Agenda Item 9.3
Report No: 32/16ts
TO: TECHNICAL SERVICES COMMITTEE - MONDAY 14 MARCH 2016
SUBJECT: ALICE SPRINGS FLOOD INVESTIGATION AND FLOODPLAIN MAPPING STUDY
AUTHOR: TECHNICAL SERVICES ADMINISTATION ASSISTANT - RAE-ELLEN SWINDELLS
EXECUTIVE SUMMARY
This report is regarding the Alice Springs Flood Investigation and Floodplain Mapping Study.
RECOMMENDATION That it be a recommendation to Council:
That this report be noted.
REPORT
1. BACKGROUND
“WRM Water & Environment was commissioned by the Department of Lands, Planning and the Environment to undertake a flood study of the Todd River in the Alice Springs area.”
As a result the Alice Springs Flood Investigation and Floodplain Mapping Study report was release in October 2015.
2. DISCUSSION
The report was tabled at the Development Committee meeting held on the 7th March 2016 the Committee requested a summary report be included at the March Technical Services Committee meeting for further discussion.
3. POLICY IMPACTS
Nil
4. FINANCIAL IMPACTS
Nil
5. SOCIAL IMPACTS
Nil
6. ENVIRONMENTAL IMPACTS
Nil Report No 32/16ts Agenda item. 9.3
7. PUBLIC RELATIONS
Nil
8. ATTACHMENTS
Attachment A - Extracts from the Alice Springs Flood Investigation and Floodplain Mapping Study
Rae-Ellen Swindells TECHNICAL SERVICES ADMINISTRATION ASSISTANT
Greg Buxton DIRECTOR TECHNICAL SERVICES 0269-02-C1 12 October 2015 Mmm water+environment
1 INTRODUCTION
WRM Water & Environment (WRM) was commissioned by the Department of Lands & Planning (DLP) to undertake a flood study of the Todd River in the Alice Springs area. The aim of the study is to develop a 2 dimensional flood model, which allows flood flow in a complex flood plain to be modelled, to determine the extent and severity of riverine flooding in the town of Alice Springs and the Alice Springs rural area south of Heavitree Gap. The purpose of the study is to produce floodplain maps of the Alice Springs and its rural area for land use planning and counter - disaster purposes. This study is an extension of the Alice Springs Farms Area Floodplain Mapping Study (WRM, 2006), undertaken by WRM on behalf of the Department of Planning & Infrastructure in 2006 in order to develop detailed Todd River floodplain maps for the rural area south of Alice Springs.
The town of Alice Springs is situated on the banks of the Todd River, north of Heavitree Gap. The north-western extents of Alice Springs are located adjacent to the western bank of the Charles River, a major tributary of the Todd River. The Charles River joins the Todd River at Anzac Hill, immediately to the north of the Alice Springs CBD, and approximately 4.2km north of Heavitree Gap. The Alice Springs rural area is located on the floodplain of the Todd River to the south of Heavitree Gap, and extends approximately 9km south-east to the Amoonguna settlement.
Both the township of Alice Springs and the rural area are potentially impacted by flooding from the Todd River (including the Charles River) as well as the various local drainage systems, including the town stormwater drains and Chinaman’s Creek north of Heavitree Gap, and llparpa Swamp, St Mary’s and Emily creeks south of Heavitree Gap. This investigation is mainly focused on riverine flooding from the Todd and Charles rivers, and should not be used to determine design flood levels or extents for any of the local drainage systems described above.
The Todd River catchment covers an area of 525km2 to the Heavitree Gap and extends some 35km to the north-east of Alice Springs. Through the study area, the Todd River has a wide and shallow channel with a sandy bed. The over bank areas are very flat with overflowing floodwater inundating large areas of land to shallow depths. The Todd River catchment and its drainage network upstream of the study are shown in Figure 1.1.
This report describes the work undertaken to calibrate and test the hydrological and hydraulic models developed for the Todd River and its floodplain and how these models were used to define design flood levels, flood depths, velocities and provisional flood hazard. Two numerical models were developed to simulate the Todd River flooding behaviour.
• An URBS hydrologic model was developed to estimate flood discharge hydrographs for a range of design floods from the 20 Year Average Recurrence Interval (ARI) to the Probable Maximum Flood (PMF) draining to the study area. • A TUFLOW (fully two dimensional) hydraulic model was developed to estimate design flood levels and the extent of flooding for the above range of design floods.
This report contains a further 11 sections and is structured as follows:
• Section 2 describes the Todd River catchment and the study area;
1 0269-02-C1 12 October 2015 Mmm water+environment
Figure 1.1 Todd River Catchment to the Alice Springs Rural Area
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[ | Pluviograph Station A Streamgauging Station 'A' Puviograph and Streamgauging Station □ Catchment Boundary Alice Springs
Figure 3.1 Rainfall and Stream Flow Gauging Station Locations, Todd River Catchment
11 Northern Territory fwrm w Government water+environment ALICE SPRINGS FLOOD MAPPING TOWN AREA - Sheet 1 COMPUTED 1% AEP (1 in 100 Year) FLOOD EXTENT and PEAK FLOOD SURFACE CONTOURS
This map shows the Mood end Headway extents In and around tho Town ol Allen Sprains caused by e ■ md ol 1% Am wot Exroodoncc PmbebUry (ACP) swerty Depth 0.0 - 0 Tho extent and Hooding shewn this map Is approximate only. This man Flood extent avail»Mi> lot sail ft mm Depth 0.1G-2.0 mslroa Lend Inlormetlon Centres Flondwey urea Department ot Lends, Planning and the Environment Depth x Vslooly Enuuli Lvidln/o^m gov *1 Ground Plaor Amhsimca House, 10 Parop Road. DARWIN. Northern Tonliory 0020 Depth > 2.0 metres T; (OB) 89D5 5300. F: I0B) 8995 0305. PO Dox IC80. Oarmn, NT 0801 sszwsMtta Rlvor channel, How diieciloii T: (01) 8951 9200. P: (08) 8951 922?. PO Oox 2130. AUce Springs, NT 0871 Lmilt ol Mood mapping This map Is nlso ovaHoblo onlmu ot: W.v55»vl4'< Properly boundar.es (Oct. 2015) www.lrni.nl.gov.iu/nrmapsnlwww.nLgov.au/llooda Road ccnlrelmoc " Dndpo. couseway
This mop flhowmp llio 1% AEP (1 hi 100 yeor) Mood atfont. Is based on IIk> ;~T1 Par* or Reserve houndflry modriind rosulls Horn llio rcparl ANco Springs Flood Investigation miri Floodplain Mapping Study. Report No. 0269-02-CT October 2015. I*y WRM Water A Environment Pty Ltd 2 Thu Hood model is based on Alice SpiinQS town and mini rlwvelopniant ns Alice Springs Talugraph Station Hietorlcal Reserve Index t o' Adjoining 3 Floodway nren Is d«l|ned ns thnthe area where thn velocSIy x wnler dapth
Floodway is dileicd ns Ihe area where iho dipih ol lloodwaicr exceeds 2.0
5 Air. AEP Mood (ollcn referred to os tho Qwo) is d?Hnod os o Hood which has n 1 in 100 chnnce ol being equaled or exceeded In any one year 6 Tlds map Is ritnidcd to be used ot o scale ol H10.000 and eny enlargement beyond this scale does not Increase the accuracy ol iho dam appearing on tho mop oud is not roccmmoivJcd 7 An accurate Hood extent ai any location can only be obtained by a survey
For turthor Inlormetlon contact: Water Resources NT, Department ol Lend Resource Mnnngomrnt Patmorslon. Notlhem ToirlViry
PO Box d96. Palmerston. NT 0831 Prepared by Spatial Data nnd Mapping Unit, Water Resources NT Depanm*nt of Land Resource Management. Norihem Territory WA October 2015
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Northern Territory "•“•'‘Government "sfwrm ALICE SPRINGS FLOOD MAPPING RURAL AREA WEST - Sheet 2 COMPUTED 1% AEP (1 in 100 Year) FLOOD EXTENT and PEAK FLOOD SURFACE CONTOURS Thu map mows the llcod and Hoooway extents m and cround the Town ol AHc-r S|m|ih|s nnirtid liy n flwirl nl Iti Annual Exceedance Probability (AGP) severity. Flood extant (Irlngn) The ciieni and Hoodmg shown on this map is jporawmalo only, lbs map Is Dcolh 0.0-0.15 met »vaWilii for sab from. Lend fnlormstlon Centres Oeperlsient of Lands, Pfenning and the Environment Floodway nr«n Depth x Velocity Cmofl: limdmfn^iiil.pov mi Ground Floor Amnendea House, 1C Parop flood, DARWIN. Noitncin Tcmlory 0320 T: (06) 6995 MOO. Fr (96) 8995 5365. PO Bo* 1660, Darwin. NT 0601 Rook flood f.urlncn contour Ground Floor, Croon Well 0u|lrl|iv|, 50 Dolli Street, maims AHD (Interval - 0.25) AUCE SPRINGS, Northern Territory. 0870 —River channel. flow direction / X T:(03) 8951 9200, F: (03) 8951 9227, PO Bo* 2130. ABco Sprmgs. NT 0871 ------Limit of flood mapping This map is olio available online at. iMfSProperly boundnrloo (Oct. 2015) www.lrm.nt.gov.au/nrmaptnlwww.nt.gov.aii/floode Road centrelines »—< Brldoo. cousowny
1 Tlib mop shewteg tiio 1% AEP (1 in 100 y*ar) flood extent. Is bosod on tin I. ~i Park nr Reserve boundary modelled results from tho repon AJko Springs Flood Investigation and Floodplain Mapping Study. Report No. 0268-02-C1 Octobor201S. by WRM V/atcr & Fnwcnm?nt Pty Ltd 2 The flood modnl Is based on Allco Springs town and rural development ns Indox to Kity)©M' 3 Floodway area Is defined as tho area where the velocity x wafer depth Adjoining Shoots a Flocdway n defined as tho area where the depth or floodwaicr exceeds 2.0
s Air. AEP flood (often rufsrrod to ns the Quo) Is defined ns o flood which 7/ has a 1 In loo ennnea of bomg equalled or axceedid in anyone yea/ fl This mop In Intended lo bo uoed nl n ooolo of Vi0.000 mid any enlargement beyond ihis scam doos not increase the accuracy of the data opining on lit* map and Is not tecommindsri j: 7 An accurate Hood extent nl any locnllcn can onlv bo obtained by n survey traverse from a known location i* <•-'
For further Information contact: Water Resources NT. Dopanmont of Land Resource Mtnneemeni AH* Floor Gnydoi Cenlro, 25 Cluing Wall Tmtoee, Palm-nofon, NoHhern Territory T: (08) 8999 <4554455 Emell:Emell; watewecource^nlwatc*rcsovrco«fr.l gov.ouoov.DU PO Box 496, Palmerston. NT 0631 Prepared by Spatial Date end Mapping Unit. V/alcr Resources NT Depiriwnl ol Land Resource Mnoegemenl. Norlhern Territory October 201S
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