A study on the impact of rainwater tanks on streamflow runoff

Rainwater tank has become an Australian icon of water conservation. This paper examines the possible reduction in streamflow volume in a catchment due to installation of large number of rainwater tanks. The study uses rainfall and runoff events data from the Bremer River Catchment in southeast Queensland in Australia. This assumes hypothetical urban development on the catchment covering 20%, 40%, 60%, 80% and 100% of the catchment area and a 10kL rainwater tank is fitted in each household of the developed part of the catchment. The study found that rainwater tanks could reduce the streamflow runoff volume. For the study catchment, 20% urbanization resulted in about 6% reduction in streamflow volume. For 100% urbanization, the reduction in streamflow volume was about 30%. Reduction in streamflow volume was found to decrease with increasing rainfall intensity and total rainfall depth. The reduction in streamflow volume from event to event showed a wide variability (1% to 17% for 20% urbanization and 1% to 86% for 100% urbanization).