Sydney
Water overview

The area-averaged rainfall over the Sydney region between July–December 2012 was only 226 mm: the driest July–December period for the region since 2002. During this period there were no days with more than 25 mm of rainfall recorded. This had an impact on the amount of runoff observed in the catchments (see 9.4 Rainfall runoff) and the amount of water observed to run out to sea (see 17.2 River outflow from the region). Despite this dry period, average rainfall was observed over the entire year due to two substantial rainfall events which can be seen in Figure W1 and Figure W2 below. The event in February–March 2013 was observed mainly in the northwestern part of the Sydney region, especially in the Blue Mountains and impacted flows in the Colo River, as shown in Figure W2. In June 2013, 138 mm fell over the Shoalhaven catchment over 3 days, and as Lake Yarrunga Dam was already full all inflows spilled to the downstream river as shown in Figure W1.

Figures W1 and W2 show streamflow pattern, volumes, and variation at two major rivers in the region:

• Colo River at Upper Colo in the Hawkesbury–Nepean catchment
• Shoalhaven River at Fossickers Flat in the Shoalhaven catchment.

The two river locations were selected for the following reasons:

• long-term flow data are available
• flows upstream of both river locations are unregulated and diversions are negligible
• both are major rivers in terms of flow volumes.

The Shoalhaven River experienced well below average flows in the 2012–13 year except for the months of October 2012; and February, March, and June 2013 (Figure W1). Very much above average flows were observed in the Shoalhaven River during October 2012 and February and June 2013.

Flow data collected in the Colo River were incomplete for the months of January, May, and June 2013. For the remainder of the 2012–13 year, the Colo River experienced below average flows for all months except February and March 2013 (Figure W2). 

Both rivers experienced relatively high flows in February and March 2013 due to high rainfall towards the end of summer (see Climate overview).

Figure W1 Graph of total monthly flow along the Shoalhaven River during the 2012–13 year compared with the long-term average and percentiles for the river



Figure W2  Graph of total monthly flow along the Colo River during the 2012–13 year compared with the long-term average and percentiles for the river

No major water initiatives were undertaken in the Sydney region during the 2012–13 year.