1 Alternative Pipeline Route

1.1 Introduction

Potentially, a container port, CT10, will be built to the west of Lantau (near Tai O). If this is the case, it will hence be necessary to alter the LNG submarine gas pipeline in order to avoid the intersection with the CT10 which may require dredging the port area to substantial depth for reclamation.

As seen from the figure below, an alternative pipeline route was designed to bypass the CT10. To assess any potential impacts due to the alternative pipeline route was thus simulated by Delft3D model.

The same modelling approach as presented in the Section 3 of Annex 6A was adopted. The modelling is mainly carried out for KP7 – 14, KP14 – KP20 and KP20 – KP34.5 since the changes are mainly at these three zones. The model results are presented in the next section of this Appendix.

1.2 Model Results

1.2.1 Suspended Solids

TSHD Dredging at Lantau Channel (KP7-14)

Modelling results (Table 1.1) indicate that SS elevations will be compliant with the WQO and tolerance criterion at all sensitive receivers in both seasons.

TSHD Dredging at West Lantau (KP14-20)

Modelling results (Table 1.1) indicate that SS elevations will be compliant with the WQO at all sensitive receivers in both seasons, with the exception of SR12 (horseshoe crab habitat near Tai O). As seen from Table 1.1, the maximum depth-averaged SS concentrations at Pak Tso Wan would be about 52.3 and 45.7 mg L^-1, exceeding the WQOs of 8.9 and 5.6 mg L^-1 in the dry and wet seasons, respectively, whereas the mean depth-averaged SS concentrations are comply with the WQO. This suggests that the exceedances are not persistent.

Jetting at the Urmston Road Crossing (KP20-34.5)

Modelling results (Table 1.1) indicate that SS elevations will be compliant with the WQO at all sensitive receivers in both seasons, with the exception of SR6a and 6b (boundary of Sha Chau and Lung Kwu Chau Marine Park).

The maximum depth-averaged SS elevations at SR6a and 6b will exceed the WQOs of 8.2 and 5.6 mg L^-1 in the dry and wet seasons, respectively, whereas the mean depth-averaged SS concentrations are well below the WQO. This indicates that the exceedances are in short duration.

Figures 1.1 – 1.3 show the contour plots (mean depth-averaged) of SS elevations for the alternative gas pipeline route for the above three zones. They show that the sediment plume is in low concentrations (mean over 15 day spring-neap cycle), i.e. below 5 mg L^-1. This shows that there are no continually unacceptable impacts to water quality.

1.2.2 Sediment Deposition

The majority of SS elevations in water have been predicted to be temporary and to remain within relatively close proximity to the dredging or jetting works and, as such, the majority of sediment has been predicted to settle within relatively close proximity of the works areas.

The simulated deposition rates ([1]) at the artificial reefs (ARs), i.e., SR6e and SR7d during the dry and wet seasons have been assessed for the respective construction works. Table 1.2 summarises the predicted deposition rates. No exceedance are predicted at both ARs and hence no unacceptable impacts are expected to be posed by the works.

Table 1.1 Predicted SS Elevation (mg L^-1) for Alternative Pipeline Route

Sensitive Receiver	Name	ID	Depth ^(a)	WQO Allowable Elevation		TSHD Dredging at Lantau Channel (KP7-14)							TSHD Dredging at West Lantau (KP14-20)								Jetting at the Urmston Road Crossing (KP20-34.5)
						Max		Mean					Max				Mean				Max			Mean
				Dry	Wet	Dry	Wet	Dry			Wet		Dry		Wet		Dry		Wet		Dry		Wet	Dry	Wet
Intertidal Mudflats	Pak Nai	SR01	s	7.1	3.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Horseshoe Crab Nursery Grounds	Pak Nai	SR01	a	9.7	6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Seagrass Beds/Mangroves/Oyster Farm	Pak Nai	SR02	s	7.1	3.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Seawater Intakes	Black Point Power Station	SR04	b	700 ^(b)	700 ^(b)	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Non-gazetted Beaches	Lung Kwu Sheung Tan	SR05a	a	8.2	5.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Non-gazetted Beaches	Lung Kwu Tan	SR05b	a	8.2	5.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Gazetted Beaches	Butterfly Beach	SR05c	a	8.2	5.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR06a	a	8.2	5.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		44.9 ^(c)		79.2^(c)		1.1	0.8
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR06b	a	8.2	5.6	0.2	0.0		0.0	0.0		0.2		0.0		0.0		0.0		12.8^(c)		12.1^(c)		0.8	0.2
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR06c	a	8.2	5.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.2		0.0		0.0	0.0
Marine Park	Designated Sha Chau and Lung Kwu Chau	SR06d	a	8.2	5.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.4		0.3		0.0	0.0
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR06e	a	8.2	5.6	0.0	0.0		0.0	0.0		0.1		0.0		0.0		0.0		3.1		4.7		0.4	0.1
Seawater Intakes	Castle Peak Power Station	SR07a	b	700 ^(b)	700 ^(b)	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Seawater Intakes	Tuen Mun Area 38	SR07b	b	14.2	9.8	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Seawater Intakes	Airport	SR07c	b	8.9	8.8	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Seawater Intakes	Airport	SR07d	b	8.9	8.8	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Artificial Reef Deployment Area	Northeast Airport	SR07d	a	4.7	5.2	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Seawater Intakes	Airport	SR07e	b	8.9	8.8	0.0	0.0		0.0	0.0		0.0		0.1		0.0		0.0		0.0		0.6		0.0	0.0
Seawater Intakes	Airport	SR07f	b	8.9	8.8	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.1		0.0	0.0
Spawning/Nursery Grounds	Fisheries Spawning Ground in North Lantau	SR08	a	8.2	5.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Horseshoe Crab Nursery Grounds	Sham Wat Wan	SR10	a	8.9	6.5	0.4	0.2		0.0	0.0		1.2		1.3		0.2		0.1		2.0		2.5		0.1	0.1
Protection Zone	Chinese White Dolphin Protection Zone in Mainland Waters	SR11	a	8.9	6.5	0.6	0.4		0.1	0.0		0.2		0.1		0.0		0.0		0.4		0.3		0.0	0.0
Protection Zone	Chinese White Dolphin Protection Zone in Mainland Waters	SR11a	a	8.9	6.5	0.6	0.7		0.1	0.1		0.2		0.2		0.0		0.0		0.3		0.2		0.0	0.0
Protection Zone	Chinese White Dolphin Protection Zone in Mainland Waters	SR11b	a	8.9	6.5	0.5	0.8		0.1	0.0		0.2		0.3		0.0		0.0		0.3		0.2		0.0	0.0
Horseshoe Crab Nursery Grounds	Tai O	SR12	a	8.9	6.5	0.7	1.1		0.1	0.1		52.3^(c)		45.7^(c)		2.4		1.9		1.3		1.3		0.1	0.1
Intertidal Mudflats	Yi O	SR14	s	6.5	3.6	0.5	0.0		0.1	0.0		2.3		1.3		0.2		0.0		0.6		0.3		0.0	0.0
Horseshoe Crab Nursery Grounds	Yi O	SR14	a	8.9	6.5	0.7	0.9		0.2	0.1		3.1		3.9		0.4		0.2		0.7		0.4		0.1	0.0
Non-gazetted Beaches	Fan Lau Sai Wan	SR15a	a	6.9	5.5	0.7	0.8		0.2	0.1		0.4		0.4		0.1		0.0		0.2		0.1		0.0	0.0
Mangroves	Fan Lau Tung Wan	SR15b	s	4.5	3	0.1	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Non-gazetted Beaches	Fan Lau Tung Wan	SR15b	a	6.9	5.5	0.1	1.3		0.0	0.1		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Non-gazetted Beaches	Tsin Yue Wan	SR15c	a	6.9	5.5	0.8	0.5		0.2	0.1		0.6		0.7		0.1		0.1		0.2		0.3		0.0	0.0
Fish Fry Habitat	Pak Tso Wan	SR16b	a	6.9	5.5	0.2	0.2		0.0	0.0		0.0		0.1		0.0		0.0		0.0		0.0		0.0	0.0
Horseshoe Crab Nursery Grounds	Sha Lo Wan	SR18	a	7.8	4.8	0.2	0.1		0.0	0.0		0.5		0.2		0.1		0.0		0.7		1.5		0.0	0.1
Spawning/Nursery Grounds	Fisheries Spawning/Nursery Grounds in South Lantau	SR24	a	6.9	5.5	0.6	0.2		0.0	0.0		0.1		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Spawning/Nursery Grounds	Fisheries Spawning/Nursery Grounds in South Lantau	SR27	a	6.9	5.5	0.5	0.2		0.0	0.0		0.1		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Subtidal Hard Bottom Habitat (coral)	Southern Side of South Soko	SR31	a	10	10	0.0	0.2		0.0	0.0		0.0		0.1		0.0		0.0		0.0		0.0		0.0	0.0
Intertidal Mudflats	Shui Hau Wan	SR33	s	3.9	2.5	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Horseshoe Crab Nursery Grounds	Tong Fuk Miu Wan	SR33	a	4.8	3.9	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Gazetted Beaches	Tong Fuk	SR34	a	4.8	3.9	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Gazetted Beaches	Upper Cheung Sha Beach	SR35	a	4.8	3.9	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Seagrass Beds/Mangroves	Tung Chung Bay	SR39	s	6.5	3.6	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0
Horseshoe Crab Nursery Grounds	Tung Chung Bay	SR39	a	8.9	6.5	0.0	0.0		0.0	0.0		0.0		0.0		0.0		0.0		0.0		0.0		0.0	0.0

Notes:

a. s = surface, m = middle, b = bottom, a = depth-averaged

b. The assessment criterion of 700 mg L^-1 was adopted for these seawater intakes.

c. Shaded area indicates non-compliance with the assessment criterion.

Table 1.2 Predicted Deposition Rate (g m^-2 day^-1) for the Alternative Gas Pipeline Route at the Artificial Reefs and Subtidal Hard Bottom Habitat

Sensitive Receiver	Name	ID	Depth	WQO Allowable Elevation		TSHD Dredging at Lantau Channel (KP7-14)		TSHD Dredging at West Lantau (KP14-20)		Jetting at the Urmston Road Crossing (KP20-34.5)
				Dry	Wet	Dry	Wet	Dry	Wet	Dry	Wet
						Max	Max	Max	Max	Max	Max
Artificial Reef Deployment Area	Sha Chau and Lung Kwu Chau	SR06e	b	200	200	0.0	0.0	0.1	0.0	15.1	3.7
Artificial Reef Deployment Area	Northeast Airport	SR07d	b	200	200	0.0	0.0	0.0	0.0	0.0	0.0

Figure 1.1 Predicted Mean Depth-Averaged SS Elevations (mg L^-1) for TSHD Dredging at Lantau Channel (KP7-14)

Dry Season

Wet Season

Figure 1.2 Predicted Mean Depth-Averaged SS Elevations (mg L^-1) for TSHD Dredging at West Lantau (KP14-20)

Dry Season

Wet Season

Figure 1.3 Predicted Mean Depth-Averaged SS Elevations (mg L^-1) for Jetting at the Urmston Road Crossing (KP20-34.5)

Dry Season

Wet Season

1.3 Conclusion

Installation for the alternative gas pipeline route has been simulated by water quality model using the same modelling approach as for the proposed route presented in the EIA report Section 6. This model results show that the SS elevations exceed the WQO at two locations whereas the SS deposition rate remain below the assessment criteria. It is expected the SS exceedances are short-term and do not have unacceptable impacts to water quality.

At the EIA stage, the alternative gas pipeline route is not considered to be a preferred option. Should the alternative gas pipeline route be selected at next stage as a result of any planning uncertainties, a further impact detailed assessment should be conducted and the following implementations should be considered:

· Jetting works next to the designated Sha Chau and Lung Kwu Chau Marine Park will be replaced by grab dredging in order to minimise the instantaneous SS elevations.

· Dredging works along the route designated Sha Chau and Lung Kwu Chau Marine Park and in West Lantau will be operated during daytime (maximum 12 hours a day) and will avoid the peak calving season of the Indo-Pacific Humpback Dolphin, i.e. March through August.

· Appropriate mitigation measures will be derived if any predicted WQO exceedances are predicted.

The residual impacts, if any, will be assessed.

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([1]) The deposition rate is simulated as the total deposition divided by the duration of complete tidal cycle.