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 104 of 139. I I I I I I I I I i i i i i i i I I I I NOTE 7 NOTE 8 NOTE 9 NOTE 10 NOTE [1 NOTE P NOTE 13 ,\n uncontrolled outlet at bed lewl has enormous erosion potential if some form of energy dissipation is not provided at the downstream end of the [ow level outlet. The type oi outlet depends on the size of the pipe, the water levei in the dam. and the downstream water level. For ease of comparison, ail pen'ormances are measured immediately downstream of the dam, based on a design 9 hour storm as derined in Australian Rainfall and Runoff. Peak flows ior the partially full option assume that the dam is at minimum water level at the commencement of the storm. The dam takes time to empty (at [east 26 days from full for a 5 m3/sec outlet) and it is possible for noods to foilow closely after one another (eg. Jan 1983 nood). The flows given in brackets are the peak nows which would occur if the dam had not drained bdow the control spiilway level prior to the occurrence of the next t1ood. The most likely peak flows would fall between these two extremes. Times are measured in hours from the commencement of the storm. The additional warmng time can be determined by calculating the difference between the times given and those for the "no dam" case. Warning times in Alice Springs can differ from these due to a number of factors induding the effect of the Charles River. This aspect is discussed more fully in the EIS, and section 4 of this report. The time to reach 200m3 Is is infinite because the peak discharge immediately downstream of the dam is less than 200m31s if the dam was at minimum water level a~ the start of the flood. All dam options have a spiilway channel on the eastern side of the river dovm which the control and main spillways discharge (main spillway only for the "empty' dam). The values given are the average frequency (in years) of !loads which will cause a discharge down the spillway channel. This is relevant because sand for replenishment of the river bed downstream of the dam is to be placed in the spillway channeL If nows in the spillway channel are infrequent, alternative proposals for introdLlcing sand for replenishment are required such as placing sand in the river channel itself. This would cause undesirable disturbance within the river channel. The time taken to empty the dam has been calculated as the time taken for the dam to empty from EL 658 assuming there is no further innow. Clearly the actual time taken to empty will depend on any tlow continuing to enter the storage. This is more relevant tor small pipe SIzes. For