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 111 of 139. I I I I I I I I , ; ~ ~ ~ j j I I I ~. WARt';1:';G TIME It has previously been demonstrated in the EIS that warnmg times for the "fuil" dam are superior to those ior the "empty" dam (refer Section 5.1 of Appendix AJ. Hydrographs at Wills Terrace for a range of !loods for a "partially full" dam are shown in Figs 3 - 5 inclusive, and compared with natural hydrographs. and hydrographs for "fuiI" and "empty" dams. The following are apparent: Tne initial rate of rise of the hydrograph is not dependant on the type of dam as it is largely contro!led by downstream catchments including the Charies River. If the "partially full" dam has not had time to empty by the time the next Hood a..rrives, its performance approaches that of the "full" dam. ~. SELECTION OF OUTLET LEVEL At EL 645 the inundation area is largely restricted to the river channel and adjoining camping and gathering areas such as the Tom's Yard area remain dry. If for anv reason there is a need to do so the dam level can be lowered temporarJy to the level of the construction drain at approximately EL640. At this level the pond would be less than 4m deep and retreat up to 800m from the Tnyere Akene site. The suriace area would reduce to less than 2ha and the storage volume reduced to approximately 26ML. The level of EL645 does not represent the "permanent" water level as the effect of evaporation and infiltration will reduce the level by at least a metre for, on average more than 40 days per year and has the potential to reduce the level by up to 2.2m during extended dry periods. From a technical viewpoint it is desirable to maintain the permanent water level as high as possible, but this needs to be balanced by the impact on Tnyere Akene. Thus EL645 is a compromise between these two conr1ictmg requirements. 6. SELECTION OF OUTLET SIZE From an examination of the various factors inHuenced by the size of outlet it is recommended that the 20 m'!s option be odopted. The principal factors iniluencing this selection are: Cost: - Options up to 20 m'/s do not significantly alter the cost of the scheme however large options do increase the cost.
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