Hydrogeology and Groundwater Quality of Highlands ... - USGS

12 Hydrogeology and Groundwater Quality of Highlands County, Florida
The lower limits of evapotranspiration occur in areas
that have well drained soils and deep water tables. Tibbals
(1990) related evapotranspiration to water-table depth in
east-central Florida and estimated that the minimum rate
of evapotranspiration occurred where the water table was
greater than 13 ft below land surface. At a Bahia grass and
palmetto site in eastern Polk County where the water table
is shallow, actual annual evapotranspiration ranged from
30.2 to 40.2 in/yr during 2001–07 (D.M. Sumner, U.S.
Geological Survey, written commun., 2009). In a deforested
area along the Lake Wales Ridge in Orange County, Sumner
(1996) determined that annual evapotranspiration was
about 27 inches. This site probably represents a minimum
evapotranspiration value for central Florida because of the
presence of shallow-rooted plants, rapidly drained soil, and a
relatively deep water table.
Water Use
Highlands County relies heavily on groundwater for its
water supply, and groundwater use has increased substantially
over the past several decades. In 1965, groundwater with-
GROUND-WATER USE, IN MILLION GALLONS PER DAY
180
160
140
120
100
80
60
40
20
0
160
140
120
100
80
60
40
20
TOTAL GROUNDWATER USE
AGRICULTURE
0
1960 1970 1980 1990 2000 2010
YEAR
Figure 9. Historical groundwater use in Highlands County, 1965-2005. From Marella (2009).
drawals in the county were about 37 Mgal/d (fig. 9). In 2000,
withdrawals totaled about 157 Mgal/d, an increase of more
than 300 percent (Marella, 2009). In 2005, total groundwater
use declined to about 107 Mgal/d, largely as a result of above
average rainfall of about 60 inches. The dominant factor causing
this increase in water use over the past 40 years has been the
expansion of agriculture or, more specifically, the expansion of
the citrus industry. Water use from agricultural irrigation has
increased dramatically, from 32 Mgal/d in 1965 to 95 Mgal/d
in 2005 (fig. 9). Water use for public supply, the second largest
water-use category for Highlands County, increased from 4 to
about 9 Mgal/d from 1965 to 2005 (Marella, 2009).
Of the six water-use categories, agricultural irrigation
accounted for the largest percentage of groundwater withdrawn
in 2005 (fig. 10). Of the total groundwater withdrawn, about 89
percent was used for agriculture, 8 percent for public supply,
2 percent for recreational irrigation, 1 percent for domestic,
and less than 0.1 percent for both commercial/industrial and
thermoelectric power generation. The Upper Floridan aquifer is
the primary source of water supply, but the surficial aquifer and,
locally, the intermediate aquifer system provide drinking water
for rural domestic wells and some irrigation and public supply.
GROUND-WATER USE, IN MILLION GALLONS PER DAY
10
9
8
7
6
5
4
3
2
1
0
3.0
2.5
2.0
1.5
1.0
PUBLIC SUPPLY
RECREATIONAL IRRIGATION
DOMESTIC
COMMERCIAL/INDUSTRIAL
0.5
THERMOELECTRIC
0
1960 1970 1980 1990 2000 2010
YEAR