The Kallang River in Bishan Park has been freed from a concrete channel and returned to a natural, meandering path. The mound in the background is known as Recycle Hill, built with concrete from the former channel. © CH2M HILL
The Kallang River is freed from a concrete canal in a project designed to better integrate the body of water into Singapore’s Bishan Park.
January 22, 2013 —The Kallang River follows a natural, meandering path through Bishan-Ang Mo Kio Park—one of the largest and most popular public parks in Singapore—after the completion of an ambitious civil engineering project to free a portion of the 10 km river from a foreboding concrete channel that once bisected the grounds.
Bishan-Ang Mo Kio Park covers an expansive 62 hectares, featuring a lotus garden, several playgrounds, performance spaces, a dog run, cafés, a reflexology footpath, and exercise stations. The park is divided into two sections: Pond Gardens and River Plains. The park is home to a wide variety of plants and animals, including basil, bladder cherry, scaly breasted munia, purple heron, little egret, variable wisp, common scarlet, and the peacock pansy.
The project to convert the concrete channel into a beautiful stream is part of the Active, Beautiful, Clean Waters (ABC Waters) initiative by PUB, Singapore’s national water agency. PUB wants to enhance Singapore’s network of drains, canals, and reservoirs into recreational and aesthetic assets by converting them into clean streams, rivers, and lakes.
CH2M HILL, based in Englewood, Colorado, helped PUB develop a master plan for one of three regions in the ABC Waters program in 2006. Work on the Bishan Park project began in 2009 and was completed in 2012.
Gently sloping banks afford residents easy access to explore the
river. © CH2M HILL
“Driven by national water agency PUB’s vision to integrate the green with the blue and draw people closer to water, the idea for this waterway was to create a naturalized river within the park so people could enjoy recreational activities, while the waterway continued to fulfill its drainage and conveyance functions,” said Tan Nguan Sen, the director of PUB’s Catchment and Waterways Department, in written comments to Civil Engineering online.
The Kallang River is the longest river in Singapore at 10 km. The $76-million Bishan Park project called for the removal of 2.7 km of concrete channel, which was 17 m to 24 m wide. The channel was replaced by 3 km of meandering river with soil-bioengineered embankments to slow the water and maintain the flood control function of the original channel during Singapore’s two annual monsoon seasons.
The new river through the park features many inviting areas that beckon parkgoers to cross the wide, gently sloping banks into the water, where they can experience some of the area’s rich biodiversity, which has increased significantly with completion of the project.
Ground conditions at the site varied. Some areas excavated for the new river included peat material, which required tight dewatering control. A 60 m test reach was constructed to test various bioengineering techniques, which are still uncommon in Singapore. Soil mixing and modification were used in some areas of the new river and the slopes to provide a better opportunity for the bioengineering plants to thrive.
Plants are also utilized in biotope that is used as a natural means to clean the water in the park. Water from the river and ponds in the park is pumped into the biotope, where carefully selected plants—paper reed, water canna, and pickerel weed—absorb nutrients and pollutants. The biotope eliminates the need to treat the water with chemicals.
The park is one of the largest and most popular in Singapore,
featuring a reflexology footpath, among other amenities.
© CH2M HILL
One major challenge during construction was to ensure that flow in the concrete canal was maintained as the river was constructed. Construction within the channel was carried out in sections, and temporary cofferdams that could be removed quickly were used. The project required tight construction controls to accommodate the intense storms.
Sustainability was an important element of the project for PUB. The team created an area called Recycle Hill, an impressive mound clad with concrete slabs recycled from the canal when it was demolished.
“Recycle Hill…represents a deliberate effort to preserve a part of the park’s history and to reuse the concrete in a creative and meaningful way,” Tan said.
The concrete slabs were also used in the riverbed and as dividers for the biotope. Sustainability efforts went beyond the concrete, however. Trees that were removed were repurposed as habitat logs. Some stumps were reused as seating in areas of the park. Tree limbs were used as wood chips. Excavated soil was reused, as well.
“The significantly wider natural river was designed to allow most of its shallow banks to be used as part of the new park space,” said Tuck Wai Lee, CH2M HILL’s project manager for the ABC Waters program, in written comments to Civil Engineering online. “Detailed hydraulics modeling was performed to ensure hydraulic performance, as well as [to] design park features that needed to be clear of high water lines in the event of a storm. Over the proposed 3 km river, more than 100 cross sections and about 7 different bioengineering and stabilization techniques were simulated for the river.”
Singapore’s tropical rain forest climate delivers frequent strong rain storms, the worst lasting for days. These heavy rains quickly swell the Kallang River, and had to be accounted for in the new design of Bishan Park. Because the new park removes the barriers between parkgoers and the river, a warning system was installed to alert residents to rising waters.
“A river-monitoring and warning system with water-level sensors, warning lights, sirens, and audio announcements are in place to provide early warning in the event of impending heavy rain or rising water levels,” Lee said. “Warning signs, red markers, and life buoys have also been put up along the river.”
The park is a natural habitat for many different plant and animal
species. The Kallang River project has improved the park’s
biodiversity. © CH2M HILL
This river-monitoring system will alert park users to move out of the river beyond the red markers in the event of impending heavy rain or rising water levels, Lee added. In addition, there are safety lines with buoys at selected locations across the river, as well as closed-circuit TVs, and an around-the-clock patrol surveillance team.
“It is very satisfying when we see how the naturalized river has turned the whole park into a more vibrant and beautiful place, with people enjoying the waters, biodiversity, and new spaces created,” Tan said.
“No longer separated by a concrete canal, the river and park [are] now integrated and more accessible to the community, and it is very nice to see families enjoying the river, especially during the weekends,” Tan said. “More importantly, the community is not only using the facilities, but also taking ownership of the river and park. Volunteer groups that patrol the park on weekends help to promote safe and responsible use of the river and park, while learning trails conducted by schools allow students to learn more about the natural features at the park.”
PUB is developing 20 such projects currently, and plans to undertake 100 projects by 2025.