Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | MAY 2015 | 37 In the know Technically speaking: hydraulic modelling H ydraulic modelling of sewer and urban drainage systems has come a long way in the last 30 years. While hydraulic equations and the other mathematical building blocks of modern hydraulic models have been around much longer, it is only in this period that computers have been brought to bear. The rapid progress of computer capabilities has been reflected in the development of hydraulic models and the expansion of their use. In the early stages of computer models, when simulation time was long and model set-up was time intensive, models were typically used to verify a solution and understand system performance. However, as run time reduced, model use has shi•ed towards design option development, allowing a modeller to efficiently assess and optimise numerous potential solutions. Drainage Area Plans use a catchment approach. They are typically risk-based and drive investment planning by assessing network performance with respect to hydraulic, structural, operational and environmental criteria. The process follows a staged approach from Scoping Study through to Model Build and Verification, and then on to Needs Identification and Option The march of the model Computing capabilities now allow a new level of integrated catchment modelling which can be harnessed to optimise sewer and drainage systems Development. Source data is commonly taken from corporate geographic information systems (GIS) and supplemented with specialist survey data. Anecdotal information from operations teams, and occasionally the public, is vital in building and verifying a model to create an accurate tool. To ensure that the model represents reality it is typically verified against a short-term flow survey. Following verification, the "needs" of the catchment are identified and solutions developed. Understanding the root cause of each problem is critical to developing an effective solution and lends itself to the development of a holistic solution in which a joined-up approach can potentially resolve multiple issues. The speed of simulation comes into its own at this stage, allowing the modeller to test numerous scenarios to understand then solve the problem. Fully-joined up approach The piecemeal approach to managing different urban wastewater system elements has been shown to be ineffective. Integrated catchment modelling allows a fully joined up approach to management and solution development. InfoWorks ICM allows the drainage systems, river systems, and overland flow routes within a catchment to be modelled simultaneously with seamless links between catchment features. This is a step forward from previous methods of simply combining model results from different so•ware packages. Integrated catchment models typically comprise: • The pipe network – foul, combined and storm systems are included where required, including ancillaries such a s combined sewer overflows (CSO) and pumping stations. The pipe network and ancillaries are commonly imported from GIS asset data and existing network models. These data sets are typically supplemented with new survey data. • The river network and associated hydraulic structures – including river channel cross sections along with bank-line information and river centreline definition. Modelling of these elements typically makes use of data from existing river models in addition to new surveys. Bridges, culverted sections and sluice type structures are also modelled and are generally created from survey data, asset data and from existing model information. • The ground model – this allows for overland flow routing across. The modelled surface is o•en created from DTM data (from LiDAR) Claire WaTson Chief engineer, neTWork Modelling, BlACk & VeATCh New so ware allows the drainage systems, river systems, and overland flow routes to be modelled simultaneously Paul MarTin Chief engineer, neTWork Modelling, BlACk & VeATCh

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