McCreadys Creek South Stormwater Trunk Infrastructure Study · The calibrated hydrologic and hydraulic models were used to derive design discharges, flood levels, depths and velocities

McCreadys Creek South Stormwater Trunk Infrastructure Study

Mackay Regional Council

0628-06-B, 2 December 2015

wrmwater.com.au 0628-06-B| 2 December 2015 | Page 2

Report Title McCreadys Creek South Stormwater Trunk Infrastructure Study

Client Mackay Regional Council

Report Number 0628-06-B

Revision Number Report Date Report Author Reviewer

0628-01_H (rev 1) 6 July 2011 GR DN

0 2 December 2015 BC GR

For and on behalf of WRM Water & Environment Pty Ltd Level 9, 135 Wickham Tce, Spring Hill PO Box 10703 Brisbane Adelaide St Qld 4000 Tel 07 3225 0200

Greg Roads Director

NOTE: This report has been prepared on the assumption that all information, data and reports provided to

us by our client, on behalf of our client, or by third parties (e.g. government agencies) is complete and

accurate and on the basis that such other assumptions we have identified (whether or not those

assumptions have been identified in this advice) are correct. You must inform us if any of the assumptions

are not complete or accurate. We retain ownership of all copyright in this report. Except where you obtain

our prior written consent, this report may only be used by our client for the purpose for which it has been

provided by us.

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5 Existing Scenario

5.1 OVERVIEW

The calibrated hydrologic and hydraulic models were used to derive design discharges, flood levels, depths and velocities throughout the study area for the 18%, 2%, 1%, 0.5% and 0.2% AEP design events and the PMF for the Existing Scenario.

5.2 DISCHARGES

Table 5.1 shows the Existing Scenario design flood discharges at various locations within the model estimated using the TUFLOW model (and RAFTS inflows). The critical duration varies across the catchment and ranges from 1 hour to 3 hour at different locations. Table 5.1 summarises the peak discharges for different storm durations at the reporting locations.

The 1% AEP peak discharge at Beaconsfield Road is 191.5 m³/s for the Existing Scenario. Climate change is expected to increase peak 1% AEP discharges at Beaconsfield Road by some 28% to 245.6 m³/s.

Table 5.1 – TUFLOW peak discharges – Existing Conditions

ID Location

Peak Discharges (m³/s)

Climate Change Discharges (m³/s)

18% AEP

2% AEP

1% AEP

0.5% AEP

0.2% AEPa

PMFa 18% AEP

2% AEP

1% AEP

6F U/S Mackay

Harbour Branch Railway

32.7 41.2 45.8 58.1 65.8 159.6 35.9 48.0 52.6

6T9 Holts Road (West) 28.9 54.7 65.0 96.8 124.5 314.4 37.9 70.1 82.3

6S8 Pioneer Street 36.1 71.1 84.2 126.8 167.0 375.0 47.7 91.4 107.4

6U5 Mackay-Bucasia

Road (South) 38.8 77.9 92.2 140.5 184.0 571.8 51.8 100.6 117.9

6H3 Holts Road (East) 62.6 119.2 142.4 217.4 285.1 947.0 82.9 154.5 182.2

6K3 Mackay-Bucasia

Road (North) 21.9 39.4 44.8 68.1 90.3 238.4 29.5 47.1 55.9

6J Beaconsfield Road 80.5 159.2 191.5 294.6 386.3 1200.1 106.3 206.3 245.6 a Not all discharges measured for the 0.2% AEP and PMF as water is distributed in many directions.

5.3 FLOOD LEVELS AND FLOOD EXTENTS

Figure 5.1 shows the Existing Scenario design flood level contours and depths within the study area for the 1% AEP design flood. Appendix B shows the design flood level contours and depths for the 18% AEP and 2% AEP design floods for existing conditions.

Table 5.2 shows the Existing Scenario design flood levels for the 18%, 2%, 1%, 0.5% and 0.2% AEP and PMF design floods at selected reporting locations. Design flood depths for the three climate change scenarios are also given. The reporting locations are shown on Figure 5.1. The following is of note:

For the 18% AEP event:

o substantial overbank flooding occurs throughout the study area including thegolf course;

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Figure 5.1 – 1% AEP flood Levels, depths and extent – Existing Conditions

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o flood depths in the Richmond Tributary and the Northern Tributary are generally less than 0.5m;

o all roads except Mackay Bucasia Road are overtopped;

o Holts Road east of Mackay Bucasia Road is just overtopped to a flood depth of 0.05 m.

o the channel from the Northview Gardens estate breaks out of the channel upstream of Mackay Bucasia Road and heads northward under the railway to the Richmond Tributary; and

o significant ponding occurs upstream of Mackay Bucasia Road for all tributaries.

For the 2% and 1% AEP events:

o Mackay-Bucasia Road is overtopped by the Richmond Tributary flows; and

o above floor level inundation potentially occurs on Baxter Drive upstream of Mackay Harbour Branch Railway. The storage yards on Beaconsfield Rd are also inundated. It is not known if above floor inundation occurs in Beaconsfield.

For the 0.5% AEP, 0.2% AEP and PMF events:

o significant inundation occurs throughout the catchment;

o above floor level inundation potentially occurs on Baxter Drive and around Stuart Hindle Drive upstream of Mackay Harbour Branch Railway; and

o some McCreadys Creek floodwater overflows to the Vines Creek catchment near Stuart Hindle Drive for these events due to the Mackay Harbour Branch Railway.

For the climate change scenarios:

o peak flood levels are between 0.02m and 0.37m higher than their corresponding design events. This suggests that peak flood levels are not overly sensitive to changes in design discharges throughout the catchment.

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Table 5.2 – TUFLOW peak flood levels – Existing Conditions

Location

Design Flood Level (m AHD)

Climate Change Design Levels

(m AHD)

18% AEP

2% AEP

1% AEP

0.5% AEP

0.2% AEP

PMF 18% AEP

2% AEP

1% AEP

Bea_01 7.47 7.53 7.54 7.63 7.69 8.14 7.50 7.56 7.60

Bea_02 6.96 7.03 7.06 7.15 7.21 7.98

7.01 7.08 7.11

Bea_03 6.71 6.90 6.95 7.06 7.14 7.95

6.78 6.97 7.02

Bea_04 6.56 6.81 6.86 6.98 7.07 7.93

6.66 6.89 6.93

Bea_05 6.41 6.67 6.73 6.86 6.96 7.89 6.52 6.75 6.80

Bea_06 6.10 6.36 6.42 6.60 6.75 7.79 6.20 6.45 6.52

Bea_07 5.97 6.25 6.32 6.52 6.67 7.72

6.09 6.36 6.43

Bea_08 5.92 6.20 6.27 6.47 6.62 7.67

6.04 6.30 6.38

Bea_09 5.78 6.08 6.16 6.38 6.54 7.59

5.92 6.20 6.29

Bea_10 5.67 6.00 6.08 6.30 6.45 7.45 5.82 6.12 6.20

Bea_11 5.64 5.98 6.06 6.28 6.43 7.42 5.81 6.10 6.19

Bea_12 5.59 5.92 6.00 6.20 6.34 7.25

5.75 6.04 6.12

Bea_13 7.73 7.87 7.94 8.09 8.17 8.75

7.78 7.96 8.03

Bea_14 7.71 7.86 7.91 8.07 8.15 8.76

7.77 7.94 8.00

Bea_15 7.71 7.86 7.91 8.05 8.11 8.55 7.77 7.93 7.99

Bea_16 7.60 7.70 7.73 7.77 7.78 8.03 7.65 7.73 7.75

Bea_17 7.15 7.24 7.25 7.33 7.43 8.11

7.18 7.26 7.29

Bea_18 6.48 6.51 6.60 6.76 6.87 7.66

6.49 6.64 6.69

Bea_19 - 5.97 6.05 6.27 6.43 7.43

- 6.09 6.17

Bea_20 5.61 5.95 6.03 6.25 6.40 7.35 5.78 6.08 6.16

HMC1 5.97 6.42 6.53 6.78 6.90 7.33 6.16 6.61 6.70

HMC2 5.67 5.78 5.89 6.22 6.33 6.72

5.71 5.98 6.13

HMC3 - - - - - -

- - -

HMC4 5.59 5.74 5.83 6.14 6.20 6.49

5.66 5.92 6.08

HMC5 5.27 5.76 5.77 6.18 6.27 6.76 5.21 5.89 6.14

HMC6 5.12 5.80 5.90 6.14 6.20 6.55 5.31 6.00 6.10

Mc0100 4.08 4.27 4.32 4.46 4.59 5.42

4.15 4.34 4.39

Mc0200 4.09 4.29 4.35 4.49 4.63 5.51

4.17 4.37 4.42

Mc0300 4.43 4.59 4.63 4.73 4.83 5.61

4.50 4.65 4.68

Mc0400 4.47 4.65 4.70 4.81 4.91 5.71 4.54 4.72 4.76

Mc0500 4.49 4.69 4.74 4.87 4.98 5.81 4.57 4.76 4.81

Mc0600 4.52 4.73 4.79 4.94 5.06 5.93

4.60 4.81 4.87

Mc0700 4.74 4.89 4.94 5.08 5.19 6.03

4.80 4.97 5.02

Mc0800 4.77 4.94 5.00 5.18 5.30 6.22

4.83 5.03 5.10

Mc0900 4.78 4.96 5.02 5.22 5.36 6.33 4.85 5.05 5.13

Mc1000 4.79 4.99 5.06 5.27 5.43 6.45 4.87 5.09 5.17

Mc1100 4.82 5.02 5.10 5.32 5.48 6.56

4.89 5.13 5.22

Mc1200 4.99 5.29 5.35 5.53 5.66 6.65

5.13 5.38 5.45

Mc1300 5.22 5.53 5.60 5.78 5.91 6.85

5.38 5.63 5.70

N0000 7.50 7.57 7.62 7.67 7.72 7.92 7.52 7.61 7.64

N0100 7.94 8.02 8.04 8.13 8.18 8.43 7.97 8.06 8.09

N0200 8.39 8.50 8.54 8.64 8.71 9.02

8.43 8.55 8.59

N0300 8.88 9.00 9.04 9.15 9.22 9.56

8.93 9.06 9.10

N0400 9.44 9.54 9.56 9.66 9.73 10.01

9.48 9.59 9.62

N0500 10.07 10.18 10.20 10.29 10.33 10.49 10.12 10.22 10.25

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Location

Design Flood Level (m AHD)

Climate Change Design Levels

(m AHD)

18% AEP

2% AEP

1% AEP

0.5% AEP

0.2% AEP

PMF 18% AEP

2% AEP

1% AEP

N1 5.35 5.67 5.74 5.95 6.09 7.01 5.51 5.79 5.87

N2 5.35 5.87 5.96 6.17 6.24 6.71

5.45 6.04 6.13

N3 5.97 6.43 6.53 6.80 6.91 7.35

6.18 6.63 6.71

R0000 7.79 8.27 8.41 8.75 8.98 10.07

7.93 8.47 8.60

R0100 8.22 8.45 8.54 8.84 9.07 10.14 8.29 8.60 8.71

R0200 8.60 8.78 8.83 9.01 9.18 10.21 8.66 8.86 8.92

R0300 8.99 9.17 9.22 9.36 9.47 10.31

9.06 9.25 9.30

R0400 9.34 9.53 9.57 9.71 9.81 10.49

9.41 9.60 9.65

R0500 9.82 9.95 9.99 10.11 10.21 10.77

9.87 10.02 10.06

R0600 10.27 10.40 10.45 10.57 10.66 11.21 10.31 10.47 10.51

R0700 10.60 10.76 10.80 10.93 11.03 11.58 10.66 10.83 10.88

R0800 11.37 11.45 11.46 11.55 11.61 11.99

11.41 11.48 11.52

R0900 11.66 11.79 11.82 11.93 12.02 12.49

11.71 11.84 11.88

R1000 11.91 12.03 12.07 12.16 12.25 12.74

11.95 12.08 12.12

R1100 12.22 12.37 12.42 12.53 12.62 13.10 12.28 12.44 12.48

R1200 12.66 12.80 12.84 12.96 13.05 13.54 12.71 12.87 12.91

R1300 13.28 13.42 13.47 13.59 13.68 14.19

13.33 13.49 13.54

R1400 13.53 13.75 13.80 13.96 14.07 14.67

13.62 13.83 13.89

R1500 14.08 14.27 14.32 14.48 14.59 15.20

14.16 14.35 14.41

R1600 14.53 14.69 14.74 14.87 14.97 15.50 14.59 14.76 14.81

R1700 14.89 15.06 15.11 15.24 15.33 15.82 14.96 15.13 15.18

R1800 15.36 15.47 15.51 15.60 15.66 16.03

15.40 15.52 15.56

R1900 15.76 15.87 15.90 15.99 16.06 16.48

15.80 15.91 15.95

R2000 16.15 16.21 16.23 16.32 16.40 16.81

16.18 16.25 16.28

R2100 16.86 16.94 16.97 17.05 17.10 17.41 16.89 16.98 17.01

R2200 17.60 17.65 17.67 17.75 17.80 18.05 17.61 17.68 17.70

R2300 17.93 18.06 18.09 18.22 18.32 18.71

17.98 18.11 18.15

S1 8.98 9.21 9.35 9.68 9.86 10.40

9.07 9.41 9.53

S2 8.74 8.86 8.93 9.06 9.13 9.71

8.79 8.96 9.01

S3 8.52 9.20 9.35 9.69 9.85 10.32 8.81 9.43 9.56

S4 8.09 8.41 8.51 8.63 8.68 9.03 8.23 8.54 8.58

S5 7.83 7.96 8.06 8.33 8.41 8.75

7.83 8.12 8.23

W2 7.53 8.09 8.17 8.34 8.44 8.90

7.73 8.21 8.28

W3 7.49 7.99 8.03 8.19 8.28 8.66

7.69 8.06 8.12

W4 7.22 7.73 7.76 7.85 7.91 8.19 7.32 7.79 7.82

W5 - 7.44 7.48 7.56 7.62 7.87 7.22 7.48 7.51

W6 6.14 6.98 7.02 7.09 7.14 7.38

6.41 7.04 7.08

W7 7.46 7.51 7.52 7.58 7.62 7.79 7.47 7.53 7.55

5.4 FLOOD VELOCITIES

Figure 5.2 shows the design velocities within the study area for the 1% AEP design flood for existing conditions. Appendix B shows the design velocities for the 18% AEP and 2% AEP design floods for existing conditions. Flood velocities throughout the study area are generally low for the three design events. Overbank velocities are generally between 0.25 m/s to 0.75 m/s and channel velocities between 1 m/s and 2 m/s. Flood velocities marginally increase with event magnitude.

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Figure 5.2 - 1% AEP flood velocities – Existing Conditions