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.
| 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:
Precipitation calculated using variable surface area
Precipitation calculated using static surface area
Precipitation not calculated as surface area of the storage was not available.
Quantification Approach
Data Source
Provided by
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.