FLUSHING TIMES FOR THE PROVIDENCE RIVER BASED ON TRACER EXPERIMENTS

The flushing time of the Providence River was estimated using three di fferent data sets an three different methodologies. Dye concentrations were measured following instantaneous dye releases during wet weather experiments performed by the Narragansett Bay Project between October 1988 and June 1989. These data were analyzed to obtain flushing time estimates. Salinity measurements collected during the Sinbadd (Samplin g In Narragansett Bay All During the Day) cruises, Spray (Sampling the Providence River All Year) cruises, and wet weather experiments were used with the fraction of fresh water method and box model to calculat e flushing time. The Sinbadd cruises performed 4 seasonal surveys at 2 2 stations in Narragansett Bay during 1986 to obtain a view of the who le Narragansett Bay with respect to the concentrations of nutrients an d trace metals. The Spray cruises collected data in the Providence Riv er at 10 stations to determine the relationship of nutrients and trace metals concentrations in the Seekonk and Providence rivers as a funct ion of point source inputs. Based on the flushing time estimates, an e xponential relationship between freshwater inflow and flushing time wa s developed (correlation coefficient of 0.826). The flushing time rang ed from 0.8 d at high (90 m3 s-1) freshwater inflows to 4.4 d at low ( 20 m3 s-1) freshwater inflows. The average flushing time of the Provid ence River was estimated as 2.5 d for the mean freshwater inflow of 42 .3 m3 s-1.