Use of continuous simulation for the selection of an appropriate urban rainwater tank

Household rainwater tanks form part of an integrated urban water cycle management system, which is a key aspect of the water sensitive urban design philosophy. They provide scope for harvesting rainwater for domestic uses, as well as mitigating the impacts of urbanisation on catchment runoff. This paper describes the development and application of a computer simulation model for the operation of a household rainwater tank. The model uses daily rainfall and consumption data to simulate the operation of the rainwater tank. The simulation model has been applied to a hypothetical household and rainwater tank system using daily rainfall data for 12 cities throughout Australia. The study indicates that the unit cost of supplying rainwater to a household from a rainwater tank increases as the consumption rate decreases. An economic optimum size rainwater tank, based on the minimum unit cost of rainwater supplied can be determined for any water consumption scenario. The climate characteristics of the site are shown to have a significant influence on the hydrologic effectiveness of the rainwater tank system. The study has shown that the yield of rainwater from the tank is a function of the monthly variation in rainfall, defined by the seasonality index, the median annual rainfall and the tank volume. This may have significant consequences on the suitability of rainwater tanks in terms of potential effects of climate change