Hydraulic Modelling of Collection Networks Study Group 2: Maths Foresees project report

This report describes the response to the ’hydraulic modelling of collection networks for civil engineering applications’ challenge set by Sweco at the second Environmental Modelling in Industry Study Group. The solution was developed in workshops hosted by the Turing Gateway to Mathematics at the Newton Institute in Cambridge on 3-6 April 2017. The industry standard modelling practice of omitting the explicit representation of the collection network, road gullies for example, was examined by the team. This approach was found to significantly underestimate the exchange of water between 2D and 1D model domains. A solution was proposed in which the gullies are replaced by a line source/sink of carefully chosen intensity in order to represent the lumped behaviour of multiple road gullies. Two separate 2D surface models, based on the full shallow water equations and their diffusive wave approximation respectively, were used to test the solution. By comparing the results of simulations in which the gully sinks are explicitly modelled with those containing a line sink the performance of the parametrisation was found to be excellent. Future test cases are proposed, most importantly involving flows with strong coupling between the 2D surface flow and 1D sewer flow, which should be carried out before implementation of the parametrisation is recommended.