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Alice Springs recreational dam hydrology report project 6



Alice Springs recreational dam hydrology report project 6


Jackson, D.; Paige, D.


E-Publications; E-Books; PublicationNT; Report no. 12/1979







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Northern Territory Government

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Report no. 12/1979

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Attribution International 4.0 (CC BY 4.0)

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Northern Territory Government



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Technical Report WRD79012 Viewed at 00:02:46 on 18/02/2010 Page 149 of 153. I I I I I I I I I I I I I I I I I I I I 46 Following on from the assumption that all bed load is trapped, a comparison between bed load and demand for sand was made. In section 3.2 bed load transport for this section of the river was calculated to approximate the 1979 relationship for suspended sediment load at GS006009. From table 3, the median annual load for this case was 8,400 tonnes while the mean annual load was 16POO tonnes. Estimates of river sand demand for the Alice Springs region based on withdrawal permits i$sued by the Water Resources Branch since 1969 show a mean annual demand of 20,000 m 3 or 53,000 tonnes. This demand figure is an underestimate since it takes no account of other sources of construction sand and gravel. In addition the withdrawal permit system was not policed and by itself would give a lower bound for demand. The figures have no definite trend and follow variable levels of build~ng and construction activity. Future demand is likely to increase as future developments in Alice Springs will require landfill in many cases. On comparing the estimates of bed load and sand and gravel demands, it is apparent that on average, demand will exceed trapped bed material. A wall 2m high will provide 70,000 mO of storage. This capacity is sufficient for bed load from historical floods having return periods of up to 25 years. Most of these floods have bed load volumes in the range 10,000-40,000 mO. During a wet period when flows are sustained or during very high return period floods, the available sediment storage capacity may be filled and bed load material will spill into the reservoir. This spillover is not expected to affect the reservoir significantly because: by the time the sediment trap is filled, a delta will have formed upstream of the sediment trap, thus reducing water slopes and transport capacity for the river section. any bed material in the reservoir will occupy a very small percentage of the total reservoir capacity (1.5% for a spillover of 70,000 m'). the bed material will deposit in the reservoir immediately downstream of the sediment trap where it is easily excavated.