GOOSEPOND CREEK (INCLUDING ) FLOOD STUDY

Mackay Regional Council 9 October 2012

REPORT TITLE: Gooseponds Creek (including Pioneer River) Flood Study CLIENT: Mackay Regional Council REPORT NUMBER: 0500-01 O(rev 1)

Revision Number Report Date Report Author Reviewer 0 3 September 2012 GR SM 1 9 October 2012 GR

For and on behalf of WRM Water & Environment Pty Ltd

Greg Roads Director

LIMITATION: This advice 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 advice. Except where you obtain our prior written consent, this advice may only be used by our client for the purpose for which it has been provided by us.

0500-01 O(rev 1) 9 October 2012

TABLE OF CONTENTS

Page

1 INTRODUCTION 1

2 BACKGROUND 2

2.1 CATCHMENT CHARACTERISTICS 2 2.1.1 Pioneer River 2 2.1.2 Fursden Creek 2 2.1.3 Goosepond Creek 2 2.2 PREVIOUS (RECENT) FLOOD STUDIES 4 2.2.1 Pioneer River and Bakers Creek Flood Study 4 2.2.2 Goosepond/ Vines Creek flood Study 4 2.2.3 Mackay Storm Tide Study 5

3 GOOSEPOND CREEK MODEL RECALIBRATION 6

3.1 OVERVIEW 6 3.2 MODEL CHANGES 6 3.3 FEBRUARY 2007 FLOOD CALIBRATION 6 3.4 FEBRUARY 2008 FLOOD CALIBRATION 10

4 DESIGN DISCHARGES AND FLOOD LEVELS 13

4.1 OVERVIEW 13 4.2 PIONEER RIVER DESIGN DISCHARGES 13 4.3 GOOSEPOND CREEK DESIGN DISCHARGES 14 4.3.1 Dominant Cause of flooding in Goosepond Creek 14 4.3.2 Design Discharges 15 4.4 DESIGN FLOOD LEVELS, DEPTHS AND EXTENTS 16 4.5 SUMMARY OF PEAK FLOOD LEVELS AND COMPARISON TO PEAK LEVELS ESTIMATED BY GHD 16 4.6 LEVEE OVERFLOWS 17

5 SUMMARY OF FINDINGS 21

6 REFERENCES 22

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LIST OF TABLES

Page

Table 3.1 Surveyed and Predicted Peak Water Levels, February 2007 Event 8 Table 3.2 Surveyed and Predicted Peak Water Levels, February 2008 Event 11 Table 4.1 Pioneer River Design Discharges, Pleystowe Mill and Mackay 14 Table 4.2 Goosepond Creek Design Discharges at Goosepond Gauge (Willetts Road) 16 Table 4.3 Predicted Peak Flood Levels at Road Crossings and comparison to GHD peak levels 17 Table 4.4 Predicted Maximum Overflows across Floodplain Levees 20

LIST OF FIGURES

Page

Figure 2.1 Pioneer River, Fursden Creek and Goosepond Creek Catchments 3 Figure 3.1 Recorded and Predicted Water Levels and Predicted Discharges, Goosepond Ck at Gooseponds (Willetts Road) Gauge (GS125915), February 2007 Event 7 Figure 3.2 Predicted Flood Depths, Levels and Extent, 2 February 2007 9 Figure 3.3 Recorded and Predicted Water Levels and Predicted Discharges, Goosepond Ck at Gooseponds (Willetts Road) Gauge (GS125915), February 2008 Event 10 Figure 3.4 Predicted Flood Depths, Levels and Extent, 15 February 2008 12 Figure 4.1 Pleystowe Mill Design Discharges 14 Figure 4.2 Goosepond Creek at Goosepond (Willetts Rd) Gauge Discharge Hydrograph, 100 year ARI 12hr and 24hr events 15 Figure 4.3 10 Year ARI Flood Depths and Extent, Pioneer River and Bakers Creek 18 Figure 4.4 100 Year ARI Flood Depth and Extent, Pioneer River and Bakers Creek 19

ii 0500-01 O(rev 1) 9 October 2012

1 INTRODUCTION

Mackay Regional Council (MRC) recently completed flood studies of the Pioneer River (WRM, 2011) and Goosepond Creek (GHD, 2012). These studies estimated design flood levels along these waterways to assist with setting planning controls for urban development. Both of these studies found that there was a significant interaction of flood flows between Goosepond Creek and the Pioneer River. However, the Goosepond Creek study did not include the overflows from the Pioneer River and the Pioneer River study did not investigate the impact of local storms in the Goosepond Creek catchment in combination with Pioneer River flows. This report integrates the two studies to determine design flood levels along Goosepond Creek.

This report is structured as follows:  Section 2 describes the catchments of interest and summarises the findings of the previous flood studies;  Section 3 outlines the changes made to the Pioneer River model to integrate Goosepond Creek and presents the results of the Goosepond Creek model calibration;  Section 4 presents the updated design flood levels and discharges along the Pioneer River and Goosepond Creek and describes the interaction of flows between the two waterways;  Section 5 summarises the findings of the study; and  Section 6 is a list of references.

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2 BACKGROUND

2.1 CATCHMENT CHARACTERISTICS

Figure 2.1 shows the location of the Pioneer River, Fursden Creek and Goosepond Creek catchments. Brief descriptions of the catchments are given below.

2.1.1 Pioneer River

The Pioneer River catchment extends from the Connors Range to the west to the to the east. It includes the major tributaries of Cattle Creek, Teemburra Creek, Blacks Creek, Stockyard Creek, Macgregor Creek, Fursden Creek, Janes Creek and Gooseponds Creek. The catchment is bordered by the Leila Creek and Murray Creek catchments to the north, the catchment to the west and Sandy Creek, Bakers Creek and the catchments to the south. The total catchment area of the Pioneer River (excluding the Bakers Creek catchment) is approximately 1,560 km2.

2.1.2 Fursden Creek

Fursden Creek commences near Fairview on the and drains in a southerly direction mostly along constructed channels through cane fields. It then turns eastward to drain parallel to the Pioneer River before entering it just upstream of the Ron Camm Bridge (Bruce Highway). The lower sections of the creek are backwater affected by both ocean tides and Pioneer River flows. For floods greater than the 5 year ARI event, the Pioneer River overflows into Fursden Creek. During large floods, the Fursden Creek channel carries a significant portion of the Pioneer River flow. The catchment area of Fursden Creek is 24.8 km2.

2.1.3 Goosepond Creek

Janes Creek, Goosepond Creek and Vines Creek drain through the northern and eastern suburbs of Mackay. Janes Creek originates near Farleigh and Richmond (north-west of the Mackay CBD) and flows into Goosepond Creek downstream of the Bruce Highway. Goosepond Creek then drains into Vines Creek upstream of Harbour Road. Vines Creek originates near Beaconsfield and drains into the Pioneer River downstream of Harbour Road in an area known as the Bassett Basin. The combined catchment area of these 3 streams is approximately 35 km2.

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BRUCEBRUCE HWYHWY

FursdenFursden GoosepondsGooseponds CreekCreek CreekCreek

NORTHNORTH MACKAYMACKAY CATTLECATTLECATTLE CREEK CREEKCREEK FINCHFINCH HAHATTONTTON PIONEERPIONEER RIVRIV ER ER MARIANMARIAN MACKAYMACKAY MIRANIMIRANI WALKERSTONWALKERSTON BAKERSBAKERS CREEKCREEK

BAKERSBAKERS CREEKCREEK

PEAKPEAKPEAK DOWNS DOWNSDOWNS HWYHWYHWY

BRUCEBRUCEBRUCE HWYHWYHWY

LEGEND Main Road Drainage Line

Water Body

Park/State Forest

Built Up Area

SARINAFursdenSARINA Creek Catchment

 Goosepond Creek Catchment 0510 Pioneer River Catchment kilometres Figure 2.1 Pioneer River, Fursden Creek and Goosepond Creek Catchments 3 0500-01 O(rev 1) 9 October 2012

2.2 PREVIOUS (RECENT) FLOOD STUDIES

2.2.1 Pioneer River and Bakers Creek Flood Study

WRM completed a flood study of the Pioneer River and Bakers Creek in 2011 for MRC. An URBS rainfall-runoff-routing model of the Pioneer River catchment was developed to estimate design discharges. The model was calibrated to six historical flood events (1958, 1970, 1990, 2000, 2007 and 2008) and then validated against annual series flood frequency analyses at five stream gauges throughout the catchment.

Design flood levels were estimated using a TUFLOW two-dimensional hydrodynamic model that extended from Mirani Weir to the . The model was calibrated to recorded water levels for four historical flood events (1958, 1970, 2007 and 2008). The main river channel upstream of the Dumbleton Weir was modelled in the one-dimensional domain and the downstream river and overbank areas were modelled within the two-dimensional domain using a 20m grid. For all events, it was assumed that the flood event coincided with the highest astronomical tide (HAT) level of 3.64m AHD.

Full details of the development and calibration of the models are given in the flood study report (WRM, 2011).

The following comments are provided on the Pioneer River Study with respect to flooding along Goosepond Creek:  Design rainfalls for the Goosepond Creek catchment were based on Pioneer River catchment design rainfalls. For a 24 hour duration storm, the design rainfall depth in the Goosepond Creek catchment is some 8% higher than in the Pioneer River catchment;  Goosepond Creek catchment inflows were based on only four URBS sub areas.  Surveyed ground levels along Goosepond Creek were found to be up to 1m lower than the ground levels adopted in the Pioneer River study, which were obtained from the Lidar survey provided by MRC.  Goosepond Creek channel capacities and Manning’s ‘n’ values were not calibrated using all of the available data.

2.2.2 Goosepond/ Vines Creek flood Study

GHD Pty Ltd was commissioned by MRC to undertate a flood study for Goosepond Creek, Janes Creek, Vines Creek and the Port Access Corridor in the area. A RAFTS rainfall- runoff-routing model was used to estimate design discharges and a MIKEFLOOD hydrodynamic model was used to estimate design flood levels. The models were calibrated to the February 2007 and February 2008 flood events.

The MIKEFLOOD model extended from the Richmond area upstream of the Mackay Harbour Railway line to the Bassett Basin between North Mackay and Mackay Harbour. The model was also used to assess a range of development scenarios and flood mitigation options.

Full details of the development and calibration of the models are given in the flood study report (GHD, 2012).

The GHD study did not include the overflows into Goosepond Creek from the Pioneer River and as such potentially underestimated design flood levels along much of Goosepond Creek. In

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addition, the hydrodynamic model adopted by GHD is different to all other models used throughout the Mackay region.

2.2.3 Mackay Storm Tide Study

BMT WBM was commissioned to undertake a storm tide inundation study for the Mackay Local Government Area. The study involved the development of a numerical modelling system to predict tropical cyclone generated storm tide inundation including a cyclone Wind model and a TUFLOW FV hydrodynamic model. The system included a model of the entire Coral Sea and a more detailed model of the nearshore area within the Mackay local government jurisdiction. The models were calibrated to two recent tropical cyclones, Hamish (2009) and Ului (2010). The calibration focused on replicating wind, ambient air pressure and storm tide measurements at various locations (BMT WBM, 2012).

The calibrated models were used to estimate the storm tide levels and inundation mapping for the 2%, 1%, 0.5%, 0.2%, 0.1% and 0.01% Annual Exceedance Probability (AEP) (1/ARI) storm tide events. The draft report (BMT WBM, 2012) gives the 1% AEP design storm tide level near the Pioneer River mouth to be about 3.46 mAHD without wave set up and runup and 4.4m AHD to 4.14m AHD with it. This compares to the Highest Astronomical Tide prediction of 3.64m AHD. When compared to the Pioneer River Flood Study results, it would appear that the flood levels generated by a Pioneer River flood dominate design flood level upstream of Forgan Smith Bridge for events greater than and equal to the 5 year ARI event. Peak 100 year ARI flood levels adjacent to all flood protection levees along the Pioneer River and Goosepond Creek are dominated by Pioneer River levels.

BMT WBM also undertook a joint probability assessment of a storm surge occurring at the peak of a Pioneer River flood. Relationships between stream flow and concurrent tailwater conditions were developed for a range of ARI’s. The analysis showed that the probability of a 100 year ARI storm tide occurring during a 100 year ARI flood event in the Pioneer is remote and in fact would produce a result that had a probability much lower than 100 years ARI. The use of HAT as the downstream boundary, as has been adopted in the Pioneer River study, would be equally remote. In other words, the use of HAT as the downstream boundary to set tailwater levels is highly conservative.

An assessment of the impact on design flood levels of adopting either the HAT or the Mean High Water Neap tide (MHWNT) level as the downstream boundary was undertaken by WRM (2011) as part of the Pioneer River Flood Study. The results show that the adoption of HAT as the downstream boundary rather than MHWNT increases peak flood levels in the Bassett Basin area of Vines Creek and further downstream by between 0.2 m and 0.3 m. Peak flood levels between the Bassett Basin and the Canelands Shopping Centre are increased between 0.1m and 0.2m. The impact reduces to zero about 2km upstream of Hospital Bridge (WRM, 2011). This would suggest that, although the use of HAT as the downstream boundary is conservative, it does not have a significant impact on design flood levels adjacent to the flood protection levees. On this basis, HAT has been adopted as the downstream boundary in this study to set design flood levels for all design events.

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3 GOOSEPOND CREEK MODEL RECALIBRATION

3.1 OVERVIEW

The Pioneer River TUFLOW model was updated and expanded to enable a single model to be used to set design flood levels along the Pioneer River and Goosepond Creek. The Goosepond Creek part of the model was updated using the information obtained from GHD (2012) and then recalibrated to the February 2007 and February 2008 flood events.

3.2 MODEL CHANGES

The following changes were made to the Pioneer River TUFLOW Model:  The XP-RAFTS model inflows estimated by GHD (2012) were used to determine Goosepond Creek discharges, replacing the Pioneer River URBS model nodes 65, 66, 67 and 79. GHD’s XP-RAFTS model parameters were not changed.  Ground levels along Goosepond Creek were updated based on GPS survey undertaken by MRC. A review found that the ground levels in the area of interest north of Sugarshed Road were up to 1m lower than those adopted in the Pioneer River Flood Study. The area of interest north of Sugarshed Road is used primarily for growing crops such as sugar cane, which can skew the ground levels obtained by aerial laser survey (ALS). WRM (2011) used ALS data for the underlying ground digital elevation model in the area of interest whereas GHD used surveyed cross sections in the area of interest. The surveyed cross sections provided more accurate ground levels in the area of interest when compared to the ALS data.  Manning’s ‘n’ values along Goosepond Creek were revised to calibrate the model to the surveyed flood level data available for the February 2007 and February 2008 flood events.  The model was extended upstream of the Bruce Highway into Janes Creek.  Rail and road culverts along Goosepond Creek and along Vines Creek in the Andergrove area were updated. The remainder of the TUFLOW model was unchanged from that described in WRM (2011) except the latest version of the TUFLOW model was used (Version: 2012 – AA).

3.3 FEBRUARY 2007 FLOOD CALIBRATION

On the 1st and 2nd February 2007, some 374mm of rainfall was recorded at the Goosepond Creek rain gauge causing moderate flooding along Goosepond Creek. Flood levels along the

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Pioneer River reached minor flood levels only. The majority of the above rainfall (189mm) fell in a 24-hour period to 1100 hours on the 2nd February. A comparison of recorded rainfalls with design rainfall intensities from Australian Rainfall and Runoff (ARR) (Pilgrim, 1998) suggests that 24-hour rainfalls had an annual recurrence interval (ARI) of about 25 years at this location. Rainfalls of 12 and 48 hour durations had an ARI of about 10 years. Shorter duration rainfalls were less severe. Rainfalls in the upper catchment of the Pioneer River were also less severe.

Figure 3.1 shows the recorded and predicted flood levels and predicted discharges at the Goosepond Creek at Gooseponds stream gauge, located just downstream of the Willetts Road Bridge in North Mackay. A comparison of recorded (surveyed) and predicted peak flood levels throughout the Goosepond Creek floodplain is shown in Table 3.1. The locations of the surveyed flood marks, as well as the predicted 2007 flood extent, are shown in Figure 3.2.

The results indicate that the TUFLOW and RAFTS models predict water levels and discharges reasonably well for this event. The predicted peak level at the gauge is 0.07m lower than the recorded value. The predicted peak flood levels at all other locations are generally within 0.2m of the surveyed level, except at one location on the Pioneer River, which is 0.57m higher. At the Goosepond Creek gauge, the predicted peak water levels are lower than the recorded values early in the event possibly due to residual flows from earlier rainfall. In comparison to the calibration achieved by GHD, also shown in Table 3.1, the levels predicted by the TUFLOW model appear closer to the surveyed levels, which would suggest a better calibration.

7.5 90

7 80

6.5 70

6 60 /s)

5.5 50 3

5 40 Discharge (m Elevation (mAHD) Elevation

4.5 30

4 20

3.5 10

3 0 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 1-Feb-07 2-Feb-07

Predicted Recorded Predicted Q

Figure 3.1 Recorded and Predicted Water Levels and Predicted Discharges, Goosepond Ck at Gooseponds (Willetts Road) Gauge (GS125915), February 2007 Event

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Table 3.1 Surveyed and Predicted Peak Water Levels, February 2007 Event Surveyed Predicted Peak Water Difference Location Level Level (m AHD) ID (see (mAHD) Figure 3.2) GHD WRM (WRM – Surveyed) 1 10.89 10.66 10.82 -0.07 2 10.53 10.32 10.67 0.14 3 10.47 10.34 10.52 0.05 4 9.84 8.92 9.76 -0.08 5 9 8.69 9.16 0.16 6 8.74 8.83 8.72 -0.02 7 8.74 8.79 8.80 0.06 8 8.06 7.54 7.73 -0.33 9 7.5 7.42 7.59 0.09 10 6.69 6.82 6.62 -0.07 11 6.15 5.9 6.11 -0.04 12 4.23 4.77 4.80 0.57 13 4.02 4.14 4.23 0.21

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131313 131313

121212 121212

MACKAYMACKAYMACKAY BUCASIA BUCASIA BUCASIA RD RD RD MACKAYMACKAYMACKAY BUCASIA BUCASIA BUCASIA RD RD RD MACKAYMACKAYMACKAY BUCASIA BUCASIA BUCASIA RD RD RD

HARBOURHARBOUR RDRD NORRISNORRISNORRIS RD RD RD NORRISNORRISNORRIS RD RD RD NORRISNORRISNORRIS RD RD RD BRUCEBRUCE HWYHWY

555

GLENPARKGLENPARKGLENPARK ST ST ST GLENPARKGLENPARKGLENPARK ST ST ST 1111 GLENPARKGLENPARKGLENPARK ST ST ST 11 MALCOMSONMALCOMSON STST

22 1010 22 1010 77

9 9 9

9 9 9

9 9 9 1111

33 666 33 666 33 777 666 888 777 888 SugarshedSugarshed RdRd 1010 66 SAMSSAMS RDRD 99 55 88 1212

1313 77

555 555 66

444 66 FLOOD DEPTH (m) LEGEND

MackayMackayMackay Bypass BypassBypass Rd RdRd Main Road 0.0m < 1.0m Rail 1.0m < 3.0m 777 Surveyed Flood Mark Flood Contour (0.5m) 3.0m < 5.0m  5.0m < 10.0m 0 250 500 1000 10.0m < 15.0m 15.0m < 20.0m metres Figure 3.2 Predicted Flood Depths, Levels and Extent, 2 February 2007 9 0500-01 O(rev 1) 9 October 2012

3.4 FEBRUARY 2008 FLOOD CALIBRATION

On the 15th February 2008, some 615mm of rainfall was recorded over a 24-hour period at the Goosepond Creek gauge. The majority of this rainfall (400mm) fell over a 6 hour period to 0830 hours on the 15th February causing severe flooding along Goosepond Creek. Several hundred properties along the Goosepond Creek were adversely affected by flooding from this event, which was predicted to have had an ARI that exceeded 500 years in Goosepond Creek (GHD, 2012). It is of note that anecdotal rainfall data recorded in Glenella for this event for durations up to 6 hours were similar to the Goosepond Creek data, but 12 hour rainfalls were some 30% higher than at the Goosepond Creek gauge.

Figure 3.3 shows the recorded and predicted flood levels and predicted discharges in the Goosepond Creek at Gooseponds stream gauge. A comparison of surveyed and predicted peak flood levels throughout the Goosepond Creek floodplain is shown in Table 3.2. The locations of the surveyed flood marks, as well as the predicted flood extent for this event, are shown in Figure 3.4.

The results indicate that the TUFLOW and RAFTS models predict water levels and discharges reasonably well for this event along Goosepond Creek. The predicted peak level at the gauge is some 0.26m higher than the recorded value. Peak flood levels are up to 0.25m lower upstream of the Bruce Highway and up to 0.4m higher downsteam of the gauge. In comparison to the GHD calibration, predicted levels are on average 0.07m higher and, overall, are closer to the surveyed levels. On the basis of the 2007 and 2008 calibration, it is expected that the TUFLOW model would represent flooding conditions along the Goosepond Creek adequately.

9 600

8 500

7 400 /s) 3 6 300 Discharge (m Elevation (mAHD)

5 200

4 100

3 0 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 15-Feb-08

Predicted Recorded Predicted Q

Figure 3.3 Recorded and Predicted Water Levels and Predicted Discharges, Goosepond Ck at Gooseponds (Willetts Road) Gauge (GS125915), February 2008 Event

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Table 3.2 Surveyed and Predicted Peak Water Levels, February 2008 Event Location Surveyed Level Predicted Level (m AHD) Difference ID (see (WRM – (mAHD) Figure 3.4)) GHD WRM Surveyed) 1 14.37 13.95 14.34 -0.03 2 12.10 12.04 12.24 0.14 3 10.60 10.34 10.37 -0.23 4 9.67 9.41 9.45 -0.22 5 9.06 9.09 8.99 -0.07 6 9.16 9.12 9.12 -0.04 7 9.32 9.13 9.15 -0.17 8 9.43 9.19 9.21 -0.22 9 9.42 9.29 9.32 -0.10 10 9.38 9.23 9.25 -0.13 11 10.15 9.77 9.96 -0.19 12 9.64 9.49 9.76 0.12 13 9.05 8.94 8.83 -0.22 14 9.11 8.98 8.87 -0.24 15 9.12 9.00 8.85 -0.27 16 9.07 9.01 8.86 -0.21 17 9.11 9.05 8.89 -0.22 18 8.41 8.93 8.76 0.35 19 8.21 8.50 8.25 0.04 20 7.70 7.91 7.96 0.26 21 7.48 7.82 7.82 0.34 22 7.56 7.65 7.75 0.19 23 7.25 7.19 7.38 0.13 24 7.12 7.06 7.35 0.23 25 7.12 7.00 7.31 0.19 26 6.91 6.90 7.21 0.30 27 6.56 6.51 6.97 0.41 28 6.56 6.33 6.45 -0.11 29 6.17 5.99 6.38 0.21 30 6.28 6.06 6.21 -0.07 31 5.96 5.77 6.08 0.12 32 6.28 6.08 6.20 -0.08 33 6.26 5.93 5.85 -0.41 34 5.09 5.91 35 5.33 5.92 5.93 0.60 36 6.05 5.92 5.90 -0.15 37 6.01 5.92 6.07 0.06 38 6.02 5.92 6.26 0.24 39 5.94 5.92 5.89 -0.05 40 6.02 5.92 5.89 -0.13 41 6.01 5.92 5.89 -0.12 42 6.07 5.92 5.90 -0.17 43 5.97 5.92 5.90 -0.07 44 5.90 5.92 5.90 0.00 45 5.96 5.92 5.90 -0.06 46 6.89 6.86 7.21 0.32 47 4.51 4.09 48 11.28 11.64 11.75 0.47 49 11.27 11.21 11.12 -0.15 50 14.97 14.76 14.49 -0.48

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111111 4242 10 10 10 9 9 9 4242 10 10 10 9 9 9 10 10 10 9 9 9 4141 7 7 7 7 7 7 7 7 7 4040 3939 3838

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MACKAYMACKAYMACKAY BUCASIA BUCASIA BUCASIA RD RD RD MACKAYMACKAYMACKAY BUCASIA BUCASIA BUCASIA RD RD RD 1414 MACKAYMACKAYMACKAY BUCASIA BUCASIA BUCASIA RD RD RD 1414 3232 3232 3131 66 3131 44 HARBOURHARBOUR RDRD NORRISNORRISNORRIS RD RD RD 44 NORRISNORRISNORRIS RD RD RD 44 NORRISNORRISNORRIS RD RD RD 2929 1313 BRUCEBRUCE HWYHWY 2929 3030 4646 4646 GLENPARKGLENPARKGLENPARK ST ST ST GLENPARKGLENPARKGLENPARK ST ST ST 22 GLENPARKGLENPARKGLENPARK ST ST ST 4848 1212 MALCOMSONMALCOMSON STST 4949 4949 2727

7 7 7 7 7 7 7 7 7 2828 33 2525 2626 1111 1111 1818 2424 44 2020 2222 101010 2020 101010 2020 101010 55

1717 8 8 8 2323 1717 8 8 8 2323 1717 8 8 8 2323

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LEGEND FLOOD DEPTH (m)

MackayMackayMackay Bypass BypassBypass Rd RdRd MackayMackayMackay Bypass BypassBypass Rd RdRd Main Road 0.0m < 1.0m Rail 888 Surveyed Flood Mark 1.0m < 3.0m 777 Flood Contour (0.5m) 3.0m < 5.0m

 5.0m < 10.0m 0 250 500 1000 10.0m < 15.0m metres 15.0m < 20.0m Figure 3.4 Predicted Flood Depths, Levels and Extent, 15 February 2008 12 0500-01 O(rev 1) 9 October 2012

4 DESIGN DISCHARGES AND FLOOD LEVELS

4.1 OVERVIEW

The revised and recalibrated Pioneer TUFLOW model was used to determine design flood levels along both the Pioneer River and Goosepond Creek. The URBS model, described in WRM (2011) and summarised below, was used to determine design flood discharges in the Pioneer River catchment and the XP-RAFTS model, described in GHD (2012) was used to determine design discharges in the Goosepond Creek catchment. It was assumed that the design storm was centred over each catchment concurrently. That is, design rainfalls and aerial reduction factors for Goosepond Creek were based on Goosepond Creek catchment rainfalls. Although the likelihood of these two design events occurring concurrently is highly improbable, it is not expected that the two flood peaks would coincide because of the differences in catchment areas (35 km2 compared to 1,560 km2). An assessment of this assumption is given below.

4.2 PIONEER RIVER DESIGN DISCHARGES

Table 4.1 shows the Pioneer River design discharges at the Pleystowe Mill and Mackay gauges estimated from an LPIII distribution fitted to an annual series flood frequency analysis (FFA), and the calibrated URBS and TUFLOW models. The results are presented graphically in Figure 4.1. The following is of note.  The Pleystowe Mill FFA is based on recorded data at Pleystowe Mill from 1916 to 1981 and Dumbleton Weir Headwater gauge data from 1982 to 2011 providing a 94 year dataset. Dumbleton Weir was constructed in 1982.  For the URBS model; the critical storm duration varied between 12 hours for the larger events and 36 hours for the events more frequent than the 20 year ARI; a continuing loss rate of 1.0mm/hour was adopted for all design events; and the initial losses varied from 200mm for the 5 year ARI event (which is consistent with earlier investigations), 100 mm for the 10 year ARI event, 95mm for the 20 year ARI and zero for the larger events.  The results show that there is a good agreement between the three estimates for events up to the 20 year ARI event. The TUFLOW model estimates are marginally lower than the FFA estimate for the larger events but are still within the confidence limits. In fact, the TUFLOW estimates fit closer to the recorded data points than the LPIII distribution for these events and have therefore been adopted for the study.  At Mackay, the TUFLOW model design discharges are lower than at Pleystowe Mill because of the storage effects in the tidal reaches of the river. Some flows also leave the

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main river and overflow into Goosepond Creek to the north and Bakers Creek to the south. Table 4.1 Pioneer River Design Discharges, Pleystowe Mill and Mackay Pleystowe Mill (GS 125001c) Mackay (GS 125903) ARI (Years) (m3/s) (m3/s) FFA URBS TUFLOW URBS TUFLOW 5 3,900 4,276 4,170 4,380 3,654 10 5,730 6,283 6,184 6,400 6,060 20 7,714 7,850 7,485 8,050 7,350 50 10,566 10,573 9,900 10,935 9,440 100 12,890 12,604 11,440 12,900 10,590 200 - 13,460 12,780 14,084 11,390 500 - 15,486 14,173 16,240 12,283

0.99 0.980.95 0.9 0.8 0.7 AEP 0.5 0.3 0.20.1 0.05 0.02 0.01 100000 Flood Series LP3 Distribution Confidence Limits URBS TUFLOW

Skew -0.363

10000 10 low flows Peak Flow m³/s

1000

100 1.111 1.25 2 5 10 20 50 100 AEP (1 in Y) Figure 4.1 Pleystowe Mill Design Discharges

4.3 GOOSEPOND CREEK DESIGN DISCHARGES

4.3.1 Dominant Cause of flooding in Goosepond Creek

Figure 4.2 shows the predicted discharge hydrographs for Goosepond Creek at Goosepond gauge (GS125915) for the 100 year ARI 12 hour and 24 hour duration storms. The first peak

14 0500-01 O(rev 1) 9 October 2012

occurs as a result of the local flows in Goosepond Creek. The second peak occurs as a result of the overflows from the Pioneer River. The second peak occurs some 6 to 7 hours after the Goosepond Creek peak. At this location, the highest peak discharge occurs as a result of the Goosepond Creek local flows for the 24 hour and 12 hour duration storms closely followed by the Pioneer River 12 hour duration storm. This suggests that design flood levels along Goosepond Creek upstream of the gauge are dominated by Goosepond Creek flows, although not by a significant amount. Downstream of Evans Avenue in North Mackay, peak flood levels are dominated by Pioneer River levels.

300

250

200 /s) 3

150 Goosepond Peak Creek Discharge (m 100 Pioneer RiverPeak Pioneer

50

0 0 5 10 15 20 25 30 35 40 Time (hours)

100yr ARI 12hr 100yr ARI 24hr

Figure 4.2 Goosepond Creek at Goosepond (Willetts Rd) Gauge Discharge Hydrograph, 100 year ARI 12hr and 24hr events

4.3.2 Design Discharges

Table 4.2 shows the design discharges in Goosepond Creek at the Goosepond gauge predicted by the XP-RAFTS model as well as by the TUFLOW model. It is noted that XP-RAFTS model design discharges given in the GHD (2012) report could not be replicated using the supplied model. The design discharges estimated by WRM using the supplied model are only marginally lower and were therefore adopted for this study.

The design discharges estimated by the TUFLOW model are substantially lower than the XP- RAFTS model discharges because of the available flood storage in the Glenella area that is not modelled by XP-RAFTS.

For events larger than the 100 year ARI event, Goosepond Creek design discharges are dominated by overflows from the Pioneer River. Of note, the predicted design discharges for the 500 year ARI event along Goosepond Creek are significantly larger than the February 2008 peak flows (shown in Figure 3.3)

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Table 4.2 Goosepond Creek Design Discharges at Goosepond Gauge (Willetts Road) Goosepond Creek at Goosepond (GS 125915) ARI (Years) (m3/s) GHD WRM WRM (RAFTS) (RAFTS) (TUFLOW) 5 215 201 124 10 - 251 168 20 -- 312 202 50 385 326 237 100 472 447 278 200 - 533 317(469)a 500 - 675 470(621)a a Values in brackets include Pioneer River overflows

4.4 DESIGN FLOOD LEVELS, DEPTHS AND EXTENTS

Figure 4.3 and Figure 4.4 show the estimated 10 year and 100 year ARI design flood depths and extents across the Pioneer River, Goosepond and Bakers Creek catchments. The TUFLOW model was run for storm events ranging from 12 to 48 hours duration and the maximum level at any location was adopted as the design level. For the 100 year ARI event, the Pioneer River overflows into Bakers Creek just downstream of the township of Walkerston and into Goosepond Creek between the North Coast Rail and the Bruce Highway. Fursden Creek is consumed by Pioneer River flows for this event. Floodwater also overflows the flood protection levees protecting Mackay City and North Mackay (along Goosepond Creek).

4.5 SUMMARY OF PEAK FLOOD LEVELS AND COMPARISON TO PEAK LEVELS ESTIMATED BY GHD

Table 4.3 shows the predicted peak flood levels upstream and downstream of the various road crossings along Goosepond Creek for the various design events. A comparison to the peak flood levels predicted by GHD (2012) (shown in brackets) at these locations is also provided. The following is of note:  All road crossings are overtopped by the 50 year and 100 year ARI design floods except the Bruce Highway and Glenpark St.  Glenella Road, Hicks Road, Willetts Road, Malcolmson and Evans Avenue would be overtopped by the 5 year ARI event.  Peak flood levels are marginally higher than the peak levels predicted by GHD (2012). The reasons for the differences are not readily apparent. The differences are greatest for the 5 year ARI event, which is possibly due to the larger grid size adopted for this study being unable to adequately define the low flow channel capacity. The differences are less apparent for the larger events because the majority of flow is carried by the floodplain and not the low flow channel.

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Table 4.3 Predicted Peak Flood Levels at Road Crossings and comparison to GHD peak levels Location Road Peak Flood Level Per Design Event (mAHD) Level 5yr 10 yr 20 yr 50 yr 100yr 200yr 500yr (mAHD) U/Sa Upper Bruce Hwy 12.03 12.46 12.71 12.93 13.35 13.74 13.98 13.22 (12.17) (12.80) (13.15) D/Sb Upper Bruce Hwy 11.89 12.21 12.41 12.53 12.66 12.87 13.13 (11.84) (12.29) (12.45) U/S Glenella Rd 8.97 9.10 9.18 9.29 9.37 9.45 9.81 8.87 (8.88) (9.09) (9.18) D/S Glenella Rd 8.71 8.85 8.95 9.07 9.19 9.33 9.79 (8.68) (8.91) (9.02) U/S Hicks Rd 7.58 7.83 7.99 8.16 8.34 9.04 9.54 6.54 (7.66) (8.12) (8.31) D/S Hicks Rd 7.44 7.70 7.87 8.04 8.22 9.00 9.51 (7.51) (7.96) (8.17) U/S Lower Bruce Hwy 7.36 7.62 7.78 7.95 8.12 8.88 9.37 9.00 (7.49) (7.92) (8.13) D/S Lower Bruce Hwy 7.34 7.59 7.75 7.92 8.08 8.81 9.24 (7.49) (7.92) (8.12) U/S Willetts Rd 6.70 6.93 7.04 7.18 7.34 8.07 8.48 6.42 (6.23) (6.73) (7.04) D/S Willetts Rd 6.47 6.70 6.83 7.02 7.22 7.99 8.42 (6.14) (6.63) (6.95) U/S Malcomson St 6.01 6.15 6.25 6.40 6.59 7.32 7.81 5.46 (5.65) (6.04) (6.41) D/S Malcomson St 5.58 5.82 6.03 6.24 6.45 7.22 7.74 (5.30) (5.85) (6.29) U/S Glenpark St 5.39 5.61 5.80 5.99 6.20 6.93 7.46 6.72 (5.11) (5.62) (6.11) D/S Glenpark St 5.66 5.55 5.73 5.89 6.07 6.57 7.10 (5.07) (5.56) (6.05) U/S Evans Av 5.33 5.54 5.72 5.87 6.06 6.53 7.02 3.95 (5.04) (5.52) (6.02) D/S Evans Av 5.28 5.49 5.67 5.82 6.02 6.49 6.97 (5.02) (5.50) (6.00) a U/S = Upstream, b D/S = Downstream, (value in brackets were estimated by GHD, (2012))

4.6 LEVEE OVERFLOWS

Table 4.4 shows the maximum overflows that are predicted to occur over the floodplain levees from the Pioneer River and Goosepond Creek for the various design storms from the 50 year ARI to the 500 year ARI events. The following is of note with respect to the 100 year ARI (12 hour) event,  up to 243m3/s is expected to overflow into Bakers Creek;  a total of up to 32.5m3/s is expected to overflow the Mackay City Levees, mostly from the levee to the west of Nebo Road adjacent to Shakespeare St  a total of up to 58m3/s is expected to overflow the North Mackay Levees from either Goosepond Creek or the Pioneer River;  up to 180m3/s is expected to overflow from the Pioneer River into Gooseponds Creek; and  up to 39m3/s is expected to overflow from Goosepond Creek into the Pioneer River upstream of the Bruce Highway.

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BRUCEBRUCE HWYHWY

555

111111 666

101010

101010 9 9 9

101010 9 9 9 7 7 7

9 9 9 7 7 7

7 7 7 8 8 8 8 8 8 8 8 8

6 6 6 6 6 6 6 6 6 22 22 22 777 22 22 22 777 22 22 22 777

5 5 5

5 5 5

5 5 5

212121 212121

888 444 999 888 444

101010 101010 131313 131313 111111 121212 111111

777 777 LEGEND FLOOD DEPTH (m)

666 Main Road 0.0m < 1.0m 555 555 555 Rail Flood Protection Levee 1.0m < 3.0m 444 Flood Level Contour (0.5m) 3.0m < 5.0m

 5.0m < 10.0m

0.5 0 1 2 10.0m < 15.0m kilometres 15.0m < 20.0m

Figure 4.3 10 Year ARI Flood Depths and Extent, Pioneer River and Bakers Creek

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BRUCEBRUCE HWYHWY

666 7 7 7 7 7 7 7 7 999 7 999 101010 101010 888 888

7 7 7 7 7 7 7 7 7

888 888 666 888 666 666

9 9 9 9 9 9 9 9 9 25 25 25 25 25 25 25 25 25

555 242424 555 242424 555 242424 101010 111111

171717 171717 161616 444 161616 151515 444 151515 12 12 12 151515 12 12 12 12 12 12

14 14 14

14 14 14

14 14 14 13 13 13 13 13 13 13 13 13

232323

222222

212121

202020 202020

181818

171717

151515

141414

131313

121212

4 4 4

4 4 4

4 4 4

111111 111111

101010

999 888 LEGEND FLOOD DEPTH (m) Main Road 0.0m < 1.0m Rail 666 777 666 Flood Protection Levee 1.0m < 3.0m

555 4 4 4 555 4 4 4 555 4 4 4 Flood Contour (0.5m) 3.0m < 5.0m

 5.0m < 10.0m

0.5 0 1 2 10.0m < 15.0m kilometres 15.0m < 20.0m

Figure 4.4 100 Year ARI Flood Depth and Extent, Pioneer River and Bakers Creek

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Table 4.4 Predicted Maximum Overflows across Floodplain Levees

Maximum Levee Overflows (m3/s) 50yr 50yr 100yr 100yr 200yr 200yr 500yr 500yr Location 12hr 24hr 12hr 24hr 12hr 24hr 12hr 24hr Pioneer River to Bakers Creek 3.7 3.3 243.0 209.5 670.4 266.0 1110. 350.0 Pioneer River to Sandy Creek 0.0 0.0 0.0 0.0 31.2 0.0 286.1 0.0 Mackay City Levees - Shakespeare St West of Nebo Rd 0.0 0.0 31.0 7.8 140.9 31.2 261.4 97.8 - Bruce Hwy to Canelands 0.0 0.0 0.2 0.0 15.5 0.0 53.9 8.4 - Canelands to Sydney St 0.0 0.0 0.3 0.0 8.8 0.0 39.5 6.3 - Sydney St to Sandfly Ck 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 - Oceanfront 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 North Mackay Levees - Sams Rd 1.0 1.1 1.7 0.9 15.8 1.5 105.7 4.4 - Bassett Basin Sth of Harbour Rd 0.8 0.7 1.0 1.6 2.4 2.8 2.6 1.1 - Bassett Basin Nth of Harbour Rd 3.0 1.3 33.8 26.9 35.0 29.4 9.8 12.7 - Goosepond (Perkins St) 2.6 2.6 20.9 18.5 30.0 31.4 75.0 46.0 - Goosepond (Burgess St) 0.1 0.1 1.0 0.9 9.5 10.0 14.1 15.3 Pioneer River to Goosepond Ck - Upstream of Mackay Bypass Rd 6.0 4.5 51.7 44.6 121.0 55.7 186.5 90.7 - Mackay Bypass to Bruce Hwy 28.3 18.4 128.3 109.0 275.0 130.5 337.6 218.1 Goosepond to Pioneer - Upstream of Mackay Bypass Rd 26.6 31.4 37.4 41.6 46.0 54.5 69.3 80.4 - Mackay Bypass to Bruce Hwy 0.5 0.5 1.6 2.4 4.1 5.6 9.3 15.4

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5 SUMMARY OF FINDINGS

The Pioneer River TUFLOW model has been updated, extended and recalibrated to estimate design flood levels along Goosepond Creek that results from either local rainfalls in the Goosepond Creek catchment or overflows from the Pioneer River.

The model was updated to include:  Goosepond Creek catchment design rainfalls and discharges;  Up to date ground levels around the Sugarshed Road area, which were up to 1m lower when compared to the original data;  Updated Rail and road culvert data along Goosepond Creek and along Vines Creek in the Andergrove area; and  The reach upstream of the Bruce Highway into Janes Creek. The model was recalibrated to the 2007 and 2008 flood events along Goosepond Creek and then run assuming design storms centred concurrently over both the Pioneer River and Goosepond Creek. Although, this scenario is improbable, it was acceptable for this study to determine peak design flood levels because the two flood peaks were found to not coincide.

The results of the modelling show that:  The Pioneer River overflows into Gooseponds Creek for events greater than and equal to the 50 year ARI design event.  Design discharges and peak flood levels along Goosepond Creek upstream of approximately Evans Avenue in North Mackay are dominated by local Goosepond Creek catchment design flows (and not Pioneer River overflows) for events up to and including the 100 year ARI design event.  For the 100 year ARI event, the overflows from the Pioneer River generate a flood peak along Goosepond Creek that is similar to the local Goosepond Creek catchment design flow.  Overflows from the Pioneer River dominate flood levels along Goosepond Creek for larger events.

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6 REFERENCES

BMT WBM Mackay Region Storm Tide Study (DRAFT) Report prepared for (2012) Mackay Regional Council by GHD Pty Ltd, July 2012.

GHD (2012) Report for Goosepond/Vines Creek Flood Study, Report prepared for Mackay Regional Council by GHD Pty Ltd, February 2012

Pilgrim (1998) Australian Rainfall and Runoff. A Guide to Flood Estimation The Institution of Engineers , 1998

WRM (2012) Pioneer River Flood Study. Report prepared for Mackay Regional Council by WRM Water & Environment Pty Ltd, October 2011.

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