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Article: Airflow induced by pumping tests in unconfined aquifer with a low-permeability cap

TitleAirflow induced by pumping tests in unconfined aquifer with a low-permeability cap
Authors
KeywordsWater resources
Earth Sciences
Hydrology
Issue Date2009
PublisherAmerican Geophysical Union.
Citation
Water Resources Research, 2009, v. 45 n. 10 How to Cite?
AbstractMost analytical and numerical models developed to analyze pumping test data focus on saturated flow below the water table. Traditionally the soil above the initial water table prior to pumping has been thought to have little influence on the test results and has usually been ignored. It is hypothesized that, if the unsaturated zone is capped by low-permeability soil, airflow in the unsaturated zone may be developed during pumping and may have impact on the drawdown in the aquifer. A transient, three-dimensional and variably saturated flow model is employed to simulate the pumping-induced air and groundwater flows in both the saturated zone and unsaturated zone with a low-permeability layer. The results demonstrate that negative pressure in the unsaturated zone can be generated by pumping. The negative pressure begins to appear as the drawdown rate increases to a maximum, approaches a peak before the drawdown rate becomes zero, and then gradually disappears. Drawdown obtained from the capped aquifer is much greater because the water in the pores in the unsaturated zone is sucked by the negative pressure and the gravity drainage from the pores is hampered. Consequently, the drawdown versus time curve does not conform to the traditional S-shaped curve for an unconfined aquifer but is similar to that of a confined aquifer. If the airflow caused by the low-permeability cap is ignored, the error in estimated drawdown could be over 80% for the specific parameters and aquifer configuration used in the study. The possible errors in parameter estimation when airflow is ignored are explored. Overall, the hydraulic conductivity of the aquifer can be overestimated and the specific yield of the aquifer underestimated if airflow is ignored. The estimation error for specific yield tends to be greater than that in hydraulic conductivity. Copyright 2009 by the American Geophysical Union.
Persistent Identifierhttp://hdl.handle.net/10722/65440
ISSN
2015 Impact Factor: 3.792
2015 SCImago Journal Rankings: 2.661
ISI Accession Number ID
Funding AgencyGrant Number
Hong Kong Special Administrative Region, ChinaHKU 7028/05P
HKU 701908P
Funding Information:

The study was supported by the Research Grants Council of the Hong Kong Special Administrative Region, China (HKU 7028/05P and HKU 701908P). TOUGH2 was run via the interface of PetraSim. The comments from Professor Shlomo Neuman and two anonymous reviewers have led to an improvement of the paper.

References
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DC FieldValueLanguage
dc.contributor.authorJiao, JJen_HK
dc.contributor.authorGuo, Hen_HK
dc.date.accessioned2010-08-05T06:46:35Z-
dc.date.available2010-08-05T06:46:35Z-
dc.date.issued2009en_HK
dc.identifier.citationWater Resources Research, 2009, v. 45 n. 10en_HK
dc.identifier.issn0043-1397en_HK
dc.identifier.urihttp://hdl.handle.net/10722/65440-
dc.description.abstractMost analytical and numerical models developed to analyze pumping test data focus on saturated flow below the water table. Traditionally the soil above the initial water table prior to pumping has been thought to have little influence on the test results and has usually been ignored. It is hypothesized that, if the unsaturated zone is capped by low-permeability soil, airflow in the unsaturated zone may be developed during pumping and may have impact on the drawdown in the aquifer. A transient, three-dimensional and variably saturated flow model is employed to simulate the pumping-induced air and groundwater flows in both the saturated zone and unsaturated zone with a low-permeability layer. The results demonstrate that negative pressure in the unsaturated zone can be generated by pumping. The negative pressure begins to appear as the drawdown rate increases to a maximum, approaches a peak before the drawdown rate becomes zero, and then gradually disappears. Drawdown obtained from the capped aquifer is much greater because the water in the pores in the unsaturated zone is sucked by the negative pressure and the gravity drainage from the pores is hampered. Consequently, the drawdown versus time curve does not conform to the traditional S-shaped curve for an unconfined aquifer but is similar to that of a confined aquifer. If the airflow caused by the low-permeability cap is ignored, the error in estimated drawdown could be over 80% for the specific parameters and aquifer configuration used in the study. The possible errors in parameter estimation when airflow is ignored are explored. Overall, the hydraulic conductivity of the aquifer can be overestimated and the specific yield of the aquifer underestimated if airflow is ignored. The estimation error for specific yield tends to be greater than that in hydraulic conductivity. Copyright 2009 by the American Geophysical Union.en_HK
dc.languageeng-
dc.publisherAmerican Geophysical Union.-
dc.relation.ispartofWater Resources Researchen_HK
dc.rightsWater Resources Research. Copyright © American Geophysical Union.-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subjectWater resources-
dc.subjectEarth Sciences-
dc.subjectHydrology-
dc.titleAirflow induced by pumping tests in unconfined aquifer with a low-permeability capen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0043-1397&volume=45&issue=10 article no. W10445&spage=&epage=&date=2009&atitle=Airflow+induced+by+pumping+tests+in+unconfined+aquifer+with+a+low-permeability+cap-
dc.identifier.emailJiao, JJ:jjiao@hku.hken_HK
dc.identifier.authorityJiao, JJ=rp00712en_HK
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.1029/2009WR007760en_HK
dc.identifier.scopuseid_2-s2.0-72149125020en_HK
dc.identifier.hkuros161989-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-72149125020&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume45en_HK
dc.identifier.issue10en_HK
dc.identifier.eissn1944-7973-
dc.identifier.isiWOS:000271326600001-
dc.publisher.placeUnited Statesen_HK
dc.relation.projectSubsurface airflow induced by pumping tests-
dc.relation.projectSubsurface air flow induced by sea tides-
dc.identifier.scopusauthoridJiao, JJ=7102382963en_HK
dc.identifier.scopusauthoridGuo, H=25226459100en_HK

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