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Report 001 rev P2a Sandon Point Flood Study Climate ... - Stockland

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Hewitt’s Creek Flood Study December 2002Wollongong City CouncilAvailable Data• Geomarine (1991) ‘Coastal Process Assessment - Lot 47 DP 737406 Surfers ParadeThirroul’• Gutteridge Haskins & Davey (1989) ‘Hooker Land Development Thirroul, Flood Study’• Gutteridge Haskins & Davey (1989) ‘Hooker Land Development, Thirroul Stage V,Major Constraints Study, Summary.’3.8 DESIGN RAINFALL INTENSITIESIn accordance with current design practice, rainfall intensities for design storm bursts of a givenAverage Recurrence Interval and duration have been calculated from the procedures of AR&R(1987). The six design rainfall stations described in Table 3.15 have been chosen to reflect thevariation of design rainfall across the catchment. It should be noted that these design gaugesare ‘synthetic’ gauges with no physical significance, developed from the data of ARR ‘87 solelyfor the purpose of representing design rainfall across the catchment in subsequent hydrologicmodelling (refer Appendix 2.1 for the plan location of these ‘design’ gauges).TABLE 3.15DESIGN GAUGE LOCATIONSDESIGN GAUGELOCATIONARR #1Bulli Lookout/Kiosk on edge of escarpmentARR #2Bulli Colliery - End of Hobart Street, BulliARR #3Mount Ousley Road above BulliARR #4Hewitts Creek at McCauley’s BeachARR #5Bulli Pass below bend and elbowARR #6End of Fords Road, ThirroulDesign Intensity - Frequency - Duration plots (IFD) for these six ‘design’ gauges are set out inAppendix 13 of the Compendium of Data together with IFD data for the nearby Public Workspluviograph stations.3.9 DESIGN TIDE & OCEAN CONDITIONSBasic tidal statistics for Port Kembla extracted from the Department of Defence (Navy Office)Australian National Tide Tables are reproduced in Table 3.16 below.Datum for the tide recorders in Sydney & Port Hacking is Indian Spring Low Water (ISLW) whiledatum for the Port Kembla recorder is Port Kembla Hydrographic Datum (PKHD). Levels canbe converted to Australian Height Datum (AHD) using the following conversions:RL (AHD) = RL (ISLW) - 0.925 mRL (AHD) = RL (PKHD) - 0.878 mLevels in the following table have been adjusted to AHD using the second of the aboverelationships.TABLE 3.16TIDAL STATISTICS - PORT KEMBLA21


Hewitt’s Creek Flood Study December 2002Wollongong City CouncilAvailable DataVALUE HAT MHHW MLHW MSL MHLW MLLW LATm AHD 1.12 0.62 0.32 -0.08 -0.58 -0.58 -0.88Source : Department of Defence Navy Office (1990)The ‘effective’ or ‘design’ ocean level at the outlet of a creek during a flood is a combination oftide, plus the rise in sea level (setup) adjacent to the shore due to:• The drop in barometric pressure• The surface shear of onshore winds• Wave set up and runupA preliminary estimate of ‘setup’ was prepared by N.S.W. Public Works (1989) for the Mouth ofLittle Lake, a small estuary some 25 km to the south of Hewitts Creek, in which the componentsof setup were as set out in Table 3.17 below.TABLE 3.17ESTIMATED SETUP - WARILLA BEACHSETUP COMPONENT 5 % AEP 2% AEP 1% AEPPRESSURE DROP (m) 0.29 0.31 0.33WIND SHEAR (m) 0.05 0.06 0.07WAVE ACTION (m) 0.61 0.76 0.81TOTAL SETUP (m) 0.95 1.13 1.21Source : NSW Public Works (1989)A ‘design’ ocean level of a given AEP may then be developed by combining an appropriatetidal level with the above setup. This approach does however require consideration of the jointprobability of occurrence of tide and setup. Notwithstanding these difficulties it is reasonable toassume that the 1% AEP design ocean level is likely to be, on a simplistic basis, somewherebetween (HAT + 1.21 = 2.33 m AHD) and (MHHW + 1.21 = 1.83 m AHD).More recent work by the NSW Pubic Works (1992) has quantified the level of Tide-Storm Surgepresent along the mid New South Wales coast, eliminating the need to consider the jointprobability of occurrence of tide and setup. This has in turn permitted more reliable estimates tobe made of elevated ocean conditions adjacent to the shore. The Tide-Storm surge levelrelationship for Sydney and Port Kembla extracted from the above study is reproduced in Table3.18 below. ‘Design’ ocean levels at the shoreline may then be determined by adding anappropriate wave setup/runup component to this level.TABLE 3.18TIDE STORM SURGE LEVELSMID NSW COASTEVENT AEP 5% AEP 2% AEP 1% AEPOCEAN LEVEL m (AHD) 1.40 1.46 1.49Source : NSW Public Works (1992)22


Hewitt’s Creek Flood Study December 2002Wollongong City CouncilAvailable DataEstimates of the elevated ‘design’ ocean level at the shoreline particular to specific sites in theregion have been made by AWACS (1991) at Warilla Beach, by Geomarine (1991) at thesubject site and by the NSW Public Works (1987) at Shoalhaven Heads.Notwithstanding the considerable difference in analytical approach, geometry of the sites andtheir geographic separation, estimates do not differ greatly as may be seen by reference toTable 3.19.TABLE 3.19ESTIMATED ELEVATED ‘DESIGN’ OCEAN LEVELSSOURCE & LOCATION5% AEP 2% AEP 1% AEPNSW PW (1987) HEADS OPEN (m AHD) 2.0 2.1 2.2NSW PW (1987) HEADS CLOSED (m AHD) 2.1 2.2 2.4AWACS (1991) WARILLA BEACH (m AHD) 1.9 2.1 2.2GEOMARINE (1989) THIRROUL (m AHD) 2.4Note :The above estimates exclude consideration of global warming (Greenhouse Effect)The above estimates include the effect of Tide, Wind Shear, Barometric Pressure and Wave Setup.Geomarine have in addition considered what an ‘extreme’ ocean event might mean in regard toelevated ocean level at the subject site and conclude that, in the long term, an extreme eventcould elevate the ‘design’ ocean level at the outlet to 3.7m AHD. This estimate is based on amid to long term estimate of ocean rise due to global warming of 0.3m, added to a 1% AEPocean Tide-Storm Surge level of 2.4m AHD, together with an additional 1m in waverunup/setup, bringing the effective wave runup/setup height to 1.8m in the ‘extreme’ event andthe total elevated ‘design’ ocean level to 3.7m AHD.On the basis of the preceding analysis, ‘design’ elevated ocean levels have been adopted asfollows:TABLE 3.20ADOPTED ‘DESIGN’ OCEAN LEVELSOCEAN CONDITION @ MCCAULEYS BEACHADOPTED LEVEL(m AHD)For an extreme ocean condition including an allowance of 0.3 m forglobal warming. 3.7For a design 1% AEP ocean condition including an allowance of0.3 m for global warming. 2.7For a design 5% AEP ocean condition including an allowance of0.3 m for global warming. 2.4For a conservatively high but ‘likely’ tidal/ocean condition at thepeak of a design flood (MLHW + 0.7 m). 1.0In considering flooding in the outfall reaches of the Creek systems, it is apparent that majorflooding in these lower reaches could occur with no runoff at all in the creek, flooding in theoutfall reach developing in response to a high tide or other elevated ocean condition.23


Hewitt’s Creek Flood Study December 2002Wollongong City CouncilAvailable DataIn recognition of the two mechanisms controlling flooding in an outfall reach, the ‘design’ floodsurface in each outfall reach has been developed from the envelope of;a) flooding due to storm runoff with a conservatively high ‘likely’ ocean level at RL 1.0mAHD; andb) flooding due to an elevated ocean of the specified ARI penetrating the outfall reachwithout attenuation, with negligible stream flow in the creek system.It is noted that the combination of the peak 1% AEP flood discharge with the unattenuated levelof a 1% AEP ocean event (an extremely rare combination) does little to alter flood levelsupstream of the rear dune line, from those obtained by the simpler approach described above.The approach described above has therefore been adopted in this study.24


Hewitt’s Creek Flood Study December 2002Wollongong City CouncilModel ApplicationTABLE 6.1PREDICTED PEAK DISCHARGES - 5% AEP DESIGN EVENTSSLACKY CK AT :KEY LOCATIONRORB 15% AEP Peak Discharge (m 3 /s)RAFTS- WBNMV2 3 PSxRMWBNM-2001XP 2 V8 4 All Clear Policy 5BlockedMixedModeAbove Coal Haulage Culvert 41.5 41.5 40.1 22.9 - Accepted by Culvert 37.5 24.9 37.1 0 - Diverted to Tramway 4.0 16.6 3 22.9 -D/S Rail Overbridge 45.9 17.5 -@ Outlet to Ocean 49.6 21.8 -TRAMWAY CK AT :U/S Railway Culvert 5.0 7.5 4.1 23.9 41.3@ Outlet to Ocean 11.0 15.9 23.0 20.6 41.1WOODLANDS CK AT :D/S Highway Culvert 34.5 41.3 34.6 34.6 -U/S Railway Culvert 40.0 48.7 35.8 44.4 35.4 35.4 - Accepted by Culvert/weir over rail 22.5 44.4 23.9 0 - Diverted to Hewitts U/S Rail. 13.3 N/A 11.5 35.4 -@ Bend D/S of Rail : 24.5 45.0 25.7 4.8 - Downstream Flow aff. div. 22.2 45.0 15.2 4.5 - Diverted to Tramway 2.3 N/A 10.5 0.3 -HEWITTS CK AT :D/S Kelton Ln Bridge 42.5 41.2 43.5 41.7 41.7 41.7D/S Lawrence Hargrave Dr 54.0 51.4 53.6 55.7 53.6 46.5 53.6D/S Railway Overbridge 70.0 52.9 68.1 58.9 64.2 80.9 88.0D/S Woodlands Confluence U/S 82.0 98.5 90.7 103 79.6 83.8 90.9@ Outlet to Ocean 83.0 100 91.1 103 80.1 84.4 91.4THOMAS GIBSONS AT :North Arm u/s Rail 6.5 6.5 -Middle arm u/s Rail 6.1 6.1 -South arm Rail 1.1 8.3 -North arm @ cnr bath +McCauley 14.5 14.5 -South arm @ McCauley (u/s 122) 7.2 5.8 -North and south arms div toFlanagans Ck (Flanagans)14 14.8 -North and south arms div to Ocean 12.3 10.2 -Peak WBNM2001 flows are shown shaded52


Hewitt’s Creek Flood Study December 2002Wollongong City CouncilModel ApplicationTABLE 6.2PREDICTED PEAK DISCHARGES - 2% AEP DESIGN EVENTSSLACKY CK AT :KEY LOCATIONRORB 12% AEP Peak Discharge (m 3 /s)RAFTS-XP 2 WBNMV2 3 PSxRMV8 4 All Clear Policy 5WBNM - 2001BlockedAbove Coal Haulage Culvert 50.0 48.1 33.7 Accepted by Culvert 38.8 39.9 0 Diverted to Tramway 11.2 8.2 33.7D/S Rail Overbridge 50.9 20.6@ Outlet to Ocean 56.0 26.1TRAMWAY CK AT :MixedModeU/S Railway Culvert 14.4 9.7 34.6 49.5@ Outlet to Ocean 22.0 27.7 30.9 52.3WOODLANDS CK AT :D/S Highway Culvert 41.5 41.5 41.5U/S Railway Culvert 43.1 42.5 42.5 Accepted by Culvert/weir over rail 23.2 24.8 0.9 Diverted to Hewitts U/S Rail. 19.9 17.8 41.7@ Bend D/S of Rail : 25.6 27.0 5.6 Downstream Flow aff. div. 22.8 15.9 4.9 Diverted to Tramway 2.8 11.2 0.7HEWITTS CK AT :D/S Kelton Ln Bridge 49.9 49.5 49.5 49.5D/S Lawrence Hargrave Dr 63.9 62.5 55.4 62.5D/S Railway Overbridge 85.5 79.7 97.2 104.3D/S Woodlands Confluence U/S 108.7 95.9 100.6 107.7@ Outlet to Ocean 109.3 96.7 101.3 108.5THOMAS GIBSONS AT :North Arm u/s Rail 7.7 7.7Middle arm u/s Rail 7.2 7.2South arm Rail 2.7 9.9North arm @ cnr bath +McCauley 16.6 16.6South arm @ McCauley (u/s 122) 8.7 8.2North and south arms div toFlanagans Ck (Flanagans)17.5 18.3North and south arms div to Ocean 13.3 11.2Peak WBNM2001 flows are shown shaded53


Hewitt’s Creek Flood Study December 2002Wollongong City CouncilModel ApplicationTABLE 6.3PREDICTED PEAK DISCHARGES - 1% AEP DESIGN EVENTSSLACKY CK AT :KEY LOCATIONRORB 11% AEP Peak Discharge (m 3 /s)RAFTS-XP 2 WBNMV2 3 PSxRMV8 4 All Clear Policy 5WBNM -- 2001BlockedAbove Coal Haulage Culvert 53.0 58.0 61.5 55.0 41.9 Accepted by Culvert 29.0 40.0 30.7 42.2 0 Diverted to Tramway 24.0 18.0 30.8 12.8 41.9D/S Rail Overbridge 55.2 22.5@ Outlet to Ocean 61.3 30.1TRAMWAY CK AT :MixedModeU/S Railway Culvert 28.0 21.8 14.5 43.1 56.7@ Outlet to Ocean 35.0 30.4 33.5 38.9 60.6WOODLANDS CK AT :D/S Highway Culvert 48.2 59.8 48.2 48.2U/S Railway Culvert 55.0 70.0 50.0 62.4 49.4 49.4 Accepted by Culvert/weir over rail 23.9 62.4 25.6 4.5 Diverted to Hewitts U/S Rail. 26.1 N/A 23.8 44.9@ Bend D/S of Rail : 26.6 62.7 28.2 6.4 Downstream Flow aff. div. 23.3 62.7 16.4 5.3 Diverted to Tramway 3.3 N/A 11.8 1.1HEWITTS CK AT :D/S Kelton Ln Bridge 60.0 56.8 62.7 57.5 57.5 57.5D/S Lawrence Hargrave Dr 75.0 71.9 74.1 80.8 71.3 64.4 71.3D/S Railway Overbridge 95.0 73.9 102.2 83.8 91.8 110.7 117.7D/S Woodlands Confluence U/S 112 140 126.0 146.0 111.6 115.3 122.3@ Outlet to Ocean 122 142 126.8 147 112.4 116.1 123.1THOMAS GIBSONS AT :North Arm u/s Rail 8.8 8.8Middle arm u/s Rail 8.3 8.3South arm Rail 4.4 11.4North arm @ cnr bath +McCauley 18.7 18.7South arm @ McCauley (u/s 122) 10.6 10.2North and south arms div toFlanagans Ck (Flanagans)21.0 21.7North and south arms div to Ocean 14.6 12.4Peak WBNM2001 flows are shown shaded54


Hewitt’s Creek Flood Study December 2002Wollongong City CouncilModel ApplicationTABLE 6.4PREDICTED PEAK DISCHARGES - PMP DESIGN EVENTSSLACKY CK AT :KEY LOCATIONPMF Peak Discharge (m 3 /s)RORB 1 RAFTS-XP 2 WBNMV2 3 PSxRMV8 4AllClearsWBNM - 2001Policy 5BlockedAbove Coal Haulage Culvert 159.9 125.4 135.1 Accepted by Culvert 55.3 61.6 0 Diverted to Tramway 104.6 63.8 135.1D/S Rail Overbridge 95.8 39.4@ Outlet to Ocean 121.0 66.4TRAMWAY CK AT :MixedModeU/S Railway Culvert 117.8 68.0 139.8 139.7@ Outlet to Ocean 147.1 95.1 184.6 184.6WOODLANDS CK AT :D/S Highway Culvert 126.4 106.1 106.1D/S Railway Culvert 133.1 111.2 111.2 Accepted by Culvert 32.2 51.4 39.5 Diverted to Hewitts U/S Rail. 100.9 59.8 71.7@ Bend D/S of Rail : 42.0 58.9 46.9 Downstream Flow aff. div. 31.0 32.2 26.0 Diverted to Tramway 11.0 26.7 20.9HEWITTS CK AT :D/S Kelton Ln Bridge 132.2 107.1 107.1 107.1D/S Lawrence Hargrave Dr 179.0 132.4 125.0 132.4D/S Railway Overbridge 290.5 202.0 206.6 214.0D/S Woodlands Confluence U/S 327.7 239.0 237.1 244.6@ Outlet to Ocean 334.2 245.6 243.8 251.3THOMAS GIBSONS AT :North Arm u/s Rail 14.1 14.1 -Middle arm u/s Rail 13.7 13.7 -South arm Rail 14.7 22.2 -North arm @ cnr bath +McCauley 27.3 27.3 -South arm @ McCauley (u/s 122) 29.6 39.4 -North and south arms div toFlanagans Ck (Flanagans)39.8 49.2 -North and south arms div to Ocean 26.9 28.3 -Peak WBNM2001 flows are shown shadedNOTES: 1. RORB modelling from "Hooker Land Development - Thirroul Stage V Major ConstraintsStudy Summary" by GHD (1989)2. RAFTS-XP modelling from "Review of Sandon Point LES" (1994) by Mitchell McCotter,(1993).3. Capacity of culverts under road and coal haulage embankment are highly dependent ondegree of blockage. WBNMV2 assumed one of the three cells beneath the coal haulage55


TABLE 9.9.1 PRIORITISATION OF WORKS - RECOMMENDED SCHEMES SCHEME SB (DIVERSION TO TRAMWAY FORMALISED) Estimated Priority LevelCostS 1.00 Ocean outfall Develop opening policy $ 6,000 HighS 1.02 Footbridge to Blackall St Flow training wall south bank $ 231,000 LowS 1.06 Princes Highway to Rail line Reconfigure basin outlet (to reduce nuisance flows into $ 29,000 HighBeacon Ave)S 1.09 Old mine rail Formalise diversion (at old rail) HighSee TB1S 1.10 Hobart St Formalise diversion (at Hobart) HighS 1.11 William St to Hobart St Channel enlargement and stabilisation $ 165,000 LowS 1.11 William St to Hobart St Sediment basin $ 105,000 MedS 1.12 William St Formalise overland flowpath $ 78,000 MedS 1.13 Rex Ave to William St Sediment basin $ 105,000 MedS 1.13 Rex Ave to William St Restore pre Aug 98 capacity $ 148,960 LowS 1.13 Rex Ave to William St Coarse debris trap $ 17,000 HighS 1.03 Southern Tributary - mine basin Retarding basin $ 518,000 LowS 2.03 Southern Tributary - mine basin Request mine owner to expedite rehabilitation of mine site $ - High(works to be carried out by owner)Total Scheme Cost $ 1,402,960T SCHEME TB1 (DIV' FORMALISED - CULVERT UPGRADE) Estimated Priority LevelCostT 3.01 Ocean outfall Develop opening policy $ 6,000 LowT 3.03 Rail line High flow culvert/bridge $ 640,000 HighT 3.04 Princes Highway to Rail line Formalise overland flowpath $ 1,340,000 MedT 3.04a Princes Highway to Rail line Voluntary purchase offer $ 600,000 HighTotal Scheme Cost $ 2,586,000W SCHEME WA (HIGH FLOW CULVERT AT RAIL) Estimated Priority LevelCostW 2.01 Diversion to Hewitts Re-divert Woodlands Ck to Tramway Ck $ 172,000 HighW 2.01a Near Sewer Pumping Station Channel enlargement and stabilisation $ 240,000 LowW 2.03 Rail line High flow culvert/bridge $ 640,000 HighW 2.04 Princes Highway to Rail line Modify safety ramp and provide sag $ 70,000 HighW 2.04 Princes Highway to Rail line Levee north bank $ 103,000 HighW 2.05 Princes Highway Sediment basin/debris control structure $ 177,000 LowTotal Scheme Cost $ 1,402,000H SCHEME HA (LEVEE AT CORBETT AVE) Estimated Priority LevelCostH 1.00 Ocean outfall Develop opening policy $ 6,000 HighH 1.02 Adjacent to Corbett Ave Levee north bank $ 196,000 HighH 1.05 LHD to the Rail line Voluntary purchase offer $ 300,000 HighH 1.05 LHD to the Rail line Rehabilitate creek channel $ 360,000 LowH 1.08 Lachlan St Culvert inlet improvements High$ 82,000H 1.08 Lachlan St Formalise overland flowpath HighH 1.09 Kelton Ln to Lachlan St Channel enlargement and stabilisation $ 193,000 MedH 1.11 Bangalow Rd to Kelton Ln Restore pre Aug 98 capacity $ 241,000 MedH 1.11 Bangalow Rd to Kelton Ln Coarse Debris trap $ 17,000 HighTotal Scheme Cost $ 1,395,000H SCHEME HS4-A (FLOOD/PROPERTY MOD'S - VIRGINIA TCE) Estimated Priority LevelCostH 4.03 Stream 4 - Virginia Tce Culvert mod's (to reduce surcharge freq'y) $ 136,000 HighH 4.03 Stream 4 - Virginia Tce Property modification (flow deflectors) $ 107,000 HighH 4.04 Stream 4 - Deborah Ave Coarse debris trap $ 17,000 HighTotal Scheme Cost $ 260,000TG SCHEME TGB (PROVIDE OVERLAND FLOW PATHS) Estimated Priority LevelCostTG 1.00 Ocean outfall - North Arm Develop opening policy $ 6,000.00 HighTG 1.00 Ocean outfall - North Arm Lower south bank $ 79,000.00 HighTG 1.01 The Esplanade - North Arm Expand floodway $ 124,000.00 LowTG 1.03 Macauley St to Cliff Pde - North Arm Raise Kerb/Driveway $ 14,000.00 HighTG 1.04 Macauley St - North Arm Investigate culvert inlet improvements $ 50,000.00 LowTG 1.08 Rail Line - North Arm Investigate culvert inlet improvements $ 50,000.00 LowTG 1.08 Rail Line - North Arm Debris Control Structure $ 94,000.00 LowTG 1.12 Sea Foam Ave - North Arm Raise Kerb/Driveway $ 28,000.00 HighTG 1.13 Phillip St to Sea Foam Ave - North Arm Culvert and Overland flow path $ 315,000.00 HighTG 2.03 Rail Line to Raymond Rd Check condition and rehabilitate pipe drainage $ 32,000.00 LowTG 2.03a Station St diversion - Station St Overland flow path $ 90,000.00 LowTG 2.04 Rail Line Investigate culvert inlet improvements $ 50,000.00 MedTG 2.07 Phillip St to LHD Overland flow path $ 92,000.00 MedTG 3.00 Ocean outfall - South Arm Develop opening policy $ 6,000.00 LowTG 3.00 Ocean outfall - South Arm Reduce diversion to north $ 86,000.00 HighTG 3.01 Cliff Pde Improve culvert capacity $ 128,000.00 MedTG 3.02 Macauley St to Cliff Pde to Blackall St Modify Existing Flood Gate $ 7,000.00 HighTG 3.02 Macauley St to Cliff Pde Debris Control Structure $ 94,000.00 MedTG 3.02 Macauley St to Cliff Pde Overland Flowpath $ 127,000.00 LowTG 3.03 Macauley St Modify culvert inlet $ 65,000.00 MedTG 3.05 Thomas Gibson Park outlet Formalise existing detention basin $ 135,000.00 HighTG 3.05 Thomas Gibson Park outlet Debris control structure $ 94,000.00 LowTG 3.10 Lachlan St to LHD Overland flow path $ 85,000.00 HighTotal Scheme Cost $ 1,851,000Total Combined Scheme Cost $ 8,896,960

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