City water balance: a new scoping tool for integrated urban water management options

Urban water scoping modelling packages are used as tools to inform decision makers of the sustainability of different water management options for a city. Previous scoping models have not taken sufficient account of natural systems in the urban environment and are often limited in terms of the range of indicators used to measure sustainability and the choice of water management options offered. A new modelling package, named City Water Balance, has been developed to address these limitations. It has the capability to assess the sustainability of a variety of water management options, including the sustainable urban drainage systems, in terms of water flow, water quality, whole life cost and life cycle energy for alternative scenarios of future urban land use, population and climate. Application of the modelling package to the City of Birmingham has demonstrated that the modelled components can describe adequately the existing system, giving confidence that it can be used for scoping strategic options for future water supply and wastewater management. The further application of the package to model alternative scenarios through to 2055 for Birmingham has also been undertaken to illustrate its application. The results from the different analyses have shown that medium scale rainwater harvesting and borehole abstraction are predicted to be more sustainable than the conventional centralised supply and that medium scale wastewater recycling would be more cost effective but less energy efficient. The most sustainable strategy was installation of water efficient appliances as there is the potential for large energy savings from reduced indoor usage and consequent water heating requirements