Environmental Impact Assessment

Marina Barrage

Outline

• Description of the proposed topic & environmental setting; Identification of potential environmental impact

• Addressing Public concern

• Identification of mitigation measures

• Description of monitoring and management plan

Description of Topic

The Marina Barrage is a dam in Singapore built at the confluence of five rivers, across the Marina Channel between Marina East and Marina South

• 3 Purposes: Water supply, flood control, lifestyle attraction

• S$226 million project turns Marina Bay and Kallang Basin into a new downtown freshwater Marina Reservoir

Tidal BarrageThe barrage, which comprises nine hydraulically operated steel crest gates, was built across the 350m wide Marina Channel to keep out sea water. Under normal conditions, the steel gates will remain closed to isolate the reservoir from the sea. During heavy rain, the steel gates will open as necessary to release excess stormwater to the sea when the tide is low. However, when it is not possible to do so during high tide, the Drainage Pumping Station will pump out the excess stormwater into the sea.

Environmental Setting

Showpiece of environmental sustainabilityGreen principles applied in all aspects of the design, construction and operation Utilize energy and water efficiently and minimize waste generated

Identification of Potential Environmental Impact• The placement of a barrage into an estuary has a considerable effect

on the water inside the basin and on the ecosystem. Through research conducted on tidal plants, it has been found that tidal barrages constructed at the mouths of estuaries pose similar environmental threats as large dams. The construction of large tidal plants alters the flow of saltwater in and out of estuaries, which changes the hydrology and salinity and possibly negatively affects the marine mammals that use the estuaries as their habitat

Turbidity

• Turbidity (the amount of matter in suspension in the water) decreases as a result of smaller volume of water being exchanged between the basin and the sea. This lets light from the Sun penetrate the water further, improving conditions for the phytoplankton. The changes propagate up the food chain, causing a general change in the ecosystem.

Salinity

• As a result of less water exchange with the sea, the average salinity inside the basin decreases, also affecting the ecosystem.

Sediment movements

• Estuaries often have high volume of sediments moving through them, from the rivers to the sea. The introduction of a barrage into an estuary may result in sediment accumulation within the barrage, affecting the ecosystem and also the operation of the barrage.

Public Concern

Public Concern

• Barrage Schemeso Permeable

• Harness tidal power for generating hydro-electricityo Impermeable

• Flood defenses against high tide surges• Total exclusion of tides• Amenity purposes

• Immediate impacts of impermeable Barrage:o Replacement of marine habitats by freshwater bodieso Effects on sedimentation regimes along coastlineo Enhancement of erosion at susceptible sites

Public Concern

Public Concern

• Health Concerno Dengue Fever

• Transmitted by Aedes mosquitoes which breed in stagnant water commonly found in man-made containers

Mitigation Measures

Elements of Mitigation

Restoring Environmental Flow

• Flow regime

• Maintain river functions (Water temperature, sediment movement, etc)

An environmental flow regime at the Itezhi-tezhi dam in Zambia.

Sediment Removal

• Mechanical dredging

• Carry away from dredged area

• Produce materials

Grab dredge Bucket dredging

Sediment Removal

• High-volume suction pumps

• Efficient

• Difficult process

Choice of Mitigation Measures

• Requires research

• Not cause more damage

• Flood management alternatives