漁業用地管理制度之演進及衍生出問題；再以宜蘭縣五結鄉季新村、錦眾村個案研究地區，深入探討台灣及宜蘭養殖漁業發展牽動五結鄉養殖區範圍擴散之可能原因及其影響，並就其耕地轉供養殖池之產業營運、違規使用、養殖環境轉變、養殖池棄養等不永續利用問題予以分析，最後提出「台灣養殖漁業與其用地管理制度改進策略」及「五結鄉養殖漁業與用地管理策略」。 經由研究發現，台灣超抽地下水及地層下陷問題最為嚴重之縣市，申請經營養殖漁業竟不需審核地下水之合法用水資格，而經個案地區研究也發現台灣及宜蘭養殖漁業發展牽動五結鄉耕地轉供養殖池之擴散，而經耕地轉供養殖池後，在養殖漁業沒落後，欲將棄養養殖池回復耕作環境困難重重，當地逐漸形成一片荒涼景象。 最後建議政府漁業單位應設計優良養殖環境之制度，即應先規劃養殖生產區並『主動』興建完成養殖專用之進水（海水、地下水）、排水之共同管線系統等相關養殖公共設施，並劃為非都市土地使用分區「養殖漁業生產區」（建議新增非都市土地使用分區），而該分區內之養殖池，有別於一般農地申請做養殖池，不應依據相同之法令規範，應放寬該養殖生產區內養殖池就地合法或是簡易申請程序以方便並快速取得合法養殖之資格，以有效管理養殖漁業減少違規使用情形發生及促進養殖漁業朝向永續發展方向邁進，並促進水土資源永續性利用。另建議政府漁業單位經全面性可行性評估後，認為不適合繼續養殖之地區應投入資源積極輔導該地區轉型，協助並引導該地區轉供較為永續利用之方向（如生態旅遊等）。 / Since 1970's the aquaculture develops rapidly in Taiwan, and becomes pre-vailing as the golden age of the aquaculture fishery in the 1980's. At that time Taiwan is well known of the kingdom of shrimp and aquaculture fishery in the world, and fishermen and farmers near the coast areas gain a new chance of incomes, so aquaculture fishery has become a very important chain of Taiwan's agriculture. It also has great contribution to flourishing village's economy and society stabilization. However, ironically, in 1980's many farms become aquaculture ponds quickly, that result in regional development of aquaculture fishery along the coast of Taiwan gradually, but overuse the resource of water and soil. Tapping groundwater inappropriately causes terrible disaster which lead to land subsi-dence and contamination of groundwater. The conversion of farms to aquacul-ture ponds cause many problems, that leads to environment being not sustaina-ble. There is an urgent need to find out relevant solutions. This research is based on two cases study the ideas of sustainable develop-ment.We adopt the modes of literature review and analysis, and depth interview. Firstly, we inquire into management system of the aquaculture industry and aq-uacultural land and the regarding problems. Secondly, we select the areas of Ji-sin village and Jin-jhong villege in Wujie Township Yilan County , in order to thoroughly inquire into possible reasons and influences that how aquaculture development in Yilan County and Wujie Township lead to the spreading of the areas for aquaculture production zone.Thirdly, we analyse problems of being not sustainable use of resources, such as the operation of the aquaculture pond, violating the rules of farmland use, changes of the cultivation environment, dis-card of aquaculture pond etc. Lastly, we put forth improvement strategies of aquaculture and its land management system both in Wujie Township and Tai-wan. Through the research, we find in counties with the most serious problems of tapping groundwater inappropriately and land subsidence in Taiwan, the gov-ernment doesn't need to examine the legality qualifications of the groundwater use when people apply for aquaculture fishery.We also find that aquaculture development in Yilan and Taiwan result in farmland conversion into aquaculture pond in the areas of Wujie Township . Because it is very difficult to make dis-carding aquaculture pond return to farmland, the region becomes a slice of desolate prospects gradually when the aquaculture decline. Finally, we suggest the Fishery Bureau of Government should design better institution for aquaculture environment. That is, they should plan for aquaculture production zone first and build public facilities of aquaculture fishery, such as the common pipeline system of using sea and groundwater for aquaculture fishery .The government should review the classification of non-urban land usage since the attributes of aquaculture ponds in "Aquaculture Production Zone" are different from others. In order to manage aquaculture fishery effec-tively, we also give some suggestions concerning decrease the occurrence of violating the rules, promoting the aquaculture fishery moving forward to sus-tainable development, and improving the sustainable use of water and soil re-source. We think to simplify application procedure of getting legal qualifications for aquaculture fishery may is not the best way but is an easy way to solve problems currently. Another suggestion is that after comprehensive feasibility evaluations, the Fishery Bureau of Government should actively invest adminis-tration resource to help areas that are not suitable for being use of aquaculture pond transferring to sustainable use, such as ecotourism etc.

臺灣西南沿海地區由於超抽地下水，地層下陷情形日益嚴重，究其原因乃地下水資源在國內仍處於「自由財」的狀態，用水兔費，使用自然缺乏效率，因而建立使用者付費制度，以確實維護地下水財產權，為當務之急。惟地下水資源具公共財的無排他性，在國內又無交易市場，其價值估算困難。是故，本文之主要目的，係應用非市場估價法中之「條件評價法」，以願付價格的形式估計地下水價值，並探求其影響因素，以做為制定政策之參考。 本文係以「準逐步競價法」為詢價結構設計，可同時獲得「單邊界樣本」、「雙邊界樣本」與「最終出價樣本」三種評價歷程，實證模型則分別以「Probit、Logit模型」、「存活模型」與「OLS模型」進行分析。 本文根據問卷調查的原始資料求出「每公頃土地」之地下水願付價格，最後則以台西地區為例，配合地下水的使用效益，計算出地下水供不同使用時之「使用價值」與「非使用價值」，而本研究對假設性問題的設計，使估計出來的地下水價值，亦可用以表示維護地下水資源對於防止地層下陷之效益。 實證結果顯示，「對水權費的認知與態度」以及「對地層下陷原因的認知」是影響支付意願的重要因素，故政府應加強宣導「使用者付費」理念，並教育用水者「超抽地下水是造成地層下陷的重要因素」，以利水權費制度的實施。