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 108 of 139. I I I I I i I I ~ ~ ~ ~ j , NOTE 26 NOTE 27 NOTE 28 NOTE 29 NOTE 30 mean annual sediment load (bed and suspended) of 71.000 lonnes/annum of '.\Inicn 42500 lonnes/annum enters the dam, and do not include material deposited in the sediment traps. Refinement of the sediment trap pen-orrnance based on up-lo-date survey of the impound areas has indicated an ability to retain a pOnIun or" the courser silts as well as the intended bed load fractions. This has resulted in a reduction in the estimated quantity or" sediment entenng the dam with a particular reduction in the coarser components. For the empty dam ease where only the coarser fractions are retained, there has been a corresponding reduction in the estimated annual deposition in the dam. This is because panicies which previously had deposited within the dam are now deposited in the sediment traps. For the full dam, a refinement of the sedimentation mooei to take into account the dilution of incoming sediment by the volume of the dam has indicated a slightly higher sediment retention than previously estimated. The results for the range of outlet capacities for a partially full dam show a logical progression between the "empty" dam and "full" dam results reflecting the progressively longer period of flow detention. The narrow gorge at the Junction Waterhole size cause some minor retention of floods down the river. Thus some deposition of sediment occurs natural! y within the area upstream, although this wouid be much smaller than after construction of the dam. A proportion of deposition wiii occur below the permanent water level ana will not be seen. Deposition of sediment wiiI occur in the area upstrea.'11 of the dam whilst n is temporarily inundated. This will result in a blanket of silty materialleit behind over the area temporarily inundated, which wiiI build up in time. Some deposition will occur In the water pool. Deposnion of sediment wili occur in the area upstream of the dam whilst it is temporarily inundated. This will result in a blanket of siity material left behind over the area temporarily inundated, which will build up in time. 11le build up in sediment within the storage of the dam may cause some loss in t100d mitigation performance. This column notes the extent to which this reduces flood mltigation performance.