Conjunctive water management and Northern Territory water policy
In the Northern Territory, the Water Act provides for the investigation, allocation, use, control, protection, management and administration of water resources, except in regard to the extraction of surface water and groundwater for mining and petroleum activities (which are subject to an inter-agency memorandum of understanding that ensures that water resources are used within sustainable limits).
Beneficial uses and a water allocation plan may be declared for water quality and quantity management in a water control district. Environment, cultural, public water supply, industry, aquaculture, irrigation, and stock & domestic beneficial uses are recognised. Water resource management must be in accordance with the water allocation plan declared for the district, which:
- allocates water to declared beneficial uses, always including the environment;
- ensures that water use does not exceed allocations;
- controls trading of licences; and
- allows for recovery of water resource management costs.
In terms of groundwater allocation, the national definition of sustainable yield agreed by the Natural Resource Management Ministerial Council has been adopted by the Northern Territory. Where annual monsoon rainfall generally assures full annual recharge of aquifers, the requirements of all ground water dependent ecosystems must be maintained and total ground water extraction must not exceed 20% of annual recharge, with at least 80% retained for environmental use. For the arid zone, where significant recharge events are relatively rare, the water requirements of all ground water dependent ecosystems must be maintained and total ground water extraction over not less than 100 years must not exceed 80% of aquifer storage as assessed before any extraction commenced.
From a water quality perspective, beneficial uses have been declared for water quality management purposes for ground waters in the Mary River, Darwin River, Blackmore River, Elizabeth River and Howard River catchments, and the Daly Basin and Ti Tree Basin. Conjunctive declarations for surface water in the other regions include environmental beneficial use.
Statutory declaration of water allocation plans and the widest application of extraction licensing controls is only possible in water control districts. Water control districts are currently centred on Alice Springs, Ti Tree, Tennant Creek, Katherine, Gove and Darwin. The only water allocation plan in the NT has been declared for the Ti Tree Water Control District. Work is in progress for the Katherine, Darwin and Alice Springs Water Control Districts.
The different time scales on the impacts of extraction from bore pumps and river pumps on river flow need to be taken into account when determining the sustainable yield of a hydraulically connected groundwater / river system. The impact of a pump in a river on river flow is immediate, the impact on river flow of extraction from a bore placed 200m from the river is delayed, and the impact on river flow of a bore placed 5km from the river in the same aquifer will be very much delayed and averaged possibly over years depending on the storage in, and transmissivity of, the aquifer.
The current intent of the Act in the Top End of the NT is that at least 80% of flow at any time in any part of a river is allocated to the environment. The intent is that the extraction regime for groundwater will be managed so that this will be achieved - mainly relates to impacts on dry season flows in the large spring-fed rivers of the Top End (e.g. the Daly River). This is the main control on the sustainable yield of the ground water resource.
At least 80% of wet season flows in any part of a river being allocated to the environment is the main control on the sustainable yield of the surface water resource.
Relevant Links
Department of Natural Resources, Environment and the Arts (NT) Northern Territory Water Legislation
References
NGC, 2004. Surface water-groundwater integration and legislative constraints. National Groundwater Committee