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 27 of 37. PRESElvT f~ATER USAGE Stock bores are spaced widely and are pumped at comparatively low rate$, so the present usage would have to be rated as fairly low. There is no evidence of wide$pread ground water level decline over time, related to the increasing number of bores, ego progressive lowering of pumps. During droughts however watertables would be expected to lower sufficiently to cause local failures ofboTes, wells and springs. Those most susceptible would be shalJo\v bores, bores tapping marginal aquifers (ie. t..!J.ose which cause a high drawdo\\TI tor a given pumping rate) and springs which norn1ally have low flows and t10ws of short duration . Drought cfl:eets would also be more severe in the lower raintall southern regions. Anecdotal evidence from landholders indicates that during past droughts only a few wells and bores. particularly shallow ones have gone dry. Some deeper bores have required pumps to be lowered to maintain a supply but most have been unaftectt!d. A more common observation is that some spring flows have been reduced and spring fed waterholes depleted earlier than. normal. The best dams generally can only hold a maximum of nine months supply and most have considerably less usable storage. Low rainfall would therefore render most dams ineffective. The same scenario applies to non-spring fed waterhules. Surfacewater supplies in general are therefore more sensitive to drought than ground\vater because the latter has a large storage to butler short term variations in recbarge. REDCCfXG THE EFFECTS OF DRorjGHT F or existing bores two options may be available to maintain a supply if V,iater levels drop too far. If there i~ "dditional depth between the pump inlet and the top of the slots in the casing, the pump can be lowered to stop the bore "forking" (drawing the water level dO\\TI to the pump inlet and causing it to take in air). r f this is not an option, then reducing the pumping rate will lessen the drawdown and may avoid larking. In the case of a ne'"" bore, drilling a bit deeper than is necessary can often result in additional water intersections. This enables a greater length of slotted casing to be placed in the aquifer, reducing the drawdown for a particular pumping rate. This will add to the cost of the bore but in the long term it will be vvonhwhile especially if it saves the pump having [0 be lowered. Even if no extra water bearing zones are found the maximum number of slots should be cut without compromising the strength of the casing. Accurate placement of the slotted inter./al is also essential in reducing drawdown when pumping. The best way to increase the reliability of a dam is to increase it's depth. increasing the area of a dam will only add more longer term storage if the depth is gre:lter than the depth uf watenvhich will be lost to evaporation. Untortunately this is only possible in a very limited number of sites in the VRD due a general lack of suitable deep suils. A way to overcome this depth limitation is to build embankment dan1s. Although these have not been recommended here because of potential damage by high flood velocities, they do provide a way to increase the storage depth beyond that possible with a ground level excavated tanle A large embankment dam may also have the potential to provide water for limited irrigation, thus extending the stock feed supply at least in the early part of a drollghL A problem that arises during droughts is that although there may be both adequate water and teed, the two may be located in different places. As drought progresses and areas are eaten out, cattle progressively move outwards from the watering points, until a point is reached where the distance that thev have to travel bet,veen feed and water becomes too great. , ~ 23