Structural Engineering International 1/2009 Structures Worldwide 17

Marina Barrage – A Unique 3-in-1 Project in SingaporeWung Hee Moh, Director and Pei Lin Su, Senior Manager, Best Sourcing, PUB, Singapore. Contact: SU_Pei_Lin@pub.gov.sg

performances, thrilling water sports competitions and river taxis plying be-tween waterfront attractions will bring an attractive new lifestyle experience for all to enjoy.

Keywords: Marina Barrage; Marina Reservoir; flood control; water supply; lifestyle attraction; crest gates; drain-age pumps.

Design Considerations for Marina Barrage

The MB project was first conceived in the mid 1980s as part of a comprehen-sive scheme to address the significant flooding that Singapore had been expe-riencing in its core urban area. Annual rainfall in Singapore exceeds 2500 mm, and daily rainfall upwards of 200 mm is not uncommon.

The design of the MB scheme has to address various major challenges:

(1) The system has to be capable of handling the very large storm dis-charges of up to 2800 m3/s from very rapidly responding urban catchments. The peak fl ows are experienced within less than 30 min for storm events.

(2) The scheme has to operate with storms up to the 100-year event without fl ooding in the down town area.

(3) Maximization of the water sup-ply yield within fl ood control

constraints and fulfi lling the re-creational needs.

(4) The facilities have to be aes-thetically pleasing, given their location in the heart of the new downtown Singapore, and be wel-coming to the public.

The area around Marina Reservoir has been slated by the urban redevel-opment planning process in Singapore as the location for many high-value projects, in particular the multi-billion dollar Integrated Resort, the second Financial “hub” for Singapore, the Gar-dens by the Bay and the Sports Hub. These shoreline developments would benefit from the pool level in Marina Reservoir being maintained at a fairly static level, and without the 3-m daily variation caused by sea tides experi-enced before the barrage is construct-ed. An operating range of less than 1 m was selected as a design goal.

Key Features of Marina Barrage

The key features of the MB (Fig. 1) include the following:

(1) barrage with nine “fi sh-belly” crest gates spanning across the Marina Channel and a 6-m-wide pedestrian bridge spanning over the barrage;

(2) drainage pumping station, which houses seven drainage pumps (six main pumps and one standby)

Introduction

The Marina Barrage (MB), located in the southern part of Singapore, is an innovative and cost-effective engineer-ing solution to meet Singapore’s needs for water supply, while providing flood control and recreational possibilities.

The barrage spans across the 350-m-wide Marina Channel and the result-ing reservoir will be fed by waterways upstream such as the Singapore River, Geylang River and Kallang River. By keeping seawater out, the water in the reservoir will eventually turn into freshwater.

The MB is much more than a dam; it has a 3-in-1 concept. The barrage is designed for flood control. It acts as a barrier against the sea and stop high tide from flooding low-lying parts of the city such as Chinatown, Boat Quay, Jalan Besar and Geylang. Dur-ing heavy rain, steel gates are opened to allow excess stormwater into the sea when the tide is low. However, when it is not possible to do so during high tide, the drainage pumps capable of pumping up to 280 m3/s are activated to pump excess stormwater out to sea. With the barrage in place, these pock-ets of low-lying areas are no longer prone to flooding.

With the completion of the MB, the Ma-rina Reservoir is the 15th reservoir in Singapore and has the largest and most urbanized catchment at 10 000 hectares or one-sixth the size of Singapore. This will help increase the existing water catchments from half to two-thirds of Singapore together with the expected completion of the Punggol Reservoir and Serangoon Reservoir by 2011. The freshwater will then be treated using advanced membrane technology to en-sure that it is safe for drinking.

As the water in the Marina Reservoir will no longer be subjected to tidal influence, its water level will be kept relatively constant all year round. This makes the reservoir an ideal venue for all kinds of recreational activi-ties such as boating, windsurfing and water skiing. Colourful water-based Fig. 1: Key features of Marina Barrage

Boat hoist facility Pedestrian bridge Structural turf green roof

Solar panels

Electrical building

Exhibition gallery/F&B outlets

Drainage pumps

Crest gates

Reservoir

Sea

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18 Structures Worldwide Structural Engineering International 1/2009

with a total pumping capacity of 280 m3/s;

(3) boat hoist facility at the eastern side of the barrage, which is ca-pable of hoisting boats up to 20 m long, 6-m wide and 70 t in and out of the Marina Reservoir;

(4) electrical building with three 4.3-MW diesel engine-generators, which will supplement utility sup-ply when more than two pumps are operated as well as to provide a back-up power supply;

(5) solar panels on the roof, which provide supplemental power for use in the facility;

(6) exhibition gallery, which show-cases Singapore’s achievements in the areas of environment and water resources management; and

(7) turfed green roof accessible to public for their enjoyment throughout the day.

Key Challenges

The SGD$250 million MB project is a large and complex engineering proj-ect involving multiple disciplines and spanning over 3 years to implement. Along the way, many challenges were encountered. To overcome these chal-lenges, an innovative and integrated approach capitalizing on strong proj-ect partnerships was required.

Construction of the Marina Barrage

Civil works

The barrage structure was construct-ed in two phases. During Phase 1 construction of the barrage (Fig. 2), a 100-m-wide channel was maintained in the deepest portion of the Marina Channel for navigation and flood con-trol requirements. To ensure the safety of boat users navigating through the narrowed channel during the day as well as the night, current velocity me-ters showing real-time readings and warning lights were installed at strate-gic locations of the marine cofferdam.

For Phase 2 of the barrage construc-tion (Fig. 3), all the four crest gates installed under Phase 1 had to be kept in the open position with marine cof-ferdam removed to allow for storm flows out to the sea. A boat hoist was installed at the eastern side of the bar-rage to facilitate the transfer of boats entering the reservoir from the seaside and vice versa.

The design of the temporary work (cof-ferdam) for MB project is specified by PUB in the contract. The detailed design

of the cofferdam is carried out by the Contractor’s professional engineer and checked by the Specialist engaged by the Contractor, PUB’s consultant as well as accredited checker engaged by PUB.

The construction of the temporary works consists of marine cofferdam with 12-m-wide double sheet pile wall of 42-m length and filled with sand (refer to Fig. 4 for aerial view of ma-rine cofferdam), joined by cut-off wall on the land side and transition wall made up by sheet pile and raker piles. Sheet pile with length of 18 m is provided as cut-off wall against water infiltration into the excavation site. The double wall marine cofferdam is

situated at the existing sand key area with two rows of tie rods. An earth berm is provided at the landward side and the water level in the cofferdam is controlled by pumping wells. Prior to the construction of the marine cof-ferdam for the barrage across the 350-m-wide Marina Channel, the seabed of the Channel here was dredged to about 12-m deep and filled with 144 000 m3 of sand to form sand keys. Sheetpiles for marine cofferdam were driven to 31-m deep into the sandkeys, which provide the required passive resistance in the design of the cofferdam.

The foundation for the various build-ing structures in MB including drain-age pumping station, east abutment,

Marinachannel

100 m min widechannel

Marina south

Marinaeast

Exhibitiongallery/

F&B outlets

Drainage pum

pingstation

Barrage

Sea

Cofferdam

Boat hoist

Fig. 2: Phase 1 construction of Marina Barrage

Marinachannel

Marina south

Exhibitiongallery/

F&B outlets

Marinaeast

Sea

Crest gates left open

Drainage pum

pingstation

Boat hoistin operation

Cofferdam

Fig. 3: Phase 2 construction of Marina Barrage

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Structural Engineering International 1/2009 Structures Worldwide 19

barrage, exhibition gallery and elec-trical building consists of base slabs supported by bored piles down to a maximum depth of 74 m. Owing to the magnitude of the pile length, specially made Kelly bars were fabricated in Italy and delivered to the site for the boring operation.

The pedestrian bridge spanning across the piers was installed after the crest gate had been installed (refer to Fig. 5 for the section across the barrage). The pedestrian bridge, comprising nine segments, is 310-m long, 6-m wide and is 5,5 m above the mean sea level. To avoid damage to the installed crest gate, the pedestrian bridge was designed to be pre-cast post-tensioned bridge and the bridge segment was launched after the installation of crest gate. One of the biggest lift capacity cranes available in

the region had to be engaged for the launching operation due to the weight of the bridge segment and reach re-quired across the marine cofferdam (see Fig. 6 showing the launching of a typical bridge segment).

Mechanical and Electrical works

There are nine “fish-belly” (self-float-ing design) steel crest gates across the barrage. Each gate is 29,75-m wide, 5-m high and weighs 70 t—or the equiv-alent of 1000 men. The nine gates will act as a tidal barrier to control flood-ing in the city and also as a channel to keep seawater out. Installation of each gate is an exciting operation as the 70-t gate has to be lifted from a crane barge outside the barrage cofferdam and lowered between the barrage piers onto the barrage foundation

and placed onto nine pivot blocks. The whole operation took about an average of 10 h to complete. The pivot blocks supporting the massive 70-tonnes crest gate had to be posi-tioned to within an accuracy of 2 mm (refer to Fig. 7 showing the installation of the crest gate).

Seven drainage pumps (see Fig. 8 for the photo of drainage pump at MB) are located in the drainage pumping station. The 3,2 m diameter, 7,5-m high and 28-t drainage pump is one of the largest vertical axial flow pumps in the world. Each pump has a pumping

Fig. 4: Aerial view of the double wall marine cofferdam

Fig. 5: Section across the barrage

Max water level

Min water levelReservoir

Barrage section

Stop logs

Hydrauliccylinder

Crest gate(raised

position)

Crest gate(loweredposition)

Concreteprotection boom

RL 101,75 (King tide)

RL 101,50 (High tide normal)

RL 98,50 (Low tide)

Sea

Energydissipation

basin92,00

Fig. 6: Launching of pedestrian bridge segment

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20 Structures Worldwide Structural Engineering International 1/2009

capacity of 40 m3/s and is capable of emptying an Olympic size swimming pool in 1 min. Excess stormwater is pumped out into the sea when the storm coincides with high tide.

There are two low-level sluices, which is a system of bypass pipes and butterfly valves located in the drainage pumping station. The sluices are used to release denser reservoir water (high salt content saline water) at the bottom of the reservoir back into the sea and to make minor adjustments to the reservoir level without the need for operating the crest gates or the drain-age pumps.

There are three 4,3-MW diesel eng-ine-generators (E-G) provided in the

electrical building. Besides serving as a back-up for utility supply, they also help to supplement power if more than two drainage pumps are required for operation. The cooling system of the E-Gs uses freshwater from the reservoir to circulate to the heat exchangers mounted on each engine-generator. A 500-kVA emergency standby gen-erator set is also available to provide power for building services during util-ity failures.

Supervisory control and data acquisition (SCADA) system and predictive barrage operating system

A supervisory control and data acq-uisition (SCADA) system provides real-time monitoring and control

Fig. 7: Installation of the 70 t crest gate

Fig. 8: Drainage pump at Marina Barrage

of the crest gates, drainage pumps and low-level sluices. There is also a predictive barrage operating system that will process the hydrological and meteorological data in real time, and forecast rainfall and runoff. This use-ful information is used to aid the oper-ation of the crest gates and drainage pumps.

Marina Barrage Experience

The MB is a distinctive landmark set in nature, a focal point where the chan-nel meets the sea as well as an icon (both by day and by night) for Singa-pore amidst the calm water surface of Marina Channel, the greenery of the surrounding area and the magnificent skyline of Marina Bay area. The MB was designed to blend well with the future Gardens by the Bay, which is being developed on both sides of the Marina Channel, adjacent to the MB. Yet, is an iconic structure in its own right, providing an attractive and wel-coming venue to residents and visitors to Singapore. The roof itself, located about 16 m above mean sea level and the pedestrian bridge across the Ma-rina Channel will provide the public with spectacular panoramic views of Singapore’s city skyline and out across the Singapore Straits.

The MB is not only an engineer-ing achievement but also a unique showcase of Singapore’s efforts and achievements towards environmen-tally sustainable development. Numer-ous green (environmentally friendly) features are incorporated within the development. Some of these green features include the large green-turfed roof, use of solar energy, energy- efficient and water-efficient fittings and recycled materials in the devel-opment. The exhibition gallery aims to raise the awareness on Singapore’s efforts and achievements in the areas of environment and water resources management and to inculcate a joint sense of ownership in the environment and water resources in the public.

Conclusion

In essence, the MB (refer to Fig. 9 for its aerial view) is a unique 3-in-1 pro-ject, which will provide Singapore with three benefits, namely flood control, water supply and a lifestyle attraction in the heart of downtown Singapore.

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Structural Engineering International 1/2009 Structures Worldwide 21

Besides being an engineering achieve-ment, it is also a unique showcase of Singapore’s efforts and achievements towards environmentally sustainable development. The MB was also deve-

SEI Data BlockSEI Data Block

Owner:Ministry of the Environment and Water Resources, Singapore

Developer: PUB, Singapore

Main Consultant:Camp Dresser & Mckee International (S) Pte Ltd

Architect:Architects Team 3 Pte Ltd

Main Contractor: Koh Brothers Building & Civil Engi-neering Contractor Pte Ltd

Contractor’s Specialist Consultant:Black & Veatch

Steel reinforcement (t): 20 000

Concrete (m3): 140 000

Total Cost (USD million): 167

Service Date: November, 2008

Fig. 9: Aerial view of Marina Barrage

loped to provide both Singaporeans and tourists a sense of place within the city. It also serves as an icon by the waterfront in the day and a beacon by the water edge at night.

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