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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 106 of 139. },;OTE 18 NOTE 19 NOTE 20 NOTE 21 The impact of the dam on "freshes" will reduce as one moves closer [0 Alice Springs and additional uncontrolled catchments contribute to tlow in the river. For exampie 20% of the river catchment at Wills Terrace (largely Charles R.) is not controlled by the dam and will continue to comnbute to the regular "freshes" although their size will obviously be reduced. Clearly the larger the pipe under the dam. the less the impact on the existing pattern of "freshes". It is sometimes difficult to visualise what various size Hows represent in physical terms in Alice Springs. One means of defining the size of the regular "freshes" is in terms of the ma,'(imum depth of flow across the Wiils Terrace causeway. Tne values quoted are the maximum depths in metres of How over Wiils Terrace causeway for "freshes" equivalent to the capacity of the outlet only. The EIS for the darn noted that a "full" dam could be used to make releases to reduce stress on the river during extended dry periods (refer Section 6.08 of EIS). 'This was seen as a potential positive impact oi the "full" dam. A darn at Junction Waterhole would have the effect of stopping the transport of sand and gravel down the river (refer Appendix G of EIS). This material would be depOSited in sediment traps and behind the dam. Discharge from the dam will be "hungry" for sand and will tend to degrade the nver bed downstream or the darn until its demand for sand is satistied. Tne EIS proposes that this degradation be overcome by carting sand in tnICks from sediment traps and fe-introducing it into the river downstream of the darn. The ligures quoted are the mean annual sand volumes estimated to be degraded from the river if a replenishment programme was not in place. Alternatively they could be considered the annual average volumes of sand which would need to be transported around the dam if bed degradation is to be controlled. Bed degradation cannot be accurately estimated but the fjgures are useful in relative terms. Units are mJ!annum. The EIS proposed that bed degradation in the Todd River be overcome by transferring sand from sediment traps into the spillway channel (refer Section 6.05 of EIS), thus avoiding potentlall y damaging earthworks in the river channel downstream of the darn.