Objective The hydrological characteristics of the Yellow River, which is easy to deposit, break dykes and migrate, have created the universal City − Lake Landscape phenomenon that city is surrounded by lake in the Yellow River Floodplain. These City − Lake Landscapes exhibit significantly different and more regular spatial features compared to other regions, such as city adjacent to the lake, city separate from the lake, and lake inlay in the city, it has systematic research value. This article attempts to take this type of City − Lake Landscape as the research object, discusses the historical experience of ancient lake type water conservancy facilities intervening in hydrological processes, responding to the Yellow River flood disaster, and thus reshaping regional landscape.
Methods The research starts from the regional perspective of landscape architecture, combines local chronicle information mining with geographical Spatial analysis, focuses on the City − Lake Landscape of 14 ancient cities in the Yellow River Floodplain, including Shangqiu, Xiayi, Yucheng, Suixian, Liaocheng, Caoxian, Chengwu and so on, and conducts from three levels of phenomenon, structure and method.
Results Firstly, the City − Lake Landscape phenomenon in the ancient city of 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 of disaster are highlighted in three aspects: 1) The high sediment concentration causes the terrain outside the city to gradually increase, resulting in the formation of overground suspended river and basin terrain; 2) The suspended river frequently overflows and changes its course, causing damage and flooding to the ancient city that flows through it; 3) The basin terrain makes it difficult to discharge waterlogging within the city, further exacerbating the difficulty of flood control. Secondly, the structural system of the City − Lake Landscape has three characteristics: 1) Composed of five types of elements: city wall, city embankment, surrounding lake, pond and ditch; 2) Each element, based on the practical needs of flood control and the feudal etiquette system, jointly forms a specific spatial structure of round outside but square inside and the urban basin; 3) In addition, in terms of functional structure, the City − Lake Landscape not only plays the hydraulic functions of flood control, sand blocking, water volume regulating and storing, and waterlogging diversion, but also has Agricultural and fishery production, tourism and other functions, which can effectively alleviate the Yellow River flood disaster and support the sustainable development of the city. Thirdly, there are five ways to construct the City − Lake Landscape: 1) The city site selection follows the principle of being high and close to the water, which not only avoids floods but also facilitates water intake; 2) Adapt to the water trend to build city walls and embankments, the construction of the city wall mainly adopts brick and stone cladding to improve flood resistance, lateral door opening to avoid floods, blocking the city gate directly towards the flood direction to prevent crevasse, and setting up water gate culverts to quickly drain floods, the construction methods of city embankment include building embankments in accordance with the water trend to disperse flood impact, connecting the city embankments into a ring to provide comprehensive flood control, building double embankments at easily eroded areas to improve local flood resistance, and further strengthening the earth embankment by planting trees; 3) Integrate the excavation of the surrounding lakes and the city ponds with the construction of the city walls and embankments, dredging surrounding lakes and ponds for flood storage and drainage, and using the resulting earthwork to build city walls and embankments for flood control and avoidance, assisted by culverts and ditches to timely divert and discharge waterlogging to reduce storage pressure; 4) The local residences pursue building near water, forming a landscape layout mode of front streets and back lakes, and the landscape planning also relies heavily on water conservancy elements such as surrounding lakes, ponds, city embankments and earth terraces, typical landscape modes include: lake − embankment − bridge − boat − lotus and willow, river − embankment − willow − fog and rain, lake − earth terrace − sunset − fog and rain; 5) If the City − Lake Landscape is still difficult 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 that the old underwater city and the new city are interdependent.
Conclusion This study 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. It 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 contemporary value be repositioned, to better protect and develop it.