Objective The Three-North Plain is situated at the estuary of Hangzhou Bay, which represents one of the most active regions in China with regard to water conservancy construction in the southeast coastal region of China. During the traditional period, the construction of water conservancy projects represented by retention pond (Beitang) and seawall (Haitang), spearheaded the advancement of local economy, production and culture, forming a traditional human settlement environment system with indelible water conservancy imprints. In the context of new urbanization, it is of paramount importance to re-examine and comprehend this traditional water conservancy human settlement environment pattern, in which nature and humanity are harmoniously integrated, for future spatial planning of the Three-North Plain.

Methods This research investigates the impact of retention pond and seawall construction on the human settlement system of the Three-North Plain by using historical literature research method and morphological graphical analysis method, with GIS as a technological support tool. Firstly, an analysis is conducted on the geographic environment for retention pond and seawall construction at the regional scale, followed by an examination of their subsequent impact on local farmland pattern and land texture after their completion. Subsequently, at the settlement scale, the role played by water conservancy facilities in shaping the layout and morphology of settlement is delved into. Finally, from the vantage point of social organization, Shenshiqiao is taken as a case in point to analyze in detail local management organization and mode within the context of traditional water conservancy construction.

Results The Three-North Plain’s distinctive geographic environment and climatic conditions have historically resulted in a range of challenges, including recurrent droughts and floods, tidal wave incursions, and soil salinization. Therefore, water conservancy construction in the Three-North Plain centers around two main aspects. Firstly, retention ponds are constructed at the foothills to store fresh water for irrigation purposes. Secondly, seawalls are erected in the coastal regions to safeguard against tidal waves and salinity intrusion. Collectively, these two components constitute a dual water conservancy system characterized by “internal storage and external obstruction”, which serves as a crucial factor in interconnecting and facilitating the development of other spatial elements within local human settlement environment. In terms of the pattern of farmland, the construction of the water conservancy systems of retention ponds and seawalls not only facilitates the formation of agriculture, but also prompts local people to implement production adaptations to further improve the water conservancy systems, thereby resulting in different land textures: The Louzhao Polder in the area of retention ponds, and the Zaogang Salt Pond, Jingbang Polder, and Regular Polder in the area of seawalls. With regard to the settlement environment system, the characteristics of water conservancy facilities exert a profound influence on the settlement construction method: Retention ponds convey irrigation water through a reticulated water network, with settlements arranged in a group-like layout at the nodes of the network; seawalls are crossed by a line, so that the settlements are arranged in a linear layout with seawalls as the reference (specifically including linear scattering, comb-toothed, herring-bone, and linear encircling layouts). At the level of social organization, the construction of water conservancy projects and the maintenance of interests have led to the formation of local management organizations with family as the core, and the establishment of robust social relations regarding water conservancy.

Conclusion This research focuses on the characteristics of the traditional human settlement environment system in the Three-North Plain region in the context of water conservancy construction from the three aspects of water conservancy − farmland pattern, settlement layout and social organization, and further provides reference for the construction of a contemporary human settlement space system with local characteristics in the new period of urbanization. In light of its significance as a heritage site that encompasses both natural and cultural values, traditional water conservancy merits renewed examination and appreciation in the context of urbanization. Specifically, in addition to focusing on the physical part of traditional water conservancy projects, attention should also be paid to the spatial elements associated with water conservancy, such as agricultural landscapes and settlement systems. This is necessary for forming a holistic protection and management mindset that can give full play to the shaping of the spatial pattern of human settlements by water conservancy. Furthermore, it is essential to proactively incorporate traditional cultural elements associated with water conservancy, such as ritual practices and literary works, and facilitate the modernization of traditional water conservancy heritage value. Finally, in the context of rural revitalization, attention should be paid to reconstructing the relationship between people and traditional water conservancy, vigorously advocating community participation, and enhancing the residents’ sense of identification with traditional water conservancy, so as to build a contemporary human settlement environment in line with the local characteristics of the Three-North Plain.