Objective  As a link between land and sea, the shoreline is a vital space for human activities and urban development, and is a limited natural and spatial resource. The unique natural and cultural landscapes in coastal zones are important motivators for urban spatial development. Through landscape construction, the development and utilization pattern of urban coastal areas can be optimized. However, with the rapid development of coastal landscape practice, there has been a trend towards homogenization, and the local characteristics of the coastline have begun to deteriorate. Indirectly, the spatial reconstruction driven by development proposals has led to such problems as downsizing of traditional industries, benefit loss of local communities, and gentrification that are detrimental to the sustainable development of local society. The rapid increase in artificial landform has also altered the hydrological conditions of coastal zones, causing damage to the long-established natural/semi-artificial environmental ecosystem. Therefore, understanding and preserving the unique natural and cultural landscape in coastal zones should be a question that needs to be answered in planning and design practice. The objective of this research is to propose a multi-level and multi-scale interdisciplinary design framework to solve the problem of how to recognize and maintain the unique natural and human landscape in coastal zones in landscape planning and design.

Methods  This research adopts an interdisciplinary and case study approach. Based on the practice of planning and design of landscape space in urban coastal zones, this research introduces the concept of time depth by combing the development history of landscape in urban coastal zones with existing research basis. On this basis, the research proposes a path framework for planning and design of landscape space in urban coastal zones in combination with the characteristics of time depth, and explains the specific application process of the research framework through a case study.

Results  Currently, people have realized the preeminent role of coastal landscape characters in urban aesthetics, development control, and strategy formulation. In Europe, the methods for seascape character assessment (SCA) have been developed, but there are still limitations in the practical application thereof for design practice. Specifically, the classification of landscape elements in SCA still exists in a binary opposition between land and sea. The spatial scale of SCA results is too large, which makes it difficult for designers to make effective value judgments on fine-grained coastal landscape elements in real sites. There is still a lack of organizational logic for coastal landscape characters in specific site design, which is prone to cause exclusive narratives. The concept of time depth regards urban space as a complex layering of multiple temporally interconnected slices. This concept has been applied in the assessment of landscape characters and has shown potential as a design cognition and thinking paradigm. By examining how the time depth characteristics of coastal landscape reflect natural changes in the coastal environment and human history, the research confirms the potential and advantages of introducing the concept of time depth into coastal landscape planning and design. In this research, slices of different time depths are superimposed to form a coastal landscape with distinct regional differences and developmental stage characteristics, which provides a landscape prototype for spatial construction. By introducing the concept of time depth, the static and sectional results in the traditional assessment methods for coastal landscape characters can be elevated, and the current material status of space can be combined with the historical evolution process of the site concerned. This can remedy the shortcomings of the current landscape character assessment results in terms of landscape character unit and landscape element scale, while providing a spectrum for establishing a lineage that includes different types of landscape, both artificial and natural, on land and at sea, which can help clarify the intrinsic logic of the natural system and human living environment in the spatiotemporal development thereof. Under the background that China has not yet established a systematic method for assessing coastal landscape characters, incorporating the composite time depth analysis into the design practice of coastal landscape is a more practical approach to addressing current issues involved in the design practice. The research proposes a design method for coastal landscape based on the time depth characteristics of coastal landscape, which involves "identification" "spatial reproduction" "system construction", and "process response". Firstly, in the preliminary stage of design, a thorough identification of the research area through time slicing is conducted. Secondly, based on the spatial characteristics of the coastal zone, the design process is divided into two steps. In the first step, based on the identified spatiotemporal information about the site concerned, spatial reproduction is conducted through various design methods, and scenarios are created by organizing site functions, forms, and other elements in a layered manner. These design methods can be managed in the form of case library or toolbox to deal with the complex situation of different time slices in the actual environment. The second step entails constructing a landscape structure to bridge the coastal landscape fragmentation that may be caused by the diverse scenario created in the previous step. Through the construction of coastal landscape subsystems, various processes are indirectly shaped to provide comprehensive ecosystem services and landscape experiences for the entire landscape system. Finally, the method framework sets up a response mechanism for both the design implementation and evaluation stages to preserve the elasticity of coastal landscape development. Moreover, the research takes the landscape planning of Xiamen East Coast Romantic Line as an example to illustrate the specific content and strategies of the four aspects of the design method just mentioned, in hope of providing a reference for future relevant projects.

Conclusion  This method, by mining and utilizing the connotation and temporal layers of coastal zones, can form a coherent thinking process from site analysis to design method, while maintaining the dynamic nature of landscape, promoting sustainable development, and addressing site complexity. Future research can focus on supplementing the toolkit in the method framework and establishing a localized assessment system for seascape character. This research believes that a non-spatial perspective should be emphasized for inspiring landscape research and practice.