Optimal strategies for discharging pollutants into narrow estuaries

Strategies for discharging pollutants into estuaries have been proposed in the literature. Here, a one-dimensional model is used to compare different strategies for discharging both conserved and decaying pollutants into narrow estuaries where the pollution outlet is more than one tidal excursion from the estuary mouth. The range of usefulness of the various strategies is defined. In particular it is seen that although the absence of a diluting flow at the turn of the tide can cause peaks in the pollutant concentration, sophisticated strategies designed to avoid these peaks are only really worthwhile in estuaries which carry a relatively large fresh water flow. In the more common situation of a very small fresh water flow these peaks become a local effect around the pollution outlet and the expedient of simply turning off the pollutant flow when the tide is turning is nearly as effective as any other method of eliminating concentration peaks. So far as pollution with organic matter is concerned, it is seen that the maximum dissolved oxygen deficit is usually quite insensitive to the discharge strategy.