9.4 Runoff to surface water

Supporting information

The volume recognised in the water accounting statements (6,794,954 ML) represents the total volume of runoff into surface water within the Ord region during the 2011–12 year. The surface water store includes drains, rivers and storages within the region.

The volume of runoff during the 2011–12 year is less than a fifth of the comparison year. This large decrease in runoff reflects the lower rainfall observed throughout the region during the 2011–12 year (see Climate overview) relative to the record high rainfall recorded during the comparison year (see the 2011 Account).

The total runoff to various sections of the Ord region during the 2011–12 year is provided in the following table.

Total runoff to various sections of the Ord region during the 2011–12 year

Surface water section

Runoff (ML)

Ord River upstream of Lake Argyle


Ord River downstream of Lake Argyle


Keep River





Quantification approach

Data source

Daily climate grids (rainfall, temperature and solar radiation), Australian Hydrological Geospatial Fabric—waterbody feature class.

Provided by

Bureau of Meteorology.


Runoff to surface water in the Ord region was based on streamflow estimates from the Australian Water Resource Assessment system Landscape (AWRA-L) version 2.0.0 model outputs.

Using climate grid data for the Ord region (including precipitation, temperature and solar radiation data), AWRA-L was used to estimate the runoff depth at each grid point within the region. Only runoff from the landscape was considered; therefore, the surface areas of the major storages were excluded from the analysis.

The average runoff depth from the landscape into the connected surface water store was determined as the weighted mean of the relevant grid points within the region boundary. Points were weighted based upon the area they represented within the reporting region to remove edge effects (where the area represented is not wholly within the reporting region) and the effect of changing area represented with changing latitude. Runoff depth was converted to a runoff volume by multiplying runoff depth by the total area of the region (excluding storages).

Assumptions, limitations, caveats and approximations

The estimated runoff was compared against historical flows at unimpaired catchments within the Ord region for the 2011–12 water year and provided a suitable representation of the runoff for this year.

The runoff estimates were subject to the assumptions of the AWRA-L model detailed by Van Dijk (2010).

Uncertainty information

The uncertainty estimate was not quantified.