Significant water events
There are three primary river systems within the Perth region: Swan–Canning, Murray and Harvey.
During the 2010–11 year, total annual flows in the Swan, Murray and Harvey Rivers were the lowest on record. Total annual flows during the 2010–11 year were an order of magnitude below the mean annual flows for these rivers.
In the Swan and Murray Rivers, monthly flow was almost entirely below the 10th percentile in all months (Figures W1 and W2). No flow was observed in the Swan River between December 2010 and April 2011 (Figure W1). At all three rivers, the total monthly flow was the lowest on record each month during a 5-month period between August and December 2010 (Figures W1, W2 and W3).
The record low flows during the 2010–11 year in these primary river systems reflect the below-average rainfalls recorded in the region, particularly in the upper catchment area, where rainfall was the lowest on record (see Figure C1 in Climate overview).
Figure W1. Graph of total monthly flow along the Swan River during the 2010–11 year compared with the long-term percentiles
Figure W2. Graph of total monthly flow along the Murray River during the 2010–11 year compared with the long-term percentiles
Figure W3. Graph of total monthly flow along the Harvey River during the 2010–11 year compared with the long-term percentiles
Major water initiatives
According to the Perth–Peel regional water plan (Department of Water 2009), the region has experienced a decline in rainfall since the 1970s. During this time, rainfall has declined by more than 10% during the average wet season (May to 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 were pursued during the 2010–11 year in the region, including:
- construction of a second desalination plant
- Target 60 campaign.
The Water Corporation is in the process of constructing the Southern Seawater Desalination Plant near Binningup, which is just below the Perth region boundary. It is due for completion in September 2011. The first stage of the plant will be capable of producing 50,000 ML of water for the Perth metropolitan area, which will more than double that currently supplied.
When the second stage of the plant is complete in late 2012, desalinated water will then provide more than 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 as outlined in Water Forever.
On average, the Perth community uses 600 litres of water per person per day. During the 2010–11 year, Water Corporation launched the Target 60 campaign, where everyone in Perth were asked to take 60 litres, or around 10%, off their daily water use. This campaign was prompted by the driest winter and spring on record in 2010 (see Climate overview).