We do not hear much these days about the water levels in our Hills dams, which are all in forested areas. Now that we have two large (and very expensive) desalination plants the importance of the Hills dams has fallen off the radar somewhat. The runoff into the dams has been poor in recent years due to the run of poor rainfall years since about 1990. Less rainfall means less runoff, but runoff is also affected by the density of forest cover and the amount of litter on the forest floor. Very little timber harvesting now takes place in the catchments, but this has in the past had a significant effect on increasing runoff for several years after a harvesting operation. It is also well known that high fuel loads reduce runoff by intercepting part of the rainfall.
As documented elsewhere on this website, large high intensity bushfires have an extremely detrimental effect on our catchments.
There are three reservoirs of critical importance for protection from wildfire by regular prescribed burning:
- The Mundaring dam which is the only supply for Kalgoorlie and the wheat-belt. The 2005 wildfire in this catchment area had a severe effect on water quality but fortunately not enough to stop supply.
- There are also the Wungong and Canning dams which store excess desalinated water and are able to provide rapid supply into Perth during periods of peak demand. However much of the catchment area is now long unburnt.
Protection of these vital water sources must be a key priority for the Water Corporation and for the Department of Biodiversity, Conservation and Attractions. Forested catchments that supply country towns (eg Manjimup, Bridgetown, Margaret River and Denmark ) also require protection from wildfire.