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 107 of 139. I I I I I , , -, ~ ~ j ~ i I I NOTE 22 NOTE 23 NOTE 24 NOTE 25 This coiumn notes whether it is possible to carry out sediment replenishment without disturbing the river channel with earthmoving equIpment. All discharges from the dam pass through the spillway channel. and hence sand can be stoclq)lled in the low now channel rathe! than having to place it in the river channel. (refer Section 6.05 of EIS). The pipe under the dam discharges directly into the river whereas the control spillway and main spiilway discharge into the spillway channeL Large Hoods (ie greater than 25 year) will still discharge into the spiilway channel and hence sand can be placed in the low now channel of the spillway channel for these larger !lows. For a small pipe under the dam, degradation b -. :ween larger t100ds should be minor, and it may only be necessa.-y to place sand in the spillway channel. Bed levels would be monitored and if long term degradation occurred, sand may have to be placed in the river channel as weil as in the spillway channeL As the size of pipe below the dam increases in size then it becomes increasingly more likely that sand will need to be placed within the river channel, as well as in the spillway channel. The spillway channel is only used for t100ds greater than a 100 year (1 % AEP) t100d. Therefore sand replenishment needs to occur within the river channel downstream of the outlet. Flood flows entering a flood mitigation dam are stored temporarily within the dam before being more gradually released. [n the case of the "full" dam. some of the water is retained. This temporary retention ot 1100d waters common to all flood mitigation dams causes some of the sediment to settle out within the storage. In general, the longer the water is stored in the dam, the more sediment is settled out. The tigures quoted represent the estimated mean annual deposition of sediment within the dam. The coarser fraction will be deposited in the sediment traps and is not included. Estimates were prepared by estimating the quantity of sediment deposited for a couple of representative design hydrographs using Vanoni's relationship derived for steady now in uniform rectangular channels. Quite cleariy this differs from the real situation with a variable water pooi. non uniform section and unsteady t1ow. however it is of interest for comparisons between dam options. Estimates are based on an existing
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