Author(s): M. Uhl; B. Hellberg
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Keywords: Rain tanks; Rain water harvesting; Retention; Detention; Water sensitive urban design
Abstract: Combined rain tanks are used for rainwater harvesting and on-site detention of runoff. They are well established as low impact design tools in urban development. Their performance was studied by continuous simulation for the Auckland region. Relationships between water demand and tank size as input and security of supply and runoff coefficient as output allow an optimized design of rainwater harvesting tanks. High retention effects can be achieved in cases of high water demand and large tank volumes. Moderate peak flow reduction could be observed as well. The analysis of a common type of combined rain tank showed that most of the peak flow reduction was due to the detention volume. The rainwater tank itself contributes to detention with a moderate additional reduction of peak flows. The length of the selected time series for simulation did only marginally affect the security of supply and the retention effect. However, peak flows are increasing significantly during the last fifteen years. This should be subject to further studies. The existing design procedure is likely to meet requirements to detention basing on the runoff in natural catchments. The detention requirements can be derived by continuous simulation of catchment runoff.
Year: 2010