Land Use and Vertical Evacuation

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Land Use and Vertical Evacuation In a Tsunami
Hazard Area
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Near-field, or locally generated tsunamis,
however, are much less tractable. A tsunami
generated by a Cascadia subduction zone
earthquake will arrive in less than 45 minutes.
For these events, as was the case in Banda Aceh,
the earthquake must be the warning. Citizens must
know where to evacuate from and where to evacuate
to, and must do so quickly and on foot.
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Note the long peninsulas or spits of low-lying
ground. Ocean Shores peninsula is 7 miles long
and Long Beach peninsula is 20 miles long with
little or no high ground over those distances.
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Typical time histories of the modeled tsunami for
the Washington coast. Note that significant
flooding is expected within 30 minutes of
earthquake.
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1 m/sec2 mph
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ATC-64 Guidelines for Design and Management
of Structures for Vertical Evacuation from
Tsunamis
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Berm combined with a community facility. This
berm conceals underground parking for a police
station. Ocean facing walls can deflect incoming
waves while sloped sides provide for quick
access.
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Sports complex. Designed for assembly use, this
type of structure can accommodate circulation and
service needs for large numbers of people.
(Photo courtesy of John Hooper, Magnusson
Klemencic Associates)
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Hotel and convention complex. (Image courtesy of
John Hooper, Magnusson Klemencic Assoc)
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4.5.6 Parking Garages Parking garages are
revenue generating facilities, especially for
locations that attract large numbers of tourists.
Parking garages are also open structures that
allow ample opportunity for ingress, and interior
ramps allow easy vertical circulation to higher
levels within the structure. Parking garages can
also be used to provide additional community
amenities on the top level, including parks,
observation decks, and sports courts. Parking
garages tend to be low-cost, efficient structures
that could be designed with higher levels of
engineering. With additional code review and
inspection by the local jurisdiction, parking
garages could also be used as vertical evacuation
structures.
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4.5.7 Existing Buildings Historic damage
patterns suggest that many structures not
specifically designed for extreme tsunami loading
can survive tsunami inundation and provide areas
of refuge. It is possible that some existing
structures could serve as vertical evacuation
structures or could be made more
tsunami-resistant with only minor modifications.
An assessment of both the functional needs and
potential structural vulnerabilities would be
required to determine if an existing building can
serve as a vertical evacuation structure. In
some situations, providing some level of
protection is better than none. An example of
this concept is shown in Figure 4-5. In a
tsunami evacuation map for Waikiki, concrete and
steel framed buildings six or more stories in
height are considered to provide increased
protection on or above the third floor, and are
identified as potential areas of refuge.
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5.1 Siting Considerations Vertical evacuation
structures should be located such that all
persons designated to take refuge can reach the
structure within the time available between
tsunami warning and tsunami inundation. Travel
time must also take into consideration vertical
circulation within the structure to levels above
the inundation depth. Structures located at one
end of a community may be difficult for some
users to reach in a timely fashion. Routes to the
structure should be easily accessible and well
marked. Location of vertical evacuation
structures within a community should take into
account potential hazards in the vicinity of a
site that could jeopardize the safety of the
structure, and should consider that natural
behaviors of persons attempting to avoid coastal
flooding.
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Tsunami Inundation Map For Seattle
This map is based on the well-studied earthquake
of circa 935 A.D. Its recurrence interval is
estimated to be about 2,500 years
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Seaside, Oregon Pilot Project
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The features of this escape berm illustrated in
Figure C-5 include the following Note 1. The
semi circular configuration was selected to help
divert tsunami flood waters and potential
floating debris around the facility and away from
the access stairs and ramp on the back side. The
elevated area is over 31,000 square foot in size
and could handle over 3,000 evacuees at 10 square
foot per person. There is sufficient space in
the elevated area to accommodate a comfort
station that could be used for both day to day
recreational purposes and emergency use. Note 2.
The ocean facing side of the berm is essentially
vertical to prevent tsunami flood waters and
potential floating debris from moving upslope
into the area of refuge. Trees and other
landscaping can be used to hide the vertical face
and create an aesthetically appealing feature.
Note 3. The sides of the berm can be slope to
provide additional access to the area of vertical
refuge. Care should be taken however to
orientate the slope so that water and debris are
not inadvertently channeled upslope. Notes 4 and
5. Stairs and ramps on the back side provide
primary access for both recreational and
emergency purposes.
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Note 1. The semi rectangular layout is selected
based on the gymnasium requirements for the
school. The elevated area is over 10,000 square
feet in size, and can handle over 1,000 evacuees
at 10 square foot per person. Using available
census information it has been determined that
this should be sufficient for the area it is
intended to serve. Note 2. Stair access is
designed using a concrete encased stair structure
that will have its own inherent strength. The
shape is intended to channel tsunami flow and
potential debris away from both the structure and
the stair system. Note 3. An additional ADA
accessible ramp system is considered for a future
phase of the project. This could utilize sheet
piles and fill to further channel tsunami flow
and waterborne debris away from the structure.
Note 4. The structural system utilizes a
concrete moment frame to create an open lower
level that will keep hydrodynamic loads on the
structure to a minimum. This includes using
circular shaped columns. Note 5. Additional
strength can be provided to the system by using
walls that parallel the anticipated tsunami
inundation flow. Note 6. The primary structure
can be either separate from the stair structures
or tied into them to provide additional strength.
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ATC-64 is scheduled to be released in October of
2007 as a joint project of the National Tsunami
Hazard Mitigation Program and the Federal
Emergency Management Agency. An outreach and
education module will be prepared in the next
year.
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Nature, to be commanded, must be obeyed Francis
Bacon, Novum Organum