With the rapid expansion of the urban area and the constant intervention of human activities, there have been some serious problems in urban rivers such as channel shrinkage, frequent flood disasters, deterioration of water quality, landscape destruction, decline in biodiversity, and so on. The research of urban river health is one of the hotspots in the current field of river ecology research. Restoration and maintenance of the urban river health is a common goal of urban river management in countries all over the world.
Urban rivers are those originate from urban areas or who meet with city rivers/river sections, some of which have a history of artificial excavation and evolution with characteristics of natural rivers and canals. In the process of formation and development of cities, river as the key carrier of resources in the natural environment, is an important factor influencing the style and beautify of the city environment, and restricting the city development. In terms of characteristics of urban rivers, it is obvious that urban rivers have lots of functions in varying aspects, not only functions of natural river system, but also social and economic service such as providing places for recreation and tourism. Therefore, urban river system is a complex system which is composed of natural ecology subsystem, social economy subsystem and landscape environment subsystem. A healthy urban river is significant for maintaining the balance of the local ecological system, meeting the needs of social economy development, and providing entertainment for local residents.
In this paper, the concept of the urban river health was discussed firstly, and then the evaluation index system was constructed based on the connotation of urban river health, including 24 indexes in natural ecology, social economy and landscape environment. The index system consists of sub-target layer, criteria layer and index layer, considering the natural ecology, social economy and landscape environment of the urban river. Taking the urban reach of the Lijiang River as a case, the river health status was evaluated using fuzzy comprehensive evaluation model and analytic hierarchy process (AHP) by determining the weights of the criteria layer and index layer. The results show that the ecosystem health scores of the urban reach of the Lijiang River is 0.2193, 0.3004, 0.3261, 0.1137, and 0.0405 respectively, which indicating that the urban reach of Lijiang River was in the medium state of health. The health level of the natural ecological subsystem, social and economic subsystem and landscape environment subsystem was medium, excellent and good respectively. It can be concluded that the management of the Lijiang River has made certain achievements in recent years, but more further studies and investment were needed to reach complete river governance. On the other hand, water volume, flood control capacity, fish diversity index and benthic animal diversity were also the main factors which affect the health of urban reach of the Lijiang River. Therefore, key measures of ecological restoration of the urban reach of the Lijiang River include water supplement in dry season, flood control, biodiversity conservation, as well as data collection and human factor research in the future. The evaluation index system and evaluation method in this paper was effective in the case of evaluating the health of Lijiang River, and could provide decision-making reference for basin planning, managing, protecting and health assessment of the urban river in other region.