HULHULE-MALE’ BRIDGE PROJECT

EIA for the proposed Hulhule-Male’ Bridge Project
6.1.2 Characteristics and changes of flow field before and after engineering
construction
The total length of the proposed bridge is 2 km; the section of the bridge that covers the
overwater area across Gaadhoo Koa channel is 1.39 km. Pile-group foundation is proposed for
the main piers and the transition piers. There will be 12 or 8 main piers of bored piles with crosssections
ranging between 2.5 – 2.8 m. There will be 6 transition piers of bored piles with a
diameter of 1.6 m.
The bridge pile foundations forms an obstacle to the water flow and may change water flow
regime in Gaadhoo Koa. In addition, erection of the pile foundation reduces the total discharge
area of Gaadhoo Koa channel, changes the water flow regime, and changes the cross-sectional
flow across the channel.
To fully comprehend the characteristics of tidal current distribution in the surrounding waters of
the project site and the effect of the constructing the bridge based on the characteristics of
surrounding flow field of the project area, a 2D horizontal mathematical model was modelled
according to the vertical-averaged motion equation. This model helps to simulate the flow field
of the whole computational domain and calculate the effect of the project on the flow field
nearby. The mathematic model was compared with analogue values of the model to verify its
accuracy. The results showed that the measured tidal level, flow velocity and direction were
identical. Thus, the result indicates that the mathematic model can be used to demonstrate the
characteristics of flow field in the project area.
In the assessment, 78 locations were selected within Gaadhoo Koa to analyse the potential
changes in high and low tide level before and after the construction. The results show that the
impact of bridge construction is limited to the surrounding water level near the project area. The
estimated maximum change is 1.5 cm and is expected to occur close to the pile foundation.
Therefore, the construction of bridge basically has no influence on the nearshore tide level of
Malé Island and Hulhulé Island.
Figure 6.1 shows the modelled flow field in the project area during high and low tides, before
and after construction of the bridge. At flood tide, tidal flow occurs out of the atoll lagoon
through the channel (Gaadhoo Koa). The flow is strongest in the channel between Funadhoo and
Male’ and close to the Hulhule reef. The strongest flow near Male’ occurs on the NE corner and
as a result the flow close to the eastern reef of Male’ is moderately slower. There is a 400 m
zone of weaker flow behind Funadhoo Island as the flow coming from atoll lagoon separates.
The outgoing flow from the atoll lagoon meets with the Vadhoo Channel flow and an anticlockwise
circulation zone is formed just south of Hulhule Island reef.
Prepared by: CDE Consulting & China Shipping Environment Technology
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