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Proposed
Riffle
Structures
Along
The
Seine
River
By
Harold
Thwaites
and
Jules
Legal
During
the
past
year
an
SOS
sub-committee
has
been
studying
the
idea
of
constructing
a
series
of
small,
"low-tech"
riffles
along
the
Seine.
It
is
encouraging
that
the
City's
Task
Force
has
independently
proposed
this
idea
as
a
possible
strategy
for
maintaining
water
levels
in
their
Hydrology
Report.
The
riffles
would
consist
of
fieldstone
piled
across
the
Seine
in
a
"V"
formation
at
selected
locations
between
the
floodway
and
the
Red
River.
Their
design
would
mimic
natural
riffles,
creating
a
backwater
effect
that
protects
upstream
banks
from
erosion
while
providing
important
spawning
habitat
for
fish.
In
the
long
term,
stabilizing
the
stream
bed
should
help
reduce
erosion
of
the
riverbank.
During
high
flows,
water
would
simply
pass
over
the
top
of
the
low
profile
riffle.
The
structures
would
not
worsen
or
contribute
to
flooding
since
maximum
flows
are
controlled
by
the
siphon
spillway
at
the
floodway.
Nor
would
they
block
all
flow
during
low
water
periods.
Benefits
from
a
system
of
riffles
include:
-
Improved
fish
habitat
and,
-
Algae
and
mosquito
control
-
Improved
habitat
for
waterfowl,
turtles
and
all
aquatic
animals
-
Enhanced
water
quality
through
increased
aeration
and
-
Decreased
fluctuation
of
river
levels
-
Promotion
of
a
more
diversified
fauna
-
Improved
recreational
qualities
for
canoeing
and
walking
-
Reduced
erosion
and
bank
failures
There
is
no
question
that
past
human
interventions
have
had
disastrous
consequences
for
our
beautiful
little
river.
Sadly
we
must
face
the
reality
that
we
can
never
undo
all
the
damage.
However,
we
believe
that
at
least
some
of
the
abuse
can
be
mitigated
by
the
relatively
passive,
judicious
use
of
weirs.
"For
every
action
there
is
an
equal
and
opposite
government
program."
-
Bob
Wells
After
seven
years
of
planning
and
obtaining
all
of
the
necessary
approvals
from
the
civic,
provincial
and
federal
governments,
S.O.S.
is
hoping
to
begin
construction
in
the
winter
of
2002-2003.
Each
riffle
would
be
built
so
it
is
in
the
backwater
of
the
next
riffle.
This
would
work
in
harmony
with
natural
sedimentation
and
erosion
by
the
river,
minimizing
erosion
of
the
riffle
and
relying
on
nature's
tendency
to
build
up
the
river
bed
at
certain
points.
However,
water
held
back
when
it
is
abundant,
usually
in
spring
and
after
heavy
rains,
would
be
released
at
a
slower
and
more
sustainable
rate.
This
particular
riffle
had
been
built
on
Sturgeon
Creek
a
few
years
ago
and
is
functioning
well.
This
riffle
(right)
was
built
on
the
Wilson
River
in
Manitoba
and
has
shown
beneficial
effects
related
to
river
habitat
and
bank
erosion.
There
is
no
question
that
past
interventions
have
had
disastrous
consequences
for
our
beautiful
little
river.
Sadly
we
must
face
the
reality
that
we
can
never
undo
all
the
damage.
However,
we
believe
that
at
least
some
of
the
abuse
can
be
mitigated
by
the
relatively
passive,
judicious
use
of
weirs.
After
seven
years
of
planning
and
obtaining
all
of
the
necessary
approvals
from
the
civic,
provincial
and
federal
governments,
S.O.S.
is
hoping
to
begin
construction
in
the
winter
of
2003-2004.
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