Study on the Economical Volume for Rainwater Harvesting

On basis of a bigger drainage area, the fundamental standard for rainwater harvesting quantity should improve or amend water circle system and eco-environment, with the suitable runoff closed to the natural catchment condition after rainwater harvesting. For rainwater harvesting systems of some smaller watershed the suitable and economical harvesting volume is important. In other special situations integral stormwater management practices with higher efficiency should be adopted to achieve required bigger design return period. When water demand compared with the runoff in a given project is greater, the volume of a rain tank could be determined with a 24h rainfall, and rainfall return period for design should not lager than 0.3 years, and design storm rainfall should not lager than 50mm for all cities in China, or using water quality volume for design storm instead. When runoff in a practical project is sufficient with small daily water consumption, the storage volume could be designed according to water quantity for 5 days water consumption. For those projects with artificial water body with great storage capacity, the storage volume should be confirmed by water balance analysis on the basis of an average year.