National Water Commission

The Gwydir River is located within the Murray-Darling Drainage Division in northern New South Wales. Although the complete Gwydir River catchment includes regulated and unregulated areas, only the regulated area was assessed for the water balance.

The Gwydir River- Regulated is a tributary of the Barwon River which in turn is a tributary of the Darling River. Irrigation that occurs within the Gwydir River – Regulated WMA is predominantly private irrigation (i.e. there are no major irrigation authorities that supply water). Copeton Dam is the major water storage and Moree is the largest town within the study area.

The Department of Natural Resources (DNR) is the licensing authority and manages both surface and groundwater diversions for urban, commercial/industrial, irrigation and environmental purposes. The Border Rivers - Gwydir CMA  is responsible for managing native vegetation, soil and other natural resources in the catchment in conjunction with the community, local government, industry and State Government. State Water manages the major water supply storages in New South Wales and supplies bulk water to the irrigation authorities, town water supply authorities, mines and electricity generators by releasing water from its dams into rivers to be accessed by downstream water users. State Water also delivers water for private irrigators and stock and domestic users and is responsible for delivering environmental flows, in accordance with rules as set out in NSW Water Sharing Plans, on regulated rivers in the state.

Local councils treat the bulk water and deliver it to urban users in the major towns within the catchment and also manage the wastewater collection and treatment network (e.g. Moree Plains Shire Council  for Moree and the surrounding area). Both surface and groundwater resources are used for town water supplies in the Gwydir River– Regulated WMA.



Figure 1 Gwydir River - Regulated water management area locality map

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Rainfall across the Gwydir River- Regulated WMA was above average in 2004-05, at around 122% of long term average rainfall. The average rainfall for the last 10 years was 111% of the long term average.

Table 1 Summary of the Gwydir River – Regulated water management area contextual information

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




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




Figure 4 Modelled pre development streamflow hydrograph for the Gwydir River – Regulated water management area for the Gwydir River at Bundarra (site 418008)




Figure 5 Modelled pre development streamflow hydrograph for the Gwydir River – Regulated water management area for the Gwydir River at Pallamallawa (site 418001)




Figure 6 Representative bore hydrograph for the Gwydir River – Regulated water management area (Bore name: Moree – Ashley)

Summary of the total water resources in the basin

The total volumes of water available and supplied from water resources in the Gwydir River- Regulated WMA are shown in Table 2.

Table 2 Summary of water balance in the Gwydir River – Regulated water management area, 2004-05

Figure 7 Water balance summary diagram for the Gwydir River – Regulated water management area
 

Outcomes from the water cycle report

The following information becomes apparent from Table 2.

• The water balance was completed for the regulated area of the Gwydir River catchment. There was a large amount of data available, including detailed modelling, for the regulated area, and hence the data quality for this water balance was relatively high. However, the balance may be misleading without considering the entire hydrological catchment (i.e. the combined regulated and unregulated areas). This is an opportunity for improvement in future assessments.
• The error in the water balance was 0%. This was due to the unaccounted for flows being incorporated with other items in the water balance. For surface water the balancing item was ‘Other losses’, the groundwater balancing item was the closing storage volume. Other jurisdictions reported unaccounted flows as an error term.
• The water balance was dominated by rainfall and diversions.
• Water use within the regulated area was predominantly for agriculture as there are few urban areas in the catchment. There was also a significant volume of environmental flows in the WMA, particularly for the Gwydir Wetlands.
• Based on the available data, 95% of water used in the regulated area was sourced from surface water in 2004-05, with the remainder from groundwater sources.
• The interaction between surface water and groundwater (predominantly seepage from streams to groundwater) was quantified as 16,000ML in 2004-05, or 1% of the total captured rainfall (sum of runoff and recharge).
• There was about 16% more surface water available in storage at the end of 2004-05 than at the start. This was because of an increased volume of water stored in rivers due to a large rainfall event in June. This water was not actually available for use. The water storages had a 5% reduction in volume over the year, in real terms the storages started at 25% of capacity in July 2004 and finished at 23% of capacity in June 2005. This includes estimates of major off river storages.
• The volume of on farm storage in farm dams / minor storages was not available explicitly, however an estimate of the volume of rainfall / runoff harvesting in the catchment was provided and is likely to include the inflows to the majority of farm dams.
• The volume of groundwater stored was estimated by DNR by calculating the volume in the aquifer(s) to a depth of 20m below the ground surface (assuming a saturated thickness, estimating the water table drawdown depth from bore levels, and using the area and aquifer porosity). For the Gwydir River – Regulated WMA, the volume of groundwater at the end of the year was determined from the volume at the start of the year plus any unaccounted for groundwater errors (i.e. it was used as the balancing item).
• Data could not be obtained for the following items in the water balance:
• Minor catchment dam volume / usage and evaporation (majority included in the rainfall / runoff harvesting estimate).
• Soil - unsaturated zone storage volumes
• Urban treated effluent (returns to the river)

Download 2004-05 water cycle report: