coastal geohazards and few mitigation methods file• flood is a overflow of water that submerges...
TRANSCRIPT
Various Geohazards
The various Geohazards along the coastline can be listed as:-
Coastal Areas
•Cyclones
•Tsunami
Rivers (At Delta)
•Tidal Bore
•Floods
Others
•Earthquakes
•Landslides
The presentation includes discussions about Cyclones, Tidal Bore,
Floods and Tsunamis
Measures to mitigate Coastal Hazards
• Reactive Measures (Post Hazard protection methods)
• Pro active Measures (Pre Hazard protection methods)
Implement Coastal Protection Systems proactively
COASTAL PROTECTION
But always be prepared to maintain it on a yearly basis . • Be prepared to give reactive measres against any of natural calamities
Cyclones
• A cyclone is an area of closed, circular fluid motion rotating in the
same direction as the earth.
• Most large-scale cyclonic circulations are centered on areas of
low atmospheric pressure.
• For a cyclone to form, the ocean waters need to be warm at least
26°C.
Destruction caused by Cyclones
• Three elements associated with cyclones cause destruction
during its occurrence.
• Strong Winds/Squall : Damages infrastructure through high
speed winds.
• Torrential rains and inland flooding: Torrential rainfall (more
than 30 cm/hour) associated with cyclones is another major
cause of damages.
• Storm Surge: Defined as an abnormal rise of sea level near
the coast caused by a severe tropical cyclone, which
causes coastal erosion
• Cyclones remove forest canopy as well as change the
landscape near coastal areas, by moving and reshaping sand
dunes and causing extensive erosion along the coast.
• Cyclones reshape the geology near the coast by eroding
sand from the beach as well as offshore, rearranging coral,
and changing dune configuration onshore.
Tidal Bore •It is the phenomenon where in, “the leading edge of the tide forms the
wave that travels in the direction opposite to the river flow” near to a
relatively narrowed river mouth.
• Occur in areas of the large tidal range (more than 6 m) and where
the incoming tides are funneled into shallow channel.
Funnel shape or narrow edge
Salient Features of Tidal Bore
•The rumbling noise, intense turbulence and turbulent mixing
generated during the bore propagation
•This funnel shape causes the tidal range to increase and decrease
the duration of the flood tide.
• Takes place only at the flood tide and not at the time of ebb tide.
•Large Bores are unsafe for shipping, but presents the opportunities
for river surfing.
• The tidal bores may be dangerous .Tidal bore occurs in
the Ganges &Brahmaputra Rivers (India); the Indus River
(Pakisthan); and the Qiantang River(China)
• Causes loss of damage to the lives.
• Tidal bores can tear vegetation like trees from their roots
• Effects shipping, Navigation activities, fishing etc
• Animals slammed by the leading edge of a tidal wave can
be left dazed or dead in the silty water.
Damages Caused due to Tidal Bore
Floods
• Flood is a overflow of water that submerges the land which is dry.
Flooding occurs most commonly from heavy rainfall when natural
watercourses do not have the capacity to convey excess water.
• Flood in coastal area can be much more problematic, as in high tide
condition there may not be access for water to drain and hence the
flood remains for a long time.
Factors causing flood
• Other factors which may contribute to flooding includes:
• Volume, spatial distribution, intensity and duration of rainfall
over a catchment
• The capacity of the watercourse or stream network to convey
runoff
• Catchment and weather conditions prior to a rainfall event;
• Ground cover
• Topography
• Tidal influences.
Tsunami
•Tsunami, also known as a seismic sea wave is the series of the
water waves caused due to the displacement of the large water
bodies.
•They consists of the waves lasting from few minutes to several hours.
•The wavelength of the waves generated during tsunami is very longer
and the wave height may be as high as 10 m.
•Tsunami initially represents the rising tide and then transforms into
the breaking wave.
•Earthquakes, volcanic eruptions and underwater explosions
landslides, glacier calving, meteorite impacts and other disturbances
have the potential to generate a tsunami.
• The principal generation mechanism of a tsunami is the
displacement of a substantial volume of water or perturbation
of the sea.
• Tsunami can be generated when the sea floor abruptly
deforms and vertically displaces the overlying water.
• when earthquakes occur beneath the sea, the water above the
deformed area is displaced from its equilibrium position.
• More specifically, a tsunami can be generated when thrust
faults associated with convergent or destructive plate
boundaries move abruptly, resulting in water displacement.
General Mechanism
Drawing of tectonic plate boundary before earthquake
Overriding plate bulges under strain, causing tectonic uplift.
Plate slips, causing subsidence and releasing energy into water.
The energy released produces tsunami waves.
• The amount of energy and water contained is very huge.
• The initial wave of tsunami is very tall.
• Most of damage is caused due to huge mass of water behind the initial
wave front.
• Destruction is caused by two mechanisms : the smashing force of the
huge wall of water and destructive power of the large volume of the
water and draining off the land.
Salient Features of Tsunami
Effects of Tsunami
• Loss of the human Life
• Flooding and the contamination of the drinking water may lead to
spreading of various diseases
• Tsunami also has adverse effect on the environment. It destroys
the animal, as well as the plant life.
• It causes the salination of the water bodies such as river, lakes etc
• Destruction to the nuclear plants.
• Impact of tsunamis is not limited to coastal areas, their destructive
power can be enormous and they can affect entire ocean basins
• The 2004 Indian Ocean tsunami ,the deadliest natural disasters in
human history with at least 290,000 people killed or missing in 14
countries bordering the Indian Ocean.
All the above said phenomenon described above have very high
impact specifically on coastal regions
Hence the need to protect coastlines .
Coastal Protection Management Types of approaches
Hard engineering approach( structural approach):
Construction of physical structures to defend against
erosive power of waves
Soft engineering approach ( Non- Structural approach):
Focuses on planning and management so that both
coastal areas and properties may not be damage by erosion
Aims at changing individual behavior towards coastal
protection by encouraging minimal human interference
Types of Coastal Protection Works
Hard Engineering Methods
Groynes
Sea Walls
Revetments
Jetties
Breakwater
Soft Engineering Methods
Beach Nourishment
Artificial Reef
Sand Dune Stabilization
Beach Drainage
Buried Revetments
Revetments Revetments are sloping structures placed on the banks or cliffs in such a way so as to absorb the energy of incoming water Advantages They catch sediment from long shore drift which helps to buildup a beach Disadvantage It stops the rest of the beach further down from getting any more sediment, so beach may become smaller
Sea walls
Seawalls are curved concrete walls that stops strong
waves hitting the cliffs.
Built along the coast to absorb energy of waves before
they can cause erosion
Can be made of blocks of concrete wood or rocks
Advantages OF SEA WALLS & BULK HEADS
Protects the foot of the cliff from erosion and also can prevent
flooding
Disadvantages
Expensive to build and maintain .
It makes the backwash very strong when wave hits it.
Break waters It can be built with one end attached to the coast or away from the coast. Usually built to protect beach that is sloping. When waves hit breakwaters the power of waves is reduced on the break water structure
Advantages
When constructed offshore it can create a zone of calm
water behind them allowing deposition to occur, forming
beaches.
Waves wont be as eroding.
Disadvantages
Unprotected areas of beach will not receive any new
sediments and beach may slowly shrink.
Materials deposited behind breakwater are protected but the
zone located away from breakwater is not
Groynes
Groynes are fences that go along the beach with angles to
prevent long shore drift.
Energy from waves is absorbed or reduced by groynes
Advantages: It slows down the flow along the shore drift and
nourishes the shore.
Disadvantages: they have to be replaced every 15-20 years
Significance of the Structures
Groynes/Spurs
Off shore Breakwater
Submerged Reefs
•Breakwaters, reduce the intensity of
wave action in inshore waters and
thereby reduce coastal erosion.
•Submerged Reefs, provide a
platform/reef such that wave breaks
over the top of the reef. It helps to
alter the waveform and refracts back
reducing the impact.
•Groynes run perpendicular to the
shore, extending from the beach into
the water
Special Applications
- Antiscour
solutions (e.g
harbors)
- Foundation filter
for lagoon works
- Foundation filter for
coastal structures
Soft Engineering Methods
Beach Nourishment
Introduction of sediment onto a beach. Create wider beaches.
Fill material is sand
Advantages :
Creates area for recreation.
Protection against coastal storms
Reduced need for hard structures.
Resorted wildlife habitat, tourism
Disadvantages :
Requires maintenance
Costly to transport large amounts of sand
to fill up the beach.
Artificial Reef
structure located offshore designed to induce wave breaking in a manner that
creates a wave suitable for surfing.
Advantages :
• Reduces wave energy reaching the shore
Creates a wider, more stable section of a beach
•Man made reefs are as productive as natural in enhancing fishing and serve
as under sea barriers to reduce the impact of wave energy
Sand Dune Stabilization : An accumulation of loose sand heaped up by the wind,
act as a flexible natural protection against erosion and flooding. held together by specially adapted sand dune vegetation Shrubs and trees are planted to stabilise with their roots reaching ground wards to tap water and anchors the sand in this process
Beach Drainage :Recent Development in draining the beaches.
A natural pipe is laid down below the high tide level and the water is pumped out to a pumping station and again returned to the sea. In this case, the sand gets dried up due to lowering of water table. Should be done during low tide. Simple to install. invisible structure.
Ashish D. Gharpure 53
Photographs Indicating the progress of the development of the Kovallam Beach.
The red dotted line indicate the shore line before the reef construction.
Yellow line in adjoining figure indicate the progressed shoreline.
CONVENTIONAL MATERIALS FOR
COASTAL STRUCTURES
Previously concrete, timber, sheet or cellular steel, rock, asphalt and rock-filled materials were used.
Drawbacks of using these materials is degradation over a period of time due to sea water salinity and environmental factors
Also these materials depends on factors such as material availability, cost and site conditions, type of soil, magnitude of wave forces, availability of construction equipments and technical expertise required for installation.
So these problems can be overcome with the use of advanced engineered products if properly designed and used.
INNOVATIVE ENGINEERED METHODS
Mechanically Woven Steel Wire Mesh Crates:-
Geosynthetic Products :-
Geotextile Bags Geotextile Tubes Geotextile Filters Ballasted Filtering Mattress SARMAC
Gabions
Reno Mattresses
Special Products Like Sarmac and ACBM:-
GEOTEXTILE BAG
Small volume containers that are filled on land or above water and then placed either near water or below water level.
Geotextile bags range in volume from 0.05m3 to 5m3
Geotextile Bag
METHOD STATEMENT TO PRODUCE GEOTEXTILE BAG
Bag Height
Proposed Area To Be Stitched
Precut Geotextile
Panel
Stitched Area
Double loop seam using PP/PET thread
Fabrication of Geotextile Bag in factory
GEOTEXTILE TUBE
• Tubular containers that are
formed in-situ on land or in
water.
• Generally large volume units
filled in barges above water
and then deposited into
submarine environments.
• Geotextile Tubes are mainly
applied in Break waters,
Groynes, Jetties, Marinas, and
Sea Walls.
• Geotextile tubes range in size
from 1m to 10m in diameter,
and up to 200m in length
GeotextileTube
Geotextile tubes are used for three main purposes
• To build coastal and river structures by filling them
with sand or mortar,
• For dewatering a wide variety of wet slurries, wastes
and sludge, and
• For containing, dewatering and beneficially re-using
dredged material
SARMAC
The SARMAC mattress is
specifically designed to
provide the ideal anchorage
and protection from damage of
high cost pipelines and cables.
SARMAC units can be made in
a wide range of sizes and
weights, and may be placed
under, alongside and over a
pipeline individually, or in any
combination, continuously or
spaced at intervals.
- Anti scouring quay
wall protection
-Pipelines Anchorage
and protection
Sarmac Bituminous Mattresses
Geotextile top covering
Liftng loop Zinc coated wire mesh
reinforcement
Flexible sand asphalt mastic
and stone filling Zinc-coated wire
mesh cage
Sand asphalt mastic
Geotextile outer
covering
to undersite
and sides
Geotextile top
covering
Sand asphalt mastic
Zinc-coated wire
mesh reinforcement
Flexible sand
asphalt mastic
and stone filling
Zinc-coated wire
mesh cage
Sand asphalt mastic
protective layer
Additional geotextile lining
Geotextile outer covering
to underside and sides
Additional geotextile lining
(if necessary and requested)
Upper sand
asphalt
mastic
protective
layer
(if necessary
and
requested)
Manufacturer’s
serial number
SARMAC Details
CASE REFERENCES
ALGERIA-ITALY
GAS PIPELINE - 1981/82
This gas pipeline is 2,500 km long, 70
km of which are across the
Mediterranean Sea, between Sicily
and Africa.
The main application for SARMAC
units was in anchoring the pipeline
when crossing the depressions of the
seabed.
400 SARMAC units were used in this
work. They were fabricated in a
facility close to the harbour of
Messina.
Product Introduction - ACMB
ACBM – Rectangular unit made up of
concrete blocks which can be
manufactured in different thickness,
joined by means of polypropylene ropes.
The ACBM’s are flexible
mattresses that can be used for
the anchorage/protection of
pipelines and for scour protection
of structures.
Characteristics
ACBM Panels are developed in such a manner to offer high degree of flexibility
in both directions and provide protection in various applications.
The concrete is made of pozzolanic cement or portland cement with w/c ratio of
0.45 having minimum resistance of Fck = 45 N/mm2 to provide the required
functionality.
The blocks are connected with PP ropes or cables having minimum diameter to
ensure the safety working factor of 7 during lifting operations. These ropes are
looped at edges to facilitate lifting operations.
Materials are non soluble in sea water and are chemically stable for the design
life of the mattress, so that there is no reduction in compressive strength.
Why ACBM solution
ACBM are specifically designed for pipe line protection works so better
performances can be achieved in pipeline protection application than other
technical solutions.
ACBM can be installed quicker than other solutions. Provide advantages on
cost savings.
ACBM have design life of minimum 25 years during which no maintenance is
required.
Best solutions in terms of handling. In case of damages to pipeline these
mattresses can be removed.
Prevent scour action on pipeline reducing flow of fines like sand.
GABIONS
Rectangular crates Different sizes as per requirement, inner space of crate is partitioned with diaphragms at 1 m c/c. Connection to Adjacent Gabion - lacing wire. Used for offshore Breakwaters, Groynes, Jetties, Marinas and Seawalls.
RENO MATTRESS
Similar to Gabion unit Large dimensions in plan and of smaller thickness. Application for Shore erosion protection
Case Studies
Ashish D. Gharpure 87
CASE STUDY- 1
Nourishment of Spurs and Bank Protection Works for Eroding Zone of Nishchintpur Bank - Kolkata Port Trust
• 5 to6 km of stretch required to be protected against erosion • Part of the river bank has lost about 80 sqkm of land during last 20 years. • Homes and lands washed away with water and life of the people was badly
affected due to the hungry tides of the river.
Material types and Quantities
Major materials used are as follows:
Material Unit Quantity
Multifilament Woven Geotextiles Sqm 58,000
Geotextile bags (Geobags) weighing 100 kgs
No 8,75,000
Jute Geotextiles Sqm 5,800
Laterite Boulders MT 53,000
Other items of work included Earthwork in excavation and filling,
surface dressing, supply and laying of rope gabions and other
Associated works
POSITION OF SITE BEFORE & AFTER COMPLETION FOR SPUR NO- 106
Position Prior to Work
Position after Completion of Work
Case Studies
Ashish D. Gharpure 93
CASE STUDY- 2
Emergent Works for the Protection of Rohmoria Area in Dibrugarh District. - Assam Water Resource Department • Rohmoria, in the upper reaches of the Brahmaputra River in Assam, is
an area most severely affected by river erosion. • The area has witnessed erosion for the last sixty years and
more than 25 villages have been wiped out by erosion
Major materials used are as follows:
Material Unit Quantity
Non Woven Geotextiles for filter Sqm 64,300
Geotextile bags (Geobags) weighing 126 kgs
No 8,01,151
DT PVC Coated Gabions Nos 3,400
Polymer Rope Gabions Nos 2,889
Other items of work included Earthwork in excavation and filling,
surface dressing, supply and laying of rope gabions and other
associated works.
Material types and Quantities
Case Studies
Ashish D. Gharpure 99
CASE STUDY- 3
LNG, PETRONET, COCHIN
• Deposition of the silt near the existing trestle, had created hindrance for the ships to halt
• Falling of the Beach material into LNG Basin.
Case Study : LNG, PETRONET, COCHIN
• Structures : A - Breakwater – In order to achieve required
transmissibility at the jetty and to reduce the siltation, it is proposed to extend the existing breakwater.
– This 500 m long structure will take care globally, for avoiding the accumulation of the silt in between the existing breakwater and the trestle, the silt which is supposed to come from the right hand site of the existing rubble mound breakwater.
Ashish D. Gharpure 100
• Structures: B - Groynes
– To trap the silt and
improve the sedimentation. This structure is parallel to the existing trestle.
– This restriction will trap the silt and will help in beach nourishment at the left zone of the existing rubble mound.
Ashish D. Gharpure 101
Beach Nourishment due to Groynes
– Structures: C - Protection Bund
– This is being provided to prevent falling of any beach material into the LNG basin due to any wave action or current caused.
– This has helped to restrict the progressive movement of high tide line towards the LNG Basin area.
Ashish D. Gharpure 102
Construction Steps:
– The geotextile tubes are placed on to the pontoon and taken to the location for under water installation of the tube.
– The tubes on the pontoon are opened up and layed on the bed.
(The erratic nature of the waves and the velocity of the waves will cause difficulty for installation)
– The loops provided at the sides are used for placing the tube at the assigned position.
– The filling ports are opened and then the sand slurry is filled. The tubes are filled upto 70 to 75%.
Ashish D. Gharpure 103
Case History – Tidal Bore
1) Bank Protection Works Along river Ganga
• Presence of the Tidal Bore has caused, Continuous meandering
change in channel geometry and configurations. It is taking away
the bank materials by the flowing water and sediments.
• Due to the high hydraulic forces prevalent at site the scouring of
the structures is caused which gives rise to high rate of soil
erosion.
Direction of Tidal Bore
Small volume containers that are filled on land or above water and
then placed either near water or below water level.
Geotextile bags range in volume from 0.05m3 to 5m3
MacBag
Environmental friendly Solutions against
Tidal Bore -GeoBag
Proposed solution
Components of the proposed solution
• Sack Gabions
• Small sized Geotextile Bags
• Gabions
Reclamation Bunds at Ponnani Fishery Harbour – Coastal Protection Work – Kerala (India)
Reclamation Bunds at Ponnani Fishery Harbor (India)
Case References – Coastal Protection
Special size Geotextile Bag Installation (Italy)
Geotextile Tube Installation (Italy)
:
Abroad Case References – Coastal Protection