coastal geohazards and few mitigation methods file• flood is a overflow of water that submerges...

Coastal Geohazards and

few mitigation methods

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

Damage Caused by Geohazards

Damage due to Cyclone

Damage due to Tidal Bore

Damage Caused by Geohazards

Damage due to Flood

Damage due to Tsunami

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

Type 1 : Cyclone

• Definition

• Mechanism

• Possible Damages

• Examples & Video

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.

Cyclones

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.

Type 2 : Tidal Bore

• Definition

• Mechanism



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

Tidal Bore

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

Type 3 : Floods

• Definition

• Mechanism



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.

Type 4 : Tsunami

• Definition

• Mechanism



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.

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.

Groynes

Revetment

Bulkhead

Seawall Grass Mats

Breakwater

COASTAL PROTECTION SYSTEM

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

Bulk heads

Revetments Sea walls

Jetty Breakwaters

groynes

ANTI SCOUR MEASURES IN SPECIAL STRUCTURES

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

Bulk Heads- An upright wall

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

Cross sectional details of Breakwater

• Option : With GeotextileTube

Cross sectional details of Breakwater

• Option : With Geotextile tubes & Gabions

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 51 Good Example – but no data or reference available

Ashish D. Gharpure 52

Kovalam Beach

Submerged Reef


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.

Ashish D. Gharpure 55 Advantages of using soft rock solutions, at Kovallam.

MATERIALS FOR CONSTRUCTION OF COASTAL STRUCTURES-

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

Applications

- Free span pipelines

- Support pipelines

Geotextile Sheet

Ready for Placement

Seam Filling of Bag

Installation

Geotextile Bag Installation

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

Geotextile tubes applications only for Coastal

Fill Port

Filling of Tube Underwater placing

Pumping Equipment

Installation steps

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

Officine Maccaferri SpA - Technical Department

Installation

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.

CASE REFERENCE

Balaguer 2011 (Spain)

Block Casting unit Rope Laying

CASE REFERENCE

Placing Concrete into moulds

De-moulding of mattress panel

CASE REFERENCE

Lifting of mattress post casting

Stocking of casted panels

CASE REFERENCE

Viterbo 2010 (Italy)

Moulds ready for casting with ropes

Casted mattress

CASE REFERENCE

Lifting of casted units

Stacking of casted units

CASE REFERENCE

Installed ACBM Panels

Algeria Project

CASE REFERENCE

CASE REFERENCE

Lifting frame arrangements

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


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.

Cross- section of Spurs

Solution Adopted

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

Siltation after construction

Case Studies


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

Work in Progress

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

Work in Progress

Geobags Installed for the protection

After completion of work

Case Studies


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.


• 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.


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.


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%.


– Construction Steps:


106 Ashish D. Gharpure

Aligning of Geo-tubes for Groins


Groin construction for LNG Petro Accretion on the drift side


Groins for LNG Petro using Geo tubes


Protection Bund ( Seawall using Geo tubes)


Spreading of anchor tubes in sea for Breakwater


CASE STUDY 4

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

Technical Solution for Tidal Bore

Direction of the Bore

Tidal Bore

Solution (Cont…)

Arriving Tidal Bore

Installed Structure

Bore Tide along the river Ganga

Case References – Coastal Protection

Sea Bund Erosion protection, Shell Hazira, Gujarat, India

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

THANK YOU

coastal geohazards and few mitigation methods file• flood is a overflow of water that submerges...

Documents