In the UK, there is a growing requirement for hydraulically modelling drainage systems to assess how it copes with extreme events. The government, approving bodies and wider society, demand protection from both pluvial and fluvial flooding caused by excess water in order for the population to live safely in new developments or retrofits. These drainage systems are also required to be sustainable and resilient for the predicted impact of climate change. To this end and to support approving authorities, engineering consultancy firms, developers, research institutes and universities worldwide, Causeway now offers a drainage design and modelling software called Flow for a complete drainage design solution.

Flow uses the state-of-the-art 1D Storm Water Management Model 5 (SWMM) engine for hydraulically analysing any new or existing storm drainage systems. EPA SWMM 5, which is made by the United States Environmental Protection Agency (EPA), is a public domain software. At Causeway, we have integrated this software with Flow after extensive work in making SWMM 5 UK specific. SWMM 5 is a dynamic rainfall-runoff-routing simulation model designed to calculate the quantity of the flow generated with each contributing area and tracks the flow rate, flow depth and quantity of water in the drainage systems during the simulation period divided into user-definable multiple time steps. The drainage systems can constitute, closed pipes, open channels, wide range of storage/infiltration structures, SuDS structures, pumps, offices, weirs, several variable third party flow controls and other products that constitute a drainage network.

SWMM 5 is designed with a flexible set of hydraulic modelling capabilities to deal with various flow regimes such as surcharging, channel storage, backwater, reverse flow, pressurized flow and surface ponding. Our Flow software utilises SWMM by defining the UK specific runoffs from each contributing area as an input hydrograph. Flow then uses SWMM’s dynamic wave routing method, which solves the complete one-dimensional Saint Venant flow equation to simulate the transport of water through the drainage systems, producing the most theoretically accurate results. These equations consists of the continuity and momentum equations for conveyance systems and a volume continuity equation at nodes. Conduits and flow controls are modelled as links and Manholes and storage/infiltration structures are modelled as storage units in SWMM and thereby Flow. The method also employs the Manning equation to relate flow rate to flow depth and bed friction slope until the pipes become pressurises at which point the Darcy-Weisbach equation is used instead.

Flow is built on the modified rational method for sizing any conveyance system, then deploys the SWMM engine for hydraulically analysing any drainage system as per UK requirements. These are the reasons why we at Causeway are confident that Flow is one of the most complete, robust and state-of-the-art drainage design and modelling software systems available for the UK market.


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