chapter  13
Environmental aspects of wastewater hydraulics
ByW.H. Hager
Pages 22

ABSTRACT: Two basic sewer flow types are considered in this research, namely transitional and supercritical flows related to wastewater hydraulics. For transitional flows from the sub-to the supercritical regime as occur for instance on spillways, the free surface and velocity profiles are known to be continuous, whereas the bottom pressure profiles may become rapidly-varied, depending on the degree of curvature variation. A similar flow pattern is established at slope breaks from mild to steep slopes associated with sewer flows. The hydraulics of these are discussed both for the open rectangular as also the closed circular profiles. Because curvature effects are demonstrated to be small in terms of free surface effects, the hydraulic approach may be employed for the latter case, resulting in particular in an expression for the minimum tailwater sewer diameter to inhibit choking flow conditions. The second problem presented relates to junction manholes under supercritical approach flow, for which again choking may become a high risk, associated with ‘geysering’ flow. These manholes include the through-flow and the bend manholes as particular cases, so that a general analysis is amenable, based on laboratory observations and a systematic data analysis. In contrast to standard knowledge, the maximum filling ratios of the approach flow and the discharge capacities of the three manhole configurations are detailed, along with a design basis that was successfully laboratory-tested. The results of both basic special manholes may thus be considered a significant advance in sewer hydraulics, by which undesirable sewage loss onto public space is prevented.