Supporting information
The Murray–Darling Basin (MDB) region’s Statement of Changes in Water Assets and Water Liabilities shows an unaccounted volume of 1,085,123 ML for the groundwater store for 2009–10 (10% of the total water assets).
The key reason for this unaccounted-for difference is the incomplete representation of groundwater processes in the account. Contributing factors are:
- Groundwater use was only estimated and taken to be zero where there is no water sharing plan (e.g. Upper Lachlan Alluvium).
- Diffuse groundwater discharge in shallow water table areas was not estimated using the Bureau of Meteorology methods but groundwater recharge was estimated.
- Groundwater – surface water interaction (both inflows and outflows from rivers) were not estimated except in groundwater model areas.
- The groundwater balance analysis was focused on key high-groundwater-use groundwater management units so the influence of other areas is not necessarily well represented. Regional groundwater flow within the borders of the MDB may be another important factor.
- A constant groundwater asset volume, equal at the beginning and end of 2009–10 was assumed. The volume was estimated using the long-term average extractable volume set in the jurisdictional groundwater management plans.
