South East Queensland
9.1 Precipitation on surface water

Supporting Information

This line item consists of precipitation on surface water within the South East Queensland (SEQ) region. As a surface area was not available for surface water, such as rivers, natural lakes or wetlands, precipitation was only provided for the surface water storages listed in line item 1.1 Storages (following table).

The volume of precipitation on surface water was considerably greater during the 2010–11 year (410,129 ML) than the 2009–10 year (164,353 ML). This was due to the 2010–11 year being significantly wetter, with major flood events occurring in December 2010 and January 2011. Further information on the rainfall within the region can be found in the Climate overview.


Precipitation on storages within the South East Queensland region
Water resource plan (WRP) area Water supply scheme (WSS) Storage name Precipitation
(ML)
Gold Coast Nerang Advancetown Lake (Hinze Dam)1           18,679
Little Nerang Dam1             1,079
Total Gold Coast WRP area          19,758
Logan Basin Logan River Bromelton Off-Stream Storage3              – 
Cedar Grove Weir2               595
Lake Maroon1             4,599
None Tingalpa Reservoir (Leslie Harrison Dam)1             9,810
Wyaralong Dam3                 – 
Total Logan Basin WRP area          15,004
Moreton Central Brisbane River and Stanley River
Mount Crosby Weir2               829
Lake Wivenhoe1         183,130
Lake Somerset1           93,102
Central Lockyer Lake Clarendon1             3,610
Lake Dyer (Bill Gunn Dam)1             1,299
Cressbrook Creek Lake Cressbrook2             9,303
Lake Perseverance2             3,390
Lower Lockyer Lake Atkinson (Atkinson Dam)1             8,256
Pine Valleys Lake Samsonvale (North Pine Dam)1           46,281
Warrill Valley Lake Moogerah1           10,521
None Enoggera Reservoir1             1,127
Gold Creek Reservoir2               320
Lake Kurwongbah (Sideling Creek Dam)1             7,917
Lake Manchester (Cabbage Tree Creek Dam)1             4,018
Splityard Creek Dam2             2,263
Total Moreton WRP area        375,367
Total SEQ region        410,129

Notes:

  1. Precipitation calculated using variable surface area

  2. Precipitation calculated using static surface area

  3. Precipitation not calculated as surface area of the storage was not available.

Quantification Approach

Data Source

Bureau of Meteorology: Australian Water Availability Project (AWAP) monthly precipitation grids; Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class; Australian Water Resources Information System (AWRIS) water storage.

Provided by

Bureau of Meteorology.

Method

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.

Uncertainty Information

The uncertainty estimate was not quantified.

Comparative year

This line item corresponds to line item 13.1 Precipitation on connected surface water reported in the 2010 Account. The data available for precipitation calculation have improved since 2010 Account publication.

The volume of precipitation on surface water estimated for the comparison year (161,153 ML) using the improved data set is less than the volume reported for the 2010 Account (164,353 ML). This is because the gridded precipitation surfaces that these estimates are produced from are derived from a large number of precipitation monitoring sites. Many of these precipitation sites are manually monitored with observed precipitation recorded on paper and mailed to the Bureau. There can be a considerable delay between the date of precipitation and the data becoming part of the interpolated precipitation surfaces; thus, historical surfaces can change as more data become available. In addition to this, surface areas for Mount Crosby Weir and Cedar Grove Weir became available during the production of the 2011 Account. Precipitation was able to be back-calculated for the 2010 Account for these storages.

The difference of 3,200 ML represents a change of approximately 1.9% of the originally published volume. The 2011 Account comparison year uses the volume of 164,353 ML reported in the 2010 Account, as this change was not considered material.