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Estimation of unconfined aquifer hydraulic properties using gravity and drawdown data

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dc.contributor.authorWoodworth, Joshua, author
dc.contributor.authorHarry, Dennis, advisor
dc.contributor.authorSanford, William, advisor
dc.contributor.authorStednick, John, committee member
dc.date.accessioned2007-01-03T08:22:40Z
dc.date.available2007-01-03T08:22:40Z
dc.date.issued2011
dc.description.abstractAn unconfined aquifer test using temporal gravity measurements was conducted in shallow alluvium near Fort Collins, Colorado on September 26-27, 2009. Drawdown was recorded in four monitoring wells at distances of 6.34, 15.4, 30.7, and 60.2 m from the pumping well. Continuous gravity measurements were recorded with a Scintrex® CG-5 gravimeter near the closest well, at 6.3 m, over several multi-hour intervals during the 27 hour pumping test. Type-curve matching of the drawdown data performed assuming Neuman's solution yields transmissivity T, specific yield Sy, and elastic component of storativity S estimates of 0.018 m2s-1, 0.041, and 0.0093. The gravitational response to dewatering was modeled assuming drawdown cone geometries described by the Neuman drawdown solution using combinations of T, Sy, and S. The best fitting gravity model based on minimization of the root mean square error between the modeled and observed gravity change during drawdown resulted from the parameters T =0.0033 m2s-1, Sy =0.45, and S =0.0052. Conservative precision estimates in the gravity data widen these estimates to T =0.002-0.006 m2s-1, Sy =0.25-0.65, and S =0-0.2. Drawdown conforming to the Neuman solution was forward modeled using combinations of T, Sy, and S. Minimization of the root mean square misfit between these forward models and observed drawdown in the monitoring wells results in T =0.0080 m2s-1, Sy =0.26, and S =0.000004. Discrepancy between type-curve matching results, gravity analysis results, and drawdown modeling is attributed to heterogeneity and anisotropy within the aquifer, and a relatively large amount drawdown compared to initial saturated thickness, conditions which fail the Neuman solution assumptions. In this aquifer test, gravity was most sensitive to transmissivity, less sensitive to specific yield, and insensitive to the specific storage-saturated thickness quotient. Simultaneous deployment of multiple gravity stations during similar tests should better constrain gravity analysis aquifer property estimates of transmissivity and specific yield.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.identifierWoodworth_colostate_0053N_10864.pdf
dc.identifierETDF2011400336GEOS
dc.identifier.urihttp://hdl.handle.net/10217/70838
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2000-2019
dc.rightsCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.
dc.subjectunconfined aquifer
dc.subjectdrawdown
dc.subjectgravity
dc.subjecthydraulic properties
dc.subjectmicrogravity
dc.titleEstimation of unconfined aquifer hydraulic properties using gravity and drawdown data
dc.typeText
dcterms.rights.dplaThis Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
thesis.degree.disciplineGeosciences
thesis.degree.grantorColorado State University
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (M.S.)

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