Chuanzi River is a thousand-year-old canal, which flows through Changde city, with a total length of 17.3 km and a drainage area of 27.97 square kilometers. 1952, the Chuanzi River was forced to cut off water due to the diversion of the water system, which became a "broken river" that could not be self-purified. With the acceleration of urbanization, the river channel is divided into multiple sections of water due to urban expansion, and the domestic garbage and wastewater generated by surrounding residential areas, farms and factories are discharged excessively, which makes the pollution of Chuanzi River intensified and the ecological environment of the basin deteriorated, which has a serious impact on the urban living environment. In 2006, in order to control the deteriorating ecological environment of the Chuanzi River, improve the supply capacity of ecological products in the basin, and promote the virtuous circle of urban economic development and ecological protection, Changde Municipal Government initiated the ecological restoration and management of the Chuanzi River, and started the five-in-one construction of the sponge city "water ecology, water security, water environment, water culture and water resources" in the Chuanzi River basin. Through unremitting efforts, Chuanzi River has been transformed from a once "stinking ditch" into an urban ecosystem and ecological value realization platform integrating "cultural river", "commercial river" and "tourist river", bringing endless ecological products and comprehensive benefits to the whole city and residents, and becoming a veritable urban "golden belt".
(2) Specific practices
The first is to formulate a governance plan and carry out the construction of sponge cities. In March, 2006, Changde Municipal Government cooperated with Hanover Government, Hanover Water Association and Utrecht Government of the Netherlands to start the Hezi River ecological control project, completed the master plan of water-sensitive city development and sustainable utilization of water resources in Jiangbei District of Changde City, and put forward the concept of "sponge city", which comprehensively planned urban rainwater, sewage and groundwater with the concept of ecology and sustainability. Since 2009, under the guidance of the Master Plan, Changde City has carried out the renovation and construction of sewage interception, dike lowering and sluice repair, rainwater pumping station, storage tank, ecological filter and river ecological shoreline, and successively started the renovation of residential quarters, roads, squares, drainage pipe networks and the construction of supporting facilities in Chuanzi River watershed. On 20 1 1 and 20 15, Changde City respectively adopted and implemented the Urban Design Planning Scheme for Crossing He Zi hatchback (Zaoguo Road to Changde Avenue) and the Constructive Detailed Planning for Crossing He Zi Scenic Belt, which further promoted the construction of supporting facilities for crossing He Zi Scenic Belt.
The second is to carry out systematic governance and improve the ecological environment. Intercept and clean up pollution, and realize source emission reduction. By repairing the damaged groundwater pipe network, upgrading 8 pumping stations and pumping stations' water storage tanks, and newly building and reforming sedimentation tanks and water storage ecological filters, the precipitation and purification capacity of mixed-flow rainwater and sewage will be enhanced, providing clean water for crossing the Hezi River. Dredging and dredging to revitalize internal water sources. Dredging works were carried out with dredgers, and 370,000 cubic meters of silt were cleared in the 8.4-kilometer-long river course, which was used as planting soil after secondary treatment; Build a willow gate to connect Chuanzi River with Yuanjiang River and Liuye Lake, an inner lake in the city, to revitalize the water source of Chuanzi River and realize water body renewal. Build ecological revetment to enhance biodiversity. Using ecological revetment instead of traditional wharf to form vegetation buffer zone in revetment area to filter sediment in surface runoff; Set up ecological floating islands in the river bend area with low water flow velocity and the area near the drain of drainage pump station to enhance the water purification function; Filter-feeding fish, carnivorous fish and benthic organisms will be released, and 58,000 local silver carp, cultured silver carp and bighead carp and 58,000 kilograms of snails and mussels will be released to establish an ecological circle of fish, insects and waterfowl, optimize the biological population structure and enhance the stability of the natural ecosystem.
The third is to promote all-round development and realize the value of ecological products. Relying on the restored scenery belt of Zihe River, we will promote the combination of natural landscape and human landscape and realize the value of ecological products. The characteristic streets such as German Street, Mayang Street, Xiaohe Street and Dahe Street will be built on the north bank to form characteristic commercial districts such as restaurants and clothing, and enhance the economic value of ecological products. The footbridge is used to connect the north and south banks of the Zihe River, and a 5.5-kilometer hydrophilic plank road and five riverbank viewing platforms are built. Live music performances such as Changde Sixian, Zhezi Opera and Liu Hai chopping firewood will be arranged along the river to form a historical and cultural landscape, publicize local cultural characteristics and realize cultural values. Open up the inland river system, connect the Chuanzi River with the water systems such as Baima Lake and Liuye Lake, open a 45-kilometer round-trip waterway and 14 wharf, and open the "water bus" to create the first water tourism route in Changde and promote the development of eco-tourism. Relying on the good ecological environment after renovation and restoration, attract commercial enterprises to settle in, build multiple residential quarters and commercial-residential complexes, and realize the value overflow of ecological products. While developing the "business, travel and housing" industries, we will plan and build a wedding industrial park to explore the industrialization and diversification of the value of ecological products.
(iii) Major achievements
First, the ecological environment continued to improve. After comprehensive management, the flood storage capacity of Chuanzi River basin has been obviously enhanced. In July, 20 16 and July, 20 17, when the 24-hour cumulative rainfall was greater than the extreme value 177.8 mm, there was no large-scale waterlogging in Changde City and no waterlogging in Chuanzi River Basin. At the same time, the water quality, water environment, water ecology and water safety of Chuanzi River were comprehensively improved, and the biodiversity and ecosystem stability were obviously enhanced. The concentration of chemical oxygen demand at the outlet of Chuanzihe ecological filter decreased by 59.6% compared with that at the inlet, and the water quality of the river gradually recovered from worse than Grade V to Grade III.
Second, the value of ecological products has gradually become prominent. With the effect of ecological restoration and management of Chuanzi River and the development of "water bus" project and commercial industries along the river, Changde characteristic tourist routes centered on Chuanzi River have gradually taken shape, and the river course of Chuanzi River, which has been interrupted for nearly 40 years, has been restored, and the related industries on both sides of Chuanzi River have realized an annual income of more than 30 million yuan. Relying on the good ecological environment of Chuanzi River, the comprehensive development of coastal business district and high-grade residential buildings has been promoted, and both ecological and economic benefits have won.
Third, the living environment has been improved and residents' happiness has been continuously improved. Chuanzi River has changed from a stinking "stinking ditch" to a "downtown green park" for citizens to walk and relax. The optimization of water quality and the improvement of climate have significantly improved the quality of human settlements in Changde City. While urban residents have good ecological products, they can also enjoy the ecological dividends generated by "water culture" and "aquaculture", forming a harmonious pattern of integration of green development and livable life.