Planning future sustainable water management in cities is a challenge. A recent study describes a new computer tool that enables quick comparisons of different water management options in cities, to help develop future strategies for effective integrated urban water management.
Growing populations, increasing energy costs, environmental pollution and increased floods and droughts under the impact of climate change, are just some of the challenges facing city planners. In the past, cities have often managed the water supply, wastewater and storm-water systems separately, but for a sustainable future, urban water management needs to become integrated and regard all types of urban water as resources.
Developed under the EU-funded SWITCH project1, City Water Balance (CWB) is a modelling tool that forms part of the City Water decision support system. CWB allows city planners to assess different options for the future management of urban water systems under a variety of changing conditions. For example, planners can explore the impact of alternative technical options to cope with pressures on water and wastewater caused by climate change or population changes.
Features of the CWB tool include: integration of the natural environment into the urban water cycle; inclusion of regulatory aspects and historical data; analysis of urban development; and a wide range of time and space horizons under which planning can be assessed.
CWB allows planners to model the balances of water, energy and pollution associated with urban water systems at the city level. The model provides indicators of the proportion of water demand to supply; wastewater production; water quality; life cycle energy and life cycle costs. CWB is based on simplified assumptions about the water storage, use and transmission of water in unit blocks of land use (e.g. apartment blocks, hospitals or golf courses) in a city. Neighbourhoods can be characterised by similar types of land use units and can be grouped together to map the water flow in the city.
CWB also enables mains water, runoff, natural water systems such as rivers, lakes and ponds, water pollution and the life cycle energy and costs associated with each water management option to be assessed. Strategic planning for sustainable water systems include: green roof provision, wastewater recycling, porous pavements and retention ponds.
The CWB model can map city waterscapes relatively quickly and can be used by planners with both advanced and less advanced mapping and monitoring capabilities, whilst still allowing valid comparisons to be made.
As a case study, the CWB tool was used to model the wastewater drainage area of one of the wastewater treatment plants located in Birmingham, UK. It performed well and its prediction of the behavior of the water supply and storm-water and wastewater drainage systems closely matched the observed historical flows.