ANALYSIS OF WIND-INDUCED AND SHIP-INDUCED SEDIMENT RESUSPENSION IN DULUTH-SUPERIOR HARBOR

Suspended solids and ammonium concentration profiles measured at five locations in Duluth-Superior Harbor during July-October 1985 were anal yzed to quantify wind and ship effects on sediment resuspension and re sulting harbor water quality. Wind components from the SE quadrant cor related strongly with depth-averaged suspended solids concentrations t hat were unaffected by ship passage or thermal stratification. Winds f rom that quadrant have the largest fetch in the harbor. The highest co rrelation (r2 = 0.93) was with the 6-hour average of the ESE wind velo city component. Multiple linear regression analysis of data from post- ship passage concentration profiles yielded numerical estimates of set tling velocities of 0.08 to 0.25 cm s-1, typical of ship-resuspended s ediments, and vertical eddy diffusivities of 4 to 13 cm2 s-1. The resu lts suggest that ambient vertical eddy diffusivities in the harbor are less than 4 cm2 s-1 in the absence of ship passages and with winds le ss than 5 m s-1 (10 knots).