基于城市水量平衡的海绵城市设计研究

The Sponge City Design Based on Urban Water Balance

近年来,我国大力推行海绵城市建设以缓解城市水资源问题,目前主要以雨水径流控制量为建设目标。水量平衡作为水资源利用的重要理论依据,对海绵城市建设水量控制更是具有重要指导意义。研究首先分析了海绵城市的水量平衡过程,并选取典型案例,提出多个达到年径流总量控制率目标要求的设计方案,通过水量平衡数值模拟,对不同方案水量平衡基本要素进行比较。研究证实达到年径流总量控制率的不同海绵城市设计方案水量平衡过程差异明显。本论文提出了基于水量平衡的海绵城市设计决策方法,并明确指出海绵城市设计应因地制宜的设定更细致的水量控制目标,根据水量平衡数值模拟方法优化规划设计,使海绵城市建设更具科学性。

In recent years, China has promoted the construction of sponge cities to help mitigate increasing urban water resource problems. The idea behind the sponge city is to achieve sustainable management of the urban water resources. Currently, sponge city constructions target mainly on water quantity and water quality. The metric used for water quantity is the volume capture ratio of annual rainfall, and for water quality it is the percentage reduction of certain pollution indicators. The most important construction goal in current research and practice is the volume capture ratio of annual rainfall. However, without equal attention to water quality and its relationship to the water balance, there is little chance that sponge city construction will be efficient. This paper introduces the relationship between a sponge city and the water balance. Four of the six guidelines proposed by the "Guiding Opinions of the General Office of the State Council of Promoting the Construction of Sponge City" are related to the water balance. The four guidelines are on seepage, storage, use, and discharge. The surface runoff involved in the sponge city control index(the volume capture ratio of annual rainfall) proposed in the relevant policy documents is one of the four basic elements of the water balance output. Groundwater level, utilization rate of sewage recycling, and utilization rate of rainwater resources are the assessment indicators for sponge city construction, which correspond to the groundwater recharge in the water balance, the amount of wastewater discharged, and the amount of rainwater reuse. The study shows that the sponge city design minimizes the impact of urban construction on the natural water balance by using various facilities to influence evaporation, reuse, and infiltration. Based on the volume capture ratio of annual rainfall, the research proposes three design schemes for the same study case, and compares the results of the water balance simulation of the Aquacycle model for the schemes. We found that the combination of various measures in a sponge city has a marked influence on the water balance, especially the ratio between evaporation and infiltration. The results show that a sponge city design with added rainwater reuse facilities is more suitable for rainwater management in the study area than the design of simply adding detention basins. The reduction in runoff was 21% and the increase in groundwater recharge was 15%. In view of the uneven distribution of regional rainwater resources in time, rainwater reuse facilities have been added to the design. As a result, the sponge city urban design not only shows good soil permeability but also a more suitable distribution of storage and discharge rate. Aquacycle is a daily urban water balance model which has been developed to simulate the total urban water cycle as an integrated whole. Our research shows that Aquacycle model is a useful tool for quantitative analysis of the water balance. With the help of Aquacycle, we suggest that the specific Lid measures should be selected according to the regional characteristics and construction needs as determined in the in-depth study of ecological rain and flood green space. Under the premise of emphasizing the volume capture ratio of annual rainfall, attention should be paid to the utilization of rainwater resources and the utilization rate of wastewater recycling when designing a sponge city in a dry and rain-stricken city. The ability of the region to benefit from rainwater is enhanced by selecting water storage and rainwater reuse facilities such as rain tanks and reservoirs. The design of a sponge city in a city where drought and floods are symptomatic, should focus on using rainwater to alleviate the water shortage in the dry season, and finding measures to mitigate water logging during the rainy season. Cities with abundant rainfall and significant rain and flood problems, should develop measures to reduce surface runoff. Consistent with the groundwater and soil conditions, sponge city design should select sponge facilities that are conducive to increasing groundwater recharge and reducing runoff. The paper also presents a decision-making method for sponge city design based on water balance. The method includes the following steps: 1) Analysis of regional water balance factors;2) formulation of water control targets consistent with local conditions;3) analysis of water-balance numerical simulation results according to the multiple sponge city design schemes that meet the target;4) select the design most suitable of the needs of the project area. Compared with the traditional method, the sponge city design based on urban water balance method allows more in-depth consideration of the impact of sponge city construction on urban hydrologic processes and water balance. The new method allows "water quantity" target to be controlled at the design level.The paper shows that the sponge city design will be more objective, if it sets more detailed water control targets consistent with local conditions.