Superblock transformation in Seoul Megacity: Effects of block densification on urban ventilation patterns

Abstract

The superblock urban planning model is a response to mass rapid urbanization with large migration to big cities commonly seen in many Asian megacities. This paper investigates the evolution and transformation of superblocks in Gangnam District in Seoul during a period of intense urbanization between 1980 s and 2020 s, and its effects on urban ventilation environment. Four superblocks were selected, and mapping studies, CFD wind simulation analysis and field measurements were performed to identify areas of poor ventilation using minimum wind velocity criteria (<1.0 m/s). Significant changes in urban form are: a) average 43% increase in site coverage ratio from 1980 s to 2020 s; b) edge densification of large and taller buildings along superblock perimeter; and c) inner-block densification of low and mid-rise buildings within narrow street networks. It is found that large areas of inner block with little open space experience poor ventilation with air flow passing over much of these dense areas. Perimeter densification of tall buildings and inner grid discontinuous streets demonstrated to worsen the ventilation conditions. Winds from large perimeter roads are blocked from reaching inner areas forming a walled effect as seen from more than 67% of poor ventilation areas occurring in the inner-block areas. Although ventilation has worsened with densification maximum block velocities has increased between 8 and 50% with high velocities of more than 6 m/s occurring at perimeters near large edge roads. Superblocks with wider through roads and large ground-level open space of recent building redevelopments improves surrounding ventilation and allows for winds to reach further into the block. Superblocks as large living blocks must be allowed to breathe through increasing porosity not only along the perimeter but also by adding voids within inner areas to become a healthy, livable, cross-connected compact urban planning model.