President’s Message
Message 17/2019
Mr Lim Soon Heng, PE, FIMarEST.
Founder President
Pulau Tekong, a SAFE* cluster of floating islands
*SAFE an acronym for SINGAPORE ARM FORCES EXPERIENCE
I have written two previous messages on Tekong (Nos. 7 and 16.) The purpose of this one is to provide a better understanding of the alternative floating island solution instead of the dyke embankment and a platform level below sea level.
The above illustration, taken from a SINTEF (a Norwegian research facility) website shows a what a floating city could like if one was built. It covers an area about 8 hectares. The proposed Tekong polder is 810 hectares. Although a hundred times smaller the illustration is useful to understand what a floating complex at Tekong may look like. The “hub” layout in this illustration is obviously for a residential complex. If Tekong is to be used for basic military training the layout would be more rectilinear to facilitate rapid movement of soldiers. The movability of each modular island makes for easy reconfiguration.
The platforms are concrete and the buildings of steel structures. The height of the building may be five or fifteen storeys depending on the size of the platform and the available depth of water to provide the buoyancy.
Each platform is linked to the adjacent one and the whole forms a complex accessible anywhere by foot, or personal mobility device (PMD). For a mega complex drone taxi is another mode of getting around between clusters.
For military training, some clusters can be shaped to feature rolling terrains secondary jungles and swamps on top. The “basement” decks below can be used as barracks and workshops. The top deck may be set at 2 meters above the waterline. At low tide there shall a 1.5 metre clearance above the seabed for water to flow as tide changes. If desired a platform can be designed to be totally immersible. Servers needing to dissipate heat can be submerged for better energy efficiency. (Likewise, heat exchanger can transfer it its heat more efficiently using seawater as heat exchange medium.)
The complex is moored to the seabed by mooring systems which will keep in in place but allow it to rise and fall as tides change. The platform is not supported by piles. Hence the its weight and the weight of the building is independent of the geology of the seabed which may be coral, rock or marine clay.
In the open sea, it may be desirable to add a peripheral breakwater as depicted by the dark arc in the distance. The breakwater may be fully floating or partially supported by the seabed (often described as gravity based.) A gravity-based structure will always maintain a fixed elevation relative to land. A floating breakwater will always maintain a fixed elevation relative to the waterline. Each has its pros and cons. The choice is dictated by environmental conditions as well as the depth of water (buoyancy increases with draft.) The gravity-based breakwater would be similar to the one installed in the harbour of Monaco. The breakwater was built more than a thousand kilometres away. The one in Monaco (pictures may be viewed on the internet) is more sophisticated with four decks of car park and linked to land by a rotary connection which of course makes it costlier. (Captain Piet Sinke based here in Singapore was responsible for the towing and hooking up. We are inviting him to deliver a talk.)
A breakwater could be installed where the dyke is planned. The break water need not be a single continuous structure. It should comprise modules with spaces between adjacent ones so that water can flow in and out of the enclosure as the tide rises and falls. This is important for two reasons. First allowing water to flow in and out the nutrients necessary for the marine bio-system is replenished every day. Second, if the breakwater is designed as a gravity-based structure it is important to keep the hydraulic forces inside and outside of the lagoon in balance.
A gravity-based or fully floating breakwater is made of concrete with water tight compartments within. It is collision- and terrorist-proof and hence vastly safer than a sand embankment of a traditional polder. Wakes generated by passing ships will not destabilise it as will happen with sand dykes.
The breakwater is rectangular in cross-section. A traditional dyke is trapezoidal in section. Land is wasted when a dyke is used because of its unusable escarpment on each side. This is something a land hungry nation can do without. A rectangular section breakwater would eliminate that wasted space. The concrete breakwater can double up berth spaces. Inside its hull are spaces which may be used as stores.
The scheme does not need a major network of monsoon drains or retention ponds to handle flash floods. Rain is allowed to run into the sea or harvested fort drinking of maintaining landscape areas. There is no need install and maintain massive dewatering pumps and outfalls. In the polder scheme it would be necessary each year to pump out some 20 million cu m of surface water and sea water seepage. If the dewatering system fails, the entire area will remain flooded until the dewatering system is restored. Much of the pump room will be under water making restoration work difficult. The dewatering system can fail for a number of technical reasons as well as by sabotage. It can fail also if the outfall is blocked which can happen when barnacles develop over time.
The polder scheme would require the removal of marine clay and the back filling with imported (and potentially laden with bio-invasive species) sand. The sand fill will need several years to consolidate. It would be uneconomical to phase the development as that would require temporary cofferdams or more dykes. With the floating scheme development can be incremental on an as-needs basis. No huge sums of money are tied up waiting for the soil to consolidate.
The lagoon may be dredged to six to eight meters. The dredged material may be used as fill material for other sites such as at Pulau Semakau. The concrete platforms will have a draft of about 5 metres leaving a clearance below it of another 3 metres to allow nutrient-rich tidal currents to flow. The sides of the concrete platforms will over time encourage corals and seaweeds to grow forming excellent habitats for marine life.
Under the state law land reclamation can only be undertaken by the government. However, with floating islands, the state could invite the private sector to participate in the provision of floating islands under a PPP arrangement. Floating assets are easily collateralised therefore attractive investments for the capital market. The state provides license to mooring within its water over an agreed period and for an agreed price. The investor will have the obligation to remove the floats after the expiry of the license. He may find a buyer in another country where the floats can be repurposed.
I have intentionally used the acronym SAFE to underline the fact that the lagoon-floating islands concept is more robust than the polder. It is also to add the SAF (Singapore Armed Forces) signature to this disruptive technology which is taking the world by storm (pun intended.) Floating military base has been contemplated in the US for a number of years including one known as MOB. The project did not materialise because waterfront land is cheap, and the US shoreline is thousands of kilometres long.
SAFE is also more resilient to the any activities that Malaysia may undertake in the Straits of Johor. If Malaysia chooses to deepen their side of the straits, expand the capacity of the Tg Langsat jetty or to reclaim land, the changes in the tidal streams will have less impact on the floating breakwater than it would on a sand dyke. Earth tremors or water spouts are also not matters of concern.
The SAFE project will save taxpayers billions of dollars over its life due to its robustness and the elimination of the dewatering system. The anxiety of a dyke collapse is dissipated. Planners and users of SAFE will be able to sleep soundly.
Lim Soon Heng
President
February 28, 2019