The Benefit Assessment Of Urban Rainwater Utilization

The urban rain water utilization is the efficient path to solve urban water resources short, reduce urban flood disaster and improve urban water environment. It not only brings economic benefit, but also significant environmental and social benefits such as saving water,alleviating flood disaster,supplying ground water, controlling runoff pollution and improving urban environment. Taking rainwater resources as study object, this paper analyzes and researches the benefit identification and quantitative assessment issues of rainwater utilization, evaluate the comprehensive benefit of a rainwater utilization project in Wafangdian city, assess the benefits of the rainwater collected by permeable surfaces in the Xigang District and the Zhongshan District of Dalian City.The main research results of this paper are as follows:(1) The benefit identification and quantitative assessment issues of rainwater utilization.Rainwater utilization under different water use patterns play different functions, and achieve many of the economic, ecological and social benefits. Application the connecting ideas of rainwater harvesting measures coupled with the function to identify the benefits of urban rainwater and build rainwater efficiency evaluation index set. this paper selected the appropriate index of economic, ecological and social arenas and established a rainwater utilization efficiency targets set. The appropriate quantitative assessment method to determine the effectiveness were choosed.(2) The comprehensive benefit evaluation and program optimization of rainwater harvesting and utilization Project.Taking Wafangdian rainwater utilization project as an example, a comprehensive evaluation and program optimization were conducted through multi-level Semi-structured fuzzy comprehensive evaluation method and AHP. The evaluation results show that appropriate expansion of water tank volume can increase the overall efficiency. However, if the reservoir volume is too big, the unit cost of rainwater will increse too much and lead to a drop of overall efficiency. The new models such as through infiltration facilities to cover groundwater water is recommended measur. According to the national economy evaluation standard, when the benefit-cost ration is≥1, the project is feasible. From the results we can see that this rainwater utilization project is economically feasible and reasonable. In addition, the volume of water demand and reservoirs have implications on the water use efficiency, so the design ofreservoir should taken into account water demand when making use of rainwater collection.(3) The benefit of the rainwater retained by urban permeable surfaces was calculated in the Xigang District and the Zhongshan District of Dalian City. From 1998 to 2005, the benefits of rainwater had a rapid growth with the expansion of permeable surface in Dalian city. The benefits of rainwater in 2005 were as follows:the total economic benefit of the retained rainwater was 10.18×106 yuan RMB, the eco benefit was 85.43×106 yuan RMB and the flood contorl benefit was 9.12 x 106 yuan RMB. Moreover, great social benefit generated because soil erosion was controlled and the urban residential environment was improved. The results shows that economic benefits, the city permeable surface can generate more ecological and social benefits.