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Water-quality characteristics of inflow to and outflow from Falls Lake, North Carolina, 1982-87

Water-Resources Investigations Report 90-4097
By R.G. Garrett

Abstract

Falls Lake, an 11,300-acre reservoir in the north-central Piedmont of North Carolina, was completed in December 1983. Hydrologic data were collected at seven inflow sites and one outflow site between 1982 and 1987 to define water-quality characteristics. Data include streamflow data and 56 physical and chemical characteristics of streamwater. Concentrations of some constituents at inflow sites were as much as 10-to 110-times greater than background concentrations in streams relatively unaffected by man. At the outflow site, these constituents generally were 2-to 3-times greater than background values. The minimum dissolved-oxygen concentration measured at an inflow site was 0.6 mg/L, whereas the minimum concentration measured at the outflow site was 6.7 milligrams per liter. Significant differences in other physical characteristics between inflow and outflow sites include a reduction in maximum concentration of suspended sediment from 1,850 milligrams per liter in an inflow sample to 100 milligrams per liter in an outflow sample, and a reduction of maximum specific-conductance values from more than 1,200 microsiemens/centimeter in an inflow sample to 140 microsiemens per centimeter in the outflow. The maximum concentration of total nitrogen at inflow sites was 33 milligrams per liter compared with 4.5 milligrams per liter at the outflow site. Similarly, the maximum total phosphorus concentration at inflow sites was 20 milligrams per liter, but 0.22 milligrams per liter at the outflow site. Average annual loads of nitrogen and phosphorus in the outflow were as much as 66 percent and 21 percent of inflow loads, respectively. Although maximum inflow yields were 13 tons per square mile for nitrogen and 2.8 tons per square mile for phosphorus, yields of these constituents at the outflow site were about 1.1 and 0.05 tons per square mile, respectively.

Garrett, R.G., 1990, Water-quality characteristics of inflow to and outflow from Falls Lake, North Carolina, 1982-87: U.S. Geological Survey Water-Resources Investigations Report 90-4097, 56 p.