Spatial sensitivity of generalised equations to predict rainwater tank outcomes: a case study for Brisbane

Abstract

Several studies have been conducted to calculate potential rainwater savings through rainwater tanks installed in residential and commercial buildings. One of the pioneering studies among those is the development of generalised equations, using which general end-users can work out potential annual rainwater savings through a rainwater harvesting system by providing data like annual rainfall amount, rainwater tank size, daily rainwater demand and roof area. However, these equations are location specific, i.e. only valid for specific locations having certain rainfall amounts and patterns. As the development of such equations for every location is a tedious task, the usefulness of using such equations for neighbouring locations warrants attention. This paper investigates the spatial sensitivity of four generalised equations developed earlier for Brisbane (Australia) to use those for neighbouring locations. Seven test locations were selected within the city to assess the sensitivity of those equations in computing potential annual water savings for those locations. Annual water savings for the selected locations were computed using the generalised equations for different water demand and roof area scenarios in an average climatic year. Water savings were then compared against a daily water balance model (eTank) simulated results for the same scenarios. It was found that the results from the model for all the test locations were almost consistently lying between the results derived from generalised equations for two locations. Hence, it was concluded that the earlier developed equations for two locations can be used for any location in the city to get an approximate estimation of potential annual water savings through rainwater tanks. Moreover, the results from this study can also be used by policymakers and stakeholders to understand the variations in water savings within a city.