Perth
Water overview

There are three primary river systems within the Perth region:

• Swan–Canning
  
• Murray
• Harvey.
  

More detail on these river systems, including location, is provided in the Surface water section of the 'Contextual information'.

Consistent with the short-term mean annual flows over the last ten years, total annual flows in the Swan, Murray, and Harvey rivers during the 2012–13 year were well below the long-term average for these rivers. Total annual flows were less than that observed during the 2011–12 year, but were at least 40% larger than the record low flows observed in these rivers during the 2010–11 year.

The below average flows during the 2012–13 year in these primary river systems reflect the well below average rainfalls recorded in the region, particularly in the Swan River catchment area (see Climate overview).

During the typically wetter months of the year (July–October and May–June), monthly flow in the three primary rivers was entirely below the long-term average (figures W1–W3). Flow in the Swan River during these wetter months was almost entirely below the 10th percentile (Figure W1). The above average rainfall in September and May (see Climate overview) did not result in above average streamflows during this period, presumably because soil water stores and groundwater levels were relatively low.

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

During the typically low-flow month of December, total flow in the Murray River was an order of magnitude greater than both the mean monthly flow and the 90th percentile for that month (Figure W2). Flows in the Swan and Harvey rivers were approximately equivalent to 90th percentile flows for that month (figures W1 and W3 respectively). This reflects the very high rainfall observed during two successive months in November–December across the region (see Climate overview).

Figure W3  Graph of total monthly flow along the Harvey River during the 2012–13 year compared with the long-term average and percentiles for the river

The region has experienced a decline in rainfall since the 1970s (Department of Water 2009a). During this time, rainfall has declined by more than 10% during the average wet season (May–October). The result has been a 50% reduction in streamflow into the urban water supply storages and a substantial reduction in aquifer recharge. As a result, a number of major water initiatives have been pursued in the region during recent years to secure water supply in the long term. Two major water initiatives which have continued during the 2012–13 year include the construction of a second desalination plant and the completion of a groundwater replenishment trial.

The Southern Seawater Desalination Plant is located near Binningup in the southern part of the Perth region (see Figure P3 in General description). The plant was designed to be constructed in two stages, each able to produce 50,000 ML of water per year for the Integrated Water Supply Scheme. The second stage of the plant will be fully commissioned in late 2013. Desalinated water will provide almost half the urban water needed for the Perth metropolitan area. 

This water resource is part of the Water Corporation's long-term water security solution for the Perth region. For more information on desalinated water in the Perth region, see the Water Corporation website.

A groundwater replenishment trial has been conducted in the Perth region since November 2010 and was completed in December 2012. In the trial, treated wastewater from the Beenyup Wastewater Treatment Plant is further treated to drinking water standards and recharged back into the groundwater system for future use.

In August 2013 the State Government announced that groundwater replenishment would continue in the region as an alternative water source for public water supply. For more information on groundwater replenishment in the region, see the Water Corporation website.