|Seven Creeks at Smiths Bridge|
The flood of 4.10.10 itself was spectacular – so much water after ten years of low rainfall. Most of us had forgotten, or were not aware, of the power of a raging flood. When the waters receded, some streams suffered considerable erosion and flooded areas were strewn with flotsam; branches and trees; leaf litter, sticks and bark wrapped around shrubs and stems, and most interestingly, large amounts of sand washed out of stream channels.
The streams draining the granitic Strathbogies are known to contain vast amounts of sand resulting from erosion since the ranges were largely cleared of native vegetation in the 19th Century. Every time these streams carry high flows, these ‘sand slugs’ become mobile, moving further downstream, or parts of the slug may be forced out of the channel by the force of the water, as happened in places during this flood.
The Bridge to Bridge Reserve at Strathbogie, with its picnic area, and walking track was hard-hit by the flood. Parts of the walking track were washed away, small trees and shrubs collected flotsam and were flattened by the strong current. Drifts of sand now cover a previously grassy floodplain and the channel of the Spring Creek altered significantly.
|Spring Creek below the bridge, Strathbogie.|
These photos of Spring Creek (below the bridge) show the effects of the flood. Boundary fences were washed away and broad sand banks now lie where once our gravel walking track once allowed visitors to stroll along the gently flowing stream.
|Meander cut-off and undercut trees in the channel.|
The flood cause a meander ‘cut-off’, creating a new channel and trees were undercut and fell into the stream. Such changes are a natural occurrence and show how floodplains and billabongs are formed. However, its a major nuisance for adjoining landholders and creates lots of work in the clean-up
|Bridge to Bridge picnic tables and entrance to the walking track.|
The picnic tables were completely submerged by the flood and collected lots of debris, but were thankfully unharmed.
|30cm high sand drifts brought down by the Sevens.|
The new sand drifts are spectacular evidence of the amount of sand that was clogging the stream channel. It looks just like the beach and has become a great playground for local kids.
With a bit of luck the flood will have ‘cleaned out’ some of the deeper parts of the channel, providing important habitat for fish, platypus and other aquatic life. Overall, the flood is likely to have improved the quality of in-stream aquatic habitat.
So now the clean-up has begun.
Lots of wooden debris was collected from the picnic ground and surrounds, and burnt.
The path is getting a new coat of gravel.
And some welcome cups of tea and snags (the edible type) after a successful FOBB working bee last Sunday morning.