Time-series plots of dissolved-oxygen
concentrations were determined for various simulated
hydrologic and point-source loading conditions along a
free-flowing section of the Catawba River from Lake
Wylie Dam to the headwaters of Fishing Creek
Reservoir in South Carolina. The U.S. Geological
Survey one-dimensional dynamic-flow model,
BRANCH, was used to simulate hydrodynamic data
for the Branched Lagrangian Transport Model. Waterquality
data were used to calibrate the Branched
Lagrangian Transport Model and included
concentrations of nutrients, chlorophyll a, and
biochemical oxygen demand in water samples
collected during two synoptic sampling surveys at
10 sites along the main stem of the Catawba River and
at 3 tributaries; and continuous water temperature and
dissolved-oxygen concentrations measured at
5 locations along the main stem of the Catawba River.
A sensitivity analysis of the simulated dissolved-oxygen
concentrations to model coefficients and data
inputs indicated that the simulated dissolved-oxygen
concentrations were most sensitive to watertemperature
boundary data due to the effect of
temperature on reaction kinetics and the solubility of
dissolved oxygen. Of the model coefficients, the
simulated dissolved-oxygen concentration was most
sensitive to the biological oxidation rate of nitrite to
nitrate.
To demonstrate the utility of the Branched
Lagrangian Transport Model for the Catawba River, the
model was used to simulate several water-quality
scenarios to evaluate the effect on the 24-hour mean
dissolved-oxygen concentrations at selected sites for
August 24, 1996, as simulated during the model
calibration period of August 23 27, 1996. The first
scenario included three loading conditions of the major
effluent discharges along the main stem of the Catawba
River (1) current load (as sampled in August 1996);
(2) no load (all point-source loads were removed from
the main stem of the Catawba River; loads from the
main tributaries were not removed); and (3) fully
loaded (in accordance with South Carolina Department
of Health and Environmental Control National
Discharge Elimination System permits). Results
indicate that the 24-hour mean and minimum
dissolved-oxygen concentrations for August 24, 1996,
changed from the no-load condition within a range of
- 0.33 to 0.02 milligram per liter and - 0.48 to
0.00 milligram per liter, respectively. Fully permitted
loading conditions changed the 24-hour mean and
minimum dissolved-oxygen concentrations from - 0.88
to 0.04 milligram per liter and - 1.04 to 0.00 milligram
per liter, respectively. A second scenario included the
addition of a point-source discharge of 25 million
gallons per day to the August 1996 calibration
conditions. The discharge was added at S.C. Highway
5 or at a location near Culp Island (about 4 miles
downstream from S.C. Highway 5) and had no
significant effect on the daily mean and minimum
dissolved-oxygen concentration.
A third scenario evaluated the phosphorus
loading into Fishing Creek Reservoir; four loading
conditions of phosphorus into Catawba River were
simulated. The four conditions included fully permitted
and actual loading conditions, removal of all point
sources from the Catawba River, and removal of all
point and nonpoint sources from Sugar Creek.
Removing the point-source inputs on the Catawba
River and the point and nonpoint sources in Sugar
Creek reduced the organic phosphorus and
orthophosphate loadings to Fishing Creek Reservoir by
78 and 85 percent, respectively.
