The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
3.11.2 Thermal characteristics of the Lower Hillsborough River
Average yearly water column temperatures for the period of record at four stations in
the Lower Hillsborough River measured by the EPCHC range from 24.13 to 24.80 o C
(Table 3-4), which are near the average temperature for Sulphur Springs. Mean water
temperatures are similar among stations; the largest difference in annual means is for
middle depths (0.94 o C), while surface means vary by only 0.31 o C.
Table 3-4 Mean water temperatures ( 0 C) for four stations monitored by the
Environmental Protection Commission of Hillsborough County
for 1999-2002.
Station Kilometer Surface Middle Bottom Water column
mean
Platt 24.5 24.6 24.5 24.5
Columbus 24.2 24.9 25.0 24.7
Sligh 24.2 25.0 25.2 24.8
Rowlett 24.2 24.1 24.1 24.1
Despite this similarity in mean values, spatial and seasonal temperature variations are
more pronounced and show a consistent pattern among stations. Box and whisker plots
of monthly water column temperatures for the period of record at the four EPCHC sites
are shown in Figure 3-28. Median monthly temperatures (Appendix F) are at or below
20 o C for December, January and February of the year at the Platt, Columbus, and
Rowlett stations. These represent months when there would be a frequent need for
thermal refuge for manatees in the lower river.
Median water column temperatures at Sligh Avenue remain near or above 20 o C for
these months, indicating the reach of the river below Sulphur Springs tends to stay
warmer during the winter. The period for Sligh Ave shown in Figure 3-28 is considerably
shorter than the other stations, which could affect these results. To correct for
differences in period of record, monthly mean and minimum water temperatures for the
1999 – 2002 at these stations are plotted in Figures 3-29 A and B. Median and
minimum temperatures at Sligh are again warmer than the other stations in the winter
months, indicating this reach of the river may have thermal advantages for manatees
and other cold sensitive species. During summer months, median water temperatures in
the upper reaches (Rowlett and Sligh) remain cooler than the lower reaches, probably
reflecting the flow of water from Sulphur Springs and also the Hillsborough River
reservoir. Seasonal water temperature fluctuations were greatest at Platt station near
the mouth of the river, which is more closely affected by water temperatures in Tampa
Bay.
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