Catchments

Find out here about the impact of our drying climate on Perth's catchments.

Since the 1970's, Perth's rainfall has decreased by around 15% and the soil in our catchments has dried out dried out so much that we would need above average rainfall year on year to make a major, ongoing difference to our dam levels.

Find out why when Perth gets heavy rainfall, our dams don't automatically rise at the same time.

Read a transcript of this video (new window)

What have we done?

We've investigated a catchment management technique to improve streamflow, called catchment thinning or silvicultural treatment, which involves the selective removal of trees and undergrowth in regrowth forests.

A trial at the Wungong Catchment in Bedfordale began in 2005 and concluded in 2013, which included the thinning of approximately 1,800 hectares of the Wungong catchment.

What did we find?

Management of a small sub-catchment of Wungong in 2007 did result in a 50% increase in streamflow by 2009. However, this increase was not sustained during poor rainfall periods of 2010 and 2012.

Overall, the Wungong Trial demonstrated catchment management can increase the groundwater level and runoff in the thinned area. However, findings showed that due to the poor rainfall over the period of the Wungong Trial, particularly in years 2006, 2010 and 2012, there was no measurable increase in streamflow at the dam as a result of catchment management.

Our Water Forever: South West report identified 6 possible catchment management areas in the South West where there is high rainfall or where rainfall has not reduced substantially. It was identified that about 50 to 60% of these catchment areas could undergo catchment thinning which could potentially generate a total of one or two billion litres of inflow across these 6 dams depending on rainfall levels.

The findings from the Wungong Trial also resulted in changes to the Forest Management Plan 2014–2023, prepared by the Conservation Commission and DPaW, to allow for silvicultural activities for the specific purpose of improving streamflow either for ecosystem health or for water production.

While there are no further proposals for catchment management, we will continue to assess the viability of catchment thinning compared to other water source options.