Hydraulics of Rectangular Clarifiers

Abstract

A simple model of the steady, two‐dimensional water flow through rectangular clarifiers is derived in the absence of wind and stratification. The water flow, or “hydraulics,” consists of steady velocity and turbulence intensity, and both properties are considered in the analysis. The inlet, settling, and outlet zones are marked by turbulent jet, uniform, and converging flow fields, respectively. Existing analytical solutions and turbulent jet data are invoked to generate a composite, independently calibrated set of velocity profiles that compare favorably with data from clarifier studies. The depth‐averaged turbulence intensity is an integral part of the present model and is shown to be generated by the inlet jet flow rather than bottom and wall friction. The intensity governs sediment resuspension in accordance with the Shields criterion for fine sediment, which is cast into a useful constraint on the clarifier geometry.