OPTIMUM USE OF HOLDING TANKS TO AVOID POLLUTION SURGES IN NARROW ESTUARIES

It is common practice to discharge sewage and industrial effluents into estuaries. The absence of an advective current at the turn of the tide may allow the immediate pollution level close to the source (or the subsequent dissolved oxygen sag) to build up to unacceptably high levels. One way of alleviating the worst excesses is to use holding tanks and to vary the rate of discharge. This paper gives explicit formulae for the optimal rate of discharge in narrow estuaries to match the dilution capacity of the tidal flow and thereby to minimize the maximum pollution level. It is also shown how oxygenation of the discharge can be optimized to satisfy a specified limit upon the permissible maximum oxygen sag.