Transcript Slide 1

Why coastal defense structures are
used?
1. To prevent shoreline erosion and flooding of
the hinterland.
2. To shelter harbor basins and harbor entrances
against waves.
3. To stabilize of nevigation channels at inlets.
4. To protect of water intakes and outfalls
5. To retain or rebuild natural sytems(cliffs,
dunes) or protect mans artifacts(buildings)
landward of the shoreline.
What kinds of conditions should be
taken into?
1.
2.
3.
4.
Stability
Safety
Serviceability
Economy
PLANNING DESIGN:
COASTAL PROTECTION
BY
COASTAL PROTECTION BY
MAN
NATURE
SHORE ROCK
SEA WALL
ROCK REEF
SUBMERGED BREAKWATER
ROCK ISLAND
OFFSHORE BREAKWATER
HEADLAND
HEADLAND BREAKWATER
ROCK PERPENDICULAR TO SHORELINE
GROINS
SEA FLOOR VEGETATION
BOTTOM MATTRESS
DUNE
DYKE
MATERIALS TRANSFER TO SHORE BY:
WIND DRIFT RIVERS LONGSHORE LITTORAL
DRIFT
ARTIFICIAL NOURISHMENT FROM LAND
SOURCES
SEA BOTTOM TRANSFER
ARTIFICIAL NOURISHMENT FROM OFFSHORE
SOURCES
Nature vs Man on coastal defense
PLANNING DESIGN:
Hard Shoreline Protection Structures
PLANNING DESIGN:
• Groins are structures built out from the
shoreline to trap sand in the longshore drift.
• Breakwaters are built offshore, parallel to the
coast. The purpose of a breakwater is to lessen
the impact of waves on the shore, much like a
natural reef, and it need not protrude from the
water to do so.
• A tombolo is a sand spit that forms between the
beach and a breakwater. A groin and a
breakwater are sometimes combined into a T
shaped structure.
• A jetty is much larger than a groin, and is built to
stabilize an inlet or other coastal feature rather
than to capture sand.
PLANNING DESIGN:
Hard and Soft Shoreline Protection Structures
PLANNING DESIGN:
• A sand hoft is an offshore island created by the
accumulation of sand around an old jetty that is
no longer attached to the land due to shoreline
retreat. These can have a stabilizing effect on
the beach in much the same way a breakwaters
and natural barrier islands.
• A seawall is an onshore construction used when
erosion is so great that there is no beach left.
Seawalls are large heavy structures that face the
sea, while bulkheads are lighter structures built
in protected areas.
Breakwaters:
The breakwaters are generally classified in two
types.
• Shore-connected Breakwaters: Acts as an
total littoral drift barrier in the surf zone. The
accretion extends along the seaward face of
breakwater building a berm. Erosion starts from
the other side of the shore
• Off-shore Breakwaters: Off-shore Breakwaters
provides protection from wave action to a area
or shoreline located on the leeward side of the
structure. Offshore breakwaters are usually
orients approximately parallel to shore and also
serve as a littoral barrier sediment trap.
Breakwaters:
The types of breakwaters according to their construction
methodology and dimensional and material characteristrics
are listed below.
A) Reef Breakwaters
B) Floating Breakwaters
C) Vertical-front breakwaters
D) Piled breakwaters
E) Rubble Mound Breakwater
CLASSIFICATION OF COASTAL PROTECTION
CONCERNS &SOLUTIONS TO THEM
SHORELINE
BACKSHORE
HARBOR
INLET
STABILIZATION
PROTECTION
PROTECTION
STABILIZATION
SEAWALL
BULKHEAD
REVETMENT
GROIN
DETACHED
BREAKWATER
BEACH
NOURISHMENT
SAND
BYPASSING
AT INLET
SEAWALL
JETTIES
PROTECTIVE
BEACH
SHORECONNECTED
BREAKWATERS
SAND DUNE
REVETMENT
BULKHEAD
JETTIES
DREDGING
OFFSHORE
BREAKWATERS
CONSIDERATIONS
Hydraulics
Sedimentation
Control Structure
Maintenance
Legal Requirements
Environment
Economics
Navigation( for harbor
pro. and inlet stabil.)
CHAPTER 6: MITIGATION
STRATEGIES
Tsunami can not be felt aboard
ships nor can they be seen from
the air in the open ocean.
Learn about :
• International Tsunami Information
Centre (ITIC)
• International Tsunami Warning
System (ITWS)
http://www.prh.noaa.gov/itic/
• Mandate
• Functions
• Research and Data Collection
Responsibilities
• Visiting Scientists Program
• Education, Preparedness &
Disaster Reduction
What is the International Tsunami
Warning System (ITWS)?
• Seismic station
• Tide station
International Tsunami Warning System
(ITWS)
• ITWS includes 31 seismic stations &
more than 60 tide stations
• The stations have ability to transmit
their data immediately & in real time
to the headquarters at PTWC in
Hawaii.
DART SYSTEM
• http://www.pmel.noaa.gov/tsunami/Dart/
How does the International
Tsunami Warning System
Work?
• Tsunami WARNING
&
• Tsunami WATCH
Mooring System
• A DART system consists of a
seafloor bottom pressure
recording (BPR) system
capable of detecting tsunamis
as small as 1 cm, and a
moored surface buoy for realtime communications.
• An acoustic link is used to
transmit data from the BPR on
the seafloor to the surface
buoy.
• The data are then relayed via a
GOES satellite link to ground
stations, which demodulate the
signals for immediate
dissemination to NOAA's
Tsunami Warning Centers and
PMEL.
USGS-NOAA
Surface Buoy
• The surface mooring uses a 2.5 m
diameter fiberglass over foam disk
buoy with a gross displacement of
4000 kg.
• The mooring line is 19 mm
8-strand plaited nylon line with a
rated breaking strength of 7100 kg
and is deployed with a scope of
0.985.
• This maintains a tight watch circle
to keep the buoy positioned within
the narrow cone of the acoustic
transmission.
• Two downward looking transducers are mounted on the buoy bridle at a
depth of 1.5 m below the sea surface.
• A multi layered baffle system of steel, lead, and syntactic foam shields
the transducers and cushions them with rubber pads for a soft mount.
Bottom Package
• Consists of a Bottom Pressure Recorder, an acoustic modem,
acoustic release unit and battery pack bolted to a platform, to
which a disposable anchor, flotation, and recovery aids are
attached.
• Moorings are designed
to free-fall to the bottom
and are deployable for
24 months at depths
of 6000 m; recovery is
initiated by triggering the
acoustic release to
separate from the anchor,
at which point the flotation
brings the unit to the surface.
Bottom Package
These systems have measured tsunamis
characterized by amplitudes less than 1
cm in the deep ocean, using a quartz
crystal pressure transducer that is
sensitive to changes corresponding to less
than a millimeter of equivalent sea level
change in the tsunami frequency band.
Dissemination of Watches & Warnings by ITIC
When Earthquake is Strong Enough to Cause a
Tsunami !!
• Monitoring the tide gauges near the epicenter
• Watch bulletins for all earthquake ≥ 7 in the
Aleutian Islands & ≥ 7.5 elsewhere in the Pacific
• Watching cancellation: Negligible tsunami
or no tsunami
Watching
Warning if a tsunami threat
No Tsunami Warning
Issued at 26 Dec 2004
Disaster !!
No Tsunami Warning System
exists for the Indian Ocean !!
The flooding of an area can extend
inland by 1000 feet (305 m) or
more, covering large expanses
of land with water
& debris.
Complicated behavior of tsunami
waves near the coast !
• The first run-up of a tsunami is
often not the largest.
• Do not return to a beach several
hours after a tsunami hits.
Are tsunamis so destructive?
Be Prepared for Tsunamis
& Protect Yourself
Be Prepared for Tsunamis
& Protect Yourself
Tsunami Preparedness
•
•
•
•
•
Know the risk.
Plan and practice evacuation routes.
Discuss tsunamis with your family.
Talk to your insurance agent.
Use a NOAA Weather Radio.
Similar Tsunamis,
Similar Strategies for
Survival
If a Strong Coastal Earthquake
Occurs . . .
Drop, cover, and hold until the
shaking stops!!
Tsunami is coming!
What you must do!
Tsunami is coming!
You are at the shore
What you must do!
Tsunami is coming!
You are at the shore
What you must do!
If a Tsunami Warning Is Issued
• If in a tsunami risk area, evacuate
immediately.
• Follow instructions issued by local
authorities.
• Get to higher ground as far inland as
possible.
After Tsunami Is Gone
• Listen to a NOAA Weather Radio or Coast
Guard emergency frequency station.
• Return home only after local officials tell
you that it is safe.
Tsunami is coming!
What you must do,
If you are on a boat!
If a Tsunami Warning Is Issued
• Do not return to port if you are at sea
• Rapid changes in water level causing
unpredictable dangerous currents in
harbors and ports.
If a Tsunami Warning Is Issued
 Contact the harbor authority before
returning to port making sure to verify that
conditions in the harbor are safe for
navigation and berthing.