The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
included inflows to the model domain from Sulphur Springs. Like the LAMFE model,
these scenarios were run assuming minimal rainfall and stormwater inflow below the
dam. Associated with these scenarios were water temperatures and salinity
concentrations of the inflow source. In order to allow predictions to be made under
varying scenario conditions, the model also allows precipitation and withdrawals from
the system to be modeled. Meteorological data (air temperature and wind speed and
direction) were input to estimate evaporation.
Water surface elevation boundary conditions were also specified at the downstream
limit of the model domain. Vertical temperature and constituent concentration profiles at
the boundaries were input. Surface heat exchange was also estimated based on the
input meteorological data, including air temperature, dew point temperature, wind speed
and direction, and cloud cover. Hydraulic parameters input to the model included a
horizontal dispersion coefficient for momentum and a horizontal dispersion coefficient
for temperature and constituents. These values were set to be constant over time and
over the entire spatial domain of the model. Bottom friction coefficient values were also
input to the model.
5.5.4 Model Construct
The grid system utilized in this study was based on that previously developed for the
LAMFE model. The grid system developed for the LAMFE model, as shown in Figure 5-
23, included 32 columns along the river length and 16 vertical layers. Column lengths
(distance along the river) varied, from 300 m in the upstream reaches of the river to
greater than 800 m at the mouth. We adopted this grid system, and then refined if
specifically for this study to provide greater resolution in the vicinity of the Sulphur
Springs outfall. Columns 12 at Sulphur Springs and column and 13 (downstream of
Sulphur Springs) of the LAMFE model were divided into 16 columns, each 50 m long
Figure 5-23). The remainder of the LAMFE grid construct was unchanged.
5.5.5 Model Input Data
The thermal model was run under two sets of ambient temperature conditions that
corresponded to two different time periods. These temperature conditions were based
on threshold water temperature values suggested by staff of the Florida Fish and
Wildlife Conservation Commission that are described in Chapter 4. The “coldest period”
was defined as that time when water temperatures in the Lower Hillsborough River were
the lowest observed during the period of record of monthly observations by the EPCHC
since 1974. The “thermal refuge period” was defined as a period when the continuous
recorders in the river and spring were operating (since 1999); water temperatures in the
river near Sulphur Springs were greater than 20° C; and temperatures in the river
upstream and downstream of Sulphur Springs were less than 20° C. Using temperature
data from these periods, the effects of various flow scenarios were evaluated by
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