exmouth hydrological study...morphology of the channel at a number of key locations (figure 2)....

Client: Shire of Exmouth

Exmouth Hydrological Study

January 2014

hyd2o EXMOUTH HYDROLOGICAL STUDY

H13043Av1 | 17 January, 2014 i

Contents

Executive Summary 1

1. Introduction 2

1.1 PREVIOUS STUDIES 2

2. Environmental Characteristics 3

2.1 LANDFORM AND TOPOGRAPHY 3

2.2 LAND USE 3

2.3 CLIMATE 3

2.4 TIDE AND STORM SURGE 4

3. Field Investigation 5

4. Catchment Mapping 7

5. Design Flow Estimation for Key Catchments 8

6. Flood Modelling and Floodplain Mapping 9 6.1.1 Unnamed Creek 9 6.1.2 Shothole Creek 10 6.1.3 Badjirrajirra Creek 11 6.1.4 Wapet Creek 12

7. Conclusions & Recommendations 13

8. References 15


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Appendices

A. Field Observations & Plates B. Rational Method Flow Estimates C. Exmouth Rainfall IFD D. HECRAS Modelling : Unnamed Creek E. HECRAS Modelling : Shothole Creek F. HECRAS Modelling : Badjirrajirra Creek G. HECRAS Modelling : Wapet Creek

Figures

1. Location Plan 2. Field Observation Locations 3. Catchment Mapping 4. Unnamed Creek 100 Year Floodplain Estimate 5. Shothole Creek 100 Year Floodplain Estimate 6. Badjirrajirra Creek 100 Year Floodplain Estimate 7. Wapet Creek 100 Year Floodplain Estimate

Tables

1. Tidal Level Summary 2. Catchment Areas 3. Estimated Design Flows 4. Unnamed Creek HECRAS 100 Year Modelling Results 5. Shothole Creek HECRAS 100 Year Modelling Results 6. Badjirrajirra Creek HECRAS 100 Year Modelling Results 7. Wapet Creek HECRAS 100 Year Modelling Results

Disclaimer

This document is published in accordance with and subject to an agreement between Hyd2o and the Client for whom it has been prepared, and is restricted to those issues that have been raised by the Client in its engagement of Hyd2o. It has been prepared using the skill and care ordinarily exercised by hydrologists in the preparation of such documents.

Hyd2o recognise site conditions change and contain varying degrees of non-uniformity that cannot be fully defined by field investigation. Measurements and values obtained from sampling and testing in this document are indicative within a limited timeframe, and unless otherwise specified, should not be accepted as conditions on site beyond that timeframe.

Any person or organisation that relies on or uses the document for purposes or reasons other than those agreed by Hyd2o and the Client does so entirely at their own risk. Hyd2o denies all liability in tort, contract or otherwise for any loss, damage or injury of any kind whatsoever (whether in negligence or otherwise) that may be suffered as a consequence of relying on this document for any purpose other than that agreed with the Client.


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Executive Summary Hyd2o was commissioned by the Shire of Exmouth to undertake a hydrological study to assist in the development of a Local Planning Strategy (LPS) within the Shire.

Taylor Burrell Barnett Planning Consultants are currently preparing the LPS for the coastal area extending south of the existing Exmouth town site to Learmonth Airport/RAAF base and focusing on areas between the coastline and the Minilya-Exmouth Road (Figure 1).

This hydrological study was guided by the following objectives:

• Map all surface water catchments within the LPS areas to the east of the range.

• Provide estimates of peak flows for key catchments.

• Estimate 100 year average recurrence interval (ARI) flood widths for key catchments.

• Provide recommendations to assist planning.

• Based on study outcomes, identify the need for future hydrological studies.

Seventeen catchments were mapped using 5 m contours derived from a Landgate 20 m gridded digital elevation model (DEM). The catchments varied considerably in size ranging from 150 ha to 16,640 ha.

Calculation of catchment peak flow rates for various ARI storm events and 100 year ARI estimated floodplain mapping was undertaken in four catchments; Unnamed Creek, Shothole Creek, Badjirrajirra Creek and Wapet Creek. Mapping was undertaken for approximately 30km of coastline, covering the area contained within the LPS area.

Design flow rates were calculated using the Rational Method (Engineers Australia, 2003). The 100 year ARI flow rates ranged from 240 m3/s up to 2000 m3/s and are considered comparable to those derived by JDA (1999) and SKM (2007) for similar sized catchments associated with the existing Exmouth townsite north of the LPS area.

A 20 m gridded DEM was used to derive catchment cross sections for estimating the 100 year ARI floodplain map for each catchment, which were modelled in HECRAS. Modelling results indicate that the 100 year floodplains were relatively confined within both Unnamed Creek and Badjirrajirra Creek, whilst Shothole and Wapet catchment experienced a wider floodplain near the coast.

The 100 year ARI floodplain mapping in this report is considered a best estimate based on the application of the modelling techniques described in this study but limited by the coarse scale of available topographic data.

For any proposed developments located in proximity to the areas defined in this report, it is recommended more detailed survey and hydrological investigations are undertaken to inform future planning and design.


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1. Introduction Hyd2o was commissioned by the Shire of Exmouth to undertake a hydrological study to assist in the development of a Local Planning Strategy (LPS) within the Shire.

Taylor Burrell Barnett Planning Consultants are currently preparing the LPS for the coastal area extending south of the existing Exmouth townsite to Learmonth Airport/RAAF base and focusing on areas between the coastline and Minilya-Exmouth Road (Figure 1).

This study was guided by the following objectives to inform the structure planning process:

• Map all surface water catchments within the LPS area to the east of the range.

• Provide estimates of peak flow from keys catchments.

• Estimate widths of flooding in four catchments identified by the planning team.

• Provide recommendations for further hydrological studies within the catchment.

The 100 year ARI floodplain mapping resulting from this study is considered a best estimate given the coarse scale of currently available topographic data for the study, and the application of the modelling techniques described in this report.

1.1 Previous Studies There are two previous studies which have investigated flooding in the Exmouth townsite:

• Exmouth Flood Management Study (JDA Consultant Hydrologists, 1999)

• Exmouth Floodplain Management Study (Sinclair Knight Merz, 2007)

These studies covered area north of the LPS area.

JDA (1999) investigated flood inundation of Exmouth following the March and May 1999 cyclone events, provided estimates of floodplain mapping for the existing Exmouth townsite based on limited topographic information, and application of Manning’s equation and the rational method for design flows, calibrated against field observations.

Sinclair Knight Merz (2007) undertook more detailed hydrologic and hydraulic modelling of current and proposed development areas surrounding the Exmouth town site. Detailed LiDAR terrain data and MIKE-21 modelling were used for flood plain mapping.

While the above studies do not cover the area investigated by this report, the results of these studies, in terms of catchment characteristics and hydrologic behaviour have been used to inform this study.

With respect to the area surrounding Learmonth Airport, the RAAF was unable to provide any previous hydrological study of this area.


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2. Environmental Characteristics

2.1 Landform and Topography The topography and landform of the Exmouth area is dominated by Cape Range anticline, a north south linear range that rises to approximately 300 mAHD (Figure 1).

The range itself is composed of sandstone and limestone with the edges of the range falling away steeply into deep canyons (Hocking et al, 1987).

The coastal terrain is typically flat at the base of the range towards the Exmouth Gulf.

Surface geology consists predominantly of alluvial, diluvial and colluvial deposits and consisting mostly of sand.

2.2 Land Use Existing development within the LPS area is limited and fragmented. The area is predominantly characterised by native vegetation.

Existing development includes some limited industrial development, a rubbish tip, two airports (Exmouth and Learmonth) and some rural residential land use located on the eastern side of the Minilya-Exmouth Rd.

2.3 Climate Exmouth has a semi-arid climate and is located in the most cyclone prone part of Australia’s coast (Bureau of Meteorology (BoM), 2013). Cyclone frequency and intensity is extremely variable from year to year although cyclones are more likely in the December to April period.

Exmouth experiences hot day time temperatures in summer between 30 C and 40 C while average winter temperatures are approximately 25 C.

Based on the Bureau of Meteorology’s Learmonth rainfall station (station 005007), the long term average rainfall is 251 mm/year but is dependent on monsoon low pressure systems, thunderstorm activity and the passage of tropical cyclones.

Major recent rainfall events include:

• Tropical cyclone Vance in March 1999 which moved along the Exmouth Gulf and is recorded as one of the most intense cyclones in Australian history recording the highest ever wind gust of 267 km/hour (BoM, 2013). Rainfall of approximately 207 mm was recorded at Learmonth for this event. Significant coastal erosion also occurred with storm surges peaking at 3.6 mAHD.

• June 2002, which recorded the wettest June day on record for WA with approximately 305 mm of rainfall recorded at Exmouth in 24 hours.

These events were examined in detail in the SKM (2007) and JDA (1999) studies.


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2.4 Tide and Storm Surge Tidal levels for Exmouth are reported in GHD (2007) and summarised in Table 1.

Storm surge is a major threat to the Exmouth Gulf which results from cyclonic activity (BoM, 2013). The storm tide is a combination of the storm surge value and the tidal variation.

Table 1: Tidal Level Summary

Tide Level (mAHD)

High Astronomical Tide 1.40

Mean High Water Springs 0.90

Mean Sea Level 0.00

Mean Low Water Springs -0.90

Low Astronomical Tide -1.40


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3. Field Investigation Hyd2o conducted a field investigation across the area on 20 and 21 August 2013.

The field investigation included assessing the condition of the four key catchments and their watercourses (Figure 2). The watercourses that were part of the field investigation include Unnamed Creek, Shothole Creek, Badjirrajirra Creek, and Wapet Creek. At the time of the investigation all creeks were dry.

The assessment methodology for each of the four watercourses included undertaking indicative cross-sectional field survey at up to six locations along the main channel and recording debris levels. The locations for survey along each watercourse represented areas where changes in the channel morphology were evident and concentrated around Minilya-Exmouth Rd (the proposed areas for development).

The cross-sectional field survey provided an estimate of the width, depth, and general morphology of the channel at a number of key locations (Figure 2). Debris levels are considered indicative of a recent high water mark for the watercourse. At the majority of the locations the debris levels were observed at close to bankfull, which approximately represents a 2 year ARI event.

This task also included estimating of catchment characteristics such as Manning’s n roughness estimates.

At three sites, where the watercourse crosses with the Minilya-Exmouth Rd a designated floodway exists with staff gauges to indicate the depth of flow. This was the case at Wapet Creek, Shothole Creek, and Badjirrajirra Creek. Staff gauges typically had indicators to a 2 m depth.

Road crossings typically had a small culvert (300 mm to 375 mm diameter) to enable very small flows to flow under the road. These culverts have very limited capacity compared to the contributing upstream catchments. The exception was Wapet Creek just south of the Learmonth Airport, which had 3 x 1125 mm diameter culverts under the Minilya-Exmouth Rd for the main watercourse channel.

Unnamed Creek, Shothole Creek and Badjirrajirra Creek were observed to have clear outlets to the coast and are not blocked by dunes. Wapet Creek is very low lying and subject to tidal inundation at its lower reaches downstream of the Minilya-Exmouth Rd. This is similar to the Exmouth townsite where limited outlets exist and ponding of floodwater between Murat Rd and the Coastal dunes occurs as noted in previous studies.

There is little existing development within the catchments. Most of the catchments upstream of the Minilya-Exmouth Rd are almost fully vegetated with no clearing or development. The exceptions to this were the Exmouth and Learmonth airports located in Shothole Creek and Wapet Creek catchments respectively. The Unnamed Creek catchment has some existing industrial development located on the coastal side of Minilya-Exmouth Rd.

The main channels contained large cobbled sediments which appear to have been mobilised during flow events. These appear to deposit in areas were velocities decrease in


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the channels such as upstream of the Minilya-Exmouth Rd. Channel cross sections and capacities are therefore likely to change between storm events.

Key field observation locations are summarised in Figure 2 and shown in more detail in Appendix A.


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4. Catchment Mapping Surface water catchment mapping was undertaken by Hyd2o for all watercourses flowing from Cape Range to the Gulf of Exmouth from south of the existing townsite to south of Learmonth Airport. Catchment mapping is shown in Figure 3. This mapping included four key catchments identified by the project planners for more detailed investigation; Shothole Creek, Wapet Creek, Badjirrajirra Creek, and Unnamed Creek (Figure 3).

The mapping extends over a 30 km stretch along the coastline between Unnamed Creek and Wapet Creek (immediately south of Learmonth airport). Catchment boundaries were estimated based on Department of Water (DoW) watercourse mapping datasets, and 5 m elevation contours derived from a Landgate 20 m gridded digital elevation model.

The coarse resolution of topographical data limits the accuracy of the catchment boundaries derived in this study, however it should be considered a best estimate based on the quality of available data and its interpretation.

A total of 17 catchments were mapped in the area. Catchment sizes are shown in Table 2, ranging in size from 150 ha to 16,640 ha. The two largest catchments are Shothole Creek and Wapet Creek catchments further discussed in Sections 5 and 6 of this report. These catchments are much larger than those in the Exmouth Townsite investigated by JDA (1999) and SKM (2007). The largest catchment in previous studies was the Market St Creek catchment and is 1,490 ha in size.

Table 2: Catchment Areas

Catchment Name Catchment Area (ha)

Key Catchments for Detailed Investigation (refer Sections 5 & 6)

Unnamed Creek 720

Badjirrajirra Creek 1520

Shothole Creek 6980

Wapet Creek 16640

Other Mapped Catchments

EX1 930

EX2 590

EX3 1340

EX4 510

EX5 1390

EX6 620

EX7 150

EX8 570

EX9 870

EX10 1730

EX11 2450

EX12 1120

EX13 5260


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5. Design Flow Estimation for Key Catchments Design flow estimates for 2 to 50 year ARI events for the four key catchments were calculated by Hyd2o based on application of the Rational Method detailed in Australian Rainfall and Runoff (Engineers Australia, 2003).

Calculations are detailed in Appendix B and summarised in Table 3 below. The 100 year ARI flow estimates are based on using a graphical Log Pearson III extrapolation of 2 to 50 year ARI results.

The rainfall used in the Rational Method calculation was calculated via the Bureau of Meteorology’s Computerised Design IFD Rainfall System (CDIRS), with reference to the methodology in Australian Rainfall & Runoff (AR&R) (Institution of Engineers, Australia 2003). Rainfall intensity frequency and duration data for Exmouth is contained as Appendix C.

Table 3 shows 100 year ARI estimates for the four catchments ranging from 240 m3/s at Unnamed Creek to approximately 2000 m3/s at Wapet Creek.

These flow rates are comparable to those made by JDA (1999), using the Rational Method, for similar sized catchments north of the LPS area.

With regard to the 2 year ARI flow estimates (channel forming flow), these correlate well to a bankfull capacity for the field surveyed sections taken by Hyd2o in August 2013.

Table 3: Estimated Design Flows

Catchment

Name

Size (ha)

Mainstream length (Km)

Estimated Flow Rate (m3/s)

2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

Unnamed 720 6 11 25 48 96 177 240

Badjirrajirra 1520 10 19 42 79 160 296 400

Shothole 6980 16 49 114 219 450 847 1150

Wapet 16640 26 88 206 398 824 1559 2000


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6. Flood Modelling and Floodplain Mapping Flood mapping of the 100 year ARI event was undertaken at each of the four key catchments (Unnamed, Shothole, Badjirrajirra, Wapet) using the HECRAS backwater model.

Cross-section channel geometry was derived along the major tributary of each catchment using a Landgate 20 m gridded digital elevation model and validated, where possible, against channel measurement made during field investigations. This data represents the best survey information available at the time of undertaking this study.

Modelled sections were verified by correlating 2 year ARI modelling results against the bankfull condition of the main creek channel for each creek and where debris lines were noted in field. This provides some confidence that the derived cross sections are suitable for use.

Cross-sections were typically spaced at distances ranging from of 100 - 500 m apart along the mainstream channel of each catchment depending on catchment size, mainstream length, and based on identifying locations with distinctive changes in channel geometry.

A Manning n roughness coefficient of 0.05 was estimated for all watercourses for both the main channel and overbank of each cross section based on field observations and correlated to Chow (1959). These values are similar to those in SKM (2007), which used Mannings n roughness coefficients for the creek and floodplain ranging from 0.04 to 0.055.

In the absence of a detailed coastal inundation study, discussions with the Department of Water (pers. comm. Richard Bretnall, 28/10/2013) recommended that a maximum estimated storm surge condition of 3 mAHD was applied as the tailwater condition for flood modelling.

Estimated 1 in 100 year ARI flow widths and associated peak discharges are shown in Figures 4 to 7 for each of the four catchments. Outputs from the HECRAS model are provided in Appendices D to G. Further detail is provided below about the four key catchments in this study.

Note that the mapping shown in Figures 4 and 7 represents mapping around the main watercourse channel and does not show the floodplain for all individual contributing tributaries.

All flood heights and widths should be considered indicative only and subject to more detailed local modelling as/if required to inform more detailed stages of planning.

6.1.1 Unnamed Creek Unnamed Creek is the smallest of the key catchment considered with an area of 720 ha. The site contains some clearing with industrial development east of the Minilya-Exmouth Rd. It also contains a portion of the rubbish tip to the west of the road.

Modelling results are shown in Figure 4 with approximate flood widths and levels at each modelled section presented in Table 4. Modelling outputs are shown in Appendix D.


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The area of inundation close to the coast at downstream Section UC1 is heavily influenced by the tidal condition. The model was run using two backwater conditions, one representing the recommended storm surge level of 3 mAHD and one with the high tide level of 1 mAHD. Figure 4 shows mapping for both a 3 mAHD and 1 mAHD downstream conditions.

The floodplain width was narrowest at Section UC2 at 60m.

Section UC5 had a flood width of 350 m, which resulted from a shallow south main channel bank that allows for overtopping and inundation of a comparatively wide, low-lying area. This is not apparent in Sections UC4, UC3 and UC2 moving further toward the coast where channel banks are steeper and higher.

Table 4: Unnamed Creek HECRAS 100 ARI Year Modelling Results

Section Model Flood Width (m)

Model Flood Height (mAHD)

UC1 240 3.0

UC2 60 3.7

UC3 80 5.0

UC4 100 7.6

UC5 350 9.5

UC6 100 11.2

UC7 70 13.8

UC8 70 15.1

UC9 100 16.0

6.1.2 Shothole Creek Modelling results for Shothole Creek are shown in Figure 5 with approximate flood widths and levels at each modelled section presented in Table 5. Modelling outputs are shown in Appendix E.

At Shothole Creek the creek system forms a delta as it approaches the coast. In this area cross sections were extended across several poorly defined channels in order to form the extent of the Shothole Creek floodplain. In a major storm even this catchment appears to have breakout flows into its adjacent catchment.

Due to the coarse scale topography the results in Shothole Creek were required to be approximated. The flow from the catchment is split between a number of braided streams, some of which are likely to only flow in major storm events, as such they are not clearly demarcated in the topography which was problematic for estimating the flood widths. Typically this watercourse geometry requires a refined topographic dataset and is best suited to a 2D model.

Modelling indicated the southern end of the Exmouth Airport to be within the floodplain, this may be a result of the coarse scale topographic information used in this study, and further detailed investigation and survey data would be required to more accurately define the floodplain at a local scale in this area.


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Depending on the extent of proposed development, it is recommended more detailed 2D modelling be undertaken to define the extent of the floodplain and establish suitable flood levels to inform development.

Table 5: Shothole Creek HECRAS 100 Year ARI Modelling Results



SC1 - 3.3

SC2 - 7.1

SC3 - 10.8

SC4 - 13.5

SC5 - 17.1

SC6 - 20.7

SC7 - 24.6

SC8 - 28.7

SC9 - 32.7

6.1.3 Badjirrajirra Creek Modelling results for Badjirrajirra Creek are shown in Figure 6 with approximate flood widths and levels at each modelled section presented in Table 6. Modelling outputs are shown in Appendix F.

The modelled flood width for Badjirrajirra Creek downstream of the Minilya-Exmouth Rd ranges from 90 to 110 m (Section BC2 and BC1 respectively).

Its widest section is upstream of the powerline corridor with an estimated flooded width of 320 m. In this area there are a number of ephemeral stream tributaries, which would appear to receive floodwaters from the main channel during large events.

Table 6: Badjirrajirra Creek HECRAS 100 ARIYear Modelling Results



BC1 110 3.8

BC2 90 6.4

BC3 230 9.7

BC4 170 13.1

BC5 100 15.8

BC6 230 20.0

BC7 320 23.4

BC8 130 27.2


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6.1.4 Wapet Creek Modelling results for Wapet Creek are shown in Figure 7 with approximate flood widths and levels at each modelled section presented in Table 7. Modelling outputs are shown in Appendix G.

Wapet Creek is the largest of the catchments and is 16,640 ha in area.

Mapping of the floodplain within Learmonth Airport/RAAF base was not undertaken as part of this study. The culverts located on the downstream end of the airport are fitted with flapgates which would protect the airport from any flooding from Wapet Creek (the eastern side of the Minilya-Exmouth Rd).

The topography of Wapet Creek catchment is significantly different from the others as it has a wider low lying floodplain which is constrained by low dunes parallel to the coast.

This large catchment has only a single outlet to the coast which results in a large low lying area being inundated as shown in Figure 7. This is similar to the Exmouth townsite where limited outlets exist and ponding of floodwater between Murat Rd and the Coastal dunes occurs.

Modelling indicates the Minilya/Exmouth Rd would be inundated over a very wide area in this catchment.

Table 7: Wapet Creek HECRAS 100 Year ARI Modelling Results

Section Model Flood Width (km)*


WC1 0.4 3.7

WC2 3.2 4.6

WC3 1.4 4.7

WC4 1.8 4.9

WC5 1.2 5.1

WC6 1.5 5.3

WC7 1.0 6.3

WC8 2.3 7.9

*Model flood width is measured to the boundary of RAAF Learmonth. Areas within RAAF Learmonth were not mapped.


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7. Conclusions & Recommendations This hydrological study was undertaken to determine the surface water hydrology of the proposed LDS with particular focus on four catchments where development may occur; Shothole Creek, Unnamed Creek, Badjirrajirra Creek and Wapet Creek.

A total of 17 catchments were mapped in the area. Catchment sizes ranged from 150 ha to 16,640 ha. The two largest of these catchments are Shothole Creek (6,980 ha) and Wapet Creek (16,640 ha). The 100 year ARI estimates for the four key catchments ranged from 240 m3/s at Unnamed Creek to 2000 m3/s at Wapet Creek.

Floodplain mapping of the 100 year ARI event was undertaken at each of the four key catchments using HECRAS. This study did not consider the delineation between floodway and flood fringe within the floodplain.

The following summarises the main findings of the modelling exercise:

• For Unnamed Creek, the area of inundation at downstream end was influenced by the modelled tidal condition. The floodplain width was narrowest (60 m) near the coast where the channel banks are incised. Near the Minilya-Exmouth Rd the estimated flood width was 350 m, which resulted from a shallow right bank that allows for overtopping and inundation of a comparatively wide, low-lying area.

• Shothole Creek was difficult to model due to the coarse topography and the use of a 1D model due to the geometry of the channel. This flow behaviour is best modelled using 2D flood modelling. Shothole Creek may cause some flooding to the existing Exmouth Airport.

• Depending on the extent of proposed development in the Shothole Creek area it is recommended more detailed 2-D modelling be undertaken to define the extent of the floodplain and establish suitable flood levels to inform development.

• The modelled flood width for Badjirrajirra Creek downstream of the Minilya-Exmouth Rd is reasonably constant ranging from 90 to 110 m. Its widest section is upstream of the powerline corridor with an estimated flooded width of 320 m. In this area there are a number of ephemeral stream tributaries, which would appear to receive floodwaters from the main channel during large events.

• The Wapet Creek is a large catchment with only a single outlet to the coast which results in a large low lying area being inundated as shown in Figure 7. This is similar to the Exmouth townsite where limited outlets exist and ponding of floodwater between Murat Rd and the Coastal dunes occurs. Modelling indicates the Minilya/Exmouth Rd would be inundated over a very wide area in this catchment.

The 100 year ARI floodplain mapping resulting from this study is considered a best estimate given the coarse scale of currently available topographic data for the study, and the application of the modelling techniques described in this report.

All flood heights and widths should be considered indicative only, subject to more detailed local modelling as/if required to inform more detailed stages of planning. For any proposed developments located in proximity to the areas defined in this report it is


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recommended more detailed survey and hydrological investigations are undertaken to inform future planning and design.


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8. References Bureau of Meteorology (2013), Tropical Cyclone Vance 18-24 March 1999.

Chow (1950), Open-Channel Hydraulics

Engineers Australia (2003), Australian Rainfall and Runoff

JDA Consultant Hydrologists (1999), Exmouth Flood Management Study

Hocking, RM, Moors, HT, Ven De Graaff WJE, (1987), Geology of the Carnarvon Basin Western Australia, Bulletin 133 Geological Survey of Western Australia, Department of Mines Western Australia.

Sinclair Knight Merz (2007a), Exmouth Floodplain Management Study, Flood Modelling Report, December 2007

Sinclair Knight Merz (2007b), Exmouth Floodplain Management Study, Floodplain Management Strategy, December 2007

FIGURES

hyd2oExmouth Flood Study

Location PlanFigure 1

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Exmouth townsite

0 2 4 6 8Kilometers

Study Area

Learmonth Airport/RAAF Base

CAPE

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Field Survey LocationsFigure 2

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Field survey channel cross-section locations

Four key catchments

Main creek channel

Unnamed Creek

Shothole Creek

Badjirrajirra Creek

Wapet Creek


Catchment MappingFigure 3

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Unnamed Catchment720 ha

Shothole Catchment6980 ha

Badjirrajirra Catchment1520 ha

16640 haWapet Catchment

Four key catchments

Additional catchments

EX1

EX2

EX3

EX4

EX5

EX6

EX7EX8

EX9

EX10

EX11

EX12

EX13

hyd2oExmouth Hydrological Study

Unnamed Creek 100 Year ARI Floodplain EstimateFigure 4

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UC1

UC2

UC3

UC4

UC5UC6UC7

UC8

UC9

0 125 250 375 50062.5Meters

Flow rates (m3/s)2 year 115 year 2510 year 4820 year 9650 year 177100 year 240

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Catchment cross sections UC1-UC9

Unnamed Creek main channel

Unnamed Creek tributary

Unnamed Creek catchment

Flood estimatesEstimated 100 year floodplain

3 mAHD tide (storm surge inundation)


Shothole Creek 100 Year ARI Floodplain EstimateFigure 5

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SC1SC2SC3SC4

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Catchment cross sections SC1-SC9

Shothole Creek main channel

Creek tributary

Shothole Creek catchment and adjacent catchment EX2

Estimated 100 year floodplain

0 0.25 0.5 0.75 10.125Kilometers


SC9

Shothole Creek Catchment

Catchment EX2

Limit of Mapping


Badjirrajirra Creek 100 Year ARI Floodplain EstimateFigure 6

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BC1

BC2

BC3BC4BC5BC6

BC7BC8

Catchment cross sections BC1-BC8

Badjirrajirra Creek main channel

Badjirrajirra Creek tributary

Badjirrajirra Creek catchment

Estimated 100 year floodplain

0 0.25 0.5 0.75 10.125Kilometers


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Wapet Creek 100 Year ARI Floodplain EstimateFigure 7

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WC1

WC2

WC3WC4

WC5WC6WC7WC8

Catchment cross sections WC1-WC8

Wapet Creek tributary

Wapet Creek main channel

Wapet Creek catchment

Estimated 100yr floodplain

RAAF Learmonth

0 0.5 1 1.5 20.25Kilometers


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APPENDIX A

Field Observations and Plates


Unnamed Creek Field Observation Locations

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Channel cross-section locations and photo points

Unnamed Creek main channel

Unnamed Creek catchment

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Figure A1

Ê

Typical lower catchment channel bed characteristics (site 2) Debris at bankfall (site 3)


Shothole Creek Field Observation Locations

Dat

e: 2

3/12

/201

3 Jo

b N

o. H

1304

3

1:83,000

21

0 1 2 3 4Kilometers



Shothole Creek catchment Figure A2

Typical lower catchment channel bed characteristics (site 1)

Roadside flood marker (site 3)

Channel bed and outlet (site 4)

Upper catchment canyons

Ê

3 4


Badjirrajirra Creek Field Observation Locations

ÊD

ate:

23/

12/2

013

Job

No.

H13

043

1:36,000

3 24

1

0 0.5 1 1.5 2Kilometers


Badjirrajirra Creek main channel

Badjirrajirra Creek catchment Figure A3

Typical lower catchment channel bed characteristics (site 4) Creek outlet (site 2)


Wapet Creek Field Observation Locations

ÊD

ate:

23/

12/2

013

Job

No.

H13

043

1:150,000

324 1

0 2 4 6 8Kilometers



Shothole Creek catchment Figure A4

Excavated channel and highway culverts (site 2)

Lower catchment channel bed characteristics (site 4)

APPENDIX B

Rational Method Flow Estimates

AR&R Peak Flow Calculator

NORTH WEST REGIONCatchment name Unnamed Creek CatchmentCatchment type 1

RATIONAL METHOD

Catchment area 7.1 km2

Mainstream length 6.3 km

C2 = 0.212 C2=3.07*10-1*L-0.20

tc = 70.7 mins tc=0.56A 0.38

1.2 hours

ARI (yrs) 2 5 10 20 50Cy/C2 1.00 1.46 2.21 3.60 5.20Itc values via IFD (mm/hr) 27.32 41.74 51.66 64.06 81.64 mm/hrQy Flow Estimate (m3/s) 11.41 25.45 47.67 96.30 177.27 m3/sQy = 0.278 C2*(Cy/C2) I tc A

INDEX FLOOD METHOD


Annual rainfall 1.0 mm

Q5 = 0.001 Q5=6.73*10-4 A^0.72 P^1.51

ARI (yrs) 2 5 10 20 50(Qy/Q2) 0.55 1.00 1.58 2.40 3.90

Qy = Q2*(Qy/Q2) Q = 0.00 0.00 0.00 0.00 0.00


NORTH WEST REGIONCatchment name Shothole Creek CatchmentCatchment type 1

RATIONAL METHOD



C2 = 0.175 C2=3.07*10-1*L-0.20

tc = 168.7 mins tc=0.56A 0.38

2.8 hours


INDEX FLOOD METHOD



Q5 = 0.001 Q5=6.73*10-4 A^0.72 P^1.51

ARI (yrs) 2 5 10 20 50(Qy/Q2) 0.55 1.00 1.58 2.40 3.90

Qy = Q2*(Qy/Q2) Q = 0.00 0.00 0.00 0.00 0.00


NORTH WEST REGIONCatchment name Badjirrajirra Creek CatchmentCatchment type 1

RATIONAL METHOD



C2 = 0.194 C2=3.07*10-1*L-0.20

tc = 94.3 mins tc=0.56A 0.38

1.6 hours


INDEX FLOOD METHOD



Q5 = 0.001 Q5=6.73*10-4 A^0.72 P^1.51

ARI (yrs) 2 5 10 20 50(Qy/Q2) 0.55 1.00 1.58 2.40 3.90

Qy = Q2*(Qy/Q2) Q = 0.00 0.00 0.00 0.00 0.00


NORTH WEST REGIONCatchment name Wapet Creek CatchmentCatchment type 1

RATIONAL METHOD



C2 = 0.160 C2=3.07*10-1*L-0.20

tc = 234.8 mins tc=0.56A 0.38

3.9 hours


INDEX FLOOD METHOD



Q5 = 0.001 Q5=6.73*10-4 A^0.72 P^1.51

ARI (yrs) 2 5 10 20 50(Qy/Q2) 0.55 1.00 1.58 2.40 3.90

Qy = Q2*(Qy/Q2) Q = 0.00 0.00 0.00 0.00 0.00

APPENDIX C Exmouth Rainfall IFD

APPENDIX D HECRAS Modelling: Unnamed Creek

0 100 200 300 400 500-1

0

1

2

3

4

5

6

7

Unnamed Creek2 Plan: Plan 08 24/12/2013

Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05

0 100 200 300 400 500 6000

2

4

6

8

10


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05 .05 .05

0 100 200 300 400 500 600 7002

3

4

5

6

7

8

9


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05 .05

0 100 200 300 400 5005

6

7

8

9

10


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05 .05

0 100 200 300 400 500 600 7007

8

9

10

11

12


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05

0 100 200 300 4009

10

11

12

13

14

15

16


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05 .05 .05

1 2 3

4 5 6

0 50 100 150 200 250 300 350 40011

12

13

14

15

16

17

18

19


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05

0 50 100 150 200 250 300 35012

14

16

18

20

22


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05 .05

0 100 200 300 400 50012

14

16

18

20

22

24

26


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .057 8 9

APPENDIX E HECRAS Modelling: Shothole Creek

0 500 1000 1500 2000 2500 3000 35000

1

2

3

4

5

6

7

8

Shothole Creek Plan: Plan 01 27/11/2013

Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05

0 500 1000 1500 2000 2500 30003.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05

0 500 1000 1500 2000 2500 30008

9

10

11

12

13

14


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05

.05

0 500 1000 1500 2000 250011

12

13

14

15

16

17

18

19


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05

0 500 1000 1500 2000 250012

14

16

18

20

22

24


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05 .05

0 500 1000 1500 200017

18

19

20

21

22

23

24

25


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Levee

Bank Sta

.05 .05

1 2 3

4 5 6

0 200 400 600 800 1000 1200 140022

24

26

28

30

32

34

36

38

40

42


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05 .05

0 100 200 300 400 50026

27

28

29

30

31

32

33


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05

0 50 100 150 200 250 30029

30

31

32

33

34

35


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.057 8 9

APPENDIX F HECRAS Modelling: Badjirrajirra Creek

0 200 400 600 800 1000 12002

3

4

5

6

7

8

Badjirrajirra Creek Plan: Plan 02 1/11/2013

Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05 .05 .05

0 200 400 600 800 1000 12003

4

5

6

7

8

9


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05 .05

0 200 400 600 800 1000 12007

8

9

10

11

12


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05 .05 .05

0 200 400 600 800 1000 120011.5

12.0

12.5

13.0

13.5

14.0

14.5

15.0

15.5


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05 .05

0 200 400 600 800 1000 1200 140013

14

15

16

17

18


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Bank Sta

.05 .05 .05

0 200 400 600 800 1000 120017.5

18.0

18.5

19.0

19.5

20.0

20.5


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05

.05 .05

1 2 3

4 5 6

0 200 400 600 800 1000 1200 140022.0

22.5

23.0

23.5

24.0

24.5


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05 .05 .05

0 200 400 600 800 1000 1200 1400 160024

26

28

30

32

34

36


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05 .05 .057 8

APPENDIX G HECRAS Modelling: Wapet Creek

0 100 200 300 400 500 600 7000

1

2

3

4

5

6

7

8

Wapet Creek Plan: Plan 01 7/11/2013

Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05

.05 .05

0 500 1000 1500 2000 2500 3000 35001.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05 .05

0 500 1000 1500 2000 2500 3000 35000

2

4

6

8

10

12


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05 .05

0 500 1000 1500 20001

2

3

4

5

6

7

8

9


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05 .05

0 200 400 600 800 1000 1200 14002

3

4

5

6

7


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05

.05

0 200 400 600 800 100012001400160018002

4

6

8

10

12


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05

1 2 3

4 5 6

0 500 1000 1500 20003.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Crit 100yr

Ground

Levee

Bank Sta

.05 .05

0 500 1000 1500 2000 25004

5

6

7

8

9

10

11


Station (m)

Ele

vatio

n (m

)

Legend

EG 100yr

WS 100yr

Ground

Bank Sta

.05

.057 8

exmouth hydrological study...morphology of the channel at a number of key locations (figure 2)....

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