South East Queensland
41.1 Precipitation on storages
This line item represents the precipitation on Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe.
The quantification approach listed below shows the method used to calculate the precipitation on all storages. Only the component for Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe is relevant to this line item.
Monthly precipitation data were produced by the Bureau of Meteorology. It was based on daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degree (approximately 5 km) national grid (Jones et al. 2007).
The precipitation at each waterbody was estimated from the proportionally weighted average of grid points that intersected each water feature. The volume was then estimated using the surface area of each waterbody. The surface area varied dynamically with changing water storage level for water storages where the relationship between storage level and surface area had been derived.
The surface area of most of the storages in the SEQ region was calculated using this dynamic method. Storage rating table data and regularly updated storage level data were not available for some storages, so static surface areas were used. The surface area for Cedar Grove and Mount Crosby weirs was provided by Seqwater. For Lake Cressbrook, Lake Perseverance and Splityard Creek Dam, the AHGF waterbody feature class was used to estimate a static surface area. Surface areas were not available for Bromelton Off–Stream Storage or Wyaralong Dam. For the SEQ region, the precipitation on the surface water store included precipitation on storages only.
Assumptions, Limitations, Caveats and Approximations
The precipitation estimates were subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2007).
The dynamic storage surface areas calculated from the levels and capacity tables represent a monthly average and therefore will not capture changes that occur on a shorter temporal scale.
The use of the static default waterbody feature class surface area is an approximation only. It represents the storage at capacity and therefore probably results in an overestimation of precipitation on the storage. This default dataset was only used for the small storages (i.e. those where a dynamic surface area could not be determined); therefore, the impact of this approximation is estimated to be small.
The uncertainty estimate was not quantified.
This line item was not reported in the 2010 Account.