Planning Method Research On The Urban Rainwater Ecological System Under Microcirculatory Idea

In recent years a number of cities in China have been hit by torrential rains, about2/3of the land area is increasingly suffering from floods of different types anddifferent degree of harm; while China’s urban development generally is facing theproblems of water shortages, drought disaster-prone and underground funnelexpansion.2/3of the cities are facing the problem of water shortage. Therefore therehas been the worsening conflict of frequent floods and the water shortage. In thiscontext, the academia are rethinking the stormwater resource planning method abouthow to improve the return period and increase the the rainwater pipe diameter in orderto achieve "rapid discharging" in traditional stormwater infrastructure plan andtherefore reached the consensus that industrialization has fragmented rainwatermicrocirculation mode and caused the coexist of floods and water scarcity. A greatdeal of research on rainwater recycling and rainwater utilization has been carried out.The theory of sustainable urban drainage and low-impact development model hasbeen proposed. On the basis of the theory a number of demonstration projects havebeen built up. The stormwater management is experiencing the transitional stage fromrain dredging to rain utilization. However, the stormwater infrastructure planningmethods currently used in China do not combine the advanced rainwater utilizationtechnologies to uniform consideration. The rainwater discharge, the rainwater cuts ofrainwater reuse and rainwater impounded of landscape are in separate state. There isshort of the research on the coordinated planning in stormwater infrastructureplanning.The article based on the concept of micro-circulation, first proposes to buildunified rainwater ecosystem planning ideas, and establishes a set of microcirculationunder the concept of urban water resources planning. The system combinesstormwater drainage infrastructure functions, rainwater utilization facilities,ecological restoration of groundwater rechargefunction, urban flood control facilitiesand mitigation functions, integrating environmental, ecological, stormwater designstrategies for sustainable development. Only to solve the city’s problems in terms offlood control, drainage and a separately independent stormwater infrastructureplanning, stormwater ecosystem more emphasizes on rainwater as a system resourcerecycling concept, while integrates the solutions to water shortages, contamination ofwater, flood control, ecological environment, groundwater recharge and many otherurban problems. Secondly, the paper defines the architecture of rainwater ecosystem by proposingthe following6sub-system elements:"collecting" system," runoff " system,"infiltration" system,"storage" system and "ponding" system and "purification"system, and streamlines the methods of calculating each individual sub-systems.Collecting means to harvest the rainwater that falls onto roof, pavement, vegetationand water body, thus advocate the adoption of roof garden in place of waterproof roof,permeable pavement in place of impermeable hard pavement, concave herbaceousfield pavement in place of conventional flowerbed-type green field to increase floodstorage capacity. Runoff means to replenish underground water sources, store andcontrol flood through, first the penetration and transportation of harvested rainwaterwith grass swales and other facilities, then with penetration and infiltration systemssuch as rain gardens, infiltration ditches and percolation wells; and simultaneously tostore rainwater using rain barrels, rainwater storage tanks, etc. for flushing, carwashing, irrigation and other reuse purposes; Storing means to detent rainwaters fromstorms for later discharge by increasing the capacity of ponds, man-made lakes andother large-capacity storage systems so as to reduce flood peaks and shift peaks.Purification means to purify rainwater with purification system like artificial wetlandsand stabilization ponds to improve water quality. This paper also provides a summaryof facility type selections, scope of application as well as the calculation methods ofeach individual subsystem.Thirdly, this paper puts forwards different rainwater ecosystem planning modelsfrom macroscopic, mesoscopic and microcosmic perspectives, that is, region, city, andcommunity. Macroscopically, humid area and arid area should employ differentrainwater infrastructure planning strategies according to their rainfall conditions incorresponding areas, namely, for urban rainwater facilities planning, in humid areas,primarily rainfall peak adjustment model should be used; in semi-humid areas,rainwater reuse pattern; in arid and semi-arid areas, the use of rainwater infiltrationmodel should be encouraged. Humid and arid areas should be treated differently withtheir characteristics highlighted. Based on the analysis above, this paper preliminarilydefines the facility systems and design processes of the three models. At themesoscopic level,"tiered" rainwater ecosystem consisting of rain gardens, stormparks and wetland gardens (from small to large in size) should be built according tothe scale of urban green space system architecture. Through this system, themicro-recycling process like detention and infiltration will be started from the very beginning, thus the rainfalls of high recurrence intervals will be dissolved gradually.At the same time, with detailed planning of runoff coefficient index control, the urbanrainfall flood control objective will be realized by distributing rainfall flood of theentire city from the global to different parts. At the microscopic level, the papersuggests building different rainwater facility planning models for residential areas androads, and proposes the new concept of "zero rainwater emissions" with somediscussions on required environment and facilities.Based on the study above, the paper presents an empirical study of the rainwaterecosystem planning method provided in this paper, using the new communityplanning of Shizhuang (located in Zhumadian, Henan Province) as an example.According to the new community planning of Shizhuang, with the employment of thefollowing design concepts of separation of pedestrian and vehicles, vertical split-leveldesign, garden space design, the planning, municipal engineering and landscapedesign are synchronized in the process of rainwater ecosystem planning.Consequently, the new community rainwater ecosystem of Shizhuang which consistsof three-level rain gardens: courtyard, group and community (from small to large) hasbeen successfully constructed. Then, using the subsystem calculation methodproposed in this paper, the author performed an empirical test of grass swales, raingardens, rain barrels and other key factors in low-impact development facilities, andverified the advantages of the rainwater ecosystem planning method through acomparative study with the rainwater infrastructure planning designed usingconventional methods, from the perspectives of rainwater pipe coverage, rainwaterflowing design, rainwater resourcization degree, runoff pollution degree andcommunity flood peak intensity. Based on the analysis above and with the worldwidely used SWMM model software as a platform, the author also built the rainwaterecosystem models for living and parking courtyards in Shizhuang new community,and concluded that the rainwater ecosystem is completely able to reduce a once-a-yearflood peak volume and runoff volume by setting their relevant parameters, analyzingits flowing process and characteristics, and evaluating the simulation results.Therefore, the flood peak reduction capacity of community rainwater ecosystem hasbeen verified from the perspective of model simulation.