Modelling mixed flow conditions within building and local drainage systems

Piped drainage systems form the backbone of urban drainage infrastructure, both in terms of foul and surface water drainage. The piped systems located in the upstream reaches of urban drainage networks include those installed within buildings and those local systems that connect buildings and their curtilages to the main sewer network; examples of local systems range from those serving a single residential property to those draining large retail parks. The purpose of this research is to improve the simulation of flow conditions within such systems, and hence facilitate the development of the integrated design methodologies required to meet the extra demands associated with the future impacts of climate change and water conservation measures.Flow conditions within building and local drainage systems are often complex, partly due to the highly unsteady nature of system inflows and partly due to their relatively complex and compact layouts; in particular, such systems commonly experience mixed flow conditions, characterised by both free surface and full bore flow regions separated by a hydraulic jump. In spite of this complexity, and the underlying importance of such systems to all sections of society, there are currently no numerical models available to accurately simulate the full range of mixed flow conditions that occur within building and local drainage systems. Without the ability to simulate such conditions, the challenges presented by system design to accommodate transitional flows can not be fully understood, and thus performance benefits remain unrealised. Whilst this situation is undesirable under current loading conditions, the consequences of these shortcomings is bound to increase in the future. It is now generally accepted that climate change will increase the frequency and severity of extreme rainfall events, and will hence result in increased surcharging of drainage systems conveying stormwater. Additional demands will also be placed on building and local drainage infrastructure due to changing demographics, increasing urbanisation and decreasing confidence in the long term viability of existing water supplies; these factors will lead to an increased emphasis on water conservation, as already highlighted by imminent changes to UK Building Regulations (which are likely to set minimum standards for water efficiency within buildings). There is clearly a very real need for enhanced tools to enable the wide range of stakeholders to develop the type of integrated designs necessary to meet both current and future performance requirements. The proposed research aims to meet this need by developing improved simulation models. The project will commence with a benchmarking exercise to assess the state of the art of mixed flow modelling. This will include the identification and experimental quantification of the key physical process, as well as a thorough assessment of existing techniques and their suitability to building and local drainage applications. These initial investigations will help drive model development activities, which will concentrate on formulating a novel numerical technique for the simulation of mixed flow conditions within small-medium diameter piped drainage systems (up to approximately 200mm). The developed technique will be incorporated into 1-D finite difference models for the simulation of conditions within building and local drainage systems. Dissemination of project findings will be critical in order to persuade relevant stakeholders of the benefits associated with the developed techniques and models, and to encourage uptake of the project recommendations and tools. In addition to traditional academic dissemination routes (journal and conference papers), project outcomes will also be publicised to a wider audience through presentations and seminars to professional bodies, industry organisations and wider research initiatives.