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Temporal Saltwateref’F’Ects On A Porous Sand Derived From Geophysical Monitoring Through A Tidal Cycle At Crescent Beach State Park, MaineNormal access

Authors: S.K. Sandberg and L.D. Slater
Event name: 12th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: Hydrology Forum - Geophysical Applications In Hydrologic Mapping
Publication date: 14 March 1999
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 805.01Kb )

Summary:
This paper presents results of an experiment in which data from a combination of geophysical
methods (resistivity, induced polarization, electromagnetic profiling, and magnetic profiling)
were used to identify shallow geologic and hydrogeologic structure, and to provide a model for
groundwater flow in a dynamic beach environment. Based on this study, the beach appears to be
underlain by a thin beach sand, overlying bedrock. Within the overlying sediments, a patch of
glacial till was mapped toward the ocean side of the beach. Bedrock has lithologic variability, as
evidenced by a non-uniform magnetic response. In particular, a northeast-southwest trending
magnetic body, believed to be a basalt dyke, was detected by its magnetic response.
During the transgressive phase of the tidal cycle, saline groundwater flow appeared to be quite
rapid, extending ahead of the surfical water by at least 4 m, as evidenced by the electromagnetic
response. During the regressive phase, a slug of saline water remained up beach from the high
tide mark for several hours prior to draining. Also during this regression, we observed
electromagnetic evidence for two fracture zones, or other preferential groundwater flow
pathways. These fracture zones appear to contain a relatively constant concentration of saltwater,
while surficial sediments above and to the side are flushed with fresh groundwater during tidal
regression.

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