Upper Dunham River water catchment:
These photos were taken on a flight down the Dunham River rainfall catchment early September 2003.
This area has seen no rain since mid April2003. The 2002/2003 wet-season
delivered about 675 mm of rain in the upper catchment area; this was a little below
what could be expected and about half of what came down from the sky the year
before. It is therefore no surprise that after the fire lit here in September 2003
there is little to burn off this year.
The smoke is from fires used as a “cattle-mustering tool”. Bare ground makes
cattle easier to spot and easier to shift with the use of ground vehicles or with helicopters.
Fresh “green pick” along watercourses (as an immediate result of fire) will cause
cattle numbers to congregate. It is then easier to keep them together by moving
them along watercourses with no vegetation where they can hide. Stress on
livestock and mustering costs are reduced.
Both the intensity and the frequency of human lit fires over time are a significant
factor in the shaping of a landscape. At this time of the year a fire will make its
own wind to propel itself forward. Provided the fuel load is there, it will keep
on burning until it runs out of fuel.
This area no longer supports the type of fire patterns that were obvious from the
air ten years ago.
Shows the direction of flow of water into a large waterhole.
As flood-water spills out the far end the flow is slowed down and sand (carried in the water) is dropped; this then further slows down the flow by partially choking up existing drainage lines
consequently sand is then dropped in the waterhole itself.
Not only is the water-holding capacity of the pool reduced, but so is the viability of aquatic habitat systems. This phenomenon is readily observable from the air and is certainly not limited to the Kimberley region. The direct correlation between the sanding up of a water hole and the loss of biodiversity in that environment is not a coincidence.
Local gully erosion (a) and local sheet erosion (b) are seldom the cause of the sanding up of a large water-hole; normally the root-cause is to be found higher up in the river-water catchment.
Lower Dunham River water catchment:
In the picture above the arrows indicate where clumps of forest/wetland areas were lost
in recent decades. Originally perennially flowing streams are now dry gullies. Fortunately
this trend can be reversed; however this will depend on communication, education and
appropriate action.
As many landscape-rehabilitation and landscape-revitalisation processes do not immediately
contribute to any commercial activity these sort of issues can only be addressed once either
the threat of flooding becomes apparent to down-stream communities or if society begins to
place a monitory value on healthy functional landscapes.
In the lower catchment areas many large “water holes” are now full of sand.
Flying Fox Yard: Physical infrastructure is threatened by both erosion and flooding whilst
the source of reliable water is sanding up.
Gully-erosion (marked by the mowed track around the perimeter – bottom left hand side
of the picture above) has not progressed in recent years. This is because the choking up
of drainage lines immediately down-stream has slowed the draining of floodwaters;
actual gullies are under water during a flood and no further local erosion occurs.
Remaining water-holes closer to the Ord Irrigation Area may also now be benefiting from a locally rising water-table. Clean water is available until the end of the dry season.
Nutrient enriched tail-water from the Packsaddle-Plains Irrigation Area perennially feeds into the Dunham River. We now have two compounding trends that promote the growth of vegetation that is choking existing drainage lines.
Frequent fires promote bare ground away from the main drainage lines and growing gullies to the West indicate the path of least resistance for future flood-water.
The rocky ridge on the East stops further gouging out of the Eastern river bank.
In most years an eroding Western riverbank makes room for the wet-season flow.
Bare ground generally offers the path of least resistance to floodwater.
“Looking upstream”: A vast and rugged setting can easily distract us from noticing subtle (and sometimes not so subtle) changes in our landscapes.
Ord
Statements like “fire is natural” can also be a distraction.
Ord
A human made wetland habitat being subjected to fire: in this case a natural physical
force/disturbance unleashed by humans. What is the net effect on biodiversity of these
prevailing practices?
Ord
No doubt ‘time’ will be the fairest judge of the benefits of current landscape management.
This update was provided by Kachana Pastoral Company: September 2003
For other contributions to local/regional environmental issues please click here
Kachana Pastoral Company promoting ‘environmental literacy’ and ‘functional science’:
www.environmental-literacy.com (Learning to read what Nature is telling us now.)
