Fishing Articles
Scouring
Scouring literally cleans rocks, gravel, and boulders
laden with algae, fungus, and parasites reenergizing rivers with oxygen
and habitable beds ideal for many species of fish.
Timothy Kusherets
These two photos are of the same reach of water running
high, blown out, and running low. Note the significant turbidity of
the image on the right, which is distinctly higher, faster, and muddier
than that of the left. As any river blows out sediments and bed loads
scour the riverbed cleaning out algae and debris. As the river recovers
and clears up oxygen levels increases making the river ideal for fish
migrations.
Any angler who has fished during fall and spring months has experienced
the effects of scouring that creates turbid conditions of stained water.
How fast a river rises directly influences the behavior of holding fish.
Pressures from suspended-loads of silt and bed-loads of moving gravel
and large rocks can easily put fish off the bite.
As silt and gravel are forced downstream, the friction action of scouring
literally cleans rocks, gravel, and boulders laden with algae, fungus,
and parasites; this is the benefit of scouring. The biggest habitat
problem with scouring is that it can decimate redds where fish may have
laid eggs and suspend choking silt that can deplete oxygen for long
reaches.
Scouring happens as a deluge, or flood, abruptly increases the volume
of water on a massive scale. It can happen just about any time of the
year but is most commonly associated with wetter months of the year.
Regions that go without measurable precipitation for extended periods
of time are particularly susceptible to scouring. Banks above and below
the surface can harden resisting saturation as sudden rainfalls fill
and overflow the entire bed within hours. During drought conditions,
surrounding soils can also harden resisting saturation that would otherwise
slow the rate from which rainfall is transported directly into streams
and rivers.
Watching the weather and monitoring hydrographs are the best weapons
to ascertain if scouring has or is about to take place. It’s important
to diligently monitor systems during the height of any season to figure
out what pressures fish may experience. It is possible to counter those
pressures that put fish off the bite during scouring by looking for
holds that are wide enough to be drift fished with shorter leaders,
larger offerings and hooks, along with scents added. Anglers who prefer
to use baits should also add scent to the offering since accumulating
silt can adversely affect the ability of fish to smell.
Rivers that run low and clear for an extended period
of time create optimal conditions where algae and fungus blossom enough
to cover every centimeter of the bed sucking the life out of entire
reaches. When riverbeds become laden with covered rocks holding fish
will move downstream to faster water where temperatures stabilize and
oxygen increases.
© Timothy Kusherets 2008/09 Copyrighted
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