Underground Water System in Tokyo Sidewalks

By Sophie Takano & Florence Li

Throughout the visit to Okinawa, Sophie and Florence were really inspired by the rainwater capture system of the Okicom building, which used slanted HPC tiles that allowed rainwater to flow into the building's internal pipe system and recycle the rainwater for storage, enabling plants to grow across the building’s exterior. The outer layer of the building was intentionally designed to guide water. After rainfall, rainwater is collected through the design of the exterior facade rather than discarded. This design is intended to promote greening, reduce heat, and support sustainable reuse. Using rain as a resource really shows an adaptation to Okinawa’s climate: the constant rainfall and humidity lead to maximizing its potential. It designs buildings to work with rainfall rather than defend against it, something that we hadn't seen often before.

Okinawa-Derived Logic

Rain conservation (pipe system and slanted concrete slabs)

Okinawa Case/Source

Observed in Okicom construction building to benefit plant support

Tokyo Condition

Heavy rainfall and scorching heat are experienced on Tokyo sidewalks, making it very uncomfortable for pedestrians.

However, in Tokyo, we found that compared to Okinawa, there are more high-rise buildings and more advanced urban designs, so we chose to focus on renovating Tokyo’s sidewalks. The main reason is that sidewalks serve as major gathering places for pedestrian traffic in the city and are often lined with trees and plants on both sides, which aligns well with our research focus. If Tokyo were to develop an Okinawan-like climate, a major issue would be increased rainfall, humidity, and heat, which would lead to increased discomfort for pedestrians (walking is the main form of transportation, especially in Tokyo).

With regard to the revised proposal, which takes into account Tokyo’s urban planning and adjustments to building types, we were inspired by the slopes of the rainwater capture system and the beneath-floor piping system that recycles water for plants. We decided to apply this logic to a regular sidewalk in Tokyo. Alongside the typical building gutter and drainage system, there are very small inlets (with a very slight tilt and gaps too narrow for a foot to fall into) that allow rainwater to flow down into a lower pipe. All of these entrances feed into a larger slope that combines the collected water and directs it downward until it reaches a flat filtration system, beneath which lies the main water conservation tank.

Read more about Sophie's and Florence's proposal here.