Informing design visioning through dynamic modelling – Better practices for nature-based solutions

Nature-based solutions (NBS) that focus on greening of the urban landscape increasingly are employed to address climate change and hydro-meteorological risk, with the goal of improving resilience to such hazards. However, development of innovative NBS designs and assessment of design performance often are not well-integrated. The objective of our study was to develop and document an interactive NBS design and modelling procedure that can guide future design practice and can be effectively implemented through virtual work necessitated by Covid restrictions. We begin our presentation by reviewing the design vision of an existing landscape at Thammasat University, Rangsit Center, in Pathumthani, Thailand, that forms part of the “green, smart” plan for the campus. Named after Professor Puey Ungphakorn, the Rector of Thammasat University in the 1970’s, the Puey Ungphakorn Centenary Hall opened in 2019. Within its distinctive, arching, H-shaped outline (“H” for Humanity), it houses an auditorium, library, archives, museum, meeting spaces, and concert hall. The 7,000 m2 green roof is Asia’s largest urban farming green roof. It was designed with an emphasis on resilience in the face of climate change and to re-connect community with nature in an increasingly urbanized landscape. The roof design is inspired by the terraced rice paddies of Southeast Asia. Subsequently, we discuss the ongoing NBS-inspired design and redevelopment for the 5.3 ha property immediately adjacent to the Centenary Hall. The existing unpaved, informal parking lot and pond area of this property will be connected to one of the ponds that is part of the Centenary Hall complex via two constructed, meandering grassed swale channels that facilitate water circulation between the two ponds. The grassed swales will be terraced, following the pattern of natural river valleys and will provide flood protection and storage for irrigation. Cleansing biotopes and floating wetlands are incorporated into the design to improve water quality and the water is pumped from the two ponds into the connecting grassed swales to avoid water stagnation, particularly an issue during the dry season.

PCSWMM was applied to examine water quantity and quality dynamics associated with runoff from the green roof and iteratively inform the design vision for the adjacent property. Sampling of the green roof runoff (irrigation water) and in the existing ponds and drainage canals during dry weather showed that TKN, TP, and TSS ranged between 1.1-4.5 mg/L, 0.27-4.6 mg/L, and 6-20 mg/L, respectively. These values, which generally indicate eutrophic conditions, were used to guide initial system representation within PCSWMM. PCSWMM parameterization for the green roof, cleansing biotopes, and floating wetlands was done based on our past projects in Southeast Asia. A 6-month simulation that covered the wettest part of the rainy season and early dry season (beginning August, 2018 to end January, 2019, with 5-minute rainfall data) was used as the basis for design evaluation. The largest 24-hour rainfall occurred on 15 Sep 2018, with 77.1 mm total depth (approximately a 2-year event) and a peak intensity of 136.8 mm/hr. Rainfall for the entire 6-month record was 463 mm, which is lower than average. PCSWMM was effective in communicating water quality results expected for different design options to the landscape architecture team. In particular, the pump operations were optimized to enhance system performance and electrical consumption, the depth of the filtration and drainage layers for the cleansing biotopes could be reduced from initial design and still provide adequate treatment, additional cleansing biotope areas were considered, the floating wetlands were sized to polish the pond quality, and treatment of the green roof runoff was recommended. The modelling indicated that nutrient levels could be reduced to attain mesotrophic status using the envisioned NBS design.

Finally, a 24-hour 100-year design storm was modelled, using the SCS Type II pattern, with a total depth of 123.3 mm and peak intensity of 169 mm/hr. The pond and swale system would be capable of managing this event without flooding, although the swale terrace areas would be inundated, as typically is observed in a natural system.

Regular online meetings and exchanges of ideas and data between the architecture and modelling groups facilitated development of an innovative, visionary, NBS design that enhances campus wellbeing, resiliency, and water management performance.