Water & Wastewater Treatment

38 | MAY 2015 | WWT | www.wwtonline.co.uk In the know Technically speaking: connected water management and supplemented with detailed topographic survey data in selected areas, such as around key surface features which may influence overland flow routes. The models are usually verified against pipe system flow surveys, river level gauging data and historic flooding records. The model can then be used to identify areas of flood risk from multiple sources, utilising a full suite of design and historic rainfall events. The results and associated high quality mapping are used to inform solution development, giving clear presentation of catchment risks and issues. Identifying the root cause of flood risk Integrated catchment models provide an excellent tool to undertake root cause analysis to confirm the mechanism of flooding and identify areas of flood risk. For example, an integrated model might show that a flooding location is at a low spot in the topography and receives overland flow via a kerbed road from a flooded manhole. The integrated model may further show that the manhole flooding is exacerbated by backing-up in the piped system caused by a high river level at the outfall. This situation would be more difficult to understand without an integrated model. These types of models also enhance the modeller's capability to consider and develop strategic catchment-wide solutions, where numerous related catchment issues can possibly be addressed in a single holistic solution. They allow the modeller to include potential sustainable drainage components as part of an integrated solution and also lend themselves to looking at how a system performs when the design capacity of a solution is exceeded. Integrated catchment modelling requires the involvement of all stakeholders in solution development, because different drainage system elements within a catchment are typically owned, managed, maintained and regulated by different parties. A joined-up view and good working relationships between stakeholders become absolutely fundamental where a solution crosses these ownership boundaries. These types of integrated solutions are o-en successful, but need to be considered carefully during the early stages of the project with complete buy-in from all parties throughout the solution development phase. The requirement to construct a model is o-en linked to the perceived performance of a system in relation to environmental criteria. A step beyond simply understanding the hydraulic performance of the network itself is to use the model outputs to carry out an urban pollution management assessment, where the modeller gains an understanding of how the performance of the network impacts on the quality of the receiving water. Watercourse impact One application of this is the setting of required consent limits for various pollutant types in discharges that impact watercourses. Typically rivers will have water quality standards expressed in percentile terms (i.e. threshold values that are only allowed to be exceeded for a given percentage of the time). Rather than use the blunt instrument of universally applied limits, environmental regulators can set site specific consents based on an analysis that takes into account the sensitivity of the local receiving water (e.g. the effect of a small discharge on a large river may be negligible even if the concentration is high). Tools have been developed to analyse the impact of trade effluents, treatment works effluents, and intermittent storm sewage discharges on rivers with known statistical variations in flow and upstream quality. Hydraulic model outputs o-en provide the input data to such calculations. This approach means that costs of pre-discharge treatment or storage based spill reduction solutions can be reduced or in some cases eliminated. It is difficult to say with certainty how wastewater network modelling may develop in the future, but there are a few predictions which can be made. Integrated catchment modelling is an advancing field and one that is set to develop further, with stakeholder engagement key to success. We need to ensure that we understand the challenge of a joined-up approach with stakeholders working together from the very beginning of a project. Integrated approaches are set to improve model capability, with more and more data required to develop increasingly complicated models. The potentially vast improvement in catchment understanding with the use of intergated catchment models is offset by increased modelling costs and longer project timescales. However, experience shows that the multiple benefits of developing these models, more o-en than not far outweighs the apparent increase in cost. In the past, hydraulic models have been used somewhat passively and reactively to assist asset planners. In the future, they will become essential proactive asset management tools. Taking these models a step further to use with real time catchment monitoring to prevent problems from occuring is also likely to be part of the network modeller's future. Smart operation of a network may help to reduce problems before they happen and is certainly something we are destined to see more of in the future. Wet weather impacts arising from urban catchments are widely recognised as a major cause of unsatisfactory receiving water quality Integrated catchment models provide an excel- lent tool to undertake root cause analysis to identify areas of flood risk in a catchment

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