Water Resources of the Victoria River District
Tickell, S. J. (Steven); Rajaratnam, L. R. (Lakshman)
Northern Territory. Department of Lands, Planning and Enviroment. Water Resources Division
E-Publications; E-Books; PublicationNT; Report no. 11/1998
Victoria River Region
The aim of this study is to map, describe and evaluate the region's water resources. The project was started in 1993 at the request of the Victoria River District Conservation Association (YRDCA) and it was funded jointly by Landcare, the NT Government and the purpose is to provide pastoralists and communities with water resource information that will assist with property planning. VRDCA.
Groundwater -- Northern Territory -- Victoria River; Water-supply -- Northern Territory -- Victoria River; Water resources development -- Northern Territory -- Victoria River
Northern Territory Government
Report no. 11/1998
33 pages : illustrations and maps ; 30 cm.
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
https://hdl.handle.net/10070/672982 [Water Resources Survey of the Western Victoria River District - Water Resources of the Victoria River District_WRD98011.pdf]; https://hdl.handle.net/10070/672981 [Water Resources Survey of the Western Victoria River District - Water Resources of the Victoria River District_WRD98011.pdf]
Technical Report WRD98011 Viewed at 15:07:47 on 29/07/2010 Page 24 of 37. Ofl~stream and drainage-line excavated tanks are the recommended types because they are simple to construct and have low initial and maintenance costs. The on-stream tanks on the other hand are not recommended because they are subject to large flood flows which can lead to embankment failures. Gully dams and hillside storages involve high costs in coping with the foundation conditions and flood flows. Though there may be suitable terrain in the region. thev are also not recommended. Excavated tanks with surrounding embankments are - - also not recommended because if they are not constructed and maintained to a high st311dard. their above ground storage capacity can be easily lost. On Auvergne where this type of tank has been used. they have experienced various problems including: Damages to inlet structures. and erosion ofbund around inlet structures (Plate 12) Rill erosion of the bund and silting of tanks (Plate 13) Inlet structures are inetlective. because of malfunctioning flap gates or inadequate . . pipe openmgs. Inadequate spil!tail channels which may lead to erosion of the bund during flood flows. ExcQ\'Qred rank design Factors which influence tank design include evaporation. winfall. water requirement (number of cat1le to be watered). slope. catchment area and soil type. Some of these are taken into account here in dereITrlining the dimensions of a tank designed to supply stock water during a "dry ye,"r" with 90% reliability (nine years out of ten). A full "dry year's" supply is taken to be tr,e twenty months from April soon after an awrage wet yec.r to December in the ne;;t year when rain stc.rts again. The size of the design tanks considered. varies from 60 x 60 x 2.0 to 100 x 80 x -+.0 metres. The w"ter requirement is calculated from the number of head and from an assumed aver<:.ge consumption of 50 litres per head per day. The annual bke e\aporation for the region is assumed to be 2.-1 metres/year or.j.4 metres for the 20 month period. The de?th of any storage should therefore be at least 6 metres to supply "'Her to a se\eral hundred head. In reality however the maximum depth of water retaining sqil is normally less than 3 metres. In some areas rippable shale is found below the soil and the water retaining depth can be increased to -+.5 metres or more. Even a 12 month supply would require a minimum depth of 3 metres and it would be hard to maintain 90% reliability, depending on the number of stock. The design dimensions also depend on the annual rainfall. In the northern part of the regior. where rainfill is twice the amount of that in the south. a water supply for 12 months would mean the depth should be more than 3 metres to supply a typical number of stock with 90% reliability. In the central VRD, a 9 month supply would mean the depth should be .j metres \Jr more. If the depth is between 2 and 3 metres. the supply is restricted to less than 6 months still maintaining a reliability of 90,'0. In the southern part of the region. for the same range of depths the reliability reduces to 80%. and the supply is restricted to four months or less. Tanks of moderate size (eg.60 x 60 x 2.5 to 100 x 80 x 3.5 metres) can supply 200 to .j00 head with 80 to 90% reliability for periods between 4 and 12 months. depending on the depth of tank and its location within the region. Large deep tanks can supply more than 500 head over a 12 month period. but it may not be feasible to construct them due to insufficient depth of suitable soiL The storage capacity of the design On:Stream and Drainage Line tanks is less than 1 'lo. and 2% of the average annual rainfall respectively. The surface runoff ranges up to 15 % of the average annual rainfall for large catchments but small catchments c>f a uniform nature may yield more than 25%. 20