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WRIR 03-4267


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Merritt, Michael, L., 2004, Estimating Hydraulic Properties of the Floridan Aquifer System by Analysis of Earth-Tide, Ocean-Tide, and Barometric Effects, Collier and Hendry Counties, Florida: U.S. Geological Survey Water-Resources Investigations Report 03-4267, 70 p.
ABSTRACT:

Aquifers are subjected to mechanical stresses from natural, non-anthropogenic, processes such as pressure loading or mechanical forcing of the aquifer by ocean tides, earth tides, and pressure fluctuations in the atmosphere. The resulting head fluctuations are evident even in deep confined aquifers. The present study was conducted for the purpose of reviewing the research that has been done on the use of these phenomena for estimating the values of aquifer properties, and determining which of the analytical techniques might be useful for estimating hydraulic properties in the dissolved-carbonate hydrologic environment of southern Florida. Fifteen techniques are discussed in this report, of which four were applied.

An analytical solution for head oscillations in a well near enough to the ocean to be influenced by ocean tides was applied to data from monitor zones in a well near Naples, Florida. The solution assumes a completely non-leaky confining unit of infinite extent. Resulting values of transmissivity are in general agreement with the results of aquifer performance tests performed by the South Florida Water Management District. There seems to be an inconsistency between results of the amplitude ratio analysis and independent estimates of loading efficiency. A more general analytical solution that takes leakage through the confining layer into account yielded estimates that were lower than those obtained using the non-leaky method, and closer to the South Florida Water Management District estimates. A numerical model with a cross-sectional grid design was applied to explore additional aspects of the problem.

A relation between specific storage and the head oscillation observed in a well provided estimates of specific storage that were considered reasonable. Porosity estimates based on the specific storage estimates were consistent with values obtained from measurements on core samples. Methods are described for determining aquifer diffusivity by comparing the time-varying drawdown in an open well with periodic pressure-head oscillations in the aquifer, but the applicability of such methods might be limited in studies of the Floridan aquifer system.

TABLE OF CONTENTS

Abstract
Introduction
    Purpose and Scope
    Acknowledgments
Description of the Study Area
    Hydrogeology of the Study Area
Naturally Occurring Stresses on Aquifers
    Solar and Lunar Stresses
    Atmospheric Stresses
        Estimates of loading efficiency and relation to tidal and barometric efficiencies
        Determination of barometric efficiency by Clark's method
        Determination of loading efficiency by Clark's method
    Harmonic Structure of Tidal and Atmospheric Stresses
        Analysis for amplitude and phase of harmonic components
Analytical Methods for Computing Aquifer Parameters from Naturally Forced Periodic Data
    Using Heads Influenced by Ocean Tides for Estimates of the Hydraulic Diffusivity of an Aquifer
        Inland extent of ocean-tide influence
        Choice of method for estimating hydraulic diffusivity
        Estimates of hydraulic diffusivity
     Using Heads Influenced by Earth Tides for Estimates of Specific Storage, Porosity, and Bulk Modulus of the Aquifer
        Recent research into methods of estimating specific storage, porosity, and bulk modulus
    Using Heads in Open Wells Penetrating Confined Aquifers for Estimates of the Transmissivity and Storage Coefficient of an Aquifer
    Using Heads or Water Levels to Estimate Vertical Hydraulic Conductivity
Conclusions
Summary
References Cited


U.S. Department of the Interior, U.S. Geological Survey
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