National Water Commission

Rainfall across the Richmond River WMA was below average in 2004-05, at around 92% of long term average rainfall (see Figure 2) and the 10 year average was 94% of the long term average.

Table 2 Summary of the Richmond River water management area contextual information

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




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




Figure 4 Modelled pre development streamflow hydrograph for the Richmond River water management area for the Richmond River at Wiangaree (site 203005)

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

Table 2 Summary of water balance in the Richmond River water management area, 2004-05

Figure 5 Water balance summary diagram for the Richmond River water management area

Outcomes from the water cycle report

The following information becomes apparent from Table 2.

• There is a large amount of data available for the regulated area, however limited data available for the unregulated areas of the catchment or for groundwater resources. Hence the data quality for this water balance is highly variable.
• 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 outflows. The volume of storages and extractions / diversion was relatively small.
• The small volume of water diverted in the WMA was predominantly for urban use.
• 72% 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 was not quantified for this catchment.
• The major surface water storages had a 12% reduction in volume over the year, in real terms the storages started at 80% of capacity in July 2004 and finished at 91% of capacity in June 2005.
• Due to the limited water usage in this catchment, studies and modelling work have not been a high priority, therefore the accuracy and availability of data for this catchment was lower than for other regulated areas within New South Wales.
• 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 Richmond River area, 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 has been used as the balancing item).
• Data could not be obtained for the following items in the water balance:
• Minor catchment dams (may be a large part of the water balance).
• Soil - unsaturated zone storage volumes
• River channels storage volumes
• Urban treated effluent (returns to the river)
• Irrigation water diversions on unregulated rivers

Summary of data availability and reliability

The data for this water balance is highly variable with most of the surface water information for regulated areas obtained from recorded data and estimates, whilst surface water data for the unregulated areas and groundwater information is less detailed as no modelling data was available.

The data for this water balance was predominantly category A (Table 3), indicating that the majority of the data was of a high standard. The overall reliability for the catchment was estimated as ±45%.

Table 3 Summary of Richmond River water management area data reliability