Theme 4-2-Sizing of storage tanks for roof-rainwater catchment systems

Abstract

Rainwater harvesting has been practised for centuries. This paper assesses the potential success of rainwater catchment systems in supplying irrigation water for residential landscape. The determining factors are dependent on the rainwater supply and its distribution, the roof catchment area, and the optimal size of storage unit. In determining the landscape area which could be supported by the rainwater catchment system, a water balance spreadsheet was devised. The spreadsheet uses a recursive approach to maximize the landscape area which can be supported by a given catchment area and the design rainfall. The traditional mass curve analysis was found inadequate in determining optimal storage size because of temporal variations in rainwater supply and water demand of residential landscape. The methodology has been illustrated using residential landscape of the City of Thunder Bay, Ontario, Canada. It is demonstrated that a saving in the order of 0.73 million dollars per year can be realized by the City when the majority of households are participating in the rainwater usage for irrigation of residential landscape. Harvesting rainwater to meet or supplement garden and lawn irrigation is a simple process which is becoming a viable solution in sustaining future water resources.