A wetland in west-central Florida was studied to characterize the local hydrostratigraphic configuration of surficial deposits overlying more-permeable limestones and conceptualize groundwater recharge. Eight continuous cores were drilled through the surficial deposits and partially into the underlying limestone. A total of 111 samples were extracted from the cores for laboratory sediment analyses and testing. The surficial deposits are roughly eight meters thick and made up of upper and lower clean-sand hydrostratigraphic layers (S1 and S3, respectively) separated by a low-permeability layer of clayey sand (S2). Also, a discontinuous low-permeability layer of clayey sand (S4) lies between S3 and the top of limestone. Equivalent hydraulic conductivity values for the S2 and S4 clayey layers (0.01 and 0.1 m/day respectively) are significantly less than those of the S1 and S3 sand layers (2 and 1 m/day respectively).Significant confinement between the surficial and Upper Floridan aquifers by means of a laterally extensive dense-clay unit immediately above the limestone is consistently reported elsewhere in the region, but was not encountered within the wetland. Partial confinement is apparently the result of low-permeability layers within the surficial deposits alone. Results of ground-penetrating radar and vertical head difference measurements suggest the presence of buried sinkhole features which perforate the low-permeability S2 layer and create preferred pathways for flow or karst drains. Comparison of results between laboratory sediment testing and a site-scale aquifer performance test (APT) suggest that the primary mechanism for drainage during the APT was by vertical percolation through the S2 layer while flow through karst drains was minimized. In this case, calculated leakances based on laboratory sediment testing are most accurate in approximation of effective leakance.It is predicted that as water table stages rise within the wetland, effective leakance will increase as flow toward karst drains becomes the more dominant mechanism for drainage. As a result, calculated leakances based on direct laboratory sediment testing are a decreasingly accurate approximation of effective leakance.

Estimating the quantity of water that reaches the water table following an infiltration event is vital for modeling and management of water resources. Estimating the time scale of groundwater recharge after a rainfall event is difficult because of the dependence on nonlinear soil characteristics and variability in antecedent conditions. Modeling the flow of water through the variably saturated zone is computationally intensive since it requires simulation of Richards' equation, a nonlinear partial differential equation without a closed-form analytical solution, with parametric relationships that are difficult to approximate. Hence, regional scale coupled (surface water - groundwater) hydrological models make simplistic assumptions about the quantity and timing of recharge following infiltration. For simplicity, such models assume the quantity of recharge to be a fraction of the total rainfall and the time to recharge the saturated groundwater is scaled proportionally to the depth to water table, in lieu of simulating computationally intensive flow in the variably saturated zone. In integrated or coupled (surface water - groundwater) regional scale hydrological models, better representation of the timing and quantity of groundwater recharge is required and important for water resources management. This dissertation presents a practical groundwater recharge estimation method and relationships that predict the timing and volume accumulation of groundwater recharge to moderate to deep water table settings. This study combines theoretical, empirical, and simulation techniques to develop a relatively simple model to estimate the propagation of the soil moisture wetting front through variably saturated soil. This model estimates the time scale and progression of recharge following infiltration for a specified depth to water table, saturated hydraulic conductivity and equilibrium moisture condition. High-resolution soil moisture data from a set of experiments conducted in a laboratory soil column were used to calibrate the HYDRUS-1D model. The calibrated model was used to analyze the time scale of recharge by varying soil hydraulic properties and simulating the application of rainfall pulses of varying volume and intensities. Modeling results were used to develop an equation that relates the non-dimensional travel time of the wetting front to excess moisture moisture content above equilibrium. This research indicates that for a soil with a known retention curve, the wetting front arrival time at a given depth can be described by a power law, where the power is a function of the saturated hydraulic conductivity. This equation relates the non-dimensional travel time of the wetting front to excess moisture content above the equilibrium moisture content. Since the equilibrium moisture content is dependent on the water retention curve, the powers in the equation governing the timing of recharge depend on the saturated hydraulic conductivity for a large variation in water retention curve. Also, the power law relates recharge (normalized by applied pulse volume) to time (normalized by the time of arrival of wetting front at that depth). The resulting equations predicted the model simulated normalized (relative) recharge with root mean square errors of less than 14 percent for the tested cases.

Increased population and recent droughts in 1996 and 2009 for the Barton Springs segment of the Edwards Aquifer have focused attention on groundwater resources and sustainability of spring flow. These springs serve as a local iconic cultural center as well as the natural habitat for the endangered Barton Springs salamander. In response to the potential compromise of these vulnerable groundwater resources, a two-dimensional, numerical groundwater-flow model was developed for the Barton Springs / Edwards Aquifer Conservation District and other governmental entities to aid in aquifer management. The objective of this study is to develop new methods of quantifying and distributing recharge for this model. The motivation for conducting this study includes the following: recent availability of more extensive data sets, new conceptual models of the aquifer system, and the desire to incorporate estimates of urban recharge. Estimates of recharge quantities and distributions for natural and artificial sources were implemented within this model to simulate discharge at Barton Springs and water-level elevations from January, 1999 to December, 2009. Results indicate that the new methods employed generated good agreement amongst simulated and observed discharge and water-level elevations (Root mean square error of 0.5 m3 sec-1 and 10.5 m, respectively). Additionally, these recharge calculations are decoupled from Barton Springs discharge which eliminates the circular logic inherent with the previous methodology. Anthropogenic, or artificial, recharge accounts for 4% of the total recharge between January, 1999 and December, 2009. Using observed data to quantify contributions from leaky utility lines and irrigation return flows, recharge estimates were completed with spatial and temporal resolution. Analyses revealed that on a month by month basis, anthropogenic contributions can vary from <1 to 59% of the total recharge. During peak anthropogenic recharge intervals, irrigation return flow is the most significant contributor. However, leakage from utility lines provides more total recharge during the study period. Recharge contributions from artificial sources are comparable to the mid-size watershed contributions over the ten-year analysis period. Urban recharge can be a critical source for buffering seasonal fluctuations, particularly during low flow periods. Outcomes are relevant for habitat conservation, drought response planning, and urban groundwater management. / text

The development of natural grass/scrubland for agricultural use within the Trans-Pecos basins has altered recharge mechanisms and raised questions about groundwater sustainability. Past efforts focused on recharge in arid basin systems used three main assumptions: there is minimal modern recharge, no widespread recharge on basin floors, and no recharge from anthropogenic sources. However, in the Trans-Pecos, nitrate (NO₃-) concentrations have increased in basin groundwater (up by 3-4 mg/l as NO₃- in 40 yrs), refuting the “classic” model and posing water quality risks. Grazing and irrigated agriculture have impacted basin hydrology by altering vegetation regime and the magnitude and spatial distribution of infiltration. This has increased recharge, Cl⁻, and mobile N flux to basin groundwater. A series of spatially-distributed net infiltration models were used to estimate potential recharge from natural and anthropogenic sources. Between 7-20% of potential recharge results from widespread recharge on the basin floors. Additionally, from 1960-2000, irrigation return flow may have contributed 3.0 × 10⁷ - 6.3 × 10⁷ m³ of recharge. These results are supported by field observations. Cores collected beneath agricultural land document changes in water content and pore water chemistry that imply increased downward flux of moisture and solute, and NO₃- and Cl- inventories beneath irrigated land are distinct in amount and profile from those in natural areas. There are significant implications for sustainability based upon the trends in groundwater NO₃- concentrations, core results, and net infiltration models: more recharge may enter the basins than previously estimated and there is a potential long-term concern for water quality. Due to thick unsaturated zones in the basins, long travel times are anticipated. It is unknown if NO3- and Cl⁻ flux has peaked or if effects will continue for years to come. Further study should be undertaken to examine anthropogenic impacts on basin water quality. Additionally, these impacts may occur in similar systems globally and there is considerable evidence for the re-evaluation of the validity of the “classic” model of recharge in arid basin systems. Future studies and management plans should incorporate potential impacts of changes in vegetation and land use on recharge processes and water budgets in arid basins. / text

With an abundant average precipitation rate, Vietnam could be considered water-reach country. Unfortunately, the non-uniform spatial and temporal distribution of rainfall, coupled with a demographic and industrial development polarized on the two major river deltas, it makes the water resources extremely vulnerable. As consequence, severe depletions of groundwater table are reported all over the country, often in the range of 1-2 m per year and more. The subsequent land subsidence is just one of the drawbacks, another being the increasing salinity of coastal aquifers as sea water level continues to rise. Under these conditions, the natural groundwater replenishment alone is not anymore able to provide for a safe water supply, different studies indicating that the groundwater exploitation in major urban agglomerations like Hanoi or Ho Chi Minh City already passed the sustainability level. The solution presented in this paper implies making use of engineered methods for enhancing the natural groundwater recharge rates by enabling better percolation rates of surface water into subsurface and thus optimizing the regional water cycle. The method known as ‘managed aquifer recharge’ (MAR) is introduced, together with general guidelines and tools for planning of MAR schemes, such as the newly web-based decision support system INOWAS_DSS. / Với tốc độ lượng mưa trung bình dồi dào, Việt Nam có thể được coi là quốc gia có nguồn nước trong tầm tay. Thật không may, sự phân bố không gian và thời gian không đồng đều của lượng mưa, cùng với sự phát triển dân số và công nghiệp phân cực trên hai vùng châu thổ sông lớn làm cho các nguồn nước rất dễ bị tổn thương. Vì vậy, sự suy giảm nước ngầm nghiêm trọng được báo cáo trên khắp đất nước, thường mỗi năm giảm 1-2 m và nhiều hơn nữa. Hiện tượng sụt lún đất xảy ra sau đó chỉ là một trong những hạn chế, mặt khác là độ mặn ngày càng tăng của các tầng chứa nước ven biển do mực nước biển tiếp tục tăng. Dưới những điều kiện này, việc bổ sung nước ngầm tự nhiên đơn thuần không còn có thể cung ứng cho một nguồn cấp nước sạch an toàn. Các nghiên cứu khác nhau cho thấy rằng việc khai thác nước ngầm tại các đô thị lớn như Hà Nội hay thành phố Hồ Chí Minh đã vượt qua mức độ bền vững. Giải pháp được trình bày trong bài báo này gợi ý việc sử dụng các phương pháp thiết kế để nâng cao tỷ lệ tái nạp nước ngầm tự nhiên bằng cách cho phép tỷ lệ thẩm thấu tốt hơn nước mặt vào dưới bề mặt và do đó tối ưu hóa chu trình nước trong khu vực. Phương pháp được gọi là 'tái nạp nước ngầm có quản lý (MAR) được giới thiệu, cùng với các hướng dẫn chung và các công cụ để lập kế hoạch đề án MAR, ví dụ như hệ thống mớihỗ trợ quyết định dựa trên kết nối mạng INOWAS_DSS.

Groundwater and surface water in the Edwards Plateau region exhibits spatial variability arising from mineral differences in aquifers and mixing of groundwaters with diverse flow paths and ages. Integration of basic hydrochemical and isotope data (⁸⁷Sr/⁸⁶Sr, [delta]¹⁸O, [delta]D, ¹⁴C, ³H) document that groundwaters in the Lower Cretaceous Edwards-Trinity (Plateau) aquifer system reflect intermixing of modern and Pleistocene recharge. Pleistocene recharge occurred under cooler paleo-climatic conditions, based on [delta]¹⁸O variance of 4.59%, and flow traversed sub-cropping Permian evaporite and Triassic strata under hydraulic conditions that promoted upward flow into the Plateau system. Recharge areas may have been in topographically elevated areas in New Mexico that no longer are connected with the Plateau. Present distribution of groundwaters with higher SO₄/Cl values occurring beneath topographic divides on the Plateau suggests that modern recharge occurs preferentially in losing-stream networks and is inhibited on divides by low-permeability soils. Relationships between ¹⁴C, tritium, [delta]¹³C, and Mg/Ca values confirm that effectively younger groundwaters occur beneath the upper parts of drainage networks, but down slope of divides. Thus, groundwater-age and hydrochemical data suggest that recharge preferentially occurs in the upper parts of drainage networks. Correlations between groundwater relative age and Mg/Ca enable estimation of the proportion of modern recharge at specific well locations based on Mg/Ca values and enables estimating local absolute recharge rates from regional-scale recharge estimates obtained from regional flow models. The Upper Colorado River bounds the northern and northeastern margin of the Plateau system and shows systematic chemical evolution along its flow path, including decreasing salinity and increasing SO₄/Cl values. The stream can be conceptually divided into three segments that each reflect groundwater inputs from five hydrochemically distinct intervals: 1) deep Permian and Pennsylvanian reservoirs similar to those that produce hydrocarbons in the region; 2) Upper Permian halite (Salado Formation); 3) the Triassic siliciclastic aquifer (Dockum Group); 4) the sulfate-evaporite-bearing Permian system (Ochoan, Guadalupian, and Leonardian Series); and 5) the Plateau aquifer system. Conservative mixing models suggest that any aquifer that the river is traversing at a specific location contributes a distinct hydrochemical signature, but the dominant contribution is from the Plateau system. / text

Alluvial groundwater systems are an important source of water for communities and biodiverse riparian corridors throughout the arid and semi-arid Basin and Range Geological Province of western North America. These aquifers and their attendant desert streams have been depleted to support a growing population, while projected climate change could lead to more extreme episodes of drought and precipitation in the future. The only source of replenishment to these aquifers is recharge. This dissertation builds upon previous work to characterize and quantify recharge in arid and semi-arid basins by characterizing the intra-annual seasonality of recharge across the Basin and Range Province, and considering how climate change might impact recharge seasonality and volume, as well as fragile riparian corridors that depend on these hydrologic processes. First, the seasonality of recharge in a basin in the sparsely-studied southern extent of the Basin and Range Province is determined using stable water isotopes of seasonal precipitation and groundwater, and geochemical signatures of groundwater and surface water. In northwestern Mexico in the southern reaches of the Basin and Range, recharge is dominated by winter precipitation (69% ± 42%) and occurs primarily in the uplands. Second, isotopically-based estimates of seasonal recharge fractions in basins across the region are compared to identify patterns in recharge seasonality, and used to evaluate a simple water budget-based model for estimating recharge seasonality, the normalized seasonal wetness index (NSWI). Winter precipitation makes up the majority of annual recharge throughout the region, and North American Monsoon (NAM) precipitation has a disproportionately weak impact on recharge. The NSWI does well in estimating recharge seasonality for basins in the northern Basin and Range, but less so in basins that experience NAM precipitation. Third, the seasonal variation in riparian and non-riparian vegetation greenness, represented by the normalized difference vegetation index (NDVI), is characterized in several of the study basins and climatic and hydrologic controls are identified. Temperature was the most significant driver of vegetation greenness, but precipitation and recharge seasonality played a significant role in some basins at some elevations. Major contributions of this work include a better understanding of recharge in a monsoon-dominated basin, the characterization of recharge seasonality at a regional scale, evaluation of an estimation method for recharge seasonality, and an interpretation of the interaction of seasonal hydrologic processes, vegetation dynamics, and climate change.

The main goal of this research is to develop and test a groundwater recharge estimation method that can address some of the key research priorities in groundwater. In this context use is made of various modelling tools including ArcGIS, field data (in situ observations of soil temperature and soil moisture), and soil physics as represented by a physically based vadose zone hydrologic model (HYDRUS-1D). The research is conducted in a pilot watershed in north Okanagan, Canada. The public version of HYDUS-1D and another version with detailed freezing and thawing module are first used to investigate seasonal distribution of heat and water movement in the vadose zone. Model performance is evaluated in different scales by using field data, the gradient-based optimization algorithm of HYDRUS-1D, and ROSETTA derived prior information about soil hydraulic parameters. The latter are fitted to statistical distributions and used in Monte-Carlo experiments to assess the potential uncertainty in groundwater recharge due to model parameters. Next, the significance of the recharge estimation method for catchment scale transient groundwater modelling is demonstrated by applying uniform and variable flux boundary condition to a saturated zone transient groundwater model, MIKESHE. The results showed that the traditional uniform recharge assumption can lead to misleading decisions related to water resources management and pumping well network design. The effect of pumping well network and the provincial Water Act on water resources sustainability are further examined in an evolving climate. The results suggest potential water resource problem in the basin, which can possibly be attributed to the previously installed pumping well network (depth and screen level), and the provincial water use policy. The findings of this study demonstrate that such problems related to inappropriate well network and water resource management can greatly be minimised with the use of the recharge estimation method developed in this study.

Ce travail de thèse a pour oblectif de simuler numériquemetn les impacts de recharges sédimentaires sur la morphodynamique du tronçon du Vieux-Rhin situé entre les barrages de Kembs et Breisach. Dans le cadre du projet InterReg de redynamisation du Vieux-Rhin, ces simulations sont primordiales pour évaluer l'efficacité des scénarios de recharge sédimentaire ainsi que lesrisques associés , tels que la fixation des dépôts ou encore la déstabilisation du lit pavé. a l'échelle du vieux-Rhin entioer (50 km) les simulations numériques 1D des années 1950, 1990 et 2009 ont permis d'appréhender la dynamique fluviale du lit en tenant compte de l'impact de la végétation. Les modélisations des processus granulométriques en jeu dans les recharges sédimentaires ont été préalablement testés et améliorés sur des expériences de laboratoires avec le modèles numériques 1D RubarBE. Dans ces modélisations, le tri granulométrique longitudinal, les évolutions morphologiques et le phénomène de capture des sédiments les plus fins ont été reproduits. Les modélisations bi-dimensionnelle à l'échelle des sites d'injections ont été réalisées avec le modèle numérique Rubar20TS. Les évolutions morphologiques des recharges ont été simulées et les zones favorisant les dépôts sédimentaires ont été identifiées. Les conclusions suivantes ont été tirées des simulations d'un banc sédimantaire et des scénarios de redynamisation : des flancs de banc pentus facilitent la mobilisation sédimentaire ; le choix du site et de la largeur du banc semblent très imporants afi de créer des conditions suffisament dynamiques en bordure de banc ; l'injection d'un banc de galets apparaît plus efficace qu'une érosion latérale de berge. Un scénario de recharge sédimentaire optimal pourrait consister en des injections de bancs latéraux étroits d'un volume d''environ 20 000 m3 répétées dans le temps et/ou dans l'espace.

This study observes how the size and type of land development can often be limited by the supply of fresh groundwater sources. Multiple-use recharge basins were found to be effective in diverting pollutants around a potable source of groundwater, thus reducing the chances of that source becoming contaminated. A computer-aided numerical model was used to simulate groundwater flow and its responses to recharge basins in a hypothetical situation.Through a series of trials, artifical recharge was able to abate the problem of groundwater contamination in certain geohydrologic conditions. Optimum rates of recharge and discharge were determined to effectively divert contaminated groundwater around several types of developments. From these findings, land use options and development intensities can be safely recommended for areas which otherwise may have been nearly undevelopable. / Department of Landscape Architecture