Estuary Processes and Managment - River Dynamics and Integrated River Management - page 493

the Jiuduansha Shoal into the south passage and north passage.
During the period of SSPIII design, the importance of the YRE's hydrodynamic characteristics has been
considered; a 2D hydrodynamic model based on Delft3D was developed to assess the effect of SSPI and
SSPII so as to provide some reference for SSPIII (Lee et al., 2001b). The velocity vector fields, the water
elevation, the trajectories of drogues, and the far field sewage dilution fields from the existing and proposed
outfalls were studied for the spring/neap tide and the dry/wet season. In general, the modeling results show
the hydrodynamic condition of the YRE is beneficial to sewage dilution and diffusion; however, it reveals
the effluents discharged through outfalls at present have relatively little impact on the water environment
of the YRE. For the SSPIII flow through 4 outfalls, the water quality of the YRE will significantly deteriorate
in the absence of any treatment, especially during the neap tide of the dry season.
Based on the calibrated model, drogue tracks released from the 4 outfalls during wet and dry seasons
have been simulated. Figure 8.28 shows the drogue trajectories after the sewage is released at different
times from Bailonggang outfall. The drogues generally follow the tidal oscillation in a “to and fro” manner,
progressively move downstream close to the shore, and eventually leave the computational boundary
between Luchaogang and Dajishan towards Hangzhou Bay. As a whole, drogues released in spring tide
move a little faster than when released between the spring and neap tide, while they move much faster in
the wet season than in the dry season. The drogues released from Zhuyuan, Bailonggang and Xinhe outfalls
can move out of the simulation boundary in 2 or 3 days in the wet season, while the drogues released
from the more upstream Shidongkou outfall need 5 days or longer. It is found that the effluent from the four
outfalls will be transported downstream towards Hangzhou Bay. The sewerage plan and SSPIII should
hence consider the self-purification capacity of both the Yangtze River estuary and Hangzhou Bay.
Fig. 8.28 Trajectories of drogues released from the Bailonggang outfall during the spring tide: (a) wet season; and
(b) dry season
8.3.5.2 Impact of Land Reclamation on Victoria Harbor
The large scale land reclamation in Hong Kong was adopted to create land for urban development. By
2003, about 3200 hectares had been reclaimed in Hong Kong. Among these, 661 hectares are existing and
committed reclamation areas in Victoria Harbor between Stonecutters Island and Lei Yue Mun (Fig. 8.29).
Currently, Hong Kong is entering the final phase of land reclamation projects in Victoria Harbor. On
Hong Kong Island, just two more projects are outstanding—the Central Reclamation Phase III (CRIII)
and the Wan Chai Development Phase II (WDII). On the Kowloon peninsula side, reclamation is planned