Hydrogeology and Groundwater Quality of Highlands ... - USGS

Table 1. Results of trend anaysis for rainfall stations and long-term observation wells in Highlands County.
evapotranspiration, defined as the combined processes of
evaporation of water from land and water surfaces and
transpiration by plants. The rate of evapotranspiration is
controlled by several factors, primarily net solar radiation,
wind speed, relative humidity, surface area of open water
bodies, density and type of vegetation cover, available
soil moisture, root depth, water-table depth, and season.
The term potential evapotranspiration is a measure of the
ability of the atmosphere to remove water from the surface
through the processes of evaporation and transpiration
assuming no limit on water supply. Actual evapotranspiration
is the quantity of water that is actually removed from
a surface due to the processes of evaporation and transpiration.
Actual evapotranspiration is always less than or equal
to potential evapotranspiration.
Estimated average monthly potential evapotranspiration
from 1996 to 2007 for Highlands County is shown in figure 8
(Michael Holmes, U.S. Geological Survey, written commun.,
2009). The methods used to create these values are described
in Jacobs and others (2008). Average monthly potential
evapotranspiration is lowest in December (1.8 inches) and
is followed by rapidly increasing rates with increasing solar
radiation and temperatures during the spring. The highest
monthly evapotranspiration (greater than 6 inches) occurs from
May to August, and then decreases steadily into December.
Although difficult to quantify, the upper and lower limits
of annual evapotranspiration can be estimated. The upper
limit of evapotranspiration is approximately equal to the rate
at which water can evaporate from a free-water surface and
is highest in the lakes, swamps, and marshes where water is
near or above land surface much of the time (Tibbals, 1990).
Description of Study Area 11
[Locations of wells and rainfall stations shown in figure 11. USGS, U.S. Geological Survey; SA, surficial aquifer; IAS, intermediate aquifer system;
UFA, Upper Floridan aquifer; NA, not applicable]
Rainfall
station
(RS) or well
number
USGS site
identification
number
Station name Aquifer
Bottom of casing
(feet below land
surface)
Depth of well
(feet below land
surface)
Period of
record
analyzed
p-value
Kendall’s
tau
RS Not applicable Archbold Biological Station NA NA NA 1932-2007 0.7212 -0.0285
RS Not applicable Avon Park NA NA NA 1931-2007 .2952 -.0817
1 270157081203101 H-15A SA 19 23 1975-2008 .1494 .0129
43 271226081194301 Bairs Den SA 28 35 1977-2008 .0000 .0906
53 271330081113401 HIF-37 Sun Ray Farms UFA 619 1,450 1982-2008 .0074 -.2880
67 271559081242501 Lake Grove Rd. SA 13 23 1972-2008 .0000 -.0629
88 272207081260402 ROMP 28 Intermediate IAS 370 420 1996-2008 .0009 .0963
89 272207081260404 ROMP 28 Suwannee UFA 485 600 1996-2008 .0000 .1194
103 272504081120101 H-11A SA 13 16 1975-2008 .0092 -.0226
105 272512081122901 HIF-13 Meztger UFA NA 1,106 1982-2008 .6376 -.0509
126 272835081251701 Maranatha Village UFA NA 841 1979-2008 .8061 -.0239
166 273704081245501 Richards IAS 140 260 1986-2008 .0687 -.1889
Actual lake evaporation measured at Lake Starr in Polk County
during August 1996 to July 1998 was 57.08 and 55.88 in/yr,
respectively (Swancar and others, 2000). Also defining the
generalized upper limits of evapotranspiration is the estimated
potential evapotranspiration for the county from 1996 to 2007
(fig. 8). Average total potential evapotranspiration for this
period was 53.17 in/yr (Michael Holmes, U.S. Geological
Survey, written commun., 2009).
POTENTIAL EVAPOTRANSPIRATION, IN INCHES
7
6
5
4
3
2
1
0
Average annual potential evapotranspiration
1996-2007 = 53.17 inches
J F M A M J J A S O N D
MONTH
Figure 8. Average monthly potential evapotranspiration for
Highlands County, 1996-2007. From U.S. Geological Survey (2009).