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Land Subsidence Related to Decline of Artesian Pressure in the Ocala Limestone at Savannah, Georgia*

By
G. H. Davis
G. H. Davis
(
Geologist
,
U. S. Geological Survey
,
Washington, D. C.
);
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J. B. Small
J. B. Small
(
Chief, Leveling Branch
,
Coast and Geodetic Survey
,
Washington, D. C.
);
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H. B. Counts
H. B. Counts
(
Engineer, U. S.
Geological Survey
,
Savannah, Ga.
);
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Published:
January 01, 1963

Abstract

Precise leveling by the Coast and Geodetic Survey in 1918, 1933, 1935, and 1955 indicates that the land surface has subsided as much as 4 inches in the Savannah area. Most of the subsidence has taken place since 1933.

Ground-water withdrawals from the Ocala and associated limestones of Eocene to Miocene age increased gradually from a rate of 7 mgd (million gallons per day) in 1888 to 23 mgd in 1936, but then nearly tripled to 57 mgd by 1955. The artesian pressure of the confined limestone aquifer has declined sharply in response to the greatly increased withdrawal since 1936. The pressure head declined about 40 feet in the 37 years before 1933, and as much as 100 feet more in the 22 years from 1933 through 1955. If it is postulated that the artesian pressure supports part of the load of the confining bed and overlying deposits, the decrease in artesian head has been accompanied by an increase of effective stress on the aquifer rock. In support of this postulate, the area affected by subsidence corresponds closely with the area of large decline in head, and most of the subsidence occurred during the period of rapid head decline from 1936 to 1955. This close agreement in time of occurrence and areal extent indicates that the decline of artesian head is a major, if not the principal, cause of land subsidence in the Savannah area.

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Contents

GSA Engineering Geology Case Histories

Engineering Geology Case Histories Number 4

Parker D. Trask
Parker D. Trask
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George A. Kiersch
George A. Kiersch
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Geological Society of America
Volume
4
ISBN electronic:
9780813759296
Publication date:
January 01, 1963

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