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Open File Report: Seismic Reflection Surveys |
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Seismic Investigations |
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Orange Lake occupies an area of north central Florida in Alachua county
that is characterized by shallow, flat bottomed lakes, level prairies and
streams that are swallowed by dolines. Historically, an extensive citrus
industry flourished until a series of hard freezes ruined the groves. The
lake is nationally renowned for sports fishing but fluctuations in lake
stage and growth of aquatic weeds have hampered this industry. Currently,
many alternatives being considered for managing lake level (Robison, 1994).
In August 1956, Orange Lake had receded to the lowest stage recorded:
50.06 feet relative to the National Gauge Vertical Datum (NGVD). At this
stage there were only 5,000 acres of submerged area. The lake reached a
high stage of 61.5 feet NGVD in November 1941 (Pirkle and Brooks, 1959),
when approximately 16,000 acres were submerged. A "normal" stage is
considered to be 58 feet NGVD (Jessen, 1972).
Though lake stage correlates with rainfall (Jessen, 1972; Pirkle and
Brooks, 1959; Robison, 1994) a doline(s) in the southwest area of the lake
at the Heagy-Burry park was observed actively draining Orange Lake at a
rate of 12 million gallons per day (mgd) (Roland 1957). On August 22, 1992,
divers Rick Spechler of the U.S. Geological Survey and William Wilson of
Subsurface Evaluations, Inc. voluntarily performed a reconnaissance dive to
measure the loss of water through the doline(s). They estimated that
approximately 5 cubic feet per second (cfs) were draining into two separate
fissures (Speckler and Wilson 1992). Another estimate was made by IFAS
(Haller and Hoyer, 1992) by constructing a temporary weir around the entire
area believed to be affected by the doline(s). A flow of 37 cfs was
calculated from the measurements made in the weir opening.
Attempts to isolate the doline(s) with fill and sand bag dams were
attempted in 1957 (Jessen, 1972). These attempts, along with heavy rains,
increased the lake stage to 56 feet NGVD by the end of 1957. When the
lake stage rose however, the dam slumped into the doline. By 1964, the
lake stage had again lowered and concerned citizens attempted to fill the
doline(s) with fill and discarded automobiles. Again, heavy rains related
to hurricanes caused the lake stage to rise. Several of the lake level
management alternatives that have recently been considered once again
include plugging the doline(s) or restricting the flow with a weir or dam
(Robison, 1994). The past experiences indicate that a more thorough site
evaluation and design phase will be needed to make these alternatives
successful.
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