Hydraulic flocculators, despite their superior plug-flow properties, negligible energy requirements and robust simplicity, are commonly perceived as being inflexible. Once built, it is argued, they do not provide the operational flexibility to compensate for flow fluctuations or changing raw water characteristics. The design procedure developed in this paper demonstrates the contrary, namely that hydraulic flocculators can be designed to satisfactorily cope with tapered velocity gradients, flow variations and water quality variations. The procedure is based on a two-step approach; the horizontal layout is first determined with average values for velocity gradient and water depth; then only the floor slope and exact water depths are determined to enable satisfactory flocculation for all design scenarios.

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