Hydraulic mixing and free chlorine residual in reservoirs

Abstract

Interior sampling of a reservoir illuminates its mixing characteristics and supports the assumption of stratification or partitioning. An extensive sampling study of reservoir water quality was conducted in Azusa, Calif. Primary emphasis was placed on providing a better understanding of the dynamics of hydraulic mixing and free chlorine residual concentration distribution in the reservoir. The reservoir approached completely mixed behavior with two exceptions: a degree of short‐circuiting between the inlet and outlet (which significantly affected the T 10 time) and the presence of a stagnant zone in the center core of the reservoir where there was less mixing and thus older water. These results support the assumption of stratification or partitioning in reservoirs. Regular field sampling is recommended to facilitate the effective management of distribution system water quality. In particular, interior sampling of reservoirs can provide useful information that could not be inferred otherwise.