Objective The hydrological characteristics of the Yellow River, which is easy to deposit, break dykes and migrate, have created a unique City – Lake Landscape phenomenon of city surrounding by lake that is commonly seen in the Yellow River Floodplain. The morphological features of such City – Lake Landscape are more regular than and significantly different from those in other regions, with the latter featuring city adjacency to the lake, city separation from the lake, lake embedding in the city, etc., which is of systematic research value. Taking the City – Lake Landscape in the Yellow River Floodplain as the research object, this research discusses the historical experience of intervening in hydrological process, responding to the Yellow River flood disaster, and accordingly reshaping regional landscape by virtue of ancient lake-based water conservancy facilities.

Methods Starting from the regional perspective of landscape architecture, this research combines local chronicle information mining with geospatial analysis with a focus on the City – Lake Landscape of 14 ancient cities in the Yellow River Floodplain, including Shangqiu, Xiayi, Yucheng, Suixian, Liaocheng, Caoxian, Chengwu, etc., and systematically explores the forming background, structure system and construction method of such City – Lake Landscape.

Results Firstly, the City – Lake Landscape phenomenon in the ancient cities in the Yellow River Floodplain is the result of the combined action of flood disaster and human intervention. The root cause of local flood disaster lies in the hydrological characteristics of the Yellow River, which is easy to deposit, break dykes and migrate, and the characteristics local flood disaster are highlighted in the following three aspects: 1) The high sediment concentration gradually elevates the terrain outside the city, giving birth to overground suspended river and basin terrain; 2) the suspended river frequently overflows and changes its course, causing damage and flooding to any ancient city flowing through it; 3) the basin terrain makes it difficult to eliminate waterlogging within the city, further exacerbating the difficulty of flood control. Secondly, the structural system of the City – Lake Landscape has three characteristics: 1) It is composed of five types of elements: city wall, city embankment, surrounding lake, pond and ditch; 2) the elements, based on the practical needs of flood control and the feudal etiquette system, jointly form a specific spatial structure of being round outside but square inside and the urban basin; 3) in addition, in terms of functional structure, the City – Lake Landscape not only has the hydraulic functions of flood control, sand blocking, water volume regulating and storing, and waterlogging diversion, but also has other functions such as agricultural and fishery production, and tourism, which can effectively alleviate the Yellow River flood disaster and support the sustainable development of the city. Thirdly, there are five construction methods for the City – Lake Landscape. 1) Follow the principle of being close to water with high altitude in city siting, which can not only avoid floods but also facilitate water intake. 2) Build city walls and embankments in line with water trend. The construction of city wall mainly adopts brick and stone cladding to improve flood resistance, reserves lateral door opening to avoid floods, blocks the city gate directly towards the flow direction of floods to prevent crevasse, and sets up water gate culverts to quickly drain floods. The construction methods of city embankment include building embankments in line with water trend to disperse flood impact, connecting city embankments into a ring to provide comprehensive flood control, building double embankments at areas vulnerable to erosion to improve local flood resistance, and further strengthening the earth embankment by planting trees. 3) Integrate the excavation of surrounding lakes and city ponds with the construction of city walls and embankments, dredge surrounding lakes and ponds for flood storage and drainage, and use the resulting earthwork to construct city walls and embankments for flood control and avoidance, assisted by culverts and ditches to timely divert and discharge waterlogging and thus reduce storage pressure. 4) Local residents prefer buildings near water, forming a landscape layout mode of front street and back lake. Besides, local landscape planning also relies heavily on water conservancy elements such as surrounding lakes, ponds, city embankments and earth terraces. Typical landscape patterns include: Lake – embankment – bridge – boat – lotus and willow, river – embankment – willow – fog and rain, lake – earth terrace – sunset – fog and rain, etc. 5) If it is difficult for the City – Lake Landscape in a city to withstand the extreme Yellow River flood disaster, the city will be relocated to a new highland outside the embankment, and the original city site will be submerged by floods, ultimately forming a landscape pattern featuring the interdependency between the old underwater city and the new city.

Conclusion This research summarizes the structural system characteristics and construction method of the ancient City – Lake Landscape in the Yellow River Floodplain through the mining of local chronicles and the analysis method of geospatial information technology. The research points out that City – Lake Landscape is a regional adaptive landscape formed by the joint action of the Yellow River flood disaster and manual intervention. Only by fully understanding the structural system and construction method of the City – Lake Landscape can the contemporary value thereof be reoriented and such landscape be better protected and developed.