Flood Warning and Damages in Alice Springs: Part 1 Executive Summary. Part 2 Tangible Damages Part 3 Intangible Damages & Emergency Procedures
Handmer, John; Smith, D. I.; Greenaway, Mark
E-Publications; E-Books; PublicationNT; Report ; 53/1989
Made available via the Publications (Legal Deposit) Act 2004 (NT).
Power and Water Authority
Report ; 53/1989
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Technical Report WRA89053 Viewed at 03:02:00 on 18/02/2010 Page 22 of 139. - - -' - -- - -- ~~'--~ .. ~. --.-.. ---.~-.~~ r-----------------------------------~ .. ~ .. ~ ... ~.= ... ~~~ -,--- .--.--.--~~'~ found in other studies undertaken elsewhere ~n Aust~alia. The original Alice Sp~i~gs ANUFLOOD study ~as unde~ta%en i~ 1986 and formed the basis for initial floodplain manageme~t strategies for the co~~cni~y. The occur~ence of the Todd River flood of Easter 1988 provided the oppor:unity to p-stimate the actual, as opposed to poten::.ial, damages. However, before p~oceeding it is necessa~y to add :~at the flood hydrology of the Todd River at Alice Springs poses a number of difficult problems. The rive:c is no:cmally d~y and floods are infrequent. Thus it is difficult to calibrate model-based hydrological flood studies against reality. The gauging record for the Todd River at flood flows is spa:cse and calibration of flood levels against measured discharges uncertain. Finally, :he ~iver's course through the built-up area of Alice Springs has a mobile sand bed, it is not contained within well-defined banks, and is liable to minor changes in flow due to va:cious natural and man-made obstructions. Methods and Sources for Direct Damage Estimation The standard approach, for an urban cOITLr-uJ.nity for ~ .. ;hich ANUFLOOD residential and commercial data are available. is to define the limits of the flood, corr~ine these with the data on the flooded properties, employ the approp:cia:e stage-damage curves and obtain an estimate of damage. Each of these steps will be described. Flood Limits The problems with uncalibrated model s:udies have been mentioned. The approach ~sed for the Easter ::ood ~as to combine informatio~ provided by the Powe~ and ~ater Authority on the t=~m line, the flood linit, ~rom wi~hin che built up area of Alice Springs wit~ information obtained by the eRES stt:dy. 'The la:ter related to depths of water associated with residential and commercial property included in the damage surveys. These two sources provided 40-50 points at which the maximum height of the flood was accurately known. They represent spot heights to which a flood surface could be fitted. The irregularities of flow on such a mobile bed with a ~ange of minor obstructions. natural and ~an-made. are many and the form of the su~face of the maximum Easter flood heightis ir:cegular. 'The surface fitting was undertaken using advanced compute~ techniques that included Laplacian spline smoothing methods. These were develooed as advanced contou:cing packages (Hutchinson, 1989). 'The surface fitting procedures 'were run on a number of occasions to obtain the best fi: to the data. A small number of the original points were omitted, as inaccurate or poorly recorded. We are confident that the final form of the flood slooe is the best that can be obtained and the detail, in" computer compatible form, will be made available to the ?ower and Water Author~ty for any subsequent studies. I I I I I I I I I I I I I I I I I I I I