Appendix 5              Noise Calculations for Grab Dredger Option between 23:00 and 07:00

The dredgers allocation and working schedules as described in Section 5.3.4 are adopted.  For each NSR under consideration, the noise levels due to one grab dredger in each sub-divided working zone are first individually calculated as shown in Table A5.1 to A5.6.  The relevant individual noise levels are then combined to obtain the resultant noise levels at each NSR for all scenarios as shown in Table A5.7.

Table A5.1      Noise levels (Leq(5min)) at Long Tsai Tsuen/Hung Shing Ye (NSR a) due to one grab dredger in each sub-divided working zone

Working Zone

Shortest distance from NSR (m)

Distance attenuation (dBA)

Air absorption correction
(-2.7 dBA/km) (dBA)

Facade correction (dBA)

Attenuation # due to screening (dBA)

Noise level at NSR (dBA)

ABn (north)

1765

-72.9

-4.8

3.0

-5

321

ABn (south)

1800

-73.1

-4.9

3.0

0

372

ABs (north)

1900

-73.6

-5.1

3.0

0

363

ABs (south)

2067

-74.3

-5.6

3.0

0

354

BCn (north)

2333

-75.3

-6.3

3.0

0

335

BCn (south)

2600

-76.3

-7.0

3.0

0

32

BCs (north)

2933

-77.3

-7.9

3.0

0

30

BCs (south)

3266

-78.3

-8.8

3.0

0

28

#              The 2nd last column refers to the topographic screening due to intervening hills.

Table A5.2      Noise levels (Leq(5min)) at Ko Long (NSR b) due to one grab dredger in each sub-divided working zone

Working Zone

Shortest distance from NSR (m)

Distance attenuation (dBA)

Air absorption correction
(-2.7 dBA/km) (dBA)

Facade correction (dBA)

Attenuation # due to screening (dBA)

Noise level at NSR (dBA)

ABn (north)

1000

-68.0

-2.7

3.0

0

44

ABn (south)

1133

-69.1

-3.1

3.0

-10

33

ABs (north)

1400

-70.9

-3.8

3.0

-10

30

ABs (south)

1733

-72.8

-4.7

3.0

-10

28

BCn (north)

2100

-74.4

-5.7

3.0

-10

25

BCn (south)

2500

-75.9

-6.8

3.0

-10

22

BCs (north)

2867

-77.1

-7.7

3.0

-10

20

BCs (south)

3267

-78.3

-8.8

3.0

-10

18

#              The 2nd last column refers to the topographic screening due to intervening hills.

 

 


Table A5.3      Noise levels (Leq(5min)) at Yung Shue Wan (NSR c) due to one grab dredger in each sub-divided working zone

Working Zone

Shortest distance from NSR (m)

Distance attenuation (dBA)

Air absorption correction
(-2.7 dBA/km) (dBA)

Facade correction (dBA)

Attenuation # due to screening (dBA)

Noise level at NSR (dBA)

ABn (north)

1175

-69.4

-3.2

3.0

0

42

ABn (south)

1367

-70.7

-3.7

3.0

0

41

ABs (north)

1667

-72.4

-4.5

3.0

-5

33

ABs (south)

2000

-74.0

-5.4

3.0

-10

26

BCn (north)

2367

-75.5

-6.4

3.0

-10

23

BCn (south)

2750

-76.8

-7.4

3.0

-10

21

BCs (north)

3133

-77.9

-8.5

3.0

-10

19

BCs (south)

3533

-78.9

-9.5

3.0

-10

17

#              The 2nd last column refers to the topographic screening due to intervening hills.

 

Table A5.4      Noise levels (Leq(5min)) at Tai Wan San Tsuen (NSR d) due to one grab dredger in each sub-divided working zone

Working Zone

Shortest distance from NSR (m)

Distance attenuation (dBA)

Air absorption correction
(-2.7 dBA/km) (dBA)

Facade correction (dBA)

Attenuation # due to screening (dBA)

Noise level at NSR (dBA)

ABn (north)

1410

-71.0

-3.8

3.0

0

40

ABn (south)

1500

-71.5

-4.1

3.0

0

39

ABs (north)

1700

-72.6

-4.6

3.0

-10

28

ABs (south)

1967

-73.9

-5.3

3.0

-10

26

BCn (north)

2333

-75.3

-6.3

3.0

-10

23

BCn (south)

2667

-76.5

-7.2

3.0

-10

21

BCs (north)

3033

-77.6

-8.2

3.0

-10

19

BCs (south)

3400

-78.6

-9.2

3.0

-10

17

#              The 2nd last column refers to the topographic screening due to intervening hills.

 

Table A5.5      Noise levels (Leq(5min)) at YMCA Lamma Island Youth Hostel (NSR e) due to one grab dredger in each sub-divided working zone

Working Zone

Shortest distance from NSR (m)

Distance attenuation (dBA)

Air absorption correction
(-2.7 dBA/km) (dBA)

Facade correction (dBA)

Attenuation # due to screening (dBA)

Noise level at NSR (dBA)

ABn (north)

2200

-74.8

-5.9

3.0

0

34

ABn (south)

2050

-74.2

-5.5

3.0

0

35

ABs (north)

2050

-74.2

-5.5

3.0

0

35

ABs (south)

2133

-74.6

-5.8

3.0

0

35

BCn (north)

2333

-75.3

-6.3

3.0

0

33

BCn (south)

2400

-75.6

-6.5

3.0

0

33

BCs (north)

2633

-76.4

-7.1

3.0

0

32

BCs (south)

2900

-77.2

-7.8

3.0

0

30

#              The 2nd last column refers to the topographic screening due to intervening hills.

 

Table A5.6      Noise levels (Leq(5min)) at Lo So Shing (NSR f) due to one grab dredger in each sub-divided working zone

Working Zone

Shortest distance from NSR (m)

Distance attenuation (dBA)

Air absorption correction
(-2.7 dBA/km) (dBA)

Facade correction (dBA)

Attenuation # due to screening (dBA)

Noise level at NSR (dBA)

ABn (north)

2500

-75.9

-6.8

3.0

0

32

ABn (south)

2233

-75.0

-6.0

3.0

0

34

ABs (north)

2100

-74.4

-5.7

3.0

0

35

ABs (south)

1900

-73.6

-5.1

3.0

0

36

BCn (north)

1880

-73.5

-5.1

3.0

0

36

BCn (south)

2000

-74.0

-5.4

3.0

0

36

BCs (north)

2000

-74.0

-5.4

3.0

0

36

BCs (south)

2233

-75.0

-6.0

3.0

0

34

#              The 2nd last column refers to the topographic screening due to intervening hills.

 

Table A5.7      Resultant noise levels (Leq(5min)) in dB(A) at each NSR

Month

NSR a

NSR b

NSR c

NSR d

NSR e

NSR f

Month 1

42*

45

45

43

42

42

Month 2

42

45

45

43

42

42

Month 3

42

45

45

43

42

42

Month 4

42

45

45

43

42

42

Month 5

42

45

45

43

42

42

Month 6

41

45

45

43

41

42

Month 7

41

35

41

40

40

42

Month 8

41

35

41

40

40

42

Footnote:

*Sample Calculation:

For NSR a in Month 1,

1Noise level due to GD1 at ABn North   =              32 dB(A)

2Noise level due to GD2 at ABn South   =              37 dB(A)

3Noise level due to GD3 at ABs North   =              36 dB(A)

4Noise level due to GD4 at ABs South   =              35 dB(A)

5Noise level due to GD5 at BCn North   =              33 dB(A)

Resultant noise level                              =              42 dB(A)