Browsing by Subject "hydrogeology"
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Item Analysis of No-Flow Boundaries in Mixed Unconfined-Confined Aquifer Systems(2010-07-14) Langerlan, Kent A.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.Item Hillslope Hydrological Processes in a Costa Rican Rainforest: Water Supply Partitioning Using Isotope Tracers(2014-04-24) DuMont, Andrea LynCosta Rican tropical premontane rainforests are among the world's most valuable ecosystems in terms of diversity of animals, plants, and natural resources. These environments are dependent on water resources which fluctuate in quantity during the dry and wet seasons and which are significantly influenced by vegetation feedbacks. Currently, tropical premontane forest watersheds are insufficiently characterized in terms of groundwater and stream water interactions due to their limited accessibility and complex geological conditions. However, water produced from these watersheds is a critical renewable resource in Costa Rica. It plays a significant role in the production of downstream hydropower and acts as a supply for water distribution systems in many rural areas. In this study, stable isotope tracing of ?^(18)O and ?D was used to determine the source of water in a stream, and the relative contributions of water budget components (e.g., groundwater, soil water). Samples were collected beginning in the dry season and continuing through the wet season from 2013-2014 as the soil became progressively wetter. The ?^(18)O and ?D samples represent precipitation in the tropical forest, as well as groundwater, soil water, and stream water at several locations. This data is important to understanding the influence of vegetation and hydrogeological properties on groundwater and stream water in tropical headwater catchments. Streamflow averaged 0.06 m^(3)/min in baseflow and greater than 0.10 m^(3)/min during storms. Groundwater was seen to contribute to 80% of streamflow and was the main stream component even during storm events. A small proportion of the total amount of streamflow came from interflow and soil water (1%). Additional findings indicated that precipitation, about 4200 mm/yr, in the rainforest can be recycled source water. Storm tracks alternate from distribution starting in the Pacific Ocean to the Caribbean Sea over the course of the wet season. Overall precipitation was seen to be dominated by deep convection and enhanced during the wet season due to the North American Monsoon and the Intertropical Convergence Zone.