The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
of the river between the dam and Sulphur Springs, as this is where flow from the spring
has its greatest effect on salinity distributions, density gradients, and DO
concentrations. The results presented below are taken from SWFWMD data collection
at fixed location stations conducted for the re-evaluation of minimum flows for the Lower
Hillsborough River.
The effect of four rates of freshwater flow on salinity and DO in the river above Sligh
Avenue are shown in Figures 3-24 A though D. The plot for Nov 21, 1996 was recorded
when there was no flow at the dam and flow from Sulphur Springs was 29 cfs (Figure 3-
24A). Salinity values at stations just below the dam (above km 14.7) were near 9 ppt,
with no difference between surface and bottom values. Further downstream surface
salinity values were lower, reflecting the effect of Sulphur Springs on shallow layers.
The salinity of bottom waters increases to values between 15 and 19 ppt, however,
resulting in a highly stratified water column in this reach of the river. Dissolved oxygen
concentrations show the effect of this density stratification, as bottom DO
concentrations drop to hypoxic levels (