关于海绵城市两种降雨控制模式的讨论

我国《海绵城市建设技术指南—低影响开发雨水系统构建(试行)》采用降雨总量控制模式以实现径流总量控制目标,但降雨总量控制率并不等同于径流总量控制率,降雨控制需将降雨转换成径流后才能与径流控制对应。按美国EPA提出的降雨场次控制模式进行设计,其降雨场次控制率等于径流场次控制率,降雨控制与径流控制直接对应。为此,本文开展了关于海绵城市建设中两种降雨控制模式的讨论。论文首先对两种降雨控制模式内涵进行了解析。然后以北京、武汉、广州为代表比较了两种不同控制模式下的城市产流雨量设计结果。研究表明,两种降雨控制模式其设计降雨量具有一定对应关系,但概念上应有所区别;相同控制条件下,按降雨总量控制的设计降雨量要明显高于按降雨场次控制,但两种模式下的最优控制率差异并不大;总量控制模式能较好地反映城市年均产流水平,有利于雨水利用目标实现,而场次控制模式则更能代表城市对场次降雨的消纳能力,有利于径流污染控制目标的实现。

Discussion about the two rainfall control approaches in Sponge City Construction

China Sponge City Construction Guide (2014) uses rainfall volume capture ratio as runoff volume capture ratio to determine the designed rainfall, which is debatable because they''re not equivalent. Rainfall need be converted to runoff before estimating runoff volume capture ratio. US EPA uses rainfall event capture ratio to determine the designed rainfall and it''s equivalent to runoff event capture ratio. This paper compared two different methodologies with rainfall volume capture ratio and rainfall event capture ratio, and discussed which one is best suitable for Sponge City based on its goals. It discussed the concepts of these two methodologies, then compared them using Beijing, Wuhan and Guangzhou as examples. The designed rainfalls based on these two methodologies have certain correlation,but they''re not same and their concepts are different. The designed rainfall based on volume capture ratio is always higher than the one based on event capture ratio. The study found the optimized ratios, or the break-even point of capture ratio, are very close based on both methodologies. In conclusion, the runoff volume capture ratio represents the capture ratio of long-term annual runoff, hence is suitable for runoff utilization. But the runoff event capture ratio represents the capture capability of each rainfall event, hence is suitable for runoff pollution control.