长江上游城市江岸生态修复与景观设计--以重庆长江南岸为例

Ecological Restoration and Landscape Design of Two Rivers and Four Banks in Chongqing:Taking the South Bank of the Yangtze River as an Example

重庆主城区两江四岸指的是地处中梁山与铜锣山之间的长江与嘉陵江区域,是三峡库区的库尾段,目前面临江岸生态环境破坏、生物多样性降低、岸线植被功能退化等生态问题,尤其是该段既存在库区消落问题,又存在上游自然河段洪水冲刷问题,江岸消落带面积大,水文变化复杂,江岸生态修复与景观设计面临的难度与挑战极大。本文以重庆主城长江南岸为例,通过系统调查江岸带鸟类、鱼类、两栖动物等野生动物的种类与分布情况、栖息地与觅食地、生活习性以及江岸带现状植物情况,对植物群落类型、优势植物种类与外来植物威胁等进行统计分析,总结提炼出长江岸线特色的“浩”“沱”“碛”“滩”“洲”“河口”六类自然生境。在现状调查与充分认识水文地貌单元的水文与生境特征的基础上,提出江岸带生态修复与景观设计策略。针江岸自然生境,遵循水文季节性变化规律,识别生境管控范围,对水域或近水域的水文地貌单元提出差异化保护与修复管控策略。天然河流因水流冲击作用,岸线呈现冲刷岸与淤积岸交替出现的情形。由于冲刷岸、淤积岸水流水势差异,对其的韧性化处理方式也存在差异。重塑滨江生态立体空间,根据水位季节性变化,配置相应的复合植被群落,优化人工植被结构,引导江岸生态自然修复,顺应长江的季节性涨落,塑造多维韧性江岸。综合考虑城市内部河流生态、景观与休闲游憩等多功能需求,结合岸线现状建设情况、水文特征、水文单元地貌、动植物生境与岸线腹地城市功能等资源禀赋的差异,将长江南岸划定为原生标本段、生态保育段、生态休闲段和城市活力段四类江岸生态分区,分段差异化引导人为活动强度与活动形式,以更好协调人与自然的关系。

“Two Rivers and Four Banks”of Chongqing are located at the end of the Three Gorges Reservoir area.The“Two Rivers and Four Banks”refers to the Yangtze River and Jialing River area between Zhongliang mountain and Tongluo mountain in the main urban area of Chongqing.The main urban section of the Yangtze River is about 60 km long,and the main urban section of Jialing River is about 50 km long.It is not only affected by the water level change in the Three Gorges Reservoir area,but also scoured by the natural river flood in the upper reaches of the Yangtze River.The seasonal fluctuation of water level,the large height difference and area of the water fluctuation zone,and the complex hydrological changes make the ecological restoration and landscape design of the river bank face great difficulties and challenges.According to statistics,in the past 20 years,the number of fish species in the Yangtze River Basin in the main city has decreased from 154 to 135.There is no record of natural wild capture of Chinese sturgeon and white sturgeon.The decline of biodiversity is closely related to the disappearance of hydrological and geomorphic units,as well as the destruction of primary vegetation groups along the river bank.River banks,beaches and Yangtze River waters are important biological habitats.Fish,birds,amphibians and other wild animals gather,inhabit,forage and breed here,forming a diverse and relatively stable ecosystem.According to incomplete survey and statistics,there are 73 species of birds along the South Bank of the Yangtze River,including 37 species of forest birds,12 species of waterfront habitat birds,24 species of water birds;136 species of fish,including 3 species of national protected fish,14 species of key protected fish in Chongqing,40 species of endemic fish in the upper reaches of the Yangtze River,25 species of macrobenthos,and 84 species of plants,including 8 species of aquatic plants.Taking the South Bank of the Yangtze River in Chongqing as an example,the species and distribution of birds,fish,amphibians and other wild animals along the river bank,their habitats,foraging places and living habits were systematically investigated.At the same time,the current situation of plants along the river bank was investigated in detail,and the types of plant communities,dominant plant species and threat of alien plants were statistically analyzed.Six types of natural habitats,such as“Hao”,“Tuo”,“Qi”,“Shallows”,“Sandbar”and“Estuary”,were summarized and refined.“Hao”is a natural dam stem structure of soil and stone,which forms a semi closed water area between the main river channel and the river bank.“Tuo”is a water flowing Tuo,which is directly impacted by the current and forms backwater in the river bay area.The riverbed is eroded by the current,and the water depth is slow.“Qi”refers to the structure of sand and stone pile exposed in the river.“Shallows”is the floodplain,which is located on one or both sides of the main channel of the riverbed.It is submerged in flood and exposed in dry water.It is formed by lateral migration of river and sedimentation of flood overtopping dike.“Estuary”is the place where the main stream of the Yangtze River interacts with its tributaries.Based on the investigation of the present situation and the full understanding of the hydrological and habitat characteristics of the hydrological and geomorphic units,the ecological restoration and landscape design strategies of the riverbank zone are proposed.For the natural habitat along the river bank,we should follow the rule of hydrological seasonal change.Due to the impact of current,the shoreline of natural river appears alternately scoured bank and silted bank.Due to the difference of water potential between the scoured bank and the silted bank,the toughness treatment method is also different.According to the seasonal change of water level,the corresponding compound vegetation community should be configured,the artificial vegetation structure should be optimized,the ecological natural restoration of the river bank should be guided,and the multi-dimensional and tough river bank should be shaped.Comprehensively considering the multi-functional needs of river ecology,landscape and leisure and recreation in the city,and combining the current construction situation,hydrological characteristics,hydrological unit landform,animal and plant habitat and shoreline,the South Bank of the Yangtze River is divided into four types(the original specimen section,the ecological conservation section,the ecological leisure section and the urban vitality section)according to the resource endowment differences in the hinterland city function.The segmented differentiation guides the intensity and form of human activities,so as to better coordinate the relationship between human and nature.