Improving the Hydraulic Integrity to Separate the Sewer System in Hilly Regions Using a New Manhole Design

Abstract

The design of the sewer system in hilly regions has a different concept from other areas due to the high flow velocity generated in the system that characterises a sloped system. The flow velocity of sewage or stormwater in the sewer system is limited by design criteria, using minimum velocity to avoid settlement of suspended solids in the pipes and maximum velocity to keep the solute homogeneous (fluid and suspended solids) and avoid pipe erosion. Maintaining these limits of the velocity within hilly regions is challenging and designers usually use steep cascade manholes to dissipate the fluid flow energy. This paper presents a new manhole design to mitigate stormwater flow energy, which is more critical than sewage flow in such areas, and using the traditional normal steps manhole for the sewage chamber. The new manhole design includes two chambers, an inner chamber used as in the traditional manhole for sewage and an outer chamber used for stormwater flow. The hydraulic properties of the new manhole have been explored using a physical model in laboratory conditions and compared with traditional manhole performance. The laboratory results are used for validation and are compared with computational fluid dynamic model outputs of the new design. The hydraulic performance of the new design reveals improvement in decrease in the flow energy of stormwater and increase in the capacity of storage for the stormwater network.