Daguragu surface water storage potential
Rajaratnam, Lakshman R
E-Publications; E-Books; PublicationNT; Report no. 6/1997
Northern Territory Government
Report no. 6/1997
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
Technical Report WRD97006 Viewed at 15:07:49 on 29/07/2010 Page 51 of 53. APPE:NDIX4 CONSTRUCTION DETAll,s OF EXCAVATED TANKS AND TURKEV NESTS 1. CONSTRUCTION OF EXCAVATED TANKS: This is a square or rectangular excavation cut below the natural surface. The site is first cleared of vegetation. The spoil should be dumped away from the site. The excavated material is usually stockpiled in the form of a bund, where a minimum berm width of 20m must be provided to ensure the bund not being washed back into the tanle The tank is fenced on three sides with the bund. Bund materials should be suitable, and sheepfoot rollers have to be used for compaction. This type of fenced excavated tank is economical if the ground slope is greater than 1 percent because there would be active storage above ground level. This type of storage is known as the hill side storage and is shown in Fig. 3. In most cases the land area is flat, that the bund does not provide any storage above the ground level. The top soil should be removed to expose the impervious layer on which the fill should be placed in constructing the bund. Three sides of the tank have a slope of 1 on 3 and the fourth side through which the flow enters the tank, has a milder slope of 1 on 10. T}1js would allow easy excavation of the tank as machinery could go into the tank, excavate, turn and come out with ease. The side through which the flow enters is rubble packed to prevent erosion. Major contractors have the capability of constructing excavated tanks with a batter of 1 on 2.5, but as for a small contractor, the maximum batter they could handle is 1 on 3. Rippers could be used to rip Angalari Siltstone, and this is available with major contractors. The inlet channel details of the off creek excavated tank is sho"Wn in Fig. 2. The tank should be located in close vicinity to the creek. The total length of the inlet channel should not be more than lOOm. The initial 50m length of the channel should have a bedslope greater than that of the creek. The bedwidth of the inlet channel should be atleast 1.5 times that of the creek. The bedwidth in the last 50m length increases gradually to the width of the tank as shown in Fig.2. This area is rubble packed to stop erosion. A sediment trap may be constructed before the tank proper along the flow path. 2. CONSTRUCTION OF TURKEY NESTS: The black soil that is generally used to construct Turkey Nests, should not have high clay content but be well graded. The Soil Sampling and Dispersion test are recommended to check the suitability of soil for bund construction. The soil should have 20 to 35 percent clay, and the balance made up of silt, sand and some gravel. The minimum slope generally recommended is 1 on 2.5 for the inside and 1 on 2 for the outside. However in the existing turkey nests, the batter varies from 1 on 2.5 to 4. Compacting is done to increase the density of the fill. There is an optimum water content to achieve the maximum compaction. Vibratory Rollers are used for compaction because of the smallness of the bund but these may not be economical in the remote areas. Compaction is best achieved if the turkey nest is built soon after the wet when the soil is moist. Any heavy machinery available in the station without tracts could be used for compaction,
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