Item 4.4 - Attach 04 - Auckland Creek Flood Study 2019 - Part B Appendices

APPENDIX A SURVEYED STORMWATER PIPE NETWORK LOWER AUCKLAND CREEK CATCHMENT

10335-R01-AucklandCkFS-D.docx

A.1

SURVEYED STORMWATER PIPE INFORMATION

Surveyed stormwater pipe details in the lower Auckland Creek catchment are listed in Table A-1. A value of ‘-99999’ indicates the data is missing. Due to the number of pits, the details have not been tabulated. They have however been provided in dwg format as part of the electronic data handover. Blanks in the ‘Number of’ column mean there is only one pipe.

Table A-1 ID

Surveyed Stormwater Pipe Information Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

83a

C

0.71

1.96

1.89

0.375

84a

C

-99999

2.22

2.2

0.3

77a

C

12.72

10.75

10.26

0.5

78a

C

7.62

11.52

10.8

0.375

79a

C

11.48

11.83

11.57

0.375

80a

C

-99999

1.43

1.35

0.75

74a

C

21.8

3.47

2.71

0.5

75a

C

50.84

5.85

3.51

0.45

140a

C

12.47

6.63

5.93

0.5

76a

C

58.92

10.18

5.95

0.6

70a

C

12.11

2.71

2.36

0.5

71a

C

7.65

-99999

2.76

0.375

72a

C

0.537

3.56

3.53

0.375

73a

C

2.11

3.58

3.603

0.375

66a

C

2.77

4.3

3.72

0.375

67a

C

21.28

5.28

3.82

0.375

68a

C

13.46

3.72

3.15

0.375

69a

C

42.81

7.02

3.66

0.375

62a

C

30.65

1.2

0.99

0.6

63a

C

10.61

1.74

1.68

0.375

64a

C

21.99

1.87

1.72

0.375

65a

C

23.19

2.1

-99999

0.9

58a

C

0.63

1.68

1.64

0.45

59a

C

19.24

1.4

1.25

0.6

60a

C

19.21

1.21

1.21

0.6

61a

C

8.467

1.64

1.6

0.375

54a

C

41.73

2.88

1.77

0.375

55a

C

11.77

3.28

2.89

0.375

56a

C

21.11

1.56

1.45

0.3

57a

C

8

1.97

-99999

0.375

113a

C

1.281

2.75

2.74

0.375

114a

C

27.14

2.73

2.68

0.375

115a

C

2.83

2.63

-99999

0.45

116a

C

9.42

2.51

-99999

0.375

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

109a

C

22.38

2.53

2.31

0.45

110a

C

-99999

2.3

1.64

0.45

111a

C

50

1.55

-99999

0.45

112a

C

1.31

3.39

3.27

0.375

105a

C

17.8

1.94

1.87

0.4

106a

C

17.36

1.71

-99999

0.4

107a

C

16.56

2.08

2

0.4

108a

C

-99999

2.54

2.54

0.45

101a

C

6.39

2.76

2.68

0.35

102a

C

64.18

1.53

1.36

0.45

103a

C

20.35

2.35

2.15

0.3

104a

C

17.03

1.81

1.74

0.4

96a

C

0.383

1.88

1.8

0.575

98a

C

1.51

2.16

2.03

0.375

99a

C

1.07

2.13

1.75

0.375

100a

C

0.467

1.82

1.817

0.375

92a

C

11.94

2.17

2.15

0.375

93a

C

11.05

2.07

2.04

0.375

94a

C

0.43

2.11

2.09

0.375

95a

C

0.44

1.94

1.94

0.375

89a

C

10.26

1.96

1.24

1.05

91a

C

0.63

1.82

1.81

0.45

141a

C

13.35

2.15

2.13

0.375

85a

C

9.16

2.45

2.19

0.25

86a

C

9.28

1.84

1.83

0.45

87a

C

32.59

1.83

1.4

0.45

88a

C

5.04

2.39

2

0.375

129a

C

7.221

1.75

1.41

0.375

126a

C

-99999

-0.3

-0.45

1.9

3

128a

C

-99999

-0.83

-0.84

1.9

3

121a

C

1.49

2.38

2.31

0.45

122a

C

1.22

2.16

2.15

0.45

123a

C

28.7

2.02

0.8

1.2

124a

C

13.37

2.29

-99999

0.375

117a

C

0.76

2.5

2.5

0.45

118a

C

26.84

3.11

2.997

0.375

119a

C

52.97

2.98

2.46

0.375

120a

C

9.31

2.93

2.77

0.375

104931a

C

15.98

2.59

2.37

0.375

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

4

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

104930a

C

11.04

2.59

2.35

0.375

104848a

C

3.65

2.5

1.6

0.375

104853a

C

20.816

2.85

2.82

0.375

104860a

C

-999999

1.59

1.59

1.05

104861a

C

-99999

1.59

1.59

1.05

104933a

C

25.83

2.6

2.59

0.375

104932a

C

7.48

2.32

1.59

0.375

104849a

C

13.92

2.7

2.6

0.375

104950a

C

42.31

1.88

1.63

1.05

104946a

C

-99999

1.9

1.9

0.75

104934a

C

1.95

2.41

2

0.375

104941a

C

7.11

2.69

2.67

0.375

104945a

C

17.18

2.22

2.25

0.825

104855a

C

11.36

2.44

2.38

0.375

104951a

C

33.64

1.63

1.59

1.05

104948a

C

-99999

2.2

2.17

0.75

103978a

C

8.16

3.21

3.05

0.375

104949a

C

-99999

2.37

2.3

0.825

104944a

C

26.67

2.13

2.06

0.75

104937a

C

12.81

2.61

-99999

0.375

104936a

C

10.583

2.95

2.72

0.25

104852a

C

31.8

3.03

-99999

0.375

104935a

C

15.97

2.72

2.66

0.375

104859a

C

-99999

2.45

2.37

0.45

104939a

C

63.99

2.55

2.47

0.75

104938a

C

48.46

2.76

2.31

0.375

105397a

C

9.15

3.49

3.27

0.375

104857a

C

16.09

2.4

2.38

0.45

104870a

C

15.17

2.83

2.45

0.375

104947a

C

38.52

2.06

1.9

0.75

104858a

C

-99999

2.37

2.224

0.45

104867a

C

-99999

0.07

-0.3

1.9

3

102842a

C

-99999

-0.6

-0.83

1.9

3

104559a

C

44.77

1.21

0.89

1.05

104478a

C

1.56

2.24

2.14

0.45

102844a

C

25.8

3.53

3.53

0.2

102656a

C

70.12

2.531

-99999

0.9

104566a

C

25.83

0.54

0.5

1.2

3

104863a

C

79.75

0.45

0.26

1.2

3

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

1049.52a

C

35.7

1.27

-99999

0.45

105798a

C

-99999

1.5

1.5

0.65

105794a

C

5.81

2.37

-99999

0.375

102833a

C

35.203

3.48

1.5

0.45

105789a

C

1.21

1.76

1.758

0.375

105742a

C

18.86

2.66

2.54

0.35

105796a

C

1.49

1.31

1.31

0.45

105799a

C

-99999

1.55

1.55

0.65

105791a

C

3.84

2.11

1.73

0.375

105752a

C

-99999

1.65

1.65

0.65

105751a

C

-99999

1.69

1.69

0.65

105790a

C

1.48

2

-99999

0.375

105797a

C

-99999

1.73

1.69

0.65

105754a

C

27

1.72

1.73

0.65

105792a

C

3.99

2.08

1.77

0.375

105753a

C

-99999

1.73

-99999

0.6

105793a

C

16.53

2.22

2.04

0.375

105745a

C

68.62

1.69

1.59

0.45

105749a

C

40

1.72

1.72

0.65

105743a

C

15.52

2.02

1.97

0.375

104953a

C

69.71

1.57

0.1

1.05

105795a

C

28.25

1.88

1.69

0.45

105748a

C

50.21

2.2

1.73

0.65

105788a

C

27.2

2.52

2.32

0.375

20a

C

66.1

2.31

2.19

0.425

138a

C

20.103

1.41

1.16

0.75

139a

C

20.103

1.41

1.16

0.7

16a

C

22

2.4

2.07

0.45

18a

C

80.55

2.23

2.162

0.375

19a

C

15.64

2.4

2.36

0.375

12a

C

129.713

2.56

2.267

0.375

13a

C

14.07

2.489

2.04

0.25

14a

C

15.662

2.561

2.16

0.3

15a

C

12.023

2.079

1.997

0.3

8a

C

10.89

2.01

1.99

0.375

9a

C

61.38

2.19

2.003

0.375

10a

C

11.902

2.285

2.215

0.375

11a

C

88.334

2.487

2.1

0.375

136a

C

18.94

2.29

2.18

0.375

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

137a

C

18.312

2.34

2.1

0.375

6a

C

7.02

3.92

3.76

0.375

7a

C

0.44

3.79

3.77

0.4

134a

C

11.74

2

1.8

0.3

135a

C

11.66

2.17

2.11

0.375

2a

C

102.538

2.361

1.89

0.375

4a

C

101.9

-99999

1.65

0.525

104481a

C

14.53

2.09

1.58

0.65

104479a

C

1.134

2.33

2.31

0.45

104480a

C

13.06

2.28

2.18

0.525

50a

C

0.858

1.93

1.85

0.35

51a

C

0.585

1.98

1.89

0.375

52a

C

12.19

1.67

1.57

0.45

53a

C

14.78

1.43

1.43

0.75

46a

C

33.72

2.104

1.978

0.3

48a

C

-99999

2.29

2.01

0.45

49a

C

12.06

0.59

0.41

0.375

43a

C

67.719

2.27

1.702

0.375

44a

C

11.605

1.958

1.89

0.45

38a

C

0.342

2.002

1.995

0.3

34a

C

0.442

2.152

2.152

0.4

36a

C

19.597

1.836

1.739

0.6

37a

C

52.313

1.97

1.853

0.6

30a

C

39.72

2.462

2.242

0.375

26a

C

39.473

1.6

1.29

0.75

27a

C

40.381

2.081

1.936

0.375

28a

C

37.64

1.92

1.74

0.525

22a

C

24.68

1.84

1.69

0.375

23a

C

13.7

1.943

1.84

0.375

24a

C

23.21

1.9

1.817

0.375

104012a

C

49.585

1.883

1.694

0.375

104096a

C

12.48

2.138

2.062

0.375

104097a

C

15.7862

2.236

2.139

0.375

104004a

C

12.31

2.1

1.95

0.375

104015a

C

9.11682

1.45

1.25

0.525

104101a

C

69.249

1.81

1.768

0.375

104021a

C

22.693

1.65

1.65

0.65

104018a

C

24.64461

1.763

1.65

0.525

103005a

C

27.79101

1.8

1.45

0.525

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

104014a

C

20.37922

1.82

1.81

0.45

103002a

C

13.8541

1.84

1.82

0.375

103004a

C

17.35664

1.9

1.85

0.375

102756a

C

98.07

1.94

1.74

0.525

100400a

C

3.96

1.5

1.43

0.75

100390a

C

23.99

2.48

2.35

0.25

100313a

C

70.11

1.32

0.71

0.75

102754a

C

118.7

2.45

1.715

0.75

100399a

C

94.08

1.41

1.134

0.75

101128a

C

10.06

1.63

1.4

0.75

101129a

C

11.95

1.73

1.66

0.75

102347a

C

12.66

1.71

1.7

0.525

100397a

C

11.81

1.7

1.7

0.525

101130a

C

11.96

1.7

1.71

0.75

101127a

C

19.69

1.66

1.51

0.75

101295a

C

72.36

1.4

0.87

0.675

100398a

C

119.72

1.68

1.47

0.75

100392a

C

11.7

2.08

2

0.375

100391a

C

26.81

1.98

1.9

0.375

100469a

C

19.08318

2.36

2.3

0.45

100471a

C

44.1589

2

0.25

0.45

101293a

C

61.86

3.71

1.72

0.375

103741a

C

55.66

2.33

1.7

0.3

104774a

C

14.8405

3.425

2.95

0.375

102596a

C

31.67

1.34

0.87

0.45

103466a

C

9.332

1.45

1.4

0.45

103465a

C

13.194

1.59

1.56

0.45

130a

C

14.84053

2.9

2.2

0.375

131a

C

13.95646

2.95

2.25

0.375

101161a

C

5.21138

3.42

2.95

0.375

103771a

C

32.76604

2.14

0.67

0.6

104649a

C

91.219

1.52

1.31

0.45

104643a

C

58.131

1.89

1.53

0.3

104646a

C

42.215

1.67

1.65

0.375

104647a

C

13.863

1.63

1.525

0.375

104644a

C

25.079

1.91

1.84

0.375

104648a

C

95.29

1.782

1.1

0.525

104650a

C

6.419

1.845

1.82

0.375

104645a

C

12.118

1.74

1.72

0.3

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

105236a

C

20.226

1.95

-99999

0.45

105235a

C

17.69

1.91

1.74

0.45

105233a

C

15.83

1.75

1.742

0.375

105238a

C

60.568

1.71

1.68

0.45

101926a

C

70.42

2.14

2.041

0.375

105239a

C

5.25

2

1.92

0.45

105234a

C

60.89

1.68

1.43

0.6

105237a

C

60.89

1.68

1.43

0.45

100393a

C

35.99

2.04

2.01

0.375

100230a

C

12.215

2.14

2.09

0.45

100228a

C

16.455

2.16

2.14

0.275

100394a

C

14.396

2

1.95

0.45

100396a

C

122.793

1.89

1.48

0.6

100229a

C

23.795

2.22

2.14

0.275

100231a

C

38.669

2.32

2.14

0.45

100232a

C

66.423

2.08

1.9

0.6

103283a

C

8.78

-99999

1.78

0.45

150a

C

14.503

1.5

1.45

0.6

103769a

C

21.838

1.6

1.5

0.45

103288a

C

14.404

1.52

1.5

0.6

103854a

C

73.513

1.93

1.61

0.45

101925a

C

61.527

2.116

-99999

0.45

103287a

C

70.644

1.7

1.56

0.6

103281a

C

12.596

2.04

1.786

0.375

103464a

C

0.834

103551a

C

65.35

2.178

1.86

0.45

103286a

C

26.148

1.77

1.73

0.6

102171a

C

3.18

0.51

0.45

0.9

102172a

C

3.182

-99999

1.95

0.9

102708b

C

70.03

1.91

0.51

0.9

103549a

C

85.41

2.94

2.22

0.3

103460a

C

12.52

1.87

1.707

0.375

103548a

C

8.39

2.81

2.68

0.275

104642a

C

10.84

2.68

2.41

0.275

102708a

C

30.38

1.9

0.51

0.35

103469a

C

11.7

1.08

0.88

0.6

102634a

C

11.32

1.71

1.53

0.375

103561a

C

48.529

2.79

1.97

0.375

102638a

C

78.6

1.45

0.59

0.375

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

2

2

0.45

2

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

101093a

C

16.31

1.72

1.61

0.375

101092a

C

6.52

1.83

1.75

0.375

101018a

C

7.063

1.54

1.46

0.375

101091a

C

8.35

2.09

1.8

0.375

103455a

C

5.06

-99999

1.68

0.375

103472a

C

60.84

-99999

0.36

0.75

103470a

C

22.304

1.33

1.12

0.6

103471a

C

20.592

0.86

-99999

0.75

101335a

C

36.74

1.45

1.37

0.675

101415a

C

12

2.08

1.89

0.375

102751a

C

25.23

1.86

1.84

0.45

102838a

C

8.77

1.32

0.84

0.75

101334a

C

78.86

1.68

1.44

0.575

101329a

C

12.24

2.12

1.94

0.375

102828a

C

3.12

2.53

2.4

0.375

102753a

C

55.64

1.81

-99999

0.45

103632a

C

7.706

2.674

2.654

0.3

101333a

C

75.91

2.06

1.71

0.525

101331a

C

28.04

-99999

2.09

0.525

101330a

C

27.26

2.24

-99999

0.375

103721a

C

32.77

2.638

2.457

0.3

103635a

C

16.608

2.08

1.695

0.375

103452a

C

41.796

2.817

2.715

0.3

103722a

C

8.568

2.658

2.64

0.3

103863a

C

14.37

1.73

1.38

0.375

103862a

C

21.314

1.58

1.42

0.375

104851a

C

16.14

1.74

1.712

0.375

103634a

C

39.575

2.462

2.183

0.375

102633a

C

9.42

1.82

1.74

0.375

104850a

C

27

1.68

1.55

0.375

2

103778a

C

59.1

1.31

0.92

0.375

3

103633a

C

24

1.6

1.4

0.375

2

103853a

C

11.854

2.029

1.974

0.375

103552a

C

87.47

1.37

-0.65

0.9

102631a

C

11.427

1.88

1.79

0.375

102653a

C

5.765

1.35

1.3

0.75

103851a

C

12.032

1.77

1.614

0.3

103768a

C

44.264

1.9

1.598

0.45

103770a

C

7.731

1.591

1.45

0.525

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

2

ID

Type

Length (m)

US IL (mAHD)

DS IL (mAHD)

Width/Diameter (m)

103852a

C

12.03

2.02

1.847

0.3

81a

C

0.68

1.6

1.48

0.375

82a

C

0.58

1.64

1.59

0.375

90a

R

25.5

2.98

2.72

0.6

0.3

125a

R

185.6

0.27

0.07

1.2

3

127a

R

-99999

-0.45

-0.59

1.9

3

21a

R

3.505

2.73

-99999

0.45

0.225

2

17a

R

11

2.5

2.45

0.45

0.225

2

132a

R

4.12

2.61

2.49

0.45

0.23

2

133a

R

3.75

2.53

2.5

0.45

0.25

2

3a

R

12

1.79

1.59

0.45

0.225

2

5a

R

11.74

1.63

1.47

0.45

0.225

2

1a

R

23.24

1.948

1.878

0.45

0.225

47a

R

10.953

1.45

1.4

1.25

0.75

42a

R

0.46

1.906

1.9

0.45

0.225

45a

R

16.631

1.86

1.73

0.45

2

39a

R

0.476

2.07

2.05

0.45

0.225

40a

R

0.627

1.941

1.94

0.45

0.225

41a

R

0.441

1.62

1.61

0.45

0.225

35a

R

0.447

2.317

-99999

0.3

0.25

31a

R

0.471

2.146

2.139

0.45

0.225

32a

R

0.583

2.09

2.09

0.45

0.225

33a

R

0.591

1.707

1.694

0.425

0.225

29a

R

0.545

1.77

1.72

0.425

0.225

25a

R

4.54

2.64

2.63

0.45

0.225

103462a

R

26.59

2.56

2.18

0.6

0.3

10335-R01-AucklandCkFS-D.docx

Height (m)

Number of

2

A.2

SURVEY DRAWINGS

10335-R01-AucklandCkFS-D.docx

APPENDIX B TEMPORAL PATTERN SELECTION

10335-R01-AucklandCkFS-D.docx

B.1

MEMORANDUM - ANALYSIS OF RAINFALL IN EAST COAST NORTH REGION

10335-R01-AucklandCkFS-D.docx

Water Modelling Solutions Pty Ltd A | Level 13, 269 Wickham Street Fortitude Valley QLD 4006 Australia

P | 07 3252 7448 E | admin@watermodelling.com.au W | www.watermodelling.com.au

GPO Box 664 Brisbane QLD 4001

ACN | 158 809 593 ABN | 75 158 809 593

MEMORANDUM To

Nikeeta Roche

From

Eoghain O’Hanlon

Copy

Celisa Faulkner

Reference

10335-M01-A

Date

7 May 2019

Pages

9

Subject

Analysis of Rainfall in East Coast North Queensland Region

Dear Nikeeta, One of the key objectives of the Auckland Creek Flood Study is to update the existing hydrological and hydraulic modelling in accordance with the new ARR 2016 data and guidelines. The new guidance of ARR 2016 recommends examining an ensemble of temporal patterns that have been developed for different regions for each duration of an AEP design storm event. ARR 2016 notes that it is not practical to run all ten temporal patterns that have been provided for each duration in hydraulic modelling. However, it is recommended to “run a separate hydrological modelling process of the whole catchment of interest in order to determine the average pattern in terms of peak flow or volume depending on the problem” and that “testing has demonstrated that on most catchments large number of events in the ensemble patterns are clustered around the mean and median” (ARR 2016, Book 2, Section 5.9.2).

In order to achieve a balance between model run times and the guidance of ARR 2016 to use an ensemble of temporal patterns, WMS put forward in its proposal to use three temporal patterns for each chosen critical duration. Initially, all ten temporal patterns for a range of storm durations were run in the hydrologic model to determine the critical durations for different regions of the catchment. The hydrological output for the median temporal pattern for each duration was modelled hydraulically in order to make a preliminary assessment as to which durations were critical throughout the catchment and would be adopted for the design event runs.

In undertaking this initial assessment, it was discovered that the results indicated the critical durations throughout the Auckland Creek catchment were not reasonable in that the overall critical duration for multiple regions in the catchment was the 12-hour duration. This was also the case for the upper sub-catchments. Given these unexpected results the objectives of this memorandum are as follows: •

To present the results from the initial hydraulic model and to explain why they are problematic;

•

To present the analysis that WMS undertook of the temporal rainfall patterns for the East Coast North Queensland Region in which Auckland Creek is located in order to discover why these results occurred; and

•

To suggest, subject to approval, some ways to proceed forward in light of the analysis undertaken.

1 INITIAL RESULTS In a catchment the size of Auckland Creek (56 km2) it is expected that the length of the critical storm will vary from shorter to longer durations when moving from upstream to downstream. The previous study undertaken by Engeny based on ARR 1987 guidelines adopted the 1-hour, 2-hour, 3-hour, 4.5-hour and 6-hour events as the critical storms for the catchment. In undertaking a critical duration analysis based upon the data derived from ARR 2016 and using the median storm for each duration from the ensemble of temporal patterns, WMS found the output from both the hydrologic and the hydraulic models to present results for the critical durations that were not acceptable to sound engineering judgement.

The output of the hydraulic model consists of a flood envelope that is derived from combining the results from the ensemble of storm durations that were run in the hydraulic model. This flood envelope indicates which storm durations contributed the maximum water level at any given location within the flood extent to determine which storm durations are critical within the catchment. For the Auckland Creek catchment ten storm event durations were examined ranging from 0.5 hours to 18 hours.

10335-M01-CriticalDurations-A.docx

Page 1

In assessing the critical flood envelope of the Auckland Creek catchment, it was noted that the 12-hour duration storm event was critical throughout nearly the entire extent of both the hydrologic and the hydraulic models. The critical duration map for the 1% AEP event is shown in Figure 1-1. It is evident the 12-hour storm duration is critical even in the upstream areas of the main flow path as well as contributing tributaries in which it would be expected that a shorter duration storm such as a 1-hour or 2-hour storm event would be critical.

Another flood envelope was created using the same modelling results but leaving out the 12-hour duration storm event. This result revealed that, though not as dominant as the 12-hour duration storm, the 9-hour storm event became critical throughout much of the catchment though not to the same extent as the 12-hour duration storm event. As shown in Figure 1-2, there is a better representation of some of the expected shorter durations such as 45 minutes and 2 hours in the catchment tributaries but still very little variation throughout the main flow path from upstream to downstream is observed. The 4.5-hour duration is the critical event in a short section of the channel towards the outlet upstream of the Mariner.

Further analysis was performed in which the flood envelope excluded both the 12-hour and 9-hour duration storm events, see Figure 1-3. The results show the 4.5-hour duration storm as critical throughout the main flow path which is within an acceptable critical response range for a catchment of this size. There is a better representation of the transition of the critical storm from shorter to longer durations in the tributaries. However, it was noted that in the main channel the 6-hour duration storm was critical further upstream than the 4.5-hour duration storm. The expected transition would be for the 6-hour duration storm to be critical downstream of the 4.5-hour storm duration.

10335-M01-CriticalDurations-A.docx

Page 2

Figure 1-1

Critical Durations for Auckland Creek Catchment – 1% AEP Event

10335-M01-CriticalDurations-A.docx

Page 3

Figure 1-2

Critical Durations for Auckland Creek Catchment Disregarding the 12-Hour Storm – 1% AEP Event

10335-M01-CriticalDurations-A.docx

Page 4

Figure 1-3

Critical Durations for Auckland Creek Catchment Disregarding 12-Hour and 9-Hour Storm Events – 1% AEP Event

10335-M01-CriticalDurations-A.docx

Page 5

2 ANALYSIS OF TEMPORAL PATTERNS In order to better understand these unusual outputs from the hydraulic model, WMS undertook a more in-depth analysis of the hydrological inputs. All the temporal patterns for the East Coast North Queensland region for the 6-hour, 9-hour, 12-hour, 18-hour and 24-hour duration storm events were analysed. This analysis included examining the rainfall hyetographs of the various temporal patterns, examining the Annual Exceedance Probability (AEP) of shorter rainfall bursts within these longer duration events, and examining the impact of the application of Areal Reduction Factors (ARFs). The findings examined in this section are applicable in varying degrees to all of the durations analysed (6 to 24 hours). In the interests of simplicity results from the 12-hour storm event which was particularly dominant will be presented in this memorandum as illustrative of the problems that were discovered.

The rainfall hyetograph of the temporal pattern of the median storm for the 12-hour 1% AEP storm is shown in Figure 2-1. This figure indicates a significant percentage of the total rainfall falling within the first two hours of this storm event.

50 45 40

Rainfall (mm)

35 30 25 20 15 10 5 0

Time (hrs) Figure 2-1

Hyetograph of the Median Temporal Pattern for the 12 hr Storm Event

An analysis was undertaken of this rainfall pattern to determine the AEP for shorter bursts of rainfall within the storm event from 0.5 hours up to 12 hours and plotting the AEPs derived against the IFD values for the BOM rainfall in this area. This analysis provides a way of assessing the intense shorter embedded bursts within this temporal pattern compared to the intensity that would be expected of a shorter duration event for the same AEP. The result of this AEP analysis is shown in Figure 2-2 for the median temporal pattern for the 12-hour duration storm.

10335-M01-CriticalDurations-A.docx

Page 6

1000

Total Rainfall Event Depth (mm)

63.2% AEP 50% AEP 20% AEP 10% AEP 5% AEP 100 2% AEP 1% AEP Median Storm

10 0.50

Figure 2-2

Duration (hrs)

5.00

Hyetograph of the Median Temporal Pattern for the 12-Hour Storm Event

Figure 2-2 shows that the median temporal pattern for the 12-hour storm event in the Auckland Creek catchment is generally tracking just above a 1% AEP for durations much shorter than 12 hours. This temporal pattern therefore has embedded bursts that are more intense than what would be expected for shorter duration events of the same AEP. These embedded storms of shorter duration within the median 12-hour temporal pattern explain why the 12-hour duration storm appears to be critical, in areas of the catchment in which a shorter duration storm event would be expected to be critical.

An additional aspect that exacerbates this effect of giving undue weight to longer duration storms is that the areal reduction factors (ARFs) that are applied to the BOM design rainfalls. ARFs are intended to account for the fact that a rainfall event will not be as intense over larger catchment areas especially for very short and therefore very intense duration events. The ARFs that have been applied to the BOM rainfall for the 1% AEP are shown in Table 2-1.

Table 2-1

Adopted ARF Factors for Auckland Creek for the 1% AEP Event

Storm Duration

0.5 hr

1 hr

1.5 hr

2 hr

3 hr

4.5 hr

6 hr

9 hr

12 hr

18 hr

24 hr

ARF

0.77

0.81

0.82

0.83

0.84

0.87

0.90

0.92

0.93

0.94

0.95

Table 2-1 shows rainfall for shorter duration events is reduced by a larger factor than longer duration events such as the 12-hour duration storm event. This difference in reduction factors will further increase internal rainfall bursts the AEP of 12-hour duration storms temporal patterns when compared to shorter duration storm events. This effect is shown in Figure 2-3 which plots the same storm as shown in Figure 2-2 but against the BOM IFD rainfall with ARFs applied.

10335-M01-CriticalDurations-A.docx

Page 7

1000

Total Rainfall Event Depth (mm)

63.2% AEP 50% AEP 20% AEP 10% AEP

100

5% AEP 2% AEP 1% AEP Median Storm

10 0.50 Figure 2-3

Duration (hrs)

5.00

Hyetograph of the Median Temporal Pattern for the 12-Hour Storm Event with Areal Reduction Factors Applied

Because larger ARFs are applied to shorter duration rainfall, the 12-hour duration storm median temporal pattern internal bursts are clearly greater than the 1% AEP line for all durations up to approximately 9 hours before becoming a 1% AEP storm at approximately 12 hours as would be expected since it is the temporal pattern for a 1% AEP 12-hour storm event. Prior to the application of ARFs to the design rainfall as in Figure 2-2, the 12-hour storm was tracking only slightly above or just on the 1% AEP line for durations shorter than 12 hours.

3 SUGGESTED SOLUTION As all the temporal patterns have been examined and subjected to an IFD analysis all of the problematic temporal patterns have been identified. The median storm, as the above analysis indicates, is one of these problematic storms. In the case of the 12-hour duration 1% AEP storm, four of the ten temporal patterns were tracking significantly above a 1% AEP event for shorter durations when plotted against the aerially reduced BOM rainfall. There are, however, a number of temporal patterns that are indicative of a more realistic pattern of rainfall for such a duration. Figure 3-1 shows an example where the AEP of shorter duration rainfall bursts for this 12-hour duration temporal pattern approximates a 10% AEP for durations up to 2 hours and steadily rises through 5% and 2% AEP events until it approximates a 1% AEP for 12 hours as would be expected.

It is suggested that in selecting the temporal patterns to run for design events for durations of 6 hours and longer that the temporal patterns that contain short duration bursts embedded within the temporal pattern be excluded, even if that is the median storm.

Instead, WMS will select a range of temporal patterns from those that do not include bursts that are more intense than what would be expected of shorter duration storms for the same AEP.

10335-M01-CriticalDurations-A.docx

Page 8

1000

Total Rainfall Event Depth (mm)

63.2% AEP 50% AEP 20% AEP 10% AEP 100

5% AEP 2% AEP 1% AEP Temporal Pattern

10 0.50

5.00 Duration (hrs)

Figure 3-1

Hyetograph of a Selected Temporal Pattern for the 12-Hour Duration Storm Event without Short Intense Embedded Rainfall Bursts

4 SUMMARY A summary is provided below.

1.

The hydraulic modelling indicated that storm durations significantly longer than those previously adopted in the Auckland Creek Flood Study were critical for the catchment. Furthermore, these longer durations were critical throughout the vast extent of the catchment including locations in the far upstream sections where much shorter durations would be expected to be critical.

2.

An analysis of the temporal patterns for storm durations ranging from 6 hours to 24 hours for the 1% AEP for the East Coast North Queensland region revealed that there was a problem with embedded bursts within some of the temporal patterns for these storm durations that had a higher intensity of rainfall than shorter events of the same AEP. The problem included the temporal pattern for the median storm. The impact of areal reduction factors which are greater for shorter events was observed to further exacerbate the problem.

3.

It is suggested that these temporal patterns be excluded from the analysis even if they include the median storm. WMS will use engineering judgement to make a selection of temporal patterns for these durations from the remaining temporal patterns that yield a more realistic result for these durations.

We request that Council provide a written agreement on the proposed methodology to progress the study prior to WMS progressing the design event modelling.

Please do not hesitate to contact me if you require further clarification.

Yours sincerely,

Eoghain O’Hanlon Principal Scientist Team Lead

10335-M01-CriticalDurations-A.docx

Page 9

B.2

TEMPORAL PATTERN SELECTION

The analysis was undertaken for all AEP events for durations ranging from 3 to 18 hours. The following design storms utilised the same temporal patterns: •

63.2% AEP, 39% AEP and 20% AEP events;

•

10% AEP and 5% AEP events; and

•

2% AEP, 1% AEP, 0.5% AEP and 0.2% AEP events.

To allow for different rainfall intensities, each AEP event was adjusted with a net depth (mm) factor taken from ARR 2016 Data Hub for the East Coast North Region.

As an example, the following graphs in Section B.2.1 show the temporal pattern rainfall for the 1% AEP event and 9-hour storm duration for each of the ten temporal patterns versus the IFD rainfall. These graphs were used as the basis for excluding and selecting which temporal patterns would be used for the hydraulic model runs.

As per the summary provided in Appendix B.1, temporal patterns for the above durations which displayed higher intensities/rainfalls than those of a shorter duration for the same AEP event were excluded from the ten temporal patterns and a new median temporal pattern was selected. Spreadsheets with plots equivalent to those in Section B.2.1 but for the remaining modelled storm durations for the 1% AEP event are provided as part of the electronic data handover for the project.

10335-R01-AucklandCkFS-D.docx

B.2.1

1% AEP 9 Hour Temporal Pattern Analysis

Figure B-1

9-Hour Storm Duration - Temporal Pattern One

Figure B-2

9-Hour Storm Duration - Temporal Pattern Two

10335-R01-AucklandCkFS-D.docx

Figure B-3

9-Hour Storm Duration - Temporal Pattern Three

Figure B-4

9-Hour Storm Duration - Temporal Pattern Four

10335-R01-AucklandCkFS-D.docx

Figure B-5

9-Hour Storm Duration - Temporal Pattern Five

Figure B-6

9-Hour Storm Duration - Temporal Pattern Six

10335-R01-AucklandCkFS-D.docx

Figure B-7

9-Hour Storm Duration - Temporal Pattern Seven

Figure B-8

9-Hour Storm Duration - Temporal Pattern Eight

10335-R01-AucklandCkFS-D.docx

Figure B-9

9-Hour Storm Duration - Temporal Pattern Nine

Figure B-10

9-Hour Storm Duration - Temporal Pattern Ten

10335-R01-AucklandCkFS-D.docx

B.2.2

Excluded and Selected Temporal Patterns for the 2% AEP to 0.2% AEP Events

Based on the analysis undertaken with a subset of data shown in the graphs in Section B.2.1, the following temporal patterns were excluded for the 2% AEP, 1% AEP, 0.5% AEP and 0.2% AEP events. With the remaining suitable temporal patterns, a new temporal pattern was selected based on what the median was of the remaining patterns. Temporal patterns which were excluded based on the above graphs are highlighted in red in Figure B-11. The newly adopted temporal pattern is highlighted in green, calculated based on the median of the remaining temporal patterns.

Figure B-11

Temporal Pattern Selection

10335-R01-AucklandCkFS-D.docx

APPENDIX C CALIBRATION MAPPING

10335-R01-AucklandCkFS-D.docx

APPENDIX D DESIGN STORM MAPPING

10335-R01-AucklandCkFS-D.docx

APPENDIX E CLIMATE CHANGE MAPPING

10335-R01-AucklandCkFS-D.docx

APPENDIX F TIDAL MAPPING

10335-R01-AucklandCkFS-D.docx

APPENDIX G PMP EVENT MAPPING

10335-R01-AucklandCkFS-D.docx

APPENDIX H SENSITIVITY ANALYSIS MAPPING

10335-R01-AucklandCkFS-D.docx