Critical Oxygen Deficit for Bank Outfall

A two-dimensional equation for the mass balance of dissolved oxygen (DO) is integrated numerically to obtain the distribution of oxygen deficit resulting from a bank outfall of BOD in a rectangular channel. The results can be categorized into three cases. In Case I for rapid transverse mixing of the BOD and DO, uniform DO levels occur within most cross sections and the critical deficit is the same as that calculated by the traditional one-dimensional representation. In Case II, the transverse mixing of the BOD and DO is slower and the critical deficit is both higher in magnitude and located upstream relative to the values obtained from the one-dimensional computation. Case III represents the transition range between Cases I and II. Criteria are given for determining which case is applicable for a given set of conditions. The results for the magnitude and location of the critical deficit are given in graphical form in relation to dimensionless parameters.