Objective  Settlement is a social-ecological system in which man and nature are closely linked, and water conservancy systems often form the basic structure of traditional agriculture-based settlement landscape in China. Putian Plain is located on the southeast coast of China, where traditional settlements are established and developed in close connection with water conservancy construction, accompanied by the formation of corresponding landscape characteristics. This research clarifies the relationship between traditional settlements and water conservancy construction in the human-land system, which will have a positive impact on the protection, development and cultural inheritance of traditional settlements in the Putian Plain.

Methods  Firstly, this research combs the evolution process of the water conservancy system and settlements in the Putian Plain through historical data combing and field investigation. Secondly, according to the settlement points recorded in Ritual Alliances of the Putian Plain, the research conducts the kernel density analysis and standard deviation ellipse analysis were performed in ArcGIS 10.6 to reveal the spatial distribution relationship between traditional settlements and water conservancy systems. Thirdly, the research selects relevant historical satellite image data published in 1975 and, by the method of spatial diagrams, reveals the spatial characteristics of different types of traditional settlements. Finally, based on the above analysis results and combined with historical materials and field investigation results, the research summarizes the formation mechanism of traditional settlements.

Results  1) The first stage of the development of the water conservancy system and traditional settlements in the Putian Plain is in Tang Dynasty. The ancestors, by virtue of the catchment area of the piedmont plain, built six main ponds for water storage, with the stored water being diverted to irrigate farmlands. Then, early settlements were formed around ponds. The second stage is in Song and Yuan dynasties. Driven by the development of economy and science and technology, the ancestors implemented a comprehensive water conservancy project dominated by four weirs and supplemented by supporting facilities such as ponds, dikes, canals and sluices, which promoted the large-scale farmland reclamation and settlement construction. The third stage is in Ming and Qing Dynasties. Due to the saturation of land development, the ancestors mainly renovated old water conservancy facilities and continuously reclaimed coastal lands. 2) The Putian Plain has formed a comprehensive water conservancy system composed of four types of units, namely defense units used to block salt water and resist sea tide, water diversion units used to store fresh water from mountain streams, transmission units used to connect ponds or rivers to better divert water for farmland irrigation, and regulating units used to control the water volume of waterways, block sea water and discharge water. These facilities provide basic support for settlement construction. 3) The spatial distribution of traditional settlements in the Putian Plain presents multiple agglomeration areas, and is roughly the same with that of water systems, only that the settlements are mostly distributed close to the mountains on the west side, indicating that the water system plays a fundamental role in settlement distribution, which, however, is also affected by other factors, such as natural risks, historical politics, and shrink westward. The traditional settlements in the Putian Plain can be divided into the following five types in terms of spatial form: dike settlements formed into belts relying on defense units; weir and sluice settlements generally distributed in pairs close to the two ends of water conservancy facilities such as weirs and sluices; canal settlements generally distributed close to irrigation canals, which have,become the most widely distributed settlement type in the Putian Plain relying on rich water resources and convenient water transportation, and can be further divided into the three subtypes of island type, river-side type, and river-crossing type; oxbow settlements mostly presenting a radial layout in the oxbow lakes formed by the Mulan River; foothill settlements presenting a ring or belt layout on the edge of hills. 4) The traditional settlements in the Putian Plain are the result of the limitation of water environment, the construction of water system, the regulation of water management and the cohesion of water belief. They have significant regional characteristics and historical value.

Conclusion  This research reveals the evolution process, landscape characteristics and formation mechanism of traditional settlements in the Putian Plain under the guidance of water conservancy construction, which contains the unique logic and of social and historical values of settlement environment construction in the Putian Plain. The research results may contribute to the re-cognition of the social and cultural values of traditional settlements in the Putian Plain, and the formation of a spatial pattern and formal language in line with the landscape characteristics of traditional settlements in the Putian Plain.