42.4 Spillage from storages

Supporting Information

During the 2011 Account, 576,421 ML of spills were recorded from storages managed by the Sydney Catchment Authority.

Spill volumes during the 2011 Account


Spills during the 2010–11 year (ML)

Lake Burragorang (Warragamba Dam)


Lake Yarrunga (Tallowa Dam)


Blue Mountains


Pheasants Nest Weir


Broughton Pass Weir






Quantification Approach

Data Source

Bureau of Meteorology: spilling volume from Danjera Reservoir for the 2010–10 year was estimated using the following input data: estimated precipitation and evaporation, and modelled inflow to Danjera Reservoir using Bureau of Meteorology data; storage voumes of the reservoir provided by Shoalhaven City Council (source: Level monitoring at the reservoirs with hydrometric sensors linking to council's radio telemetry system); diversions and other losses for the reservoir provided by Shoalhaven City Council (source: Shoalhaven City Council Telemetry System and daily data registers in respect of the operations of WTPs); the Sydney Catchment Authority; Sydney Catchment Authority Hydstra system and Daily Return System (DRS) databases.

Provided by

Bureau of Meteorology: spilling volume from Danjera Reservoir; the Sydney Catchment Authority: spilling volumes and other releases from the storage reservoirs and weirs managed by the authority.


Methods for spills from storages



Bureau of Meteorology

Storage mass balance calculations using measured storage volumes, estimated precipitation and evaporation, and modelled runoff

Sydney Catchment Authority

Spill volumes derived from water levels and rating tables for spillways

Assumptions, Limitations, Caveats and Approximations

Assumptions, limitations, caveats and approximations by agency


Approximations, assumptions, caveats/limitations

Bureau of Meteorology

Based on data provided by Shoalhaven City Council, water was not supplied from Danjera Reservoir during the 2010–11 year. Storage losses other than spills have been assumed as negligible. For other approximations and assumptions, see the following line items:

Sydney Catchment Authority


Uncertainty Information

Uncertainty information by agency



Bureau of Meteorology

The volume was estimated from measured and modelled data. Estimated uncertainties for some of the inputs used for the calculation of spilling volume from Danjera Reservoir are ungraded. These inputs are precipitation, evaporation and modelled runoff. Therefore, uncertainty for the spilling volume from Danjera Reservoir is ungraded. Estimated uncertainty for storage volume, which was the remaining input for the calculation, is +/– 5%.

Sydney Catchment Authority

The volume is based on measured data. Estimated uncertainty based on meter accuracy, and professional judgment on rating tables, site configuration issues and local issues at the time of spilling at each site is +/– 5% to 10%.