Reasearch On Rainwater Utilization Benefits Calculation Method And Utilization Model

Sponge City Construction provides a new urban management concept for solving problems such as urban floods,water shortages and water environment deterioration.Among them,the rainwater utilization technology with the main function of rainwater absorption and stagnation is one of the key elements of sponge city construction.However,the current benefit calculation methods of rainwater utilization technology have problems such as incomplete calculation indices,high data dependence,small scope of applications,and lack of objective calculation methods for social benefits.As a result,the calculation results of rainwater utilization technology benefits cannot fully reflect their overall benefits,resulting in perception bias by managers,implementation personnel and general public that hinders the overall advancement of sponge city construction.In order to effectively promote the development of rainwater utilization technology and broaden the construction of sponge city,this thesis proposes a set of economic,ecological and social benefits calculation methods for domestic sponge city rainwater utilization technology,and establishes a comprehensive evaluation system for rainwater utilization technology based on benefit calculation results combined with analytic hierarchy process.The main research contents and results of this thesis are:（1）Based on the benefits calculation methods of relevant fields at home and abroad,combined with the results of questionnaire surveys,the calculation methods of economic,ecological and social benefits of rainwater utilization are proposed,and a comprehensive evaluation system for rainwater utilization is constructed.Then according to the hydrology and geology of Tianjin,the economic,ecological and social benefits per unit area（volume）of the commonly used rainwater utilization technology are calculated under different drainage systems.The results show that regardless of the drainage system,the economic and ecological benefits per unit area of rainwater wetland are the highest,respectively 326.6 yuan/m² and 506.1 yuan/m²,and the infiltration basin has the highest value of social benefit,which is 31.4yuan/m².The comprehensive evaluation results after considering the expert opinions show that the rainwater garden is the best,and the blue roof has the lowest comprehensive evaluation score（both in the case of separate and combined rain and sewage flow system）.（2）Taking the sponge campus of Tianjin University Peiyang Campus as the study area,water quality changes of the water system on the campus are continuously monitored,and control effects of rainwater utilization project on water quality are explored.The result shows that the rainwater utilization project in Peiyang campus has obvious control effect on the water quality and quantity of the water system.Since the completion of the campus,the water quality of the water system has gradually improved.Among the Inner Lake,Huxiao River and Weijin River,the Weijin River has the best water quality,with the grade IV water quality compliance rates for TN,TP,NH₄⁺-N and CODcr achieved 20%-70%,92%-100%,100%and 50%-92%,respectively.The water quality improvement effect of Inner Lake was the most obvious.The compliance rates of grade IV water quality for TN,TP and CODcr increased from 8%,83%and 0%to 58%,92%and 67%,respectively.（3）Economic,ecological and social benefits of the rainwater utilization project on Peiyang Campus are calculated,and rainwater utilization model for the development area is optimized.According to calculations,the annual economic,ecological,social and net benefit values are 0.73 million yuan,58.7 million yuan,2.0 million yuan and 55.9 million yuan,respectively.According to the rainwater management needs and the results of rainwater utilization technology benefits calculation,rainwater utilization model in the development area is designed,and green roof,permeable pavement,rain garden and wet pond are most recommended.Therefore,under the control of expected investment costs,the construction area of the above rainwater utilization technologies should be maximized.