Mathematical Modeling of Dissolved Oxygen in Mixed Estuaries

One of the basic difficulties in modelling DO in a given estuary is the uncertainities involved in the BOD and reaeration rates. The oxidation of both carbonaceous and nitrogenous substances simultaneously and their representation by first-order kinetics may be justified in estuaries. The carbonaceous and nitrogenous BOD rate coefficients have been determined from the standard BOD tests of estuary water samples by considering the two stages of BOD separately and by adjusting the time origin of nitrification stage. The available reaeration rate coefficient equations developed for nontidal systems and applied in modeling DO in tidal estuaries do not fully represent the tidal estuaries. A new reaeration rate coefficient equation has been developed for tidal systems. The proposed equation is related to the dispersion coefficient and is a function of flow depth and four-thirds power of tidal velocity.