Quantifying Long-Term Benefits of Multi-purpose Rainwater Management Systems

This paper investigates the performance in terms of yield, peak stormwater discharges and annual stormwater reductions for a set of four rainwater management scenarios tested against a hypothetical household in England. The work builds on recent progress in modelling of rainwater management systems (RMS) using a mass balance approach. The novelty lies in the ability to investigate both; local water provision; and the reduction in stormwater discharges associated with the RMS strategies. Recent research studies and case study exemplars demonstrate a shift away from single objective rainwater harvesting systems. Projects are now being delivered using dual-purpose RMS to control discharges as well as augment water supply. The study illustrates for the first time, how a long time series rainfall record (85 years) can be used to drive mass balance simulations and enable key metrics to be calculated. The results illustrate how well-designed RMS can reduce stormwater discharges whilst also meeting design needs for water resource augmentation. The length of rainfall dataset analysed enables long performance evaluation including during low probability events that exceed the UK’s current stormwater drainage design standards (e.g. 1 in 30 year rainfall event). The study also investigates the potential for climate change to affect performance. It concludes that an actively controlled RMS with a 3000 l tank can potentially reduce the largest rainfall event in the 85 year dataset by 72%, up from just 6% for a traditional RWH configuration with the same tank storage capacity.