Surface-water quality and flow Modeling Interest Group
USGS, Water Resources Division
Stephenson Center, Suite 129
720 Gracern Road
Columbia, SC 29210-7651
Internet:
tfeaster@usgs.gov,
pconrads@usgs.gov
Phone: (803) 750-6103, (803) 750-6140
FAX: (803) 750-6181
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Citation:
Feaster, T.D. and Conrads, P.A., 1999, Characterization of water quality
and simulation of temperature, nutrients, biochemical oxygen demand, and
dissolved oxygen in the Wateree River, South Carolina, 1996-1998: U.S.
Geological Survey Water-Resources Investigations Report 99-4234, 90 p.
Figure 1. The Catawaba-Wateree River Basin, in North and South Carolina.
Figure 2. Locations of gaging stations and selected tributaries on the Wateree River, South Carolina.
Figure 3. Longitudinal profiles of dissolved-oxygen concentrations in the Wateree River, S.C., May-September 1996.
Analysis of long-term streamflow and water-quality data collected at two U.S. Geological Survey gaging stations suggests that no strong correlation exists between streamflow and dissolved-oxygen concentrations in the Wateree River. However, a strong negative correlation does exist between dissolved-oxygen concentrations and water temperature. Analysis of data from six South Carolina Department of Health and Environmental Control monitoring stations for 1980-95 revealed decreasing trends in ammonia nitrogen at all stations where data were available and decreasing trends in 5-day biochemical oxygen demand at three river stations.
The influence of various hydrologic and point-source loading conditions on dissolved-oxygen concentrations in the Wateree River were determined by using results from water-quality simulations by the Branched Lagrangian Transport Model (BLTM). The effects of five tributaries and four point-source discharges were included in the model. Data collected during two synoptic water-quality samplings on June 23-25 and August 11-13, 1997, were used to calibrate and validate the Branched Lagrangian Transport Model. The data include dye-tracer concentrations collected at six locations, stream-reaeration data collected at four locations, and water-quality and water-temperature data collected at nine locations. Hydraulic data for the Branched Lagrangian Transport Model were simulated by using the U.S. Geological Survey BRANCH one-dimensional, unsteady-flow model. Data that were used to calibrate and validate the BRANCH model included time-series of water-level and streamflow data at three locations. The domain of the hydraulic model and the transport model was a 57.3- and 43.5-mile reach of the river, respectively.
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 changes in the boundary concentration inputs of water temperature and dissolved oxygen followed by sensitivity to the change in streamflow. A 35-percent increase in streamflow resulted in a negative normalized sensitivity index, indicating a decrease in dissolved-oxygen concentrations. The simulated dissolved-oxygen concentrations showed no significant sensitivity to changes in model input rate kinetics.
To demonstrate the utility of the Branched Lagrangian Transport Model of the Wateree River, the model was used to simulate several hydrologic and water-quality scenarios to evaluate the effects on simulated dissolved-oxygen concentrations. The first scenario compared the 24-hour mean dissolved-oxygen concentrations for August 13, 1997, as simulated during the model validation, with simulations using two different streamflow patterns. The mean streamflow for August 13, 1997, was 2,000 cubic feet per second. Simulations were run using mean streamflows of 1,000 and 1,400 cubic feet per second while keeping the water-quality boundary conditions the same as were used during the validation simulations. When compared to the validation simulation using the mean streamflow for August 13, 1997, simulations indicated an increase in 24-hour mean dissolved-oxygen concentrations ranging from 0.26 to 0.47 milligram per liter and 0.12 to 0.30 milligram per liter, respectively (figure 4). A dissolved-oxygen budget was computed at branch 1 grid 9 (river mile 57.4) for the three simulations. The budgets indicated that the increase in simulated dissolved-oxygen concentrations was a result of increased reaeration from the changing hydraulic conditions at the different flows.
Figure 4. Longitudinal Profiles of 24-hour mean dissolved-oxygen concentrations for three different streamflow periods on the Wateree River, S.C., using water-quality boundary data from August 13, 1997.
A second scenario simulation was used to evaluate two point-source loading conditions to the system by comparing simulated dissolved-oxygen concentrations with a condition where there is no point-source discharge into the system. The changes in the 24-hour minimum and mean dissolved-oxygen concentrations for August 13, 1997, using the August 1997 validation flow conditions ranged from -0.08 to 0.05 milligram per liter. Setting all the point-source loadings to the current National Pollutant Discharge Elimination System permit ultimate oxygen demand levels changed the 24-hour minimum and mean dissolved-oxygen concentrations by a range of -0.26 to 0.01 milligram per liter (Figure 5).
Figure 5. Longitudinal profiles of 24-hour mean and minimum dissolved-oxygen concentration differences between the no-load condition and the to point-source loading conditions on the Wateree River, S.C., August 13, 1997.
A third scenario was run using the three different streamflow conditions from scenario one and setting point-source loadings to the current National Pollutant Discharge Elimination System permit ultimate oxygen demand levels. The results indicated increases in the 24-hour mean dissolved-oxygen concentrations ranging from 0.03 to 0.59 milligram per liter (figure 6). Once again, the influence of the atmospheric reaeration as the flows were reduced resulted in increased 24-hour mean dissolved-oxygen concentrations.
Figure 6. Longitudinal profiles of 24-hour mean dissolved-oxygen concentrations for three streamflow periods assuming fully permitted effluent loads at eight locations on the Wateree River., S.C.
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