北京聚水/排涝策略计算分析

Calculating Analysis of Strategy for Water Collection and Drainage in Beijing

北京一方面因城市规模扩张带来水资源绝对短缺问题,另一方面由于极端天气频发又常常出现逢雨必涝现象。"一少一多"现象都因水祸起,这就使得人们开始构思是否能在时间和空间上人为调节水量,将暴雨季过多的水量在城市内滞留、储存,既能避免城市内涝现象又可有效保存宝贵的水资源。通过对自然水循环的深刻认识,揭示人类只能在水循环的某些环节上(地下、地表径流)顺应自然去利用水,采取"用后即还(Use it and let it go)"方式让水以它本来的面目流归大海。对北京水资源以及雨水径流量的计算表明,各城区所有硬化地面上的水资源可能流失量之和占城市年用水总量的比例<3%。与此同时,除非存在城市地下"黑洞",否则,即使构筑人工渗水、储水设施也难以消纳大暴雨级的瞬时降雨量。从这个意义上说,对降雨在城区形成的地表径流应通过完善排水设施,采取城区快排、郊外储存方式予以滞留、储存或直接排放,以充分利用郊外非硬化区域土壤、河流、水库对水的滞留和储存作用以及环境的自净容量。换句话说,城市聚水/排涝应从区域甚至流域的"面"上考虑问题,而不应仅仅聚焦于城区单一"点"上。

Beijing is not only suffering from water shortage by urban expansion, but also has often flood disasters under extreme storm weather. As water is a key factor causing these adverse phenomena, it is proposed to regulate water quantity in time and space for both retaining water and avoiding flooding in city areas simultaneously. Based on an in-depth understanding on the natural water cycle, it becomes clear that human beings have to make use of water in some processes （ groundwater and surface water） of the water cycle and to use it and let it go. Calculations on the water resource and the runoff quantity of Beijing revealed that a probable loss of water caused by ground covering in city areas took only a share of 〈 3% of the total water consumption. Under the circumstance of heavy downpours, constructed facilities for retaining and storing water are difficult to absorb huge storm precipitation, unless there is a ＂blackhole＂ underground. For this reason, runoffs caused by sudden downpours should quickly be discharged outside city areas by facilitating municipal sewer systems, which could be retained and stored in suburb areas by use of natural soil, rivers and reservoirs with storage capacity and self-purification. In other words, water collection and drainage in cities should be considered on the basis of areas and/or catch- ments, and cannot be focused on cities themselves only.