Introduction
Problem:
Severe
roadway
and ditch
erosion
due to
water
velocities
eroding
the ditch
and
overflow
areas.
Mitigation
Objective:
To
strengthen
eroded
areas
and/or
redirect
floodwaters
away from
ditch
areas
vulnerable
to
erosion.
The
following
have been
identified
as common
mitigation
measures
used to
protect
road
facilities:
Increase
the
capacity
of the
roadway
ditch by
increasing
its depth
and/or
width.
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Effectiveness:
-
Very
effective
in
areas
of
low
to
moderate
flow
velocity
where
overtopping
of
the
roadway
ditch
causes
the
damage.
-
Effectiveness
in
high
flows
can
be
increased
by
lining
the
ditch,
embankment
slope
protection,
or
installing
check
dams.
Limitations:
-
In
areas
of
high
velocity
flows,
or
if
ditch
is
constructed
from
fine,
easily
eroded,
materials,
additional
measures
may
be
needed.
-
May
require
increased
slope
angles
on
either
side
of
ditch.
Considerations:
Line
the ditch
with rock,
concrete,
asphalt,
or
vegetation
to prevent
ditch
erosion.
Use
larger and
coarse-grained
materials
to protect
against
high
velocity
flows.
Effectiveness:
-
Very
effective.
-
Suitable
for
high-flow
velocity,
and
high-flow
condition.
-
Grass
lined
ditches
provide
bio-filtration
and
sediment
reduction.
Limitations:
Considerations:
Install
additional
culverts
across
roadway to
cut off
the flow
so as not
to exceed
the
capacity
of the
roadway
ditch.
This
measure
will
address
the
problem of
ditch
erosion
when
excessive
flow in
the ditch
is either
overtopping
the road
or is
causing
erosion of
the road
prism.
Cross
culverts
are
usually
small-sized,
ranging
from 18 to
24 inches
in
diameter.
Effectiveness:
·
Very
effective
in
reducing
the volume
of runoff
in the
ditch
line.
Install
low-height
barriers (check
dams),
usually
made of
loose
rock, to
slow the
velocity
of the
storm
water and
reduce the
scouring
action of
the flow.
Effectiveness:
Limitations:
Considerations:
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