Oxygen-Sag in a Tidal River

In the present work, freshwater flow in a tidal river is incorporated in a dimensionless solution of the derived equations for BOD and DOD and a comparison is made between the profiles obtained with both a constant and a time variable dispersion coefficient, E. The time variation of E is expressed as the ratio of the absolute value of the oscillating velocity to a reference velocity. Flow data from the Potomac River, Washington are used in the computer programs and illustrative BOD and DOD profiles are presented. Increases in the river discharge decrease and translate downstream the points of maximum BOD and DOD. Time variation of the dispersion coefficient smooths both BOD and DOD profiles, as opposed to a constant value of E, and reduces their peak values. Decisions on the maximum DOD associated with a specific effluent outfall which are based on a solution with a constant E appear, therefore, to be conservative.