Introduction

The story of the Singapore River’s transformation is a well-known one. Originally a centre of burgeoning trade and industry, the river was heavily polluted by garbage, sewage, oil spills, and even waste from upstream pig and duck farms. In 1977, then Prime Minister Lee Kuan Yew called for a massive clean up of Singapore’s rivers. It was a monumental effort, costing the government $170 million and involving relocating squatters and traders, dredging of the river bank and bottom, and clearing the copious amounts of debris and rubbish. Since then, Singapore has gained a reputation as a “clean-and-green” city, and the government has remained steadfast in its efforts to clean and beautify its rivers and waterways.

One of the persistent challenges the Singapore government has faced in maintaining the integrity of its waters has been the build up of silt, which is most evident when stream, river, or canal waters turn a murky brown after a heavy downpour. Silt and sediment control remains a key element in Singapore’s water resource management strategy, as sediments can remain suspended for a very long time and contribute to environmental pollution and increased flood risk. Silt also makes water more difficult and costly to treat, and the Singapore Public Utilities Board (PUB) already spends an estimated $5 million to $6 million a year just dredging canals where silt builds up.

Whilst a portion of silt and sediment pollution can be attributed to natural causes, the major source of such pollution are from construction sites. Construction activities disturb existing ground cover and vegetation, expose bare surfaces, and cause soil erosion. When there is rainfall, rain water then picks up the silt and sediments from construction sites and deposits them in the waterways. As such, contractors play a major role in preventing silty discharge and preserving the cleanliness of Singapore’s waters.

Singapore’s Sewerage and Drainage Act

Broadly, the Sewerage and Drainage Act governs the construction, maintenance, improvement, operation and use of sewerage and land drainage systems.

Of note:

26.-1. No person shall carry out or cause to be carried out –

a. any works which affect or are likely to affect any storm water drainage system, drain or drainage reserve, directly or indirectly; or

b. any works that could lead to the discharge of silt directly or indirectly into any storm water drainage system, drain or drainage reserve

To preserve the quality of Singapore’s waters, the discharge of silt and other forms of debris is heavily regulated, and companies found responsible for discharge with total suspended solids exceeding 50 milligrams per litre can be penalized under the Sewerage and Drainage Act. Each offence will cost contractors S$5,000, and those who fail to comply with notices to shore up their protective measures can be fined up to S$50,000. Earthworks in Singapore must also be carried out in compliance with the Code of Practice on Surface Water Drainage.

Specifically, contractors must ensure that:

1. Earth control measures must be provided and maintained in accordance with the Code of Practice
2. Runoff within, upstream of and adjacent to the work site must be effectively drained away without causing flooding within or in the vicinity of the work site.
3. All earth slopes must be set outside a drainage reserve
4. All earth slopes adjacent to any drain must be closed turfed
5. Adequate measures must be taken to prevent any earth, sand, topsoil, concrete, debris or any other material to fall or washed into the storm water drainage system from the stockpile

These regulations are enforced by PUB and its partner agencies. In 2013, two contractors were fined for letting muddy waters flow out of their construction sites. The first was at Upper Thomson’s Windsor Park: cloudy water from the estate’s drainage project filled a clear freshwater stream next to a nature reserve with silt. The stream is home to 12 species of native frogs, including several endangered ones, as well as fish and dragonflies. Build up of silt adversely affects water quality and can harm the local biodiversity. The second construction site was at in Pasir Ris: poor earth control measures caused nearby roads to be flooded with brown water, leading to traffic jams.

Innovation in Silt Water Management

To tackle the problem of silty discharge, PUB has been working with the stakeholders on education and engagement, technology upgrading, and encouraging good earth control measures (ECM) practices.

Here, we will highlight some of the PUB’s recent advances in this area.

Silt Imagery Detection System (SIDS)

SIDS was introduced in 2016 as a means of saving construction companies time and labour costs in monitoring silt and sediment runoff. Currently, most contractors assign workers to manually watch closed-circuit television footage of drains. This is a labour-intensive and inconsistent system. The new system overhauls the existing practice by using image recognition technology to analyse CCTV images, and alerting contractors if muddied or silty water is detected.

As of 1 February 2016, new construction sites at 0.2 hectares or larger are required to connect their existing drainage monitoring systems to SIDS, with 178 work sites already using it. By the end of 2017, PUB expects 800 construction sites islandwide to adopt the Sids technology, to save construction contractors an estimated 100,000 man-hours per year.

Robot “swans”

The New Smart Water Assessment Network (NUSwan) may look like a swan, but is in actuality a sophisticated robot. Built that way to blend in with the environment, the autonomous robotic platform carries out real-time monitoring of water quality. They have been tested and are ready for “release” at selected reservoirs. They can be remotely controlled or assigned pre-defined tasks (for example, perform scanning of a given area or collect water samples, measure pH, temperature, and conductivity of the water) which they can carry out autonomously. The real-time monitoring will enhance response time to emerging events at the deployed location.

Best Practices for Construction

The best way to minimise erosion is to reduce the amount of exposed earth surfaces on site. This can be achieved by phasing of earth works, covering up exposed earth areas with erosion control blankets of canvas covers, early reinstatement, and paving.

The ECM guidebook published by the PUB in partnership with the Singapore Contractor’s Associate is also available here.