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    AUTHOR:
 MONO AUTH: Mokkapati, Sreenivas Venkata
MONO TITLE: Mapping porosity variations using microgravity monitoring in the
            Blaine Aquifer, southwestern Oklahoma
 CORP INFO: University of Oklahoma; Norman, OK; United States
            Master's
    SOURCE: 80
REFERENCES: 18
      YEAR: 1995
  LANGUAGE: English
  PUB TYPE: Thesis, Monographic
    FORMAT: illus., 6 tables
  ABSTRACT: The potential of microgravity in detecting near-surface water
            level changes has been investigated. Gravity measurements sense
            mass distribution and hence are affected by the volume of water
            in an aquifer. Measurements at exactly the same positions at
            different times register a change due to variation in the volume
            of stored water. By subtracting measurements made at different
            times, complexity in geologic structure is eliminated. The
            remainder is the effect of the difference in stored water
            volume. The porosity distribution in the area is computed from
            the gravity change. The study area is in a karst aquifer located
            in southwestern Oklahoma. It was chosen in conjunction with the
            Oklahoma Water Resources Board artificial recharge demonstration
            project. This area is known to have an extensive network of
            cavities in the shallow subsurface. A Lacoste-Romberg geodetic
            gravimeter with electrostatic nulling (accuracy of approximately
            one microgal) was used for the study. Thirty-eight closely
            spaced stations were established. A repeated occupation
            procedure was adopted, and a data reduction method was devised
            for determining repeatability of gravity readings. A reference
            base station was established at the nearby Red River where the
            groundwater level was assumed constant during the period of this
            study. Data analysis indicates that the absolute gravity
            reference may not be reliable enough to determine overall
            porosity in the area. Repeat surveys were made several times
            over a period of eighteen months. Gravity differences between
            surveys were compared to water level differences obtained from
            six monitoring wells in the study area. A 42 foot change in
            water level produced smaller local anomalies than might be
            expected for a karst model with large diameter conduits in zones
            of cavernous porosity. This may in part be due to the absence of
            conduits and the presence of widely distributed smaller voids.
            It may also reflect the inability to resolve larger local
            features with measurements restricted to a small area. One
            dimensional modeling of porosity over the depth interval of
            water movement does, however, show a correlation with porosity
            inferred from the gravity measurements. The gravity differences
            over time were analyzed and relative porosity distribution over
            the study area was mapped.
DESCRIPTOR: aquifers; Blaine Aquifer; geophysical surveys; gravity surveys;
            ground water; karst hydrology; levels; mapping; monitoring;
            Oklahoma; one-dimensional models; porosity; southwestern
            Oklahoma; storage; surveys; United States