Having many rivers along its topography, Tokyo in the Edo period had a dense and intensively used water network. Today most of them have been buried and turned into covered watercourses of different sizes. Among them, narrow covered watercourses, often seen among residential areas and impossible for cars to enter, have been regarded in urban planning as spaces difficult for further development. However, in some areas it is possible to see those alleys used by the residents as part of their living environment. This paper focuses on the covered watercourses in the Shibuya River basin as a study case of a high-density urban area where residual spaces could be re-evaluated.
Discussions about transitional spaces between the public and private and its importance in urban design has been going on since the 1960s. Gehl. (1987) points out the importance of opening up and combining the public and private visually, connecting the private spaces with public spaces in terms of accessibility and expanding the use of public spaces to create lively urban spaces. This study focuses on the public - private boundary of each building along the alleys on covered watercourses and conducts analysis to grasp the urban structure where public and private spaces coexist and is full of human activities.
First, 616 buildings along 10 alleys on covered watercourses were researched by field work. Spatial typologies of public - private boundaries were obtained by focusing on visual continuity and access from the alleys. Specifically, the type of ground shape, the placement of buildings, and boundary elements such as walls and fences that compose the public - private boundary were examined. In addition, the tendencies of use within each type was clarified by quantitatively analyzing the presence and position of traces of residents' activities, such as potted plants and furniture, and the effect they have on the public - private boundary. Then, the public - private boundaries types were sorted into patterns based on the similarity of the activity elements. By sorting the boundary characteristics of urban spaces that are formed by this cluster based on the typology of use of alleys on covered water courses, this research succeeded in showing the potential of alleys on covered watercourses to transform into a more active urban space.
From this result, it can be said that a unique urban landscape was formed on the alleys on covered watercourses by the diversity of the boundary area between the public and private space created by the different attitudes of each resident towards their own living environment. This paper sheds light on an often-neglected urban space, and suggests that new value can be created by opening the public - private boundary spaces that are used as the extension of daily life area towards the alley, so that these alleys can serve as a safe pedestrian network, and a place for communication.