APPENDIX 5.5          SAMPLE CALCULATION OF MARINE TRAFFIC NOISE ASSESSMENT

 

 

1.         Marine Traffic Noise Prediction -

 

1.1.       The maximum noise level (Lmax) during a simultaneous passby of a fishing vessel and the 1 hour equivalent continuous noise levels in (Leq, 1 hr) passby of a fishing vessel and a sampan were predicted at representative NSRs to assess the marine traffic noise.

 

1.2.       For the calculation of the marine traffic noise, the barrier effect of the proposed WFM was ignored as a conservative approach.

 

2.         Predicted maximum passby noise level (Lmax) -

 

2.1.       The potential noise impact due to the marine traffic within the assessment area was assessed based on the source noise levels determined by the noise survey. The maximum sound pressure level (Lmax2) during a fishing vessel or a sampan passby can be expressed as

 

Lmax2 = Lmax1 + 20 log (R1/R2) + F                          (1)

 

Where,   Lmax1 is the measured vessel passby noise level, dB(A);

              Lmax2 is the fishing vessel passby noise level at sensitive receiver, dB(A);

              R1 is the reference distance between measurement point and the fishing vessel/sampan, m;

              R2 is the slant distance between vessel travelling route and sensitive receiver, m.

F is the façade effect correction, taken to be 3 dB(A)

 

2.2.       Two representative navigation paths were assumed for marine traffic noise prediction (see Figure 5.10). The slant distances between the noise sensitive receivers and the assumed routings are tabulated in Tables 1 & 2 below.

 

Table 1             Slant distances between the receiver and the assumed navigation path – Route 1

 

NSR ID

Slant distance between each NSR and path segment, m

1/F

6/F

11/F

16/F

21/F

1b

222

223

225

229

233

2

253

254

256

259

262

3

289

290

291

294

297

4

325

326

327

329

332

5

364

365

366

368

370

15c

202

203

205

208

213

15d

211

212

214

218

222

24a

246

248

250

253

257

24b

229

230

233

236

240

26a

465

466

467

468

470

26b

560

561

561

563

564

 

Table 2             Slant distances between the receiver and the assumed navigation path – Route 2

 

NSR ID

Slant distance between each NSR and path segment, m

1/F

6/F

11/F

16/F

21/F

1b

220

221

223

227

231

2

220

221

223

227

231

3

220

221

223

227

231

4

225

226

228

231

235

5

225

226

228

231

235

15c

225

226

228

231

235

15d

225

226

228

231

235

24a

246

248

250

253

257

24b

229

230

233

236

240

26a

115

117

121

127

134

26b

115

117

121

127

134

 

 

Sample calculation at NSR 26a – 1/F (Route 2)

 

Step 1 : Calculation of the slant distance between the source and the receiver

 

                                    R2  = [(h2 + Dh2)]½

                                          = [(10.3-1.4)2 + 1152]½

                                          = 115.3 m

 

Where,  R2 is the slant distance between the source and the receiver;

h is the receiver height between the receiver height (in mpd) and the height of sea level (in mpd) and;

Dh is the horizontal distance between the source, i.e. the Western Fairway, and the receiver, m;

 

The determination of the horizontal distance between the source and the receiver is shown in the Figure 5.13.

 

Step 2 : Calculation of the Lmax from the equation (1)

 

Noise emitted from Vessel, Lmax2      = 3 + 67.7 + 20 log (30/115.3)

                                                        = 59.0 dB(A)

 

Noise emitted from Sampan, Lmax2     = 3 + 66.6 + 20 log (25/115.3)

                                                         = 56.3 dB(A)

 

3.         Predicted 1 hour equivalent continuous noise levels (Leq, 1 hr) -

 

3.1       The single event noise exposure level (LAX) for an idealized fishing vessel/sampan (a moving point source) can be expressed as

 

LAX = Lmax + 10log(Kd/V)                              (2)

 

Where,   Lmax is the measured vessel passby noise level, dB(A);

LAX is the single event noise level, dB(A);

V is the travelling velocity of fishing vessel/sampan, m/s;

d is the perpendicular distance between measurement point and the fishing vessel/sampan, m;

K is an empirical constant

 

3.2       As stated in the Transportation Noise Reference Book, K may be less than p in reality, because of either source directivity or possible air absorption. An empirical value of 1.83 for K was suggested for aircraft noise, while a maximum value of 2 for K was estimated for diesel locomotives. For the marine vessel, K is taken as 2 in the noise prediction.

 

3.3       The single event noise exposure level at the receiver (LAX (receiver)) is determined by applying the distance correction, the angle of view correction and the façade reflection to the Leq level from Equation (2). The correction for distance attenuation a moving point source is taken as:

 

D = 20log(d/do)                      (3)

 

Where,   d is the perpendicular slant distance between the source and the receiver, m;

do is the reference distance where the source noise level is determined, m.

 

3.4       Therefore, the single event noise exposure level (LAX (receiver)) for an idealized vessel/sampan can be expressed as

 

LAX (receiver) = LAX (measured) – D              (4)

 

3.5       The noise level projected to the receiver during the passage of a single vessel/sampan is determined by

 

Leq,i = LAX(receiver) – 10logT                              (5)

 

Where,   T is the time period under consideration, s.

 

3.6       If there are N vessels passing by during T, the total predicted noise level (Leq,total) at the receiver for the passage of these N vessel/sampan is given by

 

Leq, total = Leq, i + 10logN + 3 dB(A)                (6)

 

Where,   3 dB(A) is the façade effect

 

3.7       The marine traffic flow data provided by AFCD is shown in the Table 3 below.

 

Table 3 Marine traffic flow data

 

Vessel Type

No. of Vessel, Vel/1 hr

Speed, m/s

Sampan

2

2.57 (5 knots)

Fishing Vessel

9

 

3.8       The speed of fishing vessels and sampan in the acoustic prediction is speed unit for vessel movement within the typhoon shelter.

 

3.9       Two representative navigation paths were assumed for marine traffic noise prediction (see Figure 5.10). The slant perpendicular distances between the noise sensitive receivers and the assumed routings are tabulated in Tables 4 – 6 below.

 

Table 4            Perpendicular distances between each NSRs and fishing vessels and sampan’s Route 1 segment 1

 

Slant perpendicula distance between each NSR and Route 1 segment 1, m

NSR ID

1/F

6/F

11/F

16/F

21/F

1b

215

216

218

222

226

2

250

251

253

256

259

3

285

286

288

290

293

4

325

326

327

329

332

5

360

361

362

364

367

15c

180

182

184

188

193

15d

195

196

199

202

207

24a

141

143

146

151

158

24b

106

109

113

120

128

25

478

479

480

482

484

26a

465

466

467

468

470

26b

580

580

581

582

584

 

Table 5            Perpendicular distances between each NSRs and fishing vessels and sampan’s Route 1 segment 2

 

Slant perpendicula distance between each NSR and Route 1 segment 2, m

NSR ID

1/F

6/F

11/F

16/F

21/F

1b

515

516

516

518

520

2

528

529

529

531

532

3

540

541

541

543

544

4

558

559

559

561

562

5

570

571

571

573

574

15c

510

511

511

513

515

15d

517

518

518

520

521

24a

548

549

550

551

553

24b

520

521

522

523

525

25

525

526

527

529

531

26a

520

521

521

523

525

26b

552

553

553

555

556

 

Table 6            Perpendicular distances between each NSRs and fishing vessels and sampan’s Route 2

 

Slant perpendicula distance between each NSR and Route 2, m

NSR ID

1/F

6/F

11/F

16/F

21/F

1b

220

221

223

227

231

2

220

221

223

227

231

3

220

221

223

227

231

4

225

226

228

231

235

5

225

226

228

231

235

15c

225

226

228

231

235

15d

225

226

228

231

235

24a

300

301

303

305

309

24b

280

281

283

286

289

25

484

484

484

484

484

26a

115

117

121

127

134

26b

115

117

121

127

134

 

 

Sample calculation at NSR 26a - 1/F (Route 2)

 

Step 1                                                 : Calculation of the slant perpendicular distance between the source and the receiver         

                                    R2  = [(h2 + Dh2)]½

                                          = [(10.3-1.4)2 + 1152]½

                                          = 115.3 m

 

where,      R2 is the slant perpendicular distance between the source and the receiver;

h is the receiver height between the receiver height (in mpd) and the height of sea level (in mpd) and;

Dh is the perpendicular distance between the source, i.e. the Western Fairway, and the receiver, m;

 

The determination of the perpendicular distance between the source and the receiver is shown in the Figure 5.14.

 

Step 2: Calculation of the LAX from the following equations:

 

LAX = Lmax + 10log(Kd/V)

 

Where,

K = 2

 

V = velocity of fishing vessel/sampan (m/s)

 

d = measurement distance

 

Lmax = measured Lmax level

 

LAX = single event noise exposure level

 

Equivalent noise level due to passby of a fishing vessel

LAX = 67.7 + 10log[{(2)(30)}/2.57]

       = 81.4

 

Equivalent noise level due to passby of a sampan

LAX = 66.6 + 10log[{(2)(25)}/2.57]

       = 79.5

 

Step 3: Calculation of the LAXr from the following equations:

 

LAXr = LAX – D

 

Where,

D = 20log (R2/R1)

 

R1 = measurement distance

 

R2 = slant perpendicular distance between the receiver and route

 

LAX = single event noise exposure level

 

LAxr = single event noise exposure level at receiver

 

Equivalent noise level due to passby of a fishing vessel

LAXr = 81.4 – 20log(115.3/30)

       = 69.7

 

Equivalent noise level due to passby of a sampan

LAXr = 79.5 – 20log(115.3/25)

       = 66.2

 

Step 4: Calculation of the Leq, i from the following equations:

 

Leq, i = LAXr - 10logT

 

Where,

T = time period under consideration, in s, e.g. 1 hour = 3600s

 

LAXr = single event noise exposure level at receiver

 

Leq, i = the equivalent noise level due to passby of a fishing vessel/sampan

 

Equivalent noise level due to passby of a fishing vessel

Leq, i             = 69.7 - 10log(3600)

                 = 34.1

 

Equivalent noise level due to passby of a sampan

Leq, i             = 66.2 - 10log(3600)

                 = 30.6

 

Step 5: Calculation of the Leq, total from the following equations:

 

Leq, total = Leq, i +10logN

 

Where,

N = number of fishing vessel/sampan

 

Leq, i = equivalent noise level in due to passing of a fishing vessel/sampan

 

Leq, total = total equivalent noise level

 

Equivalent noise level due to passby of a fishing vessel

Leq, total (vessel) = 34.1 +10log(9)

                     = 43.7

 

Equivalent noise level due to passby of a sampan

Leq, total (sampan)  = 30.6 +10log(2)

                        = 33.7

 

Step 6: Calculation of the total Leq (1 hr):

 

Total Leq (1 hr) = Leq, total (Vessel ) +  Leq, total (Sampan) + 3 dB(A)

 

Where,

3 dB(A) is the correction for façade effect

 

Total Leq (1 hr)         = Leq, total (Vessel ) +  Leq, total (Sampan) + 3

                          =[10 log (1043.7/10+1033.7/10)] + 3

                          = 47.1 dB(A) #

 

4.         Marine Traffic Noise Prediction Results -

 

The marine traffic noise preidction results are summarized as follows :

 

Table 1 Predicted Maximum Passby Noise Level (Lmax) – Route 1

 

NSR ID

Maximum Passby Noise Level, Lmax, dB(A)

 

1/F

6/F

11/F

16/F

21/F

1b

53

53

53

53

53

2

52

52

52

52

52

3

51

51

51

51

51

4

50

50

50

50

50

5

49

49

49

49

49

15c

55

55

55

55

55

15d

54

54

54

53

53

24a

52

52

52

52

52

24b

53

53

53

53

53

26a

47

47

47

47

47

26b

45

45

45

45

45

 

 

Table 2            Predicted Marine Traffic Noise Level (Leq(1 hour)) – Route 1

 

NSR ID

1-hour Equivalent Noise Level, Leq(1 hour) dB(A)

 

1/F

6/F

11/F

16/F

21/F

1b

42

42

42

42

42

2

41

41

41

41

41

3

40

40

40

40

40

4

39

39

39

39

39

5

39

39

39

39

39

15c

44

44

44

43

43

15d

43

43

43

43

43

24a

46

46

45

45

45

24b

48

48

47

47

46

26a

38

38

37

37

37

26b

36

36

36

36

36

 

Table 3            Predicted Maximum Passby Noise Level (Lmax) – Route 2

 

NSR ID

Maximum Passby Noise Level, Lmax, dB(A)

 

1/F

6/F

11/F

16/F

21/F

1b

53

53

53

53

53

2

53

53

53

53

53

3

53

53

53

53

53

4

53

53

53

53

53

5

53

53