Rain Garden

Category: Professional Consulting firm:Group of Architects and Thinkers Client: tional Institute of Ophthalmology and Hospital Project Type: Landscape Location: Agargoan,Dhaka, Bangladesh TBA: 00 SFT Land area: 00 Period: 2016-2017 Status: Built Principal Architect: Md Rabiul Islam Project Architect: Md Mostasim Billah, National institute of Ophthalmology and hospital stands amidst one of the significant urban areas of Dhaka occupying 3-acre site, neighboring multiple healthcare facilities, educational and public institutes as well as numerous government organizations and offices. The urban fabric of Sher-E-Bangla Nagar comprises of ubiquitous bricks, concrete, glass and asphalt paved roads and streets that absorbs and re-radiates heat. However, compared to other urban areas of Dhaka, the public and government plots in this zone are landscaped with a good number of foreign and native plant species that improve the aesthetic quality yet provides no support to the local ecosystem. Similarly, within the 3-acre site of NIOH, about 75% of the existing site is covered with non-permeable heat absorbing surfaces along with the building material of the hospital that re-radiates heat creating a hot outdoor environment for the users. The front area of about 30,000 square feet has a green cover using unplanned vegetation and 15,000 square feet of grassland sitting on top of a non-permeable concrete sub-base that prevents rainwater absorption. The purpose of the landscape for NIOH was to 1.Counterbalance the existing impact of the context as well as the hospital itself through creating a landscape that prevents heat island effect in the zone by allowing heat absorption with a combination of permeable surfaces, 2.Re-connect the detached green patches of the city by introducing certain key plant species, 3.Ensure the movement of various city dwelling avian, mammals and reptile species to improve local biodiversity and 4.Create a soothing and healing environment for the occupants. The existing landscape mostly consists of medicinal plants with some coincidental occurrences of important native species however, majority of these plants are home to butterflies that does not necessarily support any local avian species as they merely provide shelter but not food. A major challenge of the landscape proposal for NIOH was to increase the diversity and movement of species by adding selective nectar based plants, fruit bearing trees as well as some flowering species to utilize the site as a hub for the local floras and faunas. A color chart has been designed for the landscape to showcase the various changes of blooms and color with the season. To meet the ecological needs, the existing grassland over the concrete sub-base was replaced with a proposed rain garden and urban forest and the parking space was relocated to the basement of the hospital replacing it with a permeable vegetated zone. The proposal converted 25,000 square feet of unused front area with a vegetated rain garden of 10,000 square feet; a permeable ground cover of 10,000 square feet dedicated for water purifying shrubs and tall grasses and an Urban forest of 5,000 square feet. Previously the grassland collected debris and litter from the streets and surroundings, prevented rainwater absorption and channeled it towards the main roads. The proposed rain garden is designed with riparian species that filters the runoff from driveways and side walks along with the assortment of hydrophilic plants that further purifies the water that would otherwise go untreated to the city waterways. It also helps sequester carbon, creates ecological connectivity and reduces flooding risk from the site. The combination of permeable surfaces and the rain garden provides an opportunity for ground water recharge to aid the decreasing ground water table of Dhaka by capturing rainwater and increasing the absorption capacity of the site. The increased number of permeable surfaces on the site would also prevent heat re-radiation by reducing the velocity of surface runoff during rain, cool the air and promote vegetation growth. The Urban forest shall act as a natural barrier from the main roads and serve as a sanctuary and a space for recuperation for the hospital and its users.