CAPWAT – Capacity reduction in wastewater pressure mains

The CAPWAT II project focuses on more reliable pressurized wastewater transport and consequently contributes to fewer Combined Sewer Overflows, smaller design uncertainties, better decisions and more efficient operation. Pressurized wastewater mains are subject to significant capacity losses caused by gas pockets in declining sections, such as inverted siphons under channels, motorways or railways. The gas pocket head loss is approximately equal to the height of the gas pocket, which creates an unacceptable capacity reduction in transportation pipelines in urbanised delta areas, which were designed with a negligible static head. This R&D project is carried out by the Industrial Hydrodynamics department of Deltares and Delft University of Technology in close co-operation with 16 co-funding partners: 10 waterboards, 3 consultants, 1 pump manufacturer, Stowa and the Ministry of Economic Affairs.

Scientific Challenge  

• To integrate recent developments in turbulence and multiphase flow research to solve an urgent problem in urbanised delta areas
• To develop a numerical model which is complex enough to capture the relevant multiphase fluid dynamics, but still simple enough to be incorporated in existing design tools
• To transfer the results into practical design and operational guidelines

Research goals

• Detection of gas pockets during Dry Weather Flow conditions
• Multiphase flow simulation of gas pocket transport in inverted siphons
• Model validation with large-scale lab and field measurements
• Guidelines for hydraulic design and operational control of wastewater mains