Critical Point Method for Mixing Zones in Rivers

Abstract

Expressions for the coordinates of a critical point, occurring along a given lateral boundary of a limited use zone within a mixing zone below a bank outfall in a river channel, are developed. A family of curves is developed for a range of dimensionless coordinates of the critical point. An expression for allowable effluent concentration of a pollutant is obtained in terms of critical concentration and water quality criterion. A graphical procedure for determining the longitudinal boundary of a limited use zone is described. The predictions of the critical point method are validated using total residual chlorine distribution data from a natural stream. The application of the methodology is outlined in a step‐by‐step design procedure and illustrated by an example for ammonia. In general, the method is applicable to exponentially decaying nonconservative pollutants.