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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 147 of 153. I I I I I I I I I I I I I I I I I I I I 44 TABLE 7 SETTLING VELOCITIES OF SEDIMENTS IN WATER AT 16 0 C (AMERICAN GEOPHYSICAL UNION CLASSIFICATIONS) SEDIMENT CLASS ABBREVIATION DIAMETER SETTLING (mm) Velocity (m!s) Very Coarse Sand VSCa 2.000-1. 000 0.27 - 0.15 Coarse Sand CSa 1. 000-0.500 0.15 - 0.07 Medium Sand MSa 0.500-0.250 0.07 - 0.03 Fine Sand FSa 0.250-0.125 0.03 - 0.01 Very Fine Sand VFSa 0.125-0.062 102 - 3.0xl0- 3 Coarse Sil t CS 0.062-0.031 3.0xlOa - 8.2xlO-' Medium Silt MS 0.031-0.016 8.2xl0-' - 2.0xlO4 Fine Silt FS 0.016-0.008 2.0xlO-' - S,2xlO- s Very Fine Silt VFS 0.008-0.004 5.2xlO s - 1.3xlO-s 3.4.3 Discussion The estimates of capacity depletion in Table 4 'and the estimates of time to fill the reservoir with sediment are conservative for two reasons. Firstly, Brune's method flakes no allowance for flow through velocities which would be expected to be significent because of the short length of the reservoir. Camp's method shows that trap efficiences decrease as flow through velocities increase. This result is ' hinted at in deriving the 5% trap efficiency estimates' (Table 5) using Brune's method. Secondly, no differentiation is made between particle sizes in Brune 1 s method. Camps method shows (Table 6 ) that only VFSa, CS, and MS fractions are likely to be trapped at a trap efficiency in the order of 95%. Better estimates of useful reservoir capacities and reservoir life will require the measurement of suspended sediment particle size fractions. These measurements are not available at present.

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