Introduction
Problem:
Damage
caused by
erosion of
inadequately
protected
slopes.
Mitigation
Objective:
Harden
the
damaged
embankment
slope or
redirect
flows to
avoid
higher
velocities.
Provide
bio-engineered
embankment
slope
protection
by
covering
the slope
with deep
rooting
vegetation
and where
it is
adjacent
to and in
contact
with a
live
stream,
strategically
anchor
large
woody
debris
(i.e. root
wads) that
will hold
the soil
in place
and
protect it
from
erosion.
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Effectiveness:
- Very
effective
in
areas
of
low
flow
velocity.
- Environmentally
friendly.
- Contributes
to
settling
of
particulate
matter.
Limitations:
Vegetation
must have
sufficient
time to
become
established
prior to
being
exposed to
floodwaters.
Generally
not
suitable
for areas
of
sustained
high
velocity
flows.
Considerations:
B.2
Install
Half-Round
or
Spillway
Pipes, or
Rock
Channels
Concentrate
flows in a
collection
structure
and
install
half-round
or
spillway
pipes, or
rock
channels
down steep
slopes to
eliminate
erosion.
Effectiveness:
- Most
effective
for
intermittent
streams
or
surface
water
collection.
- Pipes
very
effective
when
properly
connected
to
drainage
collection
structures
or
roadway
ditches.
Limitations:
- Requires
good
anchors
to
eliminate
failure
by
slippage
of
the
pipes
on
the
steep
slope.
- Consider
constructing
an
energy
dissipater
at
bottom
of
slope.
B.3
Change
Geometry
of Roadway
Section
Alter
the angle
of an
embankment
slope
through
shoulder
rounding
and slope
reduction
to reduce
erosion.
Reducing
the angle
of slope
generally
reduces
the
velocity
of the
water
running
across it.
Effectiveness:
Very
effective
in areas
of roadway
overtopping
with low
velocity
flows.
Particularly
effective
if
combined
with
armoring
of the
downstream
embankment
slope and
road
shoulder.
Limitations:
May
reduce
carrying
capacity
of ditch
or stream.
Considerations:
B.4
Construct
a Wall
Construct
a wall to
protect
the slope
from
erosion
and
consequent
sloughing
and
slumping.
Walls can
be
constructed
of various
materials
including
rock,
gabions,
sheet
pile,
concrete,
etc.
Effectiveness:
Very
effective.
Suitable
for high
velocity,
high
volume
flood
events.
May be
designed
to
accommodate
replanting
of a
damaged
riparian
area.
Limitations:
May
preclude
regrowth
of
riparian
areas.
Considerations:
Place
appropriately
sized riprap
along the
eroded
embankment
slope in
sufficient
quantities
to resist
scouring
effects of
higher
velocity
flows and
protect
the
embankment
slope from
future
flood.
damage.
Effectiveness:
Very
effective
in areas
of
moderate
flow
velocity
and volume
when
appropriately
graded
material
is placed
in
sufficient
quantity
and
layered so
fines are
not
eroded.
Water
velocity
will
determine
size and
volume of
riprap.
Limitations:
Extensive
use of
riprap may
preclude
re-growth
of
riparian
areas.
Access
may limit
where
riprap can
be placed.
Considerations:
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