Author: Bridget R. Scanlon
Publisher:
ISBN:
Category : Aquifers
Languages : en
Pages : 127

Get Book Here

Book Description

Author: Allan K. Clark
Publisher:
ISBN:
Category : Edwards Aquifer (Tex.)
Languages : en
Pages : 24

Get Book Here

Book Description

Author: Thomas Anders Evans
Publisher:
ISBN:
Category : Groundwater
Languages : en
Pages : 280

Get Book Here

Book Description

Author: Amy Richter Clark
Publisher:
ISBN:
Category : Edwards Aquifer (Tex.)
Languages : en
Pages : 34

Get Book Here

Book Description

Author: Dipankar Dwivedi
Publisher:
ISBN:
Category :
Languages : en
Pages :

Get Book Here

Book Description
Numerical models of flow and transport are commonly applied for the sustainable management of water resources and for the selection of appropriate remediation techniques. However, these numerical models are not always accurate due to uncertain parameters and the disparity of scales across which observations are made, hydrological processes occur, and modeling is conducted. The modeling framework becomes further complex because hydrologic processes are coupled with chemical and biological processes. This dissertation focuses on the most widespread contaminants of surface and ground water, which are E. coli and nitrate, respectively. Therefore, this research investigates the linkages between bio-chemical and hydrologic processes for E. coli transport, explores the spatio-temporal variability of nitrate, quantifies uncertainty, and develops models for both E. coli and nitrate transport that better characterize these biogeochemical linkages. A probabilistic framework in the form of Bayesian Neural Networks (BNN) was used to estimate E. coli loads in surface streams and was compared with a conventional model LOADEST. This probabilistic framework is crucial when water quality data are scarce, and most models require a large number of mechanistic parameters to estimate E. coli concentrations. Results indicate that BNN provides better characterization of E. coli at higher loadings. Results also provide the physical, chemical, and biological factors that are critical in the estimation of E. coli concentrations in Plum Creek, Texas. To explore model parameters that control the transport of E. coli in the groundwater (GW) and surface water systems, research was conducted in Lake Granbury, Texas. Results highlight the importance of flow regimes and seasonal variability on E. coli transport. To explore the spatio-temporal variability of nitrate across the Trinity and Ogallala aquifers in Texas, an entropy-based method and a numerical study were employed. Results indicate that the overall mean nitrate-N has declined from 1940 to 2008 in the Trinity Aquifer as opposed to an increase in the Ogallala Aquifer. The numerical study results demonstrate the effect of different factors like GW pumping, flow parameters, hydrogeology of the site at multiple spatial scales. To quantify the uncertainty of nitrate transport in GW, an ensemble Kalman filter was used in combination with the MODFLOW-MT3DMS models. Results indicate that the EnKF notably improves the estimation of nitrate-N concentrations in GW. A conceptual modeling framework with deterministic physical processes and stochastic bio-chemical processes was devised to independently model E. coli and nitrate transport in the subsurface. Results indicate that model structural uncertainty provides useful insights to modeling E. coli and nitrate transport. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148125

Author: Allan K. Clark
Publisher:
ISBN:
Category : Edwards Aquifer (Tex.)
Languages : en
Pages : 9

Get Book Here

Book Description

Author: Michael J. Focazio
Publisher:
ISBN:
Category : Drinking water
Languages : en
Pages : 46

Get Book Here

Book Description

Author: O. Lehn Franke
Publisher:
ISBN:
Category : Artificial groundwater recharge
Languages : en
Pages : 20

Get Book Here

Book Description

Author: Timothy D Oden
Publisher: CreateSpace
ISBN: 9781500266288
Category :
Languages : en
Pages : 58

Get Book Here

Book Description
Montgomery County is in the northern part of the Houston, Texas, metropolitan area, the fourth most populous metropolitan area in the United States. As populations have increased since the 1980s, groundwater has become an important resource for public-water supply and industry in the rapidly growing area of Montgomery County. Groundwater availability from the Gulf Coast aquifer system is a primary concern for water managers and community planners in Montgomery County and requires a better understanding of the rate of recharge to the system. The Gulf Coast aquifer system in Montgomery County consists of the Chicot, Evangeline, and Jasper aquifers, the Burkeville confining unit, and underlying Catahoula confining system. The individual sand and clay sequences of the aquifers composing the Gulf Coast aquifer system are not laterally or vertically continuous on a regional scale; however, on a local scale, individual sand and clay lenses can extend over several miles. The U.S. Geological Survey, in cooperation with the Lone Star Groundwater Conservation District, collected groundwater-quality samples from selected wells within or near Montgomery County in 2008 and analyzed these samples for concentrations of chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), tritium (3H), helium-3/tritium (3He/3H), helium-4 (4He), and dissolved gases (DG) that include argon, carbon dioxide, methane, nitrogen and oxygen. Groundwater ages, or apparent age, representing residence times since time of recharge, were determined by using the assumption of a piston-flow transport model. Most of the environmental tracer data indicated the groundwater was recharged prior to the 1950s, limiting the usefulness of CFCs, SF6, and 3H concentrations as tracers. In many cases, no tracer was usable at a well for the purpose of estimating an apparent age. Wells not usable for estimating an apparent age were resampled in 2011 and analyzed for concentrations of major ions and carbon-14 (14C). At six of these wells, additional 4He and DG samples were collected and analyzed.

Author: Richard W. Healy
Publisher: Cambridge University Press
ISBN: 1139491393
Category : Science
Languages : en
Pages :

Get Book Here

Book Description
Understanding groundwater recharge is essential for successful management of water resources and modeling fluid and contaminant transport within the subsurface. This book provides a critical evaluation of the theory and assumptions that underlie methods for estimating rates of groundwater recharge. Detailed explanations of the methods are provided - allowing readers to apply many of the techniques themselves without needing to consult additional references. Numerous practical examples highlight benefits and limitations of each method. Approximately 900 references allow advanced practitioners to pursue additional information on any method. For the first time, theoretical and practical considerations for selecting and applying methods for estimating groundwater recharge are covered in a single volume with uniform presentation. Hydrogeologists, water-resource specialists, civil and agricultural engineers, earth and environmental scientists and agronomists will benefit from this informative and practical book. It can serve as the primary text for a graduate-level course on groundwater recharge or as an adjunct text for courses on groundwater hydrology or hydrogeology. For the benefit of students and instructors, problem sets of varying difficulty are available at http://wwwbrr.cr.usgs.gov/projects/GW_Unsat/Recharge_Book/