"Kallang", possibly due to its location on either side of the Kallang River. The subzone was later renamed to its current name, taken after a nearby road of the same name, and is a constituent part of Toa Payoh Planning Area. Geology Kallang sits on the Kallang Formation which consists of soft marine clay, loose alluvial muddy sand, loose beach sand, soft peaty and organic mud, and coral. Aside from the eponymous Kallang, the Kallang Formation is also found in other parts of Singapore, particularly at river valleys, as well as around river mouths and coastal regions. Terrain The terrain of Kallang is generally flat and low, with elevation no more than 15 metres above sea level. Though not located within Kallang Planning Area, the geographic point of Bukit Kallang (also spelt as "Bukit Kalang") is a hill in the Central Water Catchment and has an elevation of 97 metres. Bukit Kallang is situated at the southeastern corner of the Upper Peirce Reservoir, west of the TreeTop Walk suspension bridge, and within the territory of the former Ulu Kallang mukim. The Bukit Kalang Service Reservoir maintained by the Public Utilities Board (PUB) is within its vicinity, so is the source of the Kallang River, the Lower Peirce Reservoir. Water bodies The Kallang River is the main waterway that meanders through Kallang. The source of the Kallang River is the Lower Peirce Reservoir (formerly known as the "Kallang River Reservoir"; renamed in honour of Municipal Engineer Robert Peirce in 1922) and the river mouth is located at Kallang Basin, near to the Merdeka Bridge. Flowing for more than 10 kilometres, the Kallang River is the longest river in Singapore and drains areas as far north as Bishan and Ang Mo Kio. The Kallang Basin is an enclosed bay in Kallang, and is a popular location for water sports. The Singapore Sports Hub is located on the eastern bank of the Kallang Basin. In 1977, the Singapore government embarked on a ten-year-long clean-up project for the Kallang Basin and the nearby Singapore River, transforming them into the clean waterways of today. The Kallang Basin area used to form part of mainland Singapore's southeastern coastline, as evident from the location of Beach Road. Kallang River used to empty into the Singapore Straits at Kallang Basin, as did Rochor River and Geylang River. One of the Republic of Singapore Navy's (RSN) Bedok-class mine countermeasures