As human population increases, demand for water supplies will cause an increase in pumping rates from confined aquifers which may become unconfined after long-term pumping. Such an unconfined-confined conversion problem has not been fully investigated before and is the focus of this thesis. The objective of this thesis is to use both analytical and numerical modeling to investigate groundwater flow in an unconfined-confined aquifer including the no-flow lateral boundary effect and the regional flow influence. This study has used Girinskii’s Potential in combination with MATLAB to depict how changes in aquifer dimensions, hydraulic properties, regional flow rates, and pumping rates affect the size and shape of the unconfined-confined boundary. This study finds that the unconfined-confined conversion is quite sensitive to the distance between the piezometric surface and the upper confining bed when that distance is small, and the sensitivity lessens as that distance increases. The study shows that pumping rate is the dominating factor for controlling the size of the unconfined-confined boundary in comparison to the regional flow. It also shows that the presence of a no-flow boundary alters the normally elliptical shape of the unconfined-confined boundary.

As human population increases, demand for water supplies will cause an increase in pumping rates from confined aquifers which may become unconfined after long-term pumping. Such an unconfined-confined conversion problem has not been fully investigated before and is the focus of this thesis. The objective of this thesis is to use both analytical and numerical modeling to investigate groundwater flow in an unconfined-confined aquifer including the no-flow lateral boundary effect and the regional flow influence. This study has used Girinskii’s Potential in combination with MATLAB to depict how changes in aquifer dimensions, hydraulic properties, regional flow rates, and pumping rates affect the size and shape of the unconfined-confined boundary. This study finds that the unconfined-confined conversion is quite sensitive to the distance between the piezometric surface and the upper confining bed when that distance is small, and the sensitivity lessens as that distance increases. The study shows that pumping rate is the dominating factor for controlling the size of the unconfined-confined boundary in comparison to the regional flow. It also shows that the presence of a no-flow boundary alters the normally elliptical shape of the unconfined-confined boundary.

A flow duration curve (FDC) defines the relation between the flow amount of any time (daily, yearly, or another time) and its frequency. Moreover, FDCs are used in many water resources projects. However, the ungauged basins or limited amount of gauging in a basin is a common problem. Therefore, regional FDCs are needed to be developed in ungauged basins. Oltu basin has been chosen as the study area, which is located in the north-eastern part of Turkey in &Ccedil / oruh Basin. Two parametric approaches and a statistical approach have been applied to develop regional flow duration curves (FDCs) in Oltu Basin. Parametric approaches cover two different models, namely Model Kocatepe, which is a five parameter model depending on the regression analysis between discharge having certain probability of occurrences and geomorphologic and climatic factors / Model Quimpo, which is a two parameter model proposed by Quimpo. Lognormal distribution has been used in the statistical approach. Several performance indices have been evaluated to decide on if the model dependable or not. As a result of these analysis, it is concluded that, Model Quimpo gives good results in small basins, whereas, Model Kocatepe is effective in large areas. Statistical approach is not an appropriate method to use while regionalizing FDCs in Oltu basin.The analysis performed for short-term duration has revealed that 5-years record lengths of discharges are enough to develop a dependable FDC compared to regional FDC. The validation results and the performance indices are presented with the analysis results.

Springs in the Ash Meadows, Nevada wetland area are discharging groundwater at a high volume that cannot be sustained by local, present-day precipitation and associated recharge. Previous groundwater flow models for this region have required groundwater to flow through complex geology for long distances (160km) through fractures that, in the current stress field, should be closed in many instances in the presumed flow direction. This thesis examines several possible flow paths and evaluates each flow path using chemical and isotopic signatures in the water, as well as geologic and geophysical constraints, and determines that flow from beneath the Yucca Mountain area is the most viable source of groundwater for the springs at Ash Meadows. Isotopic signatures also indicate that recharge likely occurred during the last pluvial, a cooler, wetter period about 13,000 or more years ago, and that present-day water is discharging from storage. Geophysical investigations show the relationship of a deep-seated crustal feature (the Gravity Fault) with shallow offset faults near the Ash Meadows springs. The damage zone of the Gravity Fault appears to provide a conduit for groundwater flow; the north-south fractures should have the greatest aperture under the current stress field, and the buried tufa mounds (revealed with ground penetrating radar data) indicate localized upwelling from a deeper regional water source.

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