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Flood Warning and Damages in Alice Springs: Part 1 Executive Summary. Part 2 Tangible Damages Part 3 Intangible Damages & Emergency Procedures



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).





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Power and Water Authority

Place of publication

Alice Springs


Report ; 53/1989

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Technical Report WRA89053 Viewed at 03:02:00 on 18/02/2010 Page 121 of 139. I I I I I I I I I I I I I I I I I I I I G ' "-',' "...... J ' - _ J ~ i '----.--' Control Spillway The control spillway would comprise three rectangular culverts through the concrete main spillway, which would become operational once the water level in the darn rose above EL658.0. This would only be expected to occur once in 3 years on average. Each culvert would have dimensions of 5m high and 4m wide, and they would have the effect of throtting t100d t10ws up to the 100 year tlood back to within bank flow. The location of the control spillway was previously on a saddle at the head of the spillway channel Valley. Incorporating the control spillway into the main spillway has the advantage of reducing the length of the spillway channel excavation. This arrangement has been shown to operate successfully in model testing. Main Spillway The main spillway remains almost identical to that described in the EIS, and has a crest level of EL665.0. Its width has been reduced from 250m to 230m. It would only be overtopped by a flood greater than the 100 year flood. Auxiliary Spillway An auxiliary spillway totalling 680m in length would be located on some saddles at the extreme eastern end of the dam, replacing three saddle dams described in the EIS. The crest of the auxiliary spillway is mostly in cut, with a crest level of EL667.0, ie, 2m above the main spillway. It would comprise an unlined rock surface with two short and very low saddle dam embankments which would be sacrificial in the event of an extreme flood. The auxiliary spillway would discharge into the valley on the southern side of the splllway channel vailey, with flows returning to the Todd River further downstream. Discharge over the auxiliary spillway would only be significant for floods greater than the 2000 year flood. Main Dam and Saddle Dam The main dam and saddle dam would be similar to those described in the EIS although their crest level has been lowered to EL670.0. They are designed not to be overtopped by the probably ma.,imum t100d (PMF). Rather than retain all water below the level of the control spillway (EL658), the dam would gradually empty out from the control spillway down to the level of the low level outlet at EL64S. If no further water was entering from upstream, the dam would take 6.5 days to empty from EL658.0 to EL64S.0. At the level of the low level outlet (EL64S.0) the volume of water stored is approximately 300 ML, ie, only 3 % of that for the" full" dam. 3