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Imaging rainfall drainage within the Miami oolitic limestone using high‐resolution time‐lapse ground‐penetrating radar
Author(s) -
Truss Steven,
Grasmueck Mark,
Vega Sandra,
Viggiano David A.
Publication year - 2007
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2005wr004395
Subject(s) - vadose zone , ground penetrating radar , geology , infiltration (hvac) , drainage , phreatic , hydrology (agriculture) , geomorphology , sink (geography) , groundwater , aquifer , radar , geotechnical engineering , meteorology , telecommunications , ecology , physics , computer science , biology , cartography , geography
The vadose zone of the Miami limestone is capable of draining several centimeters of rainfall within a fraction of an hour. Once the water enters the ground, little is known about the flow paths in the oolitic rock. A new rotary laser‐positioned ground‐penetrating radar (GPR) system enables centimeter‐precise and rapid acquisition of time‐lapse surveys in the field. Two‐dimensional (2‐D) GPR time‐lapse surveying at a 3‐min interval before, during, and after rainfall shows how buried sand‐filled dissolution sinks efficiently drain the bulk of the rainwater. Hourly repeated 3‐D imaging of a dissolution sink in response to surface infiltration shows how the wetting front propagates at a rate of 0.6–1.2 m/h traversing the 5‐m‐thick vadose zone within hours. At the same time, some of the water migrates laterally into the host rock guided by stratigraphic unit boundaries. Average lateral propagation measured over a 28‐hour period was of the order of 0.1 m/h. On a seasonal time frame, redistribution involves the entire rock volume. Comparing 3‐D surveys acquired after wet summer and dry winter conditions shows good GPR event correspondence, but also time shifts up to 20 ns caused by the change of overall water content within the vadose zone. High‐precision time‐lapse GPR imaging can therefore be used to noninvasively characterize natural drainage inside the vadose zone ranging from transient loading to seasonal variation.