Abstract:

The “volume capture ratio of annual rainfall” as a new term has emerged in Sponge City Construction in recent years. It has been applied widely in planning, design, construction of LID (low impact development) in Sponge City Construction, and been a key index during acceptance inspection and management of the LID construction as well. However, due to its unclear physical concept and indistinct connotation, it has caused confuse understandings within the water-related communities and hinders people from understanding of Sponge City Construction. In fact, from academic points of view, the Volume Capture Ratio of Annual Rainfall is simply the Percentile of Empirical Sorting of Dairy Rainfall Series, which is usually associated with the goal given to the Sponge City Construction, i.e. “to absorb and utilize 70% of the rainfall locally”. Having had computation based on historical rainfall series, on average nationwide, the design daily rainfall amount is 30% (0.304) of the 1-year quantile corresponding to 70% percentile of the empirical sorting of daily rainfall series while 50% (0.534) of the 1-year quantile corresponding to 85% percentile of the empirical sorting of daily rainfall series. The Sponge City Construction should be phased into two: Phase I is focused on LID and Phase II is focused on mitigation of the urban flooding. We suggest that it is better to replace the term of “Volume Capture Ratio of Annual Rainfall” with “Design daily rainfall to basin watershed source treatment” for better understanding and application.

Key words: volume of annual runoff, daily rainfall amount, percentile, frequency analysis, L-moments, regional analysis