Stormwater Cooling Enclosure | Melissa Tan Zhi Qun, Janice Yong Qi Hui - Architecture and Sustainable Design (ASD)

Option Studio: Building an Urban Forest
Instructor: Christine Yogiaman

Cities are on the front lines of the growing physical risks associated with climate change. The Intergovernmental Panel on Climate Change, IPCC, predicts the onset of prolonged periods of rain and heat spells that will continue to accelerate in the near future.

On Alexandra Woodlands, we propose to reconsider our urban stormwater infrastructure. Current infrastructure that builds on an engineering efficiency of removing water for a dry urban landscape breaks down at the onset of this prolonged periods of unpredictable rain. The project proposes a new form of infrastructure that enable multiple use scenarios and capitalize on the continuingly evolving and uncertain supply of rainwater.

Buildings on Alexandra Woodlands are part players in the network of urban formations that constitute this new form of infrastructure.

Research was conducted on flooding around the Alexandra area and to identify ways in which our site can be used for flood mitigation. Statistics derived from the Meteorological Service Singapore have shown a rising trend in rainfall intensity around the area. The flood on 3 June 2019 had a rainfall of 80.4mm while that on 17 April 2021 had a higher rainfall of 160.4mm. The total volume of rainfall accumulated from the 17 April 2021 flood was calculated to be 264000 m³. Further analysis of water flow was conducted across the entire catchment area to identify areas of pooling as shown. These would serve to drive our landscaping strategies for the project.

For the landscaping strategies, we implemented the use of cut-and-fill to deepen the existing terrain depressions and elevate the land around the boundary for better containment of stormwater within our site and the prevention of leakage into the surrounding roads. Concrete plazas were also integrated to act as secondary overspill pools during flooding conditions. Under dry conditions, these plazas would serve as open spaces for a multitude of activities to take place in. Another round of analysis was then conducted to evaluate the effectiveness of our strategy both under current flooding conditions and under projected flooding conditions in 10 years time. The figure for this projection of rainfall was calculated based on the Intergovernmental Panel on Climate Change’s (IPCC) sixth assessment report. The strategy has been observed to be largely effective at containing the stormwater runoff under both flooding conditions.

Based on the water flow analysis of the site, the soil saturation or water content of the soil was evaluated and categorized into four zones as shown. A plant swatch was also created for the different zones of land. Zone 1 has the highest soil saturation and is most suitable for plants with the greatest water tolerance. This is followed by Zones 2 and 3 with decreasing soil saturation and hence, the plants used have decreasing water tolerance. The last zone comprises of hardscape concrete on which no planting is conducted.

We also did research on extreme heat conditions in Singapore. Cities are on average 12 degree celsius higher in temperature due to the Urban Heat Island Effect and Singapore is no exception. This is due to hard synthetic materials such as asphalt and concrete that trap heat compared to softscape materials such as grass. We did a mapping on site to identify the heat trapped from the surrounding area and envisioned our project to be a cooling refrigerator on site through the use of evaporative cooling and using water collected on site as an asset. Evaporative cooling is a cooling method that is similar to how humans keep cool when they sweat.

To speed up evaporation over our water bodies, we would need to ensure that wind passing over our water bodies is maximized. We found the two dominant winds in Singapore, February North-East wind and October South wind, and ensured that our building forms do not obstruct the winds. We tested various building angles and concluded a few angles that our building form would have to strictly follow.

This shows the overall axonometric drawing of our design for the project inclusive of the pools of water, plazas, plants, built form, boardwalks and canopy. On the right shows the eThis shows our ecological and human process diagram. With purple arrows being the natural water and heat cycles on site, we also wish to intervene and supplement the natural cooling process with dry misting. Misting is the spraying of tiny water particles into the atmosphere and allowing evaporation of these tiny particles to leave a cooling effect behind. With water collected from the flooding, it would be used to distribute misting to the entire site through a canopy and even enter the building through the roofs to ensure cooling both outdoors and indoors.

This shows the overall axonometric drawing of our design for the project inclusive of the pools of water, plazas, plants, built form, boardwalks and canopy. On the right shows the exploded view of each element and how all the elements come together to form our final project. The programmes of the individual buildings are also listed out in the exploded axonometric drawings. The buildings in the top right are dedicated to recreational activities, hosting a variety of sports courts. The building in the bottom right hosts a diverse range of retail shops, entertainment facilities and several dance studios and tuition centers. The building on the left is a mix-used development containing offices, a community center, a hawker center and so on. All four buildings are connected by the elevated boardwalk that allows for connection even during flooding and which doubles up as a running track for those engaging in sports and recreational activities.

The three sectional perspectives shown highlight the spatial experiences within our site. The first shows a view taken from the rail corridor, the second is one taken from walking along our elevated boardwalks and the last one shows a view taken from within the central forested area where the mature trees are preserved looking out towards our buildings and canopy pipelines that are interweaving amongst the trees. All three highlight the sources of heat radiation in pink including the hardscape building surfaces and human activities while the pools of water, pipelines and mist are highlighted in blue, signifying their cooling effects across the site.