National Water Commission

The Roper River water management area covers 79,605 km2 and is located in the far north of the Northern Territory east of Darwin discharging into the Gulf of Carpentaria. Water use is generally low in the WMA with <0.1% of the surface and groundwater resource used for extractive purposes. However, this does not necessarily mean that there is excess water available for exploitation due to the combination of seasonality and lack of infrastructure to transport and store water. There were no urban or rural water restrictions on water use over the season.

In the Roper River WMA, NRETA is responsible for bulk water supply and licensing. A Macarena Water Advisory Committee will be established in 2007 to advise Government on a future Water Allocation Plan which is to be developed and implemented to ensure sustainability of consumptive use. A plan was yet to be developed for the groundwater resources.



Figure 1 Roper River water management area locality map

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Rainfall in 2004-05 was 625 mm, which is about 88% of the long term average, although it was about 68% of the rainfall over the last 10 years (Figure 2). Rainfall decreases steadily across the water supply area from north to south (~50% decline). Rainfall in the area occurs almost exclusively during the wet season, which generally runs from November to March (Figure 3).

The volume of streamflow in rivers in the water management area varies with the season. Flow can be up to 200 times greater during the wet season. Indeed, many smaller streams and river cease to flow altogether during the dry season. Figure 4 shows the variable nature of streamflow in the catchment depending on the intensity of the wet season. The low flow recorded for 2004-05 is due to equipment failure at the gauge.

Table 1 Summary of Roper River water management area contextual information

Figure 2 Annual rainfall for the Roper River water management area (modified from BOM, 2006)




Figure 3 Monthly rainfall and evaporation for the Roper River water management area (modified from BOM, 2006 & Climate Atlas)




Figure 4 Representative streamflow hydrograph for the Roper River water management area for Roper River at Red Rock (gauge G9030250)




Figure 5 Representative hydrograph for the Roper River water management area

Summary of the total water resources in the basin

The total volumes of water available and supplied from water resources in the Roper River are shown in Table 2.

In 2004-05 there was no formal environmental water reserve established in the Roper River WMA. The 80:20 Rule was in effect (80% for the environment and 20% for consumption) via the Roper River management plan. In 2004-05 the environment’s share of total flow within the Roper River was 5,540,000 ML (i.e. approximately 99% of total inflows).

Table 2 Summary of water balance in the Roper River water management area, 2004‑05

Figure 6 Water balance summary diagram for Roper River water management area

Outcomes from the water cycle report

The following information becomes apparent from Table 2.

• The error in the water balance was 0%; this was mainly due to the sparse nature of information.
• The runoff and outflow estimates dominated the water balance representing more than 95% of the overall balance. The Water 2010 estimates were too high for surface water flow and too low for groundwater recharge.
• Runoff figures were based upon Water 2010 and were modified by back calculation.
• Data accuracy for the groundwater / surface water interactions was low.
• Data accuracy for water use was high.
• Almost all (99%) groundwater recharge was discharged to surface water as baseflow.
• Water use was from a mix of groundwater and surface water sources.
• All extractions were from self-extracted water (e.g. catchment dams, private diversions and groundwater bores) which is not metered or well known.
• There was no effluent recycling.
• In 2004-05 the environments’ share of the total flow in the Roper River basin was 99% of total streamflow.
• Data could not be obtained for the following items in the water balance:
• Onstream minor and farm dams
• Offstream minor catchment dams
• Groundwater aquifer volume
• Soil - unsaturated zone
• River channels
• Seepage from surface water features
• Minor catchment dams
• Environmental extractions
• Groundwater discharge to Springs
• Groundwater discharge to ET
• Groundwater Stock and Domestic Use
• Aquifer flow out of entity

Download 2004-05 water cycle report: