Introduction
Roads
are the
most
commonly
damaged
facility
in a flood
event.
Damage
to roads
may be
caused by
floodwaters
overtopping
and
eroding
road
surfaces,
shoulders,
and
embankment
slopes,
and by
washing
out
roadway
prisms.
Mitigation
measures
identified
may also
be
applicable
to
railroads
or other
embankment
facilities
damaged by
flood
events.
Damages
to roads
and other
embankment
facilities
can be
mitigated
by:
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Assessing
the Causes
of Road
Damage
Selection
of
appropriate
mitigation
measures
for
damaged
road
facilities
depends
upon the
flow
conditions
that
caused the
damage.
Some
observations
of these
flow
conditions
can be
made
during or
immediately
after the
damage
occurrence.
If
the
elevations
of the
upstream
and
downstream
high water
marks are
nearly the
same, the
flow
conditions
across the
road were
tranquil
or
streaming,
and scour
of the
entire
road
surface
and
shoulders
will be
evident.
Erosion
of the
upstream
embankment
may have
also
occurred
and there
may be
deposition
of gravel
across the
road
surface.
Appropriate
mitigation
for this
flow
condition
includes:·
-
Hardening
the
entire
road
surface
and
shoulders
in
the
road
overflow
section,
and
-
Armoring
the
top
of
the
upstream
embankment.
If
the
upstream
and
downstream
high water
marks are
significantly
different,
the flood
flow was
likely in
a
'supercritical'
state
(rapid and
turbulent
flow) at
the
downstream
side of
the road,
and scour
of the
downstream
road
shoulder
and
embankment
will be
evident.
Appropriate
mitigation
for this
flow
condition
includes:
If
the road
prism was
washed
out, a
determination
of the
flow
conditions
will be
critical
in order
to
appropriately
design the
restoration
and
mitigation.
To
identify
the flow
conditions
that
caused
damage to
roads and
their
embankments,
determine:
-
The
upstream
and
downstream
water
surface
elevations,
and
-
The
scour
and
erosion
features
on
the
remaining
road
surfaces,
shoulders,
and
embankments.
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