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
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Power and Water Authority
Report ; 53/1989
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Technical Report WRA89053 Viewed at 03:02:00 on 18/02/2010 Page 105 of 139. NOTE 14 NOTE is NOTE 16 NOTE 17 "h'JU',!I1tl'T example a "pamaily full" dam with an outlet capacny of Sm)/s would not begin to drain until the 110"1 in the river from upstream is less than the discharge through the pipe. For larger pipe sizes, now in the river fairly quickly drops below the discharge capacIty of the pipe and the dam therefore stam to drain. The "full" dam would not normally be emptied below EL 658. Some variation in water level would occur as a result of evaporation but this would nonnally only be in the order of a couple of metres. TIle" full" dam can be drained for maintenance purposes through a pipe in the bottom of the dam. and would take less than a month to drain. During public consultations about the dam. concern was expressed that regular freshes" which occur in the river would not be experienced following construction of the dam. Exactly what now constitutes a "fresh" has never been defined. however Appendix 0 of the EIS deals with this matter. "Freshes" currently occur on average 2 - 3 times per year. A "full" dam is estimated to reduce the mean annual flow in the river by 12 - 13 %. but only have a negligible impact on the frequency of regular If freshes!t Refer Appendix "0" of EIS. A "partially fuiI" dam would have negiigible impact on the frequency of freshes in the river. but would have an j'mpact on the size and duration of the nows. Because discharge throug,h the control spillway or over the main spillway would occur infrequently. the balance of t10ws will be restricted to the capacity of the pipe below the dam (low level outlet). Thus ior a partially full dam with a 5mJ/s capacity low level outlet. "freshes in the river immediately downstream of the dam would be restricted to 5mJ/s except for the occasional larger t10ws which would occur on average once or twice per ye:.ir. The river would however 110"1 at close to 5mJ/sec for an average of more than 37 days per year. For a partially full dam with a lOOml!s capacity pipe, "freshes" in the river downstream of the dam would be restricted to IOOm3/, except for the occasional larger llows which occur on average once in 2-5 years. TIle river would t10w at more than 5mJ/sec for an average of only 5 days per year,