Late last month, national water agency PUB announced its battle plan to reduce floods in Singapore over the next five years. It will spend $750 million on 20 drainage projects, including the expansion of six major canals across the island. Also promised are smaller engineering fixes such as rooftop gardens to slow rain water and flood barriers to keep the water out.
Arguably, it is a complete management system to tackle floods at various points of the rain-water chain. But the devil is in the details. Independent engineers told The Straits Times that PUB may find the plan difficult to implement, raising other issues which should also be addressed.
The $750 million figure sounds impressive. But PUB is already spending about $150 million a year on drainage projects. This amounts to $750 million over five years. The canals run through built-up estates such as Rochor and Bukit Timah, and widening them in these crowded areas may be difficult.
Where possible, the expansions will take away space from future and existing roads, homes and businesses. The excavation works and expansions could lead to intrusions into private property, said Dr Ho Nyok Yong, president of the Singapore Contractors Association.
Associate Professor Tan Soon Keat, an Institution of Engineers fellow, said the capacity of the canals is likely to be reduced during the construction work, leading to a higher risk of floods. Widening the canals could also change the water’s speed and how sediment is transported, affecting eco-systems in reservoirs.
Four of the canals for enlargement are upstream of the Marina Reservoir, magnifying the risk. Computer models should be used to predict the environmental impact of the work, said National University of Singapore Assistant Professor Vivien Chua. Whether the drainage projects would reduce floods or simply shift them from one place to another is another pertinent question.
Only sections of the canals in flood-prone areas will be enlarged. If sections farther downstream cannot handle more water from these expansions, the projects will only transfer the floods downstream. But PUB explained that its hydraulic checks ensure the problem will not be transferred farther downstream, and conditions will be no different than before.
PUB’s other measures could also bring it into conflict with other agencies. It will work with developers to install features such as rooftop gardens to help slow and retain rain water during storms. These will be built into new and, if necessary, existing buildings.
But flood-prone areas such as Orchard Road and Bukit Timah are built-up and are unlikely to have many new developments. For the features to be effective, they will have to be compulsory and applied to existing buildings.
But other agencies may have their own plans for the rooftops of existing buildings. The Housing Board (HDB), for example, plans to install solar panels on rooftops in 30 precincts by 2014. Engineering fixes at the street level may also affect other services such as train systems and water, sewage and power utilities.
Associate Professor Susanto Teng of Nanyang Technological University’s civil and environmental engineering school said changes in the soil pressure could affect the stability of MRT tunnels. ‘When both MRT works and canal works happen at the same location, things can be tricky,’ he said.
PUB said the expansion of canals near tunnel works will be led by the Land Transport Authority (LTA) to better coordinate the projects.
Potential conflicts with other agencies is why a whole-of-government approach to flooding is necessary. Such an approach will address other issues such as pedestrian and traffic flow disruptions, urban planning and the effect of the projects on homes and businesses.
Such coordination is important as land use - on rooftops, at the street level and even underground - will become more competitive.
Minister for the Environment and Water Resources Vivian Balakrishnan has said an underground detention pond to relieve Stamford Canal and reduce floods in Orchard Road would have to be the size of two to three football fields. PUB is studying its feasibility and will announce its findings by May.
But last month, the Government said a masterplan was under way to map out possible uses of underground space across the country. The Singapore Geology Office, set up in 2010 to provide subterranean data for future underground planning, is yet to complete this work.
Currently, the land-use masterplan is reviewed every five years, while the drainage masterplan will be updated every three years, from next year. Engineers point out that the different timetables do not make sense as work on one level affects the others. Greater alignment between the agencies would also result in more efficient use of limited available land.
The Ministry of National Development (MND), for example, is considering plans to add more car spaces to ease shortages in older estates. Theoretically at least, MND can work with PUB so that the new spaces can absorb rain water.
In the United States and Brazil, the authorities have jointly redeveloped carparks with porous material instead of normal asphalt. This allows the carpark spaces to double as water retention areas during storms.
An inter-agency committee was formed in 2010 to tackle floods, comprising the PUB, HDB, Singapore Land Authority, LTA, Building and Construction Authority, National Parks Board and industrial landlord JTC Corp. But little has been heard from it since its recommendations last year for higher platform and crest levels for buildings.
Let it lead the way. Give it a deadline, task it with integrating the masterplans and solutions and put its findings up for public discussion. Explain the trade-offs between flood prevention and other goals clearly.
This will not only improve the plans, but also restore confidence in the flood situation being resolved - not just punted into another arena.
