Weeki Wachee River System Recommended Minimum Flows and ...

Attachement 3. – Sharps Ferry Well
Potential Impacts to Sharp’s Ferry Well
The Sharp’s Ferry well has been used to monitor Upper Floridan aquifer water levels since
1947. The well measurements were discontinued in 2002. Because this monitor well has the
long history of recorded water levels, it makes an excellent candidate to use as a surrogate to
observe long-term climatic variability in west-central Florida.
The peer review panel on the Upper Hillsborough River indicated that the MFL report for Crystal
Springs did not provide enough support that the Sharp's Ferry well represented an area of
relatively little anthropogenic influence. To address that issue, the USGS Mega Model was
utilized to predict water level drawdown in the Upper Floridan aquifer in the vicinity of the
Sharp’s Ferry well under current withdrawal conditions (Figure 1) The Mega Model 1 withdrawals
were 55.2 mgd for Marion County using the 1993-94 well package. Estimated and metered
groundwater withdrawn in the County averaged 54.2 mgd for the three-year period from 2001-
2003. The model predicts a decline of 0.3 ft in the Upper Floridan aquifer due to existing
withdrawals in the area.
In addition to the model run, existing 2002 water use near the Sharp’s Ferry was plotted and is
illustrated in Figure 2. Closest groundwater withdrawals are located two miles to the northeast
and they average less than 0.1 mgd. The City of Ocala municipal wellfield withdrawals, which
averaged 12 mgd in 2002, are located approximately seven miles west of the Sharp’s Ferry
well.
As a final tool to measure potential impact to the Sharp’s Ferry water level, a cumulative sum
graph was created of annual rainfall versus mean annual water level from the Sharp’s Ferry
well. (Figure 3). In the cumulative sum analysis, any major deviation in slope that occurs for
more than five years would indicate an influence other than rainfall affecting water levels in the
well. To make the analysis more sensitive to potential changes, 30 feet was subtracted from
each year’s water level at the Sharp’s Ferry well. The plot indicates no significant deviation in
slope suggesting climatic influences dominate the historic fluctuation of water levels at this well.
1 Sepulveda, N. 2002. Simulation of Ground-Water Flow in the Intermediate and Floridan
Aquifer Systems in Peninsular Florida, U.S. Geological Survey WRI Report 02-4009, 130 p.
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