Hydrologic Design and Economic Benefit Analysis of Rainwater Harvesting Systems in Shanghai, China

摘要

Innovative stormwater management strategies (e.g., the low impact development, the water sensitive urban design, and the sponge city) advocate the use of rainwater harvesting systems to collect rainwater for non-potable water uses such as irrigation, washing, or toilet flushing. It not only alleviates the pressure of urban water supply but also reduces stormwater runoff which would otherwise be handled through urban stormwater management systems. Sizing the storage units is a key problem in the hydrologic design of rainwater harvesting systems. In this study, a spreadsheet based daily water balance model was developed to analyze the performances and benefits of rainwater harvesting systems with different storage unit sizes. This model considers daily rainfall data, contributing roof area, rainfall loss factors, design storage capacity, overflow, and daily rainwater demand and can be used to determine stormwater capture efficiency, tap water replacement rate, water supply reliability, benefit-cost rate, and the optimum storage capacity of a rainwater harvesting system. Daily rainfall data from 1984 to 2013 and a multistory residential building and the lawns surrounding it in Pudong District of Shanghai was taken as an example to illustrate the application of this model. The resulting formulas and procedures may be used by engineers and municipal governments for the estimation or recommendation of suitable rainwater storage unit size.