An interim report on flows in the lower Roanoke River, and water quality and hydrodynamics of Albermarle Sound, North Carolina, October 1989-April 1991

Abstract

In 1990, a 3-year investigation was begun in North Carolina to: (1) develop a model for computing flows in the lower 67 mi of the Roanoke River; (2) characterize water-quality conditions in Albemarle Sound; and (3) describe the circulation regime of Albemarle Sound, particularly in relation to inflows. This report summarizes data and results obtained during the first year of the study. The water level in Albemarle Sound may affect flows in the Roanoke River as far as 60 mi upstream from the mouth of the river. The presence of higher water levels downstream relative to those upstream indicates that reverse flows likely occurred in the lower 20 mi of the Roanoke River in October and December 1990. A one-dimensional, unsteady flow model has been calibrated and validated for a 30-mi segment of the lower Roanoke River. Simulated and observed water levels typically differed by less than 0.5 ft, and simulated flows were generally within 10% of observed values. Near-surface and near-bottom specific conductances, near-surface water temperature, and near-surface, mid-depth, and near-bottom dissolved-oxygen concentrations were monitored at 10 locations in Albemarle Sound from October 1989 to April 1991. Observed salinities ranged from virtually 0 to more than 9 ppt, and maximum observed water temperatures were about 32C. Dissolved oxygen concentrations ranged from supersaturated to hypoxic conditions. The daily range in dissolved-oxygen concentrations was typically larger during the summer months than during the rest of the year, and the lowest dissolved-oxygen values were observed during the summer.