5.10 Assessment of Environmental Impacts - Operation

5.10.1 The assessment of impacts to water quality from the operation of the Theme Park is split into two main aspects.

· The surrounding marine waters; and

· The Chok Ko Wan Link Road.

Marine Waters

5.10.2 The operation of the Northshore Lantau Development will have the potential to affect the water quality of the surrounding marine waters in two ways, by changing the hydrodynamics and through the discharges of pollutants from the Northshore Lantau Development. These two aspects have been assessed separately using computational modelling.

Hydrodynamics

5.10.3 The residual discharges across major flow channels are shown in Table 5.10a for all three scenarios and include a calculation of the percentage differences between the completed Northshore Lantau Development and the Baseline scenario and between the completed Northshore Lantau Development and Container Terminal Development and the Baseline scenario. The average flood and ebb discharges are shown in Tables 5.10b and 5.10c, including a calculation of the percentage differences between the baseline and two development scenarios.

Table 5.10a - Residual Discharges (m³s^-1) through Major Flow Channels and Percentage Change from Baseline

	Wet Season					Dry Season
Channel	Baseline	NSLD		NSLD + CT		Baseline	NSLD		NSLD + CT
	Discharge	Discharge	Difference	Discharge	Difference	Discharge	Discharge	Difference	Discharge	Difference
Urmston Road	799	819	2.5	867	8.5	1480	1499	1.3	1464	-1.1
Kap Shui Mun	-164	-89	-45.7	-90	-45.1	651	647	-0.6	665	2.2
Ma Wan Channel	1527	1508	-1.2	1510	-1.1	1111	1134	2.1	1095	-1.4
Rambler Channel	-564	-601	6.6	-553	-2.0	-284	-284	0.0	-298	4.9
East Lamma Channel	1823	1864	2.2	1557	-14.6	1226	1264	3.1	1691	37.9
West Lamma Channel	-1563	-1653	5.8	-1114	-28.7	-512	-457	-10.7	-1150	124.6
Victoria Harbour	-120	-44	-63.3	-152	26.7	1058	1031	-2.6	1068	0.9
Notes : 1. Positive discharge is in the flood direction, as defined in Figure 5.9a 2. Positive change represents an increase in discharge and a negative change a decrease in discharge.

Table 5.10b - Average Flood Discharges (m³s^-1) through Major Flow Channels and Percentage Change from Baseline

	Wet Season					Dry Season
Channel	Baseline	NSLD		NSLD + CT		Baseline		NSLD		NSLD + CT
	Discharge	Discharge	Difference	Discharge	Difference	Discharge	Discharge		Difference	Discharge	Difference
Urmston Road	24446	24035	-1.4	23577	-3.6	26346	25990		-1.4	25537	-3.1
Kap Shui Mun	5718	5238	-5.4	5106	-10.7	7001	6621		-5.4	6542	-6.6
Ma Wan Channel	15332	15475	0.6	15020	-2.0	16205	16296		0.6	15957	-1.5
Rambler Channel	776	796	2.3	823	6.1	1065	1089		2.3	1083	1.7
East Lamma Channel	13845	13763	-0.2	14454	4.4	14370	14338		-0.2	15500	7.9
West Lamma Channel	10549	10077	-3.2	8261	-21.7	11343	10984		-3.2	8633	-23.9
Victoria Harbour	3765	3836	1.9	3799	0.9	4504	4463		-0.9	4660	3.5
Notes : 1. Positive change represents an increase in discharge and a negative change a decrease in discharge.

Table 5.10c - Average Ebb Discharges (m³s^-1) through Major Flow Channels and Percentage Change from Baseline

	Wet Season					Dry Season
Channel	Baseline	NSLD		NSLD + CT		Baseline	NSLD			NSLD + CT
	Discharge	Discharge	Difference	Discharge	Difference	Discharge	Discharge	Difference		Discharge	Difference
Urmston Road	22718	22270	-2.0	21708	-4.4	23212	22828	-1.7		22447	-3.3
Kap Shui Mun	6043	5413	-10.4	5283	-12.6	5761	5398	-6.3		5285	-8.3
Ma Wan Channel	12596	12759	1.3	12326	-2.1	14142	14176	0.2		13912	-1.6
Rambler Channel	2128	2259	6.2	2132	0.2	1688	1703	0.9		1733	2.7
East Lamma Channel	10567	10407	-1.5	11643	10.2	12090	11977	-0.9		12377	2.4
West Lamma Channel	13670	13392	-2.0	10489	-23.3	12358	11889	-3.8		10987	-11.1
Victoria Harbour	4000	3920	-2.0	4094	2.4	2666	2674	0.3	2800		5.0
Notes : 1. Positive change represents an increase in discharge and a negative change a decrease in discharge.

5.10.4 The data in the above tables for average ebb and flood discharges for the Northshore Lantau Development and Container Terminal scenario show that the reclamations for these developments result in a re-distribution of flows between the East and West Lamma Channels. This is evidenced by the predicted decrease in flows through the West Lamma Channel and increases in flows through the East Lamma Channel. There are predicted to be decreases in discharges through both the Ma Wan and Kap Shui Mun channels, which indicates that the total volume of water entering and exiting the Western Harbour past Ma Wan Island is being reduced. It is worth noting that the average flood and ebb discharges through Victoria Harbour are predicted to increase.

5.10.5 The data for average ebb and flood discharges for the Northshore Lantau Development only scenario show that there is a re-distribution of flows around Ma Island, with decreases through Kap Shui Mun and increases through the Ma Wan Channel. The flows through the Urmston Road are predicted to decrease by a small amount, less than 2%, which may indicate an overall reduction in flows entering and exiting the Western Harbour past Ma Wan Island. There are predicted to be decreases in flows through the East and West Lamma Channels, while the flows through Victoria Harbour are generally predicted to increase for most cases.

5.10.6 The data in the table of residual discharges show that the modelling predicts that the Northshore Lantau Development and Container Terminal scenario results in a decrease in residual discharges through both the East and West Lamma Channels in the wet season, while in the dry season residual discharges increase. In both the wet and dry seasons there is predicted to be an increase in the residual discharges through Victoria Harbour. In the wet season residual discharges through Kap Shui Mun residual discharges decrease, while in the dry season they are predicted to increase.

5.10.7 The changes in residual discharges in the dry season for the Northshore Lantau Development only scenario are generally predicted to be small with the exception of the West Lamma Channel, which shows a decrease of slightly over 10%. In the wet season residual discharges are also only predicted to change by small amounts, with the exception of Kap Shui Mun and Victoria Harbour where large relative decreases are predicted. It should be noted that although the reduction in residual discharges through Victoria Harbour is large, over 63%, this does not represent a large absolute change in residual discharge, and in fact represents a small absolute change in a small residual discharge. The small residual discharges through Victoria Harbour are due to the fact that in both the wet and dry seasons the ebb and flood discharges are almost balanced, as shown by the similarity in the discharges in the above tables. It is thought that the large reduction in residual discharges is not likely affect water quality in Victoria Harbour because the ebb and flood discharges are the main controlling factors in maintaining water quality in the harbour. This assessment will be confirmed through water quality modelling, the results from which are discussed below.

5.10.8 The graphs of momentary and accumulated discharge are shown in Figures D3a to D3n in Annex D3. The graphs generally show that the Baseline and Northshore Lantau Development only scenario (marked as Scheme 4 on the graphs) have similar discharges, while the Northshore Lantau Development plus Container Terminal scenario results in identifiable changes in discharges. It is worth noting that the predicted large decrease in residual discharges through Victoria Harbour in the wet season is not evident from the graphs and that there is only a small change in momentary and accumulated discharges in the wet season.

5.10.9 The overall conclusion from the data presented on tidal discharges is that the Northshore Lantau Development generally does not result in large changes in discharge patterns, with the exception of the residual flows through Victoria Harbour in the wet season which are not considered to be detrimental. There is therefore the possibility of changes to water quality due to the predicted changes in discharge patterns, which has been investigated through detailed water quality modelling, the results of which are presented below. The combined scenario of the Northshore Lantau Development and Container Terminal is predicted to have larger effects on discharge patterns than the Northshore Lantau Development alone and may similarly have the potential to cause changes in water quality, which is investigated through detailed water quality modelling, as discussed below.

5.10.10Vector plots of current speed and direction, which also include contours of salinity for the wet season, are presented in Figures D3o to D3w in Annex D3. The modelling results for the Northshore Lantau Development plus Container Terminal scenario predicts that on the ebb tide in both the surface and bed layers there are shown to be increases in speed in the main flow channel to the east of the reclamations. The container terminal reclamation and breakwater are predicted to reduce current speeds to the south east, which results from a sheltering effect. Current speeds in area between the container terminal reclamation and the reclamation for the International Theme Park reclamation in Penny’s Bay are predicted to increase on the ebb tide as the water is funnelled through this area. There are also current speed increase predicted between the south western tip of the container terminal and Peng Chau, which is likely to be caused by a narrowing of the flow path. On the flood tide the current pattern changes are predicted to be less radical than on the ebb tide. The current directions in the vicinity of the container terminal and breakwater are altered and follow the line of the structures, with speed increase predicted between the container terminal and Penny’s Bay reclamation. The additional reclamation to the east of the Penny’s Bay reclamation for the Theme Park is shown to cause the both the ebb and flood tide currents to undergo a sharp turn entering and exiting the area between the container terminal and the Penny’s Bay reclamation and this results in localised speed increases. Such an obstruction to flows is also likely to reduce the volumes of water flowing through this area. On both the ebb and flood phases of the tide the current speeds between the container terminal and breakwater are very low and hence the flushing capacity of this area is also likely to be low. The reclamation along the northern shore of Lantau Island is predicted to have little effect on current speeds and directions, with only a small deviation in an offshore directions in the currents in the immediate vicinity of the reclamation. Current speeds in the small embayed area, the remainder of the Yam O bay, at the western end of the reclamation are predicted to be very low and hence the flushing rate of this area will be low.

5.10.11The predicted changes in current patterns resulting from the Northshore Lantau Development only are much less than those for the combined scenario of the Northshore Lantau Development plus Container Terminal. The main effect is shown to the be the reduction in current speeds in the Sze Pak Wan and Discovery Bay areas, which will result in a reduction in the flushing of this area. This may have implications in terms of water quality and has been determined through detailed water quality modelling, as discussed below. The other main effect is the increase in current speeds at the north western tip of the Theme Park Extension, which is caused by the flows having to undergo a sharp turn entering and exiting the main flows in the Kap Shui Mun flow channel.

5.10.12The major changes in salinity are predicted to occur in the vicinity of the container terminal and breakwater for the combined Northshore Lantau Development plus Container terminal scenario. In the surface layer there are increases in salinity predicted to the west of the container terminal, around Peng Chau and Hei Ling Chau. There are also increases in salinity along the edge of the main flow channel to the east of the container terminals. In the bed layer increase in salinity are predicted over virtually the whole area bounded by the container terminals, Hei Ling Chau and Discovery Bay. In the vicinity of Yam O there are only small changes in salinity predicted, which are mainly shown to be increases in the vicinity of the small embayed area at the western end of the Yam O reclamation.

5.10.13The main changes in salinity for the Northshore Lantau Development only scenario are increases in salinity in the Discovery Bay and Sze Pak Wan areas and reflect the decreased flushing of these areas, as evidenced by the reduced current speeds. There is also shown to be an increase in salinity in the Sze Pak Wan are, as discussed above, and is clearly the result of the Northshore Lantau Development reclamation to the east.

5.10.14The above discussed changes in tidal current patterns and salinity distributions may have the potential to cause impacts to marine ecological resources and fisheries. The potential impacts are discussed in Sections 8 and 9, which assesses marine ecology and fisheries.

Water Quality

5.10.15The results of the water quality modelling at sensitive receivers are contained in Tables 5.10d and 5.10e for the wet and dry seasons respectively. In these tables the water quality modelling results are presented as statistical parameters (10^th percentile, mean, geometric mean and maximum) for comparison against the Water Quality Objectives. The locations of the sensitive receivers are shown in Figure 5.3a. In Tables 5.10f and 5.10g the water quality modelling results have been analysed to provide relevant statistical comparisons (minimum and maximum) for comparison against the Water Supplies Department’s criteria for seawater intakes in the wet and dry seasons respectively.

5.10.16The data in Tables 5.10d and 5.10e show that the water quality modelling predicts there will be no exceedances of the WQO for dissolved oxygen, unionised ammonia and suspended solids. There are predicted to be minimal changes in dissolved oxygen concentrations, except at Discovery Bay Beach and Sze Pak Wan in the wet season. At Discover Bay Beach the dissolved oxygen concentrations in the bottom of the water column are predicted to decrease from 3.7 mg L^-1 to 3.2 mg L^-1, which is most likely to a decrease in the flushing of this area resulting from the sheltering effect of the Penny’s Bay reclamations for the Northshore Lantau Development and Container Terminal. However, this impact is not considered to be adverse as the WQO is not predicted to be breached. At Sze Pak Wan both the depth averaged and bottom dissolved oxygen concentrations are predicted to increase and this is most likely due to the reduced flushing of this area providing conditions more conducive to algal growth, as shown by the increase in chlorophyll-a concentrations. The impact of the increased algal growth is discussed below.

5.10.17There are predicted to be a number of exceedances of the WQO for total inorganic nitrogen in both the wet and dry seasons. However, in the majority of cases the exceedances are predicted to occur in all three scenarios and it may be concluded that the operation of the Northshore Lantau development alone and in combination with the Container Terminal is not contributing to the exceedance of the WQO. Furthermore, the operation of the Northshore Lantau Development is not predicted to increase the level of exceedance of the WQO, and in some cases actually results in a reduction in the level of exceedance. There are predicted to be only small changes in the chlorophyll-a concentrations as a result of the operation of the Theme Park. At Sze Pak Wan concentrations increase from 5.4 mg L^-1 to 8.6 mg L^-1 and 7.9 mg L^-1 for the completed Northshore Lantau Development and the Northshore Lantau Development combined with the Container Terminal respectively in the dry season and from 9.1 mg L^-1 to 10.2 mg L^-1 and 9.8 mg L^-1 for the completed Northshore Lantau Development and the Northshore Lantau Development combined with the Container Terminal respectively in the wet season. It is assessed that these changes do not represent excessive or nuisance growths of algae and as such should not be considered as an adverse impact.

5.10.18Exceedances of the WQO for E. coli at bathing beaches are predicted to occur in both the wet and dry seasons. In all cases the operation of the Northshore Lantau Development and Container Terminal is not predicted to contribute to the level of exceedances, and only results in small increases at a few of the bathing beaches. It is therefore assessed that the developments are not causing adverse impacts in terms of E. coli concentrations.

5.10.19The data in Tables 5.10f and 5.10g show that the water quality modelling results predict that there will be exceedances of WSDs criteria at a number of seawater intakes, primarily in terms of E. coli concentrations. However, these exceedances are predicted to occur in all three scenarios and it can be seen that the operation of the Northshore Lantau Development and Container Terminal is not contributing significantly to the levels of exceedance of these standards. It is therefore assessed that the operation of neither the Northshore Lantau Development nor the Container Terminal is causing adverse impacts to the water quality at WSDs intakes.

5.10.20Contours of the various water quality parameters for the three modelling scenarios are contained in Figures D4a to D4af in Annex D4. The contours for depth averaged dissolved oxygen concentrations (Figures D4a to D4d) show that there are not predicted to be any exceedances of the WQO for any of the three scenarios. The Northshore Lantau Development alone is predicted to have only minimal impacts on dissolved oxygen concentrations, with the only noticeable effects being a small increase in the vicinity of Sze Pak Wan and a small decrease in the waters to the west of Hei Ling Chau. The contours for bottom dissolved oxygen concentrations (Figures D4e to D4h) show that the only predicted exceedance of the WQO is within the embayment formed by the container terminal and its associated breakwater. The breach of the WQO is most likely due to the low rates of flushing within this embayed area. The Northshore Lantau Development is shown to result in decreases in dissolved oxygen concentrations in the vicinity of Cheung Chau and to the west of Hei Ling Chau, and a small increase in Sze Pak Wan. The completed Northshore Lantau Development and Container Terminal Development scenario is predicted to result in larger decreases in dissolved oxygen concentrations to the west of Hei Ling Chau and in the vicinity of Peng Chau, compared with the Northshore Lantau Development alone. It may be concluded that the Northshore Lantau Development alone is not predicted to result in adverse impacts to dissolved oxygen concentrations. The Container Terminal, however, is predicted to cause a breach of the WQO within the facility and it is considered necessary that suitable mitigation measures be devised to reduce this predicted impact.

5.10.21The contours of BOD (Figures D4i to D4l) show that the modelling predicts that the operation of both the Northshore Lantau Development and Container Terminal will result in little changes to the BOD concentrations. The main effect will be a slight reduction in concentrations in and to the south of Discovery Bay. Such an impact may be considered to be an environmental improvement and may serve to offset the potential impact to dissolved oxygen which may have been caused by the reduced flushing of this area, as discussed above.

5.10.22The contours of total inorganic nitrogen (Figures D4m to D4p) show that in the wet season the modelling predicts a reduction in concentrations in the Western Harbour as a result of the operation of the Northshore Lantau Development and Container Terminal. This improvement is likely to have been caused by the reduction in flows past Ma Wan transporting less of the polluted Pearl River flows into the Western Harbour. There are predicted to be exceedances of the WQO in the Southern WCZ, to the south of the Northshore Lantau Development and Container Terminal. These exceedances are present in all three scenarios and neither the Northshore Lantau Development nor the Container Terminal are predicted to cause an increase in the concentrations in this area. This means that the two developments are not responsible for the exceedance nor are they predicted to make the existing conditions any worse. To the north of Lantau Island there are not predicted to be any exceedances of the WQO and the two developments are predicted to only result in a slight increase in total inorganic nitrogen concentrations to the south of the Brothers. There are, therefore, predicted to be no adverse impacts to water quality in terms of total inorganic nitrogen from the operation of the Northshore Lantau Development and Container Terminal.

5.10.23The contours of unionised ammonia concentrations (Figures D4q to D4t) show that the modelling results predict that there will be no exceedances of the WQO. There are predicted to be increases in the unionised ammonia concentrations in the wet season to the west of Hei Ling Chau and Peng Chau and in the vicinity of the Northshore reclamation for the Northshore Lantau Development. There are small increases in the unionised ammonia concentrations at the location of the discharge point for the Siu Ho Wan outfall. It is concluded that there will be no adverse impacts to water quality in terms of unionised ammonia concentrations as the predicted increases in concentrations do not result in a breach of the WQO.

5.10.24The contours of chlorophyll-a concentrations (Figures D4u to D4x) show that the modelling predicts that the operation of the Northshore Lantau Development and Container Terminal will have minimal effects on algal growth. It is evident that there is an increase in algal growth in Sze Pak Wan, which has likely caused the predicted increase in dissolved oxygen concentrations. The predicted increase in algal growth is not considered to be excessive and would not cause a nuisance and is therefore not considered to be an adverse impact. The only other evident changes are that there are predicted to be small decreases in algal growth to the south of the Container Terminal.

5.10.25The contours of E. coli concentrations (Figures D4y to D4ab) show that there are predicted to be no exceedances of the WQOs for secondary contact recreation sub-zones and bathing beaches due to the operation of the Northshore Lantau Development and Container terminal as any exceedances are shown for the Baseline scenario. In the dry season there are predicted to be increases in E. coli concentrations in the vicinity of Peng Chau due to the operation of the Northshore Lantau Development and Container terminal, although the concentration do not breach the WQO for secondary contact recreation sub-zones. There are also predicted to be increases in the vicinity of the discharge point for the Siu Ho Wan outfall, which again do not breach the WQO. It is therefore concluded that there will be no adverse impacts to water quality with respect to E. coli from the operation of the Northshore Lantau Development and Container Terminal.

5.10.26The contours of suspended sediment concentrations (Figures D4ac to D4af) show that the water quality modelling predicts that the operation of the Northshore Lantau Development and Container Terminal will not cause a breach of the WQO. The operation of the Northshore Lantau Development is predicted to result in a reduction in suspended sediment concentrations in the Ma Wan Channel, possibly by a reduction in the discharge through this channel from the Pearl River Estuary. The operation of the Container Terminal is additionally predicted to cause a reduction in suspended sediment concentration between the berths and the breakwater, which is most likely due to the sheltering effect of these two structures reducing the rate of exchange with the outside waters. There are therefore not predicted to be any adverse impacts to water quality in terms of suspended sediment concentrations due to the operation of the Northshore Lantau Development and the Container Terminal.

5.10.27The water quality modelling has predicted that there will be no exceedances of the WQOs at sensitive receivers caused by the operation of the Northshore Lantau Development and the Container Terminal. There are, however, a number of exceedances of the WQO predicted at sensitive receivers for all three modelling scenarios, but in these cases the operation of the Northshore Lantau Development and Container Terminal is not contributing to the exceedance. The contour plots support the above conclusions and show that in general the operation of the Northshore Lantau Development and Container Terminal has little effect on water quality. The only exception is a predicted exceedance of the WQO for dissolved oxygen within the Container terminal and it is recommended that suitable mitigation measures be devised to reduce the predicted impact to acceptable levels.

5.10.28The water quality modelling has been able to predict water quality conditions in the majority of the areas surrounding the Northshore Lantau Development and Container Terminal due to the refined grid resolution used in the modelling for this study. However, the Yam O Bay following completion of the Northshore Lantau Development is too narrow to be represented by the model used for this study and as such it is not possible to quantitatively determine the water quality conditions within the bay. The modelling has been able to determine that the water quality conditions at the mouth of the bay, through the positioning of a sensitive receiver output point at this location, will be acceptable, which gives an indicator of conditions in the bay. However, due to the expected long retention times within the bay it is to be expected that the water quality will be lower than that at the mouth, particularly with regard to dissolved oxygen. The potential for poor water quality within the bay has been partially mitigated by the prevention of polluted discharges into the bay the diversion of any polluted stormwater to the west of the Luk Keng headland. Clean run-off from the surrounding hillsides will still be discharged into the bay to maintain a salinity gradient, which may serve to provide suitable conditions for continued mangrove growth on the mudflats at the head of the bay. However, it cannot be guaranteed that these measures will be successful in preventing adverse water quality conditions from occurring within the bay and it is recommended that at this stage further mitigation measures be adopted. The need for any further mitigation measures would be verified and tested during further more detailed studies. The detailed studies should include the use of a detailed local area water quality model with sufficient resolution to represent the bay at Yam O.

Chok Ko Wan Link Road

5.10.29The potential impacts from contaminated run-off fall into two broad categories, which are acute and chronic contamination. Acute contamination results from high concentrations of toxic substances in the runoff water. This is particularly associated with 'first flushes' of stormwater, where 'plugs' of contaminated deposits are washed off the road surfaces or are scoured from the deposits within the storm drainage system. The magnitude of such impacts increases in proportion to amount of sediment which can become mobilised, which is partly determined by the length of time since the previous storm event. Chronic contamination results from the continual discharge of run-off water to the receiving waters. This run-off is generally less contaminated than that occurring under storm conditions, as much of the sediment which is contaminated with heavy metals and PAHs is removed by settling out. It is likely that the impacts described here will be minimal provided that suitable mitigation measures are employed, which are described in Section 5.11.2.

5.11 Mitigation of Adverse Environmental Impacts - Operation

5.11.1 The identification and discussion of suitable measures to mitigate any adverse impacts to water quality from the operation of the Theme Park is split into two main aspects.

· The surrounding marine waters; and

· The Chok Ko Wan Link Road.

Marine Waters

5.11.2 The operation of the Northshore Lantau Development will have the potential to affect the water quality of the surrounding marine waters in two ways, by changing the hydrodynamics and through the discharges of pollutants from the development. Any identified mitigation measures for these two aspects are discussed separately.

Hydrodynamics

5.11.3 The hydrodynamic modelling has predicted that the reclamations for the Northshore Lantau Development will not cause major changes in tidal current patterns. The main effects are a reduction in current speeds in the Sze Pak Wan and Discovery Bay area. This is likely to cause a reduction in the flushing of these areas, which may in turn lead to effects on water quality. The potential impacts to water quality have been assessed through water quality modelling, which whether such impacts would be unacceptable. The need for mitigation measures in these areas is discussed below. Along the northern shore of Lantau Island it was determined that the current speeds in the vicinity of the remainder of the Yam O bay would be significantly reduced due to the formation of an embayment, which could again cause adverse impacts to water quality. This issue is also discussed below and suitable mitigation measures identified.

5.11.4 The Container Terminal was found to have large effects on tidal current patterns, particularly in the vicinity of Peng Chau and in the Kap Shui Mun main flow channel. The main effect was in reducing current speeds in areas to the west of the Container Terminal and hence reducing the flushing of these areas. The potential impacts to water quality have been assessed through detailed water quality modelling and the need for mitigation measures is discussed below. In the Kap Shui Mun the Container terminal was found to cause an increase in current speeds by constraining the flows. This is unlikely to cause any adverse environmental impacts and as such no mitigation measures will be required.

5.11.5 Both the Northshore Lantau Development and Container Terminal were predicted to cause changes to tidal discharges through the major flow channels in the vicinity of the developments, with the impacts due to the combined effect of the Northshore Lantau Development and Container Terminal being generally greater than those from the Northshore Lantau Development alone. The Northshore Lantau Development was predicted to cause a small reduction in the quantities of water flowing into and out of the Western Harbour, with the main effect being a large reduction in the residual flows through Victoria Harbour. These effects could have the potential to cause adverse impacts to water quality and the need for mitigation measures is discussed below. The combined effect of the Northshore Lantau Development and Container Terminal was predicted to cause large changes in the discharge patterns into and out of the Western Harbour, which is a cause for concern with regard to water quality. The need for mitigation measures is discussed below.

Water Quality

5.11.6 In terms of global effects on water quality the operation of the Northshore Lantau Development was not predicted to cause adverse impacts to water quality. However, on a precautionary principle it is recommended that silt traps be installed on all storm drains serving developed and landscaped/managed areas. This will serve to ensure that the pollutants in the stormwater discharges are minimised as far as is practicable.

5.11.7 The assessment has assumed that the Siu Ho Wan Sewage Treatment Works will be able to cater for the increased from the Northshore Lantau Development, whilst maintaining the same level of treatment and that the sewerage system to convey the sewage effluents from the Northshore Lantau Development to the Siu Ho Wan STW will have sufficient capacity. The capacities of both the Siu Ho Wan STW and of the sewerage system are being assessed as part of the engineering feasibility study for the Northshore Lantau Development under the Sewerage Impact Assessment (SIA). The SIA has determined that there will be no insurmountable problems with providing sufficient capacity at both the Siu Ho Wan STW and in the sewerage system.

5.11.8 It has been determined that there is the potential for poor water quality conditions within the embayed area of the Yam O bay. The stormwater system has been designed to mitigate this potential by removing polluted stormwater discharges from the bay. However, it is not possible at this stage to quantitatively determine whether additional measures will be required. On a precautionary basis it is recommended that consideration be given to reducing the size of the reclamation adjacent to the Yam O bay, which could potentially increase the flushing of the bay by increasing the width of the mouth of the bay. The need for a reduction in the size of the reclamation in the vicinity if Yam O Bay would be determined during further, more detailed water quality modelling, which would be capable of representing the features of the Yam O Bay.

5.11.9 It was predicted that adverse water quality conditions would occur between the Container Terminal and the breakwater at Kau Yi Chau. This is most likely to be due to the low flushing rates of this embayed area. In order to improve the flushing of this area and hence improve the water quality it is recommended that the Container Terminal be connected to Kau Yi Chau by a bridge or causeway. This will mean that water will be allowed to flow through the area between the Container terminal and Kau Yi Chau and hence prevent the accumulation of pollutants. This measure will also serve to improve the flows around Peng Chau, where the currents were predicted to be decreased.

Chok Ko Wan Link Road

5.11.10The following mitigation measures should be implemented to prevent adverse operational impacts to water quality from the Chok Ko Wan Link Road.

· all road run-off should be collected and discharged via a stormwater drainage system;

· oil and grit interceptors should be incorporated into areas where spills are likely to remove any oil or grease and sediment before being diverted to the public stormwater system;

· the contents of oil and grit interceptors should be transferred to an appropriate disposal facility on a regular basis, the frequency of which would depend upon the amount of rainfall (ie more frequent removal during the wet season);

· silt traps or sedimentation tanks should be installed to remove suspended solids, which may contain heavy metals and PAHs, from run-off water and, in the same way as oil and grit interceptors, they should be regularly cleaned and maintained in good working condition.

5.11.11The implementation of the above described mitigation measures will be sufficient to prevent adverse impacts to water quality from the operation of the Chok Ko Wan Link Road.

5.12 Residual Environmental Impacts

Construction

5.12.1 No residual environmental impacts were predicted to occur during the construction phase, provided that the mitigation measures, described in Section 5.7 are implemented. The mitigation measures were specified in the form of constraints on the construction programme and as a series of ‘best practice’ methods of working.

Operation

5.12.2 Water quality modelling of the impacts of the operational phase of the Northshore Lantau Development predicted that there would be no exceedances of the Water Quality Objectives which could be attributed to the Northshore Lantau Development. For total inorganic nitrogen and E. coli there were predicted to be exceedances of the WQOs in the baseline and operational scenarios and it was therefore concluded that the breaches in the WQOs could not be attributed to the operation of the Northshore Lantau Development. Furthermore, it was predicted that the operation of the Northshore Lantau Development would not cause a deterioration in water quality in those areas where the WQOs were already breached.

5.12.3 The reclamation for the Northshore Lantau Development on the northern shore of Lantau Island will lead to the formation of an embayed area in Yam O Bay. It was not possible to provide a quantitative assessment of water quality within the bay using the water quality model. It was determined that there was the potential for poor water quality within the bay and a number of mitigation measures. The need for and effectiveness of these mitigation measures would be determined during further, more detailed studies using a high resolution local area water quality model. However, at this time it has been assessed that the above described mitigation measures will be sufficient to prevent adverse water quality conditions occurring in Yam O Bay.

5.12.4 The water quality modelling predicted that there would be a breach of the WQOs within the area between the Container Terminal and breakwater at Kau Yi Chau, which was directly attributed to the operation of the Container Terminal. Mitigation measures were defined to reduce the predicted impact to below acceptable levels.

5.12.5 No residual impacts to marine water quality are therefore predicted from the operation of the Northshore Lantau Development and the Container Terminal, provided that the specified mitigation measures are implemented.

5.12.6 No residual impacts to water quality are predicted to occur during the operation of the Chok Ko Wan Link Road, provided that the mitigation measures described in Section 5.11.2 are implemented. The measures were specified in terms of the design of the drainage system and management practices.

5.13 Environmental Monitoring and Audit

Construction

Reclamation Formation

5.13.1 An Environmental Monitoring and Audit (EM&A) programme will be required during construction of the reclamations for the Northshore Lantau Development to ensure that no adverse water quality impacts occur at nearby sensitive receivers. Should adverse impacts be detected then the EM&A programme would act to trigger suitable mitigation measures. Full details of the EM&A programme are given in Section 15.4.

Construction Activities

5.13.2 No monitoring of water quality would be required during the construction activities on the reclaimed land. It is recommended, however, that audit be carried out to confirm that compliance with the ‘best practice’ site procedures, as defined in Section 5.7.2, are being undertaken. Full details of the audit requirements are presented in Section 15.4.

Operation

5.13.3 No monitoring of water quality during the operation of the Northshore Lantau Development and Chok Ko Wan Link Road will be required, beyond that which is required to satisfy WPCO discharge licence standards.

5.14 Conclusions

Construction

5.14.1 The construction phase assessment has considered the following aspects.

· the potential impacts to marine water quality from the construction of the reclamations associated with the Northshore Lantau Development, which are those at Siu Ho Wan, Northshore, Fa Peng and Theme Park Extension; and

· the potential impacts to marine water quality from land based construction works associated with the developments, including the Chok Ko Wan Link Road.

Reclamation Construction

5.14.2 The potential impacts to marine water quality from the construction of the reclamations for the Northshore Lantau Development was assessed through sediment plume modelling using a particle tracking model. The sediment plume modelling predicted that there would be no adverse impacts at sensitive receivers due to elevations in suspended sediment concentrations and that there would be no adverse impacts in terms of sediment deposition. Sediment quality data was obtained as part of this project for the areas to be dredged and this data, in combination with the modelling predictions on suspended sediment concentrations, to calculate the impacts of the construction works on water quality in terms of dissolved oxygen, nutrients and the release of micro-pollutants. It was determined that there would be no adverse impacts to water quality, with the exception of the release of TBT. However, the assessment methodology for TBT impacts was very conservative and despite this the predicted release of TBT was not predicted to significantly increase the background levels. It was recommended that elutriate testing be carried out to obtain better estimates of the potential release of TBT to the surrounding marine waters, which would then enable a determination to be made of the necessity for mitigation measures.

5.14.3 Mitigation measures for the construction of the reclamations were specified in terms of operational constraints, ie limiting the rates of working to those simulated in the sediment plume modelling and the sequence of construction, to ensure that the impacts would remain below those predicted. A series of ‘best practice’ methods of working were also specified. The implementation of these measures would prevent adverse impacts to water quality during the construction of the reclamations.

5.14.4 It was recommended that Environmental Monitoring and Audit be carried out to ensure that there would be no adverse impacts to sensitive receivers during the construction of the reclamations for the Northshore Lantau Development.

Land Based Construction Activities

5.14.5 It was determined that the potential for adverse impacts to water quality from land based construction activities for the Northshore Lantau Development and the Chok Ko Wan Link Road would primarily be from contaminated surface run-off and from sewage effluent generated by the construction workforce. A number of mitigation measures were specified to reduce the potential adverse impacts to acceptable levels.

Operation

5.14.6 The operation phase assessment has considered the following aspects.

· the potential impacts to hydrodynamics from the Northshore Lantau Development reclamations alone and in combination with a Container Terminal;

· the potential impacts to water quality from changes in hydrodynamics and treated sewage effluent and stormwater discharges from the Northshore Lantau Development and the Container Terminal; and

· the potential impacts to marine water quality from the operation of the Chok Ko Wan Link Road.

Hydrodynamics and Water Quality

5.14.7 The potential impacts to hydrodynamics from the operation of the Northshore Lantau Development and Container terminal were assessed using computational modelling. The computational modelling predicted that the reclamations would cause the tidal current patterns and tidal discharges in the vicinity of the developments to be altered. The predicted changes in the hydrodynamic patterns could have effects on water quality, which is discussed below.

5.14.8 The potential impacts to water quality from the changes in hydrodynamics and discharges of treated sewage effluent and stormwater from the Northshore Lantau Development and Container Terminal were assessed using computational water quality modelling. The sewage effluent from the Northshore Lantau Development and Container Terminal will be conveyed to the Siu Ho Wan Sewage Treatment Works, while the stormwater will be discharged via culverts along the face of the reclamations. The increased treated effluent flows from the Siu Ho Wan STW due to the load from the Northshore Lantau Development and Container Terminal and the stormwater discharges were included in the water quality modelling. The water quality modelling predicted that there would be no adverse impacts to water quality from the operation of the Northshore Lantau Development. It was predicted that there would be an exceedance of the WQOs within the Container Terminal development and suitable mitigation measures were devised, which specified a change in the design of the Container Terminal.

5.14.9 It was determined that there would be the potential for poor water quality to occur within the embayed area in Yam O bay, formed as a result of the Northshore Lantau Development reclamations. The modelling carried out for this study was not sufficiently detailed to quantitatively assess the water quality within the bay. A number of mitigation measures were devised to reduce the risk of poor water quality in terms of re-locating polluted stormwater discharges away from the bay and reducing the size of the Northshore reclamation to provide a wider mouth to the bay and encourage flushing. The need for and extent of these mitigation measures would be determined through further, refined modelling during the detailed EIA stage for this portion of the Northshore Lantau Development.

5.14.10It was not recommended that Environmental Monitoring and Audit be carried out during the operation phase of the Northshore Lantau Development, beyond that which would be required to apply for discharge licences under the WPCO.

Chok Ko Wan Link Road

5.14.11The operation of the Chok Ko Wan Link Road would have the potential to cause adverse impacts to water quality through the discharge of contaminated surface run-off to the stormwater system. Suitable mitigation measures were specified to minimise the potential impacts. It was therefore assessed that there would be no adverse impacts to water quality from the operation of the Chok Ko Wan Link Road.

5.15 Impact Summary

5.15.1 Water quality impacts due to construction and operation of the proposed NLDFS developments and the preferred CKWLR alignment have been summarised in Table 5.15a as follows.

Table 5.15a - Impact Summary Table

Issue	Construction Impact	Operational Impact
Assessment Points	· Impacts to water quality from dredging and filling for the Northshore Lantau Development; and · Impacts to water quality from land based construction works from the land based construction works associated with the developments, including the Chok Ko Wan Link Road.	· Impacts to hydrodynamics from the Northshore Lantau Development reclamations alone and in combination with those for a container terminal development to the south east; · Impacts to marine water quality due to changes in hydrodynamics and treated sewage effluent and stormwater discharges from the Northshore Lantau Development and container terminal development; · The impacts to marine water quality from the operation of the Chok Ko Wan Link Road.
Relevant Criteria	· Water Pollution Control Ordinance; · Technical Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters; · Environmental Impact Assessment Ordinance (Cap. 499 S16), Technical Memorandum on Environmental Impact Assessment Process, Annexes 6 and 14; and · Practice Note for Professional Persons, Construction Site Drainage (ProPECC PN 1 /94).	· Water Pollution Control Ordinance; · Technical Memorandum for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters; · Environmental Impact Assessment Ordinance (Cap. 499 S16), Technical Memorandum on Environmental Impact Assessment Process, Annexes 6 and 14; and · Drainage Services Department Sewerage Manual.
Potential Impacts	· No adverse impacts to water quality in terms of increased suspended sediment concentrations and increased sediment deposition were predicted from the construction of the Northshore Lantau Development reclamations; · Potential adverse impacts were predicted due to the release of TBT from sediments suspended during dredging but it was determined that, despite a very conservative assessment methodology, that the release of TBT would not significantly increase background concentrations ; and · No adverse impacts to water quality during land based construction activities, provided that ‘best practice’ measures implemented.	· No adverse impacts water quality due to changes in hydrodynamics and due to the discharge of sewage effluents and stormwater were predicted for the Northshore Lantau Development alone; · The present modelling work was not detailed enough to determine the potential impacts to the embayed area at Yam; · No adverse impacts to water quality were predicted due to the cumulative impacts of the Northshore Lantau Development and Container Terminal Development, except in the immediate vicinity of the container terminal; and · No adverse impacts to water quality from the operation of the Chok Ko Wan Road Link were predicted, provided certain design features were incorporated.
Mitigation Measures	· Operational constraints were specified for the construction of the reclamations, in terms of rates of working, methods of construction and sequence of construction; · In addition, ‘best practice’ working methods were specified for reclamation construction; and · For the land based construction activities measures were specified to minimise the potential for contaminated surface run-off entering marine waters and to prevent the discharge of untreated sewage effluent.	· It was recommended that consideration be given to decreasing the size of the Northshore reclamation to prevent reductions in the flushing of Yam O and that the necessity for such reductions be determined through detailed modelling during further studies for the Northshore reclamation; · It was recommended that the container terminal be connected via a bridge to Kau Yi Chau to encourage greater mixing in the immediate area to mitigate the predicted adverse impact; and · Measures were devised to mitigate the potential impacts due to surface run-off from the road and rail links.
Residual Impacts	No residual impacts were predicted to occur provided suitable mitigation measures were implemented.	No residual impacts to occur were predicted to occur provided that the recommended mitigation measures were implemented.
Environmental Acceptability	Acceptable.	Acceptable.

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^{([1]) EPD (1999). Marine Water Quality in Hong Kong in 1998.}

^{([2]) EPD (1998). Marine Water Quality in Hong Kong in 1997.}

^{([3]) Data provided by EPD.}

^{([4]) ERM (1997). Environmental Impact Assessment: Dredging an Area of Kellett Bank for Reporvisioning of Six Government. Working paper on Design Scenarios.}

^{([5]) Babtie BMT Harris and Sutherland (1998). Supplementary Agreement No 1 to Agreement No CE 31/96. Green Island Development - Studies on Ecological, Water Quality and Marine Traffic Impacts. Dredging Study for New Fairway and Reprovisioning of Mooring Buoys. Working Paper for Dredging and Disposal Scheme.}

^{([6]) Maunsell Consultants Asia Ltd (1995). Lantau Port Development Stage 1. Design of Reclamation and Edge Structures for Container Terminals 10 and 11 and Back-up Areas. Environmental Impact Assessment. Final Report.}

^{([7]) ERM (1997). Environmental Impact Assessment for the Disposal of Contaminated Mud in the East Sha Chau Marine Borrow Pit. Final Report.}

^{([8]) Personal correspondence with EPD.}

^{([9]) EPD (1999). Op cit.}

^{([10]) EPD (1999). Op cit.}

^{([11]) HMIP (1994). Environmental Economic and BPEO Assessment Principles for Integrated Pollution Control. Environmental Quality Standards and Assessment Levels for Surface Water.}

^{([12]) ERM (1999). Environmental Impact Assessment: Dredging an Area of Kellett Bank for Reprovisioning of Six Government Mooring Buoys. Final Report.}

^{([13]) HMIP (1994). Op cit.}

^{([14]) Sittig (1981).}

^{([15]) Aspinwall Clouston Limited (1998). A Study of Tributyltin Contamination of the Marine Environment of Hong Kong. Final Report.}

^{([16]) ERM (1998). Environmental Impact Assessment : Dredging an Area of Kellett Bank for Reprovisioning of Six Government. Final Report.}

^{([17]) ERM (1997). Environmental Impact Assessment Study for Disposal of Contaminated Mud in the East Sha Chau Marine Borrow Pit. Final Report.}

^{([18]) ERM (1998). Op cit.}

^{([19]) ERM (1997). Op cit.}

^{([20]) Delft Hydraulics (1998). Upgrading of the Water Quality and Hydraulic Mathematical Models. Final Model Calibration and Validation Report; Part 2, Hydraulic Validation and WQ Calibration.}

^{([21]) Hyder Environmental (1999). Update on Cumulative Water Quality and Hydrological Effect of Coastal Developments and Upgrading of Assessment, Calibration and Verification of the Hydrodynamic Model.}

^{([22]) Hyder Environmental (1999). Op cit.}

^{([23]) Delft Hydraulics (1998). Op cit.}

^{([24]) Communication with the Planning Department of the HKSAR Government.}

^{([25]) Drainage Service Department. Sewerage Manual.}

^{([26]) Communication with the Sewage Infrastructure Group of the Environmental Protection Department of the HKSAR Government.}

^{([27]) Scott Wilson (Hong Kong) Ltd (1999). Agreement No CE 60/96. Northshore Lantau Development Feasibility Study. Stormwater Pollution Loading Working Paper.}

^{([28]) Scott Wilson 9Hong Kong) Ltd (1999). Op cit.}