Canberra
Water overview
Significant water events
There were no significant water events in the region during the 2013–14 year.
Soil moisture
Figure W1 shows that soil moisture was generally average in the Canberra region during the 2013–14 year (compared with the 1970–2014 period). The soil moisture is based on a simple conceptual representation of soil water storage and transfer processes averaged over a 5 km x 5 km grid cell derived from the Australian Water Resources Assessment system landscape model (AWRA-L) version 3.0. The model produces a soil moisture grid for the region at a daily time step, which is then averaged over the entire year to produce an annual soil moisture grid. The annual grid represents the mean daily volume of soil moisture across the region during the year.
Figure W1 Annual soil moisture deciles for the Canberra region during the 2013–14 year
Despite the combination of generally average rainfall (see Climate overview) and soil moisture conditions across the region during the 2013–14 year, streamflow in the Molonglo and Cotter rivers was below average. This is likely to be attributed to when the majority of the rainfall occurred throughout the year, which is discussed in the Streamflow section below.
Streamflow
There are five major rivers within the Canberra region:
- Cotter
- Gudgenby
- Molonglo
- Murrumbidgee
- Queanbeyan.
The Murrumbidgee is the major river system that flows through the Canberra region, with all rivers and creeks in the region draining into the Murrumbidgee River.
Figure W2 Flow gauging stations along the main rivers within the Canberra region
As shown in Figure W2, these gauging stations are located at the upstream of rivers above the reservoirs. The river flow at these stations depends on the runoff from local rainfall experienced in the respective catchment.
Total annual flows in the Cotter and Molonglo rivers were approximately 60–70% of the mean annual flow for these rivers; total annual flow in the Queanbeyan River was equivalent to the mean annual flow. Figures W3 and W4 show that flows in the Cotter and Molonglo rivers were below average for almost the entire year, particularly in the Molonglo River where, except for September 2013, flow was well below average. Flow in the Queanbeyan River was only above average for four months of the year (Figure W5).
Flow was above average in September 2013 in all three rivers as a result of very high rainfall in the region during this month (see Climate overview). Although there were other periods of above average rainfall during the 2013–14 year, these wet months followed particularly dry months, which meant that the rainfall did not lead to the expected streamflow response.
Figure W3 Total monthly flow along the Molonglo River during the 2013–14 year compared with the long-term average and percentiles for the river
There are three key water storages located on the Cotter River: the Corin, Bendora, and Cotter reservoirs. They supply urban water for the Canberra region. Figure W4 shows flows down the Cotter River at gauge 410730 located upstream of the Corin Reservoir. These flows enter the Corin Reservoir where water is released or spilled flowing downstream to the Bendora Reservoir and eventually to the Cotter Reservoir.
Figure W4 Total monthly flow along the Cotter River during the 2013–14 year compared with the long-term average and percentiles for the river
The Googon Reservoir, southeast of Queanbeyan, is located on the the Queanbeyan River, a tributary of the Murrumbidgee River. The total annual flow in Queanbeyan River was slightly above the long-term average annual flow. High inflows into the Googong catchment saw increased streamflows and runoff into the storage in the 2013–14 year.
Figure W5 Total monthly flow along the Queanbeyan River the 2013–14 year compared with the long-term average and percentiles for the river
Major water initiatives
Following the National Plan for Water Security (2007), the ACT Government announced a range of new water supply projects that ACTEW Water continued to implement throughout the 2013–14 year.
These include:
- Enlarging Cotter Reservoir to increase the total capacity to 79,374 ML: The reservoir began impounding water on 1 March 2013 and has since allowed total storage in the region to exceed the previous capacity. During the 2013–14 year, the reservoir continued to fill to its new capacity; the volume of water in the reservoir increased from 12% to 57% capacity during the year (see Surface water note). It is likely it will achieve full capacity in early 2015.
- The Murrumbidgee to Googong water transfer pipeline: This will allow the transfer of water from the Murrumbidgee River to Burra Creek, where it will flow into the Googong Reservoir. The Murrumbidgee to Googong water transfer was completed in August 2012 but was not operated during the 2013–14 year except for maintenance purposes.
- ACTEW Water has purchased 9,549 ML of high security entitlements and 12,523 ML of general security entitlements. These water entitlements are from the NSW Regulated Murrumbidgee River and are to be utilised under the Tantangara Transfer Option. This option is to be available for use only during extreme droughts.
- The Tantangara Transfer Option agreements were completed during 2013–14 year to enable the delivery of water if required. Some details regarding the obligations of ACT and NSW Governments are still to be finalised, but these are not essential for ACTEW to access the water. Present high storages mean that it will be some time before a Tantangara Transfer is required.