9.4 Runoff to surface water
The volume reported (287,548 ML) represents runoff into surface water features including rivers and major storages in the Adelaide region during the 2011–12 year.
National Climate Centre daily climate grids (rainfall, temperature and solar radiation), Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class; Commonwealth Scientific and Industrial Research Organisation (CSIRO): Australian Water Resources Assessment system Landscape model version 2.0.0 (AWRA-L) model parameters; South Australian Department of Environment, Water and Natural Resources (DEWNR): Geographic Information System layers.
Rainfall runoff to surface water was estimated based on the AWRA-L version 2.0.0 (Van Dijk 2010) model output—streamflow.
Using climate grid data for the Adelaide 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 and the off-channel water storages (local catchment reservoir e.g. farm dams) were excluded from the analysis.
Runoff from the landscape is divided into two components: runoff into the surface water (surface water storages and weirs, rivers and drains) and runoff into off-channel water storages. Only runoff into the surface water store was considered here because for the National Water Account, off-channel water storages are not included in the definition of surface water.
The average runoff depth from the landscape into surface water 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 surface water storages, weirs and off-channel storages).
Finally, runoff into off-channel water storages (estimated using the STEDI model; see Sinclair Knight Merz 2010) was subtracted from the total modelled runoff into the surface water to establish the rainfall runoff into surface water storages, weirs and rivers only.
Assumptions, limitations, caveats and approximations
- Runoff estimates were compared to flows at unimpaired catchments within the Adelaide region for the 2011–12 year and found to be a reasonable representation of the runoff in this region for this year
- Runoff estimates were subject to the assumptions of the AWRA-L model detailed by Van Dijk (2010).
- Where the volume of water intercepted by the off-channel water store has been calculated, the runoff estimates inherit the approximations, assumptions and caveats of the STEDI local catchment reservoir model and the associated parameters used.
A new quantification method (AWRA-L version 2.0.0) was used for the 2012 Account. When applying this new method to the 2010–11 year the difference with the volume quantified for the 2011 Account using the previous version of the model (AWRA-L version 1.0.0) is material (13%). Consequently, the 2010–11 year volume has been restated from 598,040 ML (as published in the 2011 Account) to 523,213 ML.