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 112 of 139. Site InundatIon: . Options down to 20 m'!s result in nooding of the site for less than 5 days per year which is not significantly greater than the frequency at' natural Hooding. Smaiier optIOns extend this period significantly. Downstream Flows: - All options provide minor improvements to the mitigation effect for small to medium t100ds and provide regular flushing flows for the downstream channel. The smaller options sIgnificantly prolong downstream t10ws with the result that the Wills Terrace crossing would be closed for UP to 30 day per year for the 5 mJ/s option. The 20 m 3/s option reduces this to 5 days per year which is not significantly greater than lor natural nooding. Bank Stability: Sedimen ration: Design difticulty: All options have an adverse effect on stability of the embankment compared with a full danl which necessitates a more conservative design. The slow rate of drawdown for smaller outlets is counteracted by the greater degree of saturation and no single option can be identified as an optimum. All options reduce the rate of sediment accumulation in the dam and the rate of degradation downstream (if no replenishment). The smaller outlets have the disadvantage oi dropping more tine sediment in the area upstream of the dam while the largest outlets have the disadvantage of greatest downstream bed degradation combined '.vith a need to add replenishment sand to the stream bed directly rather than in the spillway channel. The 20 mJ/s option represents an acceptable compromise. Options up to 20 ml/s require pipe sizes in the range of normal production and involve t10w velocities within the range lor which standard design solutions can be adopted. The larger outlets wOllld require non-standard pipes and additional model studies may be warranted to contirm the performance of inlet structures and energy dissipaters.
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