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Short‐Time Geodetic Determination of Aquifer Storage Coefficient in Taiwan
Author(s) -
Chen KuanHung,
Hwang Cheinway,
Chang LiangCheng,
Ke ChienChung
Publication year - 2018
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2018jb016630
Subject(s) - gravimeter , geodetic datum , aquifer , geology , geodesy , groundwater , subsidence , hydrogeology , gravimetry , geotechnical engineering , geomorphology , geophysics , casing , structural basin , reservoir modeling
Specific yield ( S y ) and specific storage ( S s ) are two hydrogeological parameters often estimated in a costly pumping test (hydraulic method). Pumping or a natural aquifer recession can cause gravity change and surface deformation, useful for S y and S s determination by the more economic geodetic method. From 2013 to 2017, over a few days we measured gravity changes at four sites and subsidence at one site in Taiwan by a FG5 gravimeter and a precision level to estimate S y and S s . Using short‐time gravity and level records avoids complicated logistic supports and temporal effects. The measured gravity changes are associated with the MODFLOW‐modeled groundwater depletion. We succeeded in estimating S y at two sites and failed at the other two. One successful case uses rapid postrain declines of gravity and groundwater level. We did leveling only at one site, but here the 500‐min, continuous, submillimeter subsidence records result in a S s consistent with the hydraulic result. Lessons on the failed cases of S y are suggested to avoid disrupting factors in gravity surveys. A semiautomatic leveling procedure is proposed to maximize the chance for S s determination. Our simulations show that gravity changes increase with S y and decrease with initial hydraulic head and horizontal gravimeter‐pumping well distance, helping to predict if the gravity‐based method works at a site and to best plan a gravity survey. Drilling data show that the S y values from the hydraulic and geodetic methods represent aquifer storage coefficients over different aquifer layers.