CHAPTER 1: INTRODUCTION- HAZARDS-OCEANS-WAVES NATURAL HAZARDS: FLOODS FLOODS VOLCANIC ERUPTIONS...

CHAPTER 1: CHAPTER 1: INTRODUCTION- HAZARDS-INTRODUCTION- HAZARDS-OCEANS-WAVESOCEANS-WAVESNATURAL HAZARDS:NATURAL HAZARDS:

• FLOODSFLOODS

• VOLCANIC ERUPTIONSVOLCANIC ERUPTIONS

• HURRICANEHURRICANE

• DROUGHTDROUGHT

• EARTHQUAKESEARTHQUAKES

NATURAL HAZARDS:NATURAL HAZARDS:

• Hazards are unpreventable natural events Hazards are unpreventable natural events that, by their nature, may expose our that, by their nature, may expose our Nation's population to the risk of death or Nation's population to the risk of death or injury and may damage or destroy private injury and may damage or destroy private property, societal infrastructure, and property, societal infrastructure, and agricultural or other developed land.agricultural or other developed land.

NATURAL HAZARDS:NATURAL HAZARDS:• FLOODS:FLOODS: Floods are the most common and widespread of all Floods are the most common and widespread of all

natural disasters--except fire. Floods have been an natural disasters--except fire. Floods have been an integral part of the human experience ever since the integral part of the human experience ever since the start of the agricultural revolution when people built the start of the agricultural revolution when people built the first permanent settlements on the great riverbanks of first permanent settlements on the great riverbanks of Asia and Africa. Asia and Africa.

NATURAL HAZARDS:NATURAL HAZARDS:• VOLCANIC ERUPTIONS:VOLCANIC ERUPTIONS:

Volcanic eruptions are one of Volcanic eruptions are one of Earth's most dramatic and Earth's most dramatic and violent agents of change. Not violent agents of change. Not only can powerful explosive only can powerful explosive eruptions drastically alter land eruptions drastically alter land and water for tens of and water for tens of kilometers around a volcano, kilometers around a volcano, but tiny liquid droplets of but tiny liquid droplets of sulfuric acid erupted into the sulfuric acid erupted into the stratosphere can change our stratosphere can change our planet's climate temporarily. planet's climate temporarily.

• According to a new USGS According to a new USGS reports, since 1980, 45 reports, since 1980, 45 eruptions and 15 cases of eruptions and 15 cases of notable volcanic unrest have notable volcanic unrest have occurred at 33 U.S. occurred at 33 U.S. volcanoes. Volcanic activity volcanoes. Volcanic activity since 1700 A.D. has killed since 1700 A.D. has killed more than 260,000 people, more than 260,000 people, destroyed entire cities and destroyed entire cities and forests, and severely forests, and severely disrupted local economies for disrupted local economies for months to years .months to years .

NATURAL HAZARDS:NATURAL HAZARDS:Effects of volcanic eruptions:Effects of volcanic eruptions:1) pyroclastic eruptions can smother large areas of landscape 1) pyroclastic eruptions can smother large areas of landscape

with hot ash, dust, and smoke within a span of minutes to with hot ash, dust, and smoke within a span of minutes to hours;hours;

2) red hot rocks spewed from the mouth of a volcano can ignite 2) red hot rocks spewed from the mouth of a volcano can ignite fires in nearby forests and towns, while rivers of molten lava fires in nearby forests and towns, while rivers of molten lava can consume almost anything in their path as they reshape can consume almost anything in their path as they reshape the landscape; the landscape;

3) heavy rains or a rapidly melting summit snowpack can trigger 3) heavy rains or a rapidly melting summit snowpack can trigger lahars-sluices of mud that can flow for miles, overrunning lahars-sluices of mud that can flow for miles, overrunning roads and villages; and roads and villages; and

4) large plumes of ash and gas ejected high into the atmosphere 4) large plumes of ash and gas ejected high into the atmosphere can influence climate, sometimes on a global scale.can influence climate, sometimes on a global scale.

NATURAL HAZARDS:NATURAL HAZARDS:Effects of volcanic eruptions:Effects of volcanic eruptions:1) pyroclastic eruptions can smother large areas of 1) pyroclastic eruptions can smother large areas of

landscape with hot ash, dust, and smoke within a span landscape with hot ash, dust, and smoke within a span of minutes to hours;of minutes to hours;

2) red hot rocks spewed from the mouth of a volcano can 2) red hot rocks spewed from the mouth of a volcano can ignite fires in nearby forests and towns, while rivers of ignite fires in nearby forests and towns, while rivers of molten lava can consume almost anything in their path molten lava can consume almost anything in their path as they reshape the landscape; as they reshape the landscape;

3) heavy rains or a rapidly melting summit snowpack can 3) heavy rains or a rapidly melting summit snowpack can trigger lahars-sluices of mud that can flow for miles, trigger lahars-sluices of mud that can flow for miles, overrunning roads and villages; and overrunning roads and villages; and

NATURAL HAZARDS:NATURAL HAZARDS:Effects of volcanic eruptions:Effects of volcanic eruptions:1) pyroclastic eruptions can smother large areas of landscape 1) pyroclastic eruptions can smother large areas of landscape

with hot ash, dust, and smoke within a span of minutes to with hot ash, dust, and smoke within a span of minutes to hours;hours;

2) red hot rocks spewed from the mouth of a volcano can ignite 2) red hot rocks spewed from the mouth of a volcano can ignite fires in nearby forests and towns, while rivers of molten lava fires in nearby forests and towns, while rivers of molten lava can consume almost anything in their path as they reshape can consume almost anything in their path as they reshape the landscape; the landscape;

3) heavy rains or a rapidly melting summit snowpack can trigger 3) heavy rains or a rapidly melting summit snowpack can trigger lahars-sluices of mud that can flow for miles, overrunning lahars-sluices of mud that can flow for miles, overrunning roads and villages; and roads and villages; and

4) large plumes of ash and gas ejected high into the atmosphere 4) large plumes of ash and gas ejected high into the atmosphere can influence climate, sometimes on a global scale.can influence climate, sometimes on a global scale.

NATURAL HAZARDS:NATURAL HAZARDS:• HURRICANE:HURRICANE: Few things in nature can compare to the destructive force of a Few things in nature can compare to the destructive force of a

hurricane. In fact, during its life cycle a hurricane can expend as hurricane. In fact, during its life cycle a hurricane can expend as much energy as 10,000 nuclear bombs! Hurricane winds blow much energy as 10,000 nuclear bombs! Hurricane winds blow in a large spiral around a relative calm centre known as the in a large spiral around a relative calm centre known as the "eye." "eye." The term hurricane is derived from Huracan, a god of evil The term hurricane is derived from Huracan, a god of evil recognized by the Tainos, an ancient aborigines Central recognized by the Tainos, an ancient aborigines Central American tribe .American tribe .

• DROUGHT:DROUGHT: Many different climatic events can trigger Many different climatic events can trigger

crop failures including excess rainfall crop failures including excess rainfall leading to flood damage or crop disease, leading to flood damage or crop disease, heat waves, drought, fire, unexpected cold heat waves, drought, fire, unexpected cold snaps, severe storms, climate-related snaps, severe storms, climate-related disease outbreaks, and insect invasions. disease outbreaks, and insect invasions.

Nationwide losses from the U.S. drought Nationwide losses from the U.S. drought of 1988 exceeded $40 billion,. In the Horn of 1988 exceeded $40 billion,. In the Horn of Africa the 1984–1985 drought led to a of Africa the 1984–1985 drought led to a famine which killed 750,000 people.famine which killed 750,000 people.

NATURAL HAZARDS:NATURAL HAZARDS: Drought can be defined as;Drought can be defined as;• MeteorologicalMeteorological drought drought is usually based on long- is usually based on long-

term precipitation departures from normal, but there is no term precipitation departures from normal, but there is no consensus regarding the threshold of the deficit or the consensus regarding the threshold of the deficit or the minimum duration of the lack of precipitation that make a minimum duration of the lack of precipitation that make a dry spell an official drought.dry spell an official drought.

NATURAL HAZARDS:NATURAL HAZARDS: Drought can be defined as;Drought can be defined as;• MeteorologicalMeteorological drought drought is usually based on long- is usually based on long-

term precipitation departures from normal, but there is no term precipitation departures from normal, but there is no consensus regarding the threshold of the deficit or the consensus regarding the threshold of the deficit or the minimum duration of the lack of precipitation that make a minimum duration of the lack of precipitation that make a dry spell an official drought.dry spell an official drought.

• HydrologicalHydrological drought drought refers to deficiencies in refers to deficiencies in surface and subsurface water supplies. It’s measured as surface and subsurface water supplies. It’s measured as stream flow, and as lake, reservoir, and ground water stream flow, and as lake, reservoir, and ground water

levels.levels.

NATURAL HAZARDS:NATURAL HAZARDS: Drought can be defined as;Drought can be defined as;• MeteorologicalMeteorological drought drought is usually based on long-term is usually based on long-term

precipitation departures from normal, but there is no precipitation departures from normal, but there is no consensus regarding the threshold of the deficit or the consensus regarding the threshold of the deficit or the minimum duration of the lack of precipitation that make a minimum duration of the lack of precipitation that make a dry spell an official drought.dry spell an official drought.

• HydrologicalHydrological drought drought refers to deficiencies in surface refers to deficiencies in surface and subsurface water supplies. It’s measured as stream and subsurface water supplies. It’s measured as stream flow, and as lake, reservoir, and ground water levels. flow, and as lake, reservoir, and ground water levels.

• AgriculturalAgricultural drought drought occurs when there is insufficient occurs when there is insufficient soil moisture to meet the needs of a particular crop at a soil moisture to meet the needs of a particular crop at a particular time. A deficit of rainfall over cropped areas particular time. A deficit of rainfall over cropped areas during critical periods of the growth cycle can result in during critical periods of the growth cycle can result in destroyed or underdeveloped crops with greatly depleted destroyed or underdeveloped crops with greatly depleted yields. Agricultural drought is typically evident after yields. Agricultural drought is typically evident after meteorological drought but before a hydrological meteorological drought but before a hydrological drought.drought.

NATURAL HAZARDS:NATURAL HAZARDS:• EARTHQUAKES:EARTHQUAKES:

One of the most frightening and One of the most frightening and destructive phenomena of nature is a destructive phenomena of nature is a severe earthquake and its terrible after severe earthquake and its terrible after effects. An earthquake is a sudden effects. An earthquake is a sudden movement of the Earth, caused by the movement of the Earth, caused by the abrupt release of strain that has abrupt release of strain that has accumulated over a long timeaccumulated over a long time. .

• EARTHQUAKES:EARTHQUAKES:

• One of the most frightening and One of the most frightening and destructive phenomena of nature is a destructive phenomena of nature is a severe earthquake and its terrible severe earthquake and its terrible after effects. An earthquake is a after effects. An earthquake is a sudden movement of the Earth, sudden movement of the Earth, caused by the abrupt release of caused by the abrupt release of strain that has accumulated over a strain that has accumulated over a long timelong time. .

Earthquake generate seismic waves which Earthquake generate seismic waves which can be recorded on a sensitive instrument can be recorded on a sensitive instrument called a called a seismographseismograph. The record of . The record of ground shaking recorded by the ground shaking recorded by the seismograph is called a seismograph is called a seismogram.seismogram.

The Earth's outermost surface is broken The Earth's outermost surface is broken into 12 rigid plates which are 60-200 km into 12 rigid plates which are 60-200 km thick and float on top of a more fluid zone, thick and float on top of a more fluid zone, much in the way that icebergs float on top much in the way that icebergs float on top of the oceanof the ocean

OCEANSOCEANS

• cover about 70% of the Earth's cover about 70% of the Earth's surfacesurface

• contain roughly 97% of the Earth's contain roughly 97% of the Earth's water supplywater supply

• moderate the Earth's temperature by moderate the Earth's temperature by absorbing incoming solar radiation absorbing incoming solar radiation

OCEANSOCEANS

•Until the year 2000, there were four recognized oceans: Until the year 2000, there were four recognized oceans: the Pacific, Atlantic, Indian, and Arctic. In the spring of the Pacific, Atlantic, Indian, and Arctic. In the spring of 2000, the International Hydrographic Organization 2000, the International Hydrographic Organization delimited a new ocean, the delimited a new ocean, the Southern Ocean (surrounds (surrounds Antarctica).Antarctica).

OCEANSOCEANS

OceanArea (square

miles)Average Depth

(ft)Deepest depth (ft)

Pacific Ocean

64,186,000 15,215Mariana Trench, 36,200

ft deep

Atlantic Ocean

33,420,000 12,881Puerto Rico Trench,

28,231 ft deep

Indian Ocean

28,350,000 13,002Java Trench, 25,344 ft

Southern Ocean

7,848,300 sq. miles (20.327

million sq km )

13,100 - 16,400 ft deep (4,000 to 5,000 meters)

the southern end of the South Sandwich Trench, 23,736 ft (7,235 m) deep

Arctic Ocean 5,106,000 3,953Eurasia Basin, 17,881 ft

OCEANSOCEANS

• Pacific →Pacific → the most active tsunami the most active tsunami zone, according to the zone, according to the U.S. National U.S. National Oceanic and Atmospheric Oceanic and Atmospheric AdministrationAdministration (NOAA). (NOAA).

• But tsunamis have been generated in But tsunamis have been generated in other bodies of water, including the other bodies of water, including the CaribbeanCaribbean and and Mediterranean SeasMediterranean Seas, , and the and the IndianIndian and and Atlantic OceansAtlantic Oceans..

• The The CaribbeanCaribbean has been hit by 37 has been hit by 37 verified tsunamis since 1498verified tsunamis since 1498..

WAVESWAVES

OCEANSOCEANS

WAVESWAVES

1.3 WAVES, CLASSIFICATION, 1.3 WAVES, CLASSIFICATION, TRANSFORMATIONSTRANSFORMATIONS

BASIC WAVE PARAMETERS

• wave amplitude or wave heightwave amplitude or wave height

• wave period or wavewave period or wave lengtlengthh

• water depth. water depth.

WAVES, CLASSIFICATION, WAVES, CLASSIFICATION, TRANSFORMATIONSTRANSFORMATIONS

BASIC WAVE PARAMETERS

WAVESWAVES

•BASIC WAVE PARAMETERS

WAVESWAVES

The shape of a wave is defined by the vertical displacement of the water surface from the undisturbed sea level, as a function of both time and space. It is called the wave profile or the waveform. The profile of the sinusoidal wave is given as

WAVESWAVES

• wave amplitudewave amplitude, , wave heightwave height

• wave periodwave period, , wavewave lengtlengthh

• water depth water depth

WAVESWAVES• Wave profile (η)Wave profile (η)• Wave crestWave crest• Wave troughWave trough• Wave amplitude (a)Wave amplitude (a)• Wave height (H)Wave height (H)• Wave length (L)Wave length (L)• Wave period (T)Wave period (T)• Wave frequency (f)Wave frequency (f)• Wave number (k)Wave number (k)• Angular wave frequency (σ)Angular wave frequency (σ)• Wave celerity (C):Wave celerity (C): (C=L/T).(C=L/T).• α and β: horizontal and vertical water particle α and β: horizontal and vertical water particle

displacements respectively, displacements respectively, and and functions of time and functions of time and depth.depth.

Mean Sea Level MSL

f= 1/ T

k= 2 / L

= 2 / L

C= L / T Cg = Group Velocity

WAVE LENGTH AND WAVE WAVE LENGTH AND WAVE

CELERITYCELERITY • RRelation between wavelength, wave period elation between wavelength, wave period

and water depth and water depth isis

• Wave celerity is equal to the ratio of Wave celerity is equal to the ratio of wavelength to wave period aswavelength to wave period asC=L/T (3)C=L/T (3). Thus;. Thus;

→ →

)/2tanh(2

CLASSIFICATION OF WAVES ACCORDING CLASSIFICATION OF WAVES ACCORDING

TO PERIOD (SHORT, INTERMEDIATE TO PERIOD (SHORT, INTERMEDIATE

ANDAND LONG WAVES)LONG WAVES) Wave Classification (Ippen 1966)

Range of d/L Range of kh= 2πd/L Types of waves

0 to 1/20 0 to π/10 Long waves (shallow-water wave)

1/20 to ½ π/10 to π Intermediate waves

½ to ∞ π to ∞ Short waves (deepwater waves)

Water Particle TrajectoriesWater Particle Trajectories

Water Particle Trajectories for Long, Short and Intermediate Waves as A Function Depth

How Water Moves in a WaveHow Water Moves in a Wave

WAVE BEHAVIOR IN SHALLOW WAVE BEHAVIOR IN SHALLOW

WATERWATER

Near shore Wave Processes

CLASSIFICATION OF WATER CLASSIFICATION OF WATER

WAVESWAVES

• Classification of Water depthClassification of Water depth

• Classification of Wave Height Classification of Wave Height

• Classification of Height, Length and Classification of Height, Length and DepthDepth

WAVE REFRACTIONWAVE REFRACTION

Wave Refraction in a bay

Top View of Refraction Phenomenon

Wave Refraction at Headland

WAVE DIFFRACTIONWAVE DIFFRACTION

WAVE WAVE BREAKINGBREAKING

• The separation of water particles The separation of water particles from the wave under the action of from the wave under the action of gravity is known as wave breaking. gravity is known as wave breaking.

• Wave breaking process causes Wave breaking process causes energy dissipation by turbulence.energy dissipation by turbulence.

• Breaking is always a nonlinear Breaking is always a nonlinear phenomenon and is therefore phenomenon and is therefore extremely difficult to describe extremely difficult to describe analyticallyanalytically

Types of Wave BreakingTypes of Wave Breaking

Spilling Breaker

Plunging and Collapsing Breaker

Surging Breaker

LONG WAVE AND LONG WAVE AND

ABNORMAL ABNORMAL WAVEWAVESS

1.41.4 LONG WAVES and ABNORMAL LONG WAVES and ABNORMAL WAVES IN NATUREWAVES IN NATURE

• TIDAL WAVESTIDAL WAVES

• SWELL WAVESSWELL WAVES

• SEICHESSEICHES ( (RESONANCE OF RESONANCE OF BASINSBASINS))

• FREAK WAVESFREAK WAVES

1. 1. TIDAL WAVESTIDAL WAVES

• Tides are the alternating rise and fall of Tides are the alternating rise and fall of the surface of the seas and oceansthe surface of the seas and oceans. .

• They are due mainly to the gravitational They are due mainly to the gravitational attraction (pull) of the moon and sun on attraction (pull) of the moon and sun on the rotating earththe rotating earth..

• Two high and two low tides occur daily Two high and two low tides occur daily and, with average weather conditions, and, with average weather conditions, their movements can be predicted with their movements can be predicted with considerable accuracy. considerable accuracy.

When the moon is new or full, the gravitational forces of the sun and moon are pulling at the same side of the earth → extra large "spring" tides occur.

When the moon is at first or third quarter, the gravitational forces of the sun and moon are pulling at 90 degrees from each other→ little net tides called “neap" tides occur.

• The General characteristics of tides in different locations The General characteristics of tides in different locations are shown below:are shown below:Wind waves: T<20sec, H<20 mWind waves: T<20sec, H<20 mTidal waves:Tidal waves: T=24 hours, diurnal typeT=24 hours, diurnal type

T=12 hours, semidiurnal typeT=12 hours, semidiurnal typeH=1-6 m. in Pacific OceanH=1-6 m. in Pacific Ocean Mombasa:Kenya 6 m.Mombasa:Kenya 6 m.

Rio: 1.6 m.Rio: 1.6 m.Tokyo: 1.6 m.Tokyo: 1.6 m. England: 6 m.England: 6 m. La Haye (Den La Haye (Den

Haag)=2.5 m.Haag)=2.5 m.Black Sea: H<0.20 m.Black Sea: H<0.20 m.The Sea of Marmara: H<0.30 m.The Sea of Marmara: H<0.30 m.The Mediterranean Sea: H<0.40 m.The Mediterranean Sea: H<0.40 m.

SWELL WAVESSWELL WAVES

2. 2. SWELL WAVESSWELL WAVES

• a wave system not raised by the local wind blowing at the time of a wave system not raised by the local wind blowing at the time of observation, but raised at some distance away due to winds observation, but raised at some distance away due to winds blowing there, and which has moved to the vicinity of the ship, or blowing there, and which has moved to the vicinity of the ship, or to waves raised nearby by winds that have since died awayto waves raised nearby by winds that have since died away

• travel out of a stormy or windy area and continue on in the travel out of a stormy or windy area and continue on in the direction of the winds that originally formed them as sea wavesdirection of the winds that originally formed them as sea waves

• may travel for thousands of miles before dying away may travel for thousands of miles before dying away

• Its length increases until it is approximately from 35 to 200 or Its length increases until it is approximately from 35 to 200 or more times its height.more times its height.

• normally come from a direction different from the direction of the normally come from a direction different from the direction of the prevailing wind and sea waves at the time of observation prevailing wind and sea waves at the time of observation

Difference Between Sea Difference Between Sea (Wind) and Swell Waves(Wind) and Swell Waves::

• "Sea (Wind) Waves""Sea (Wind) Waves" are produced by local winds and are produced by local winds and measurements show they are composed of a chaotic mix of height measurements show they are composed of a chaotic mix of height and period. In general, the stronger the wind the greater the and period. In general, the stronger the wind the greater the amount of energy transfer and thus larger the waves are amount of energy transfer and thus larger the waves are produced. produced.

• As sea waves move away from where they are generated they As sea waves move away from where they are generated they change in character and become swell waves.change in character and become swell waves.

• "Swell Waves""Swell Waves" are generated by winds and storms in another are generated by winds and storms in another area. As the waves travel from their point of origin they organize area. As the waves travel from their point of origin they organize themselves into groups (Wave trains) of similar heights and themselves into groups (Wave trains) of similar heights and periods. These groups of waves are able to travel thousands of periods. These groups of waves are able to travel thousands of miles unchanged in height and period. miles unchanged in height and period.

• Swell waves are uniform in appearance, have been sorted by Swell waves are uniform in appearance, have been sorted by period, and have a longer wave length and longer period than sea period, and have a longer wave length and longer period than sea waves. Because these waves are generated by winds in a different waves. Because these waves are generated by winds in a different location, it is possible to experience high swell waves even when location, it is possible to experience high swell waves even when the local winds are calm.the local winds are calm.

3. 3. SEICHESSEICHES

• Seiches are Seiches are periodic oscillations of water level set in motion periodic oscillations of water level set in motion by some atmospheric disturbance passing over a Great Lake. by some atmospheric disturbance passing over a Great Lake.

• The disturbances that cause seiches include the rapid The disturbances that cause seiches include the rapid changes in atmospheric pressure with the passage of low or changes in atmospheric pressure with the passage of low or high pressure weather systems, rapidly-moving weather high pressure weather systems, rapidly-moving weather fronts, and major shifts in the directions of strong winds. fronts, and major shifts in the directions of strong winds.

• Seiches exist on the Great Lakes, other large, confined water Seiches exist on the Great Lakes, other large, confined water bodies, and on partially-enclosed arms of the sea. The bodies, and on partially-enclosed arms of the sea. The intervals (or periods) between seiche peaks on the Great intervals (or periods) between seiche peaks on the Great Lakes range from minutes to more than eight hours. Lakes range from minutes to more than eight hours.

• The term was first promoted by the Swiss The term was first promoted by the Swiss hydrologisthydrologist François-Alphonse ForelFrançois-Alphonse Forel in in 18901890, who had observed the , who had observed the effect in effect in Lake GenevaLake Geneva, , SwitzerlandSwitzerland. The word originates in a . The word originates in a Swiss FrenchSwiss French dialect word that means "to sway back and dialect word that means "to sway back and forth", which had apparently long been used in the region to forth", which had apparently long been used in the region to describe oscillations in alpine lakes.describe oscillations in alpine lakes.

RESONANCE OF BASINSRESONANCE OF BASINS

• ResonanceResonance may be described as the coincidence of natural may be described as the coincidence of natural period of oscillatory motion of a system with the period of period of oscillatory motion of a system with the period of external effect on this motion and the resultant increase in external effect on this motion and the resultant increase in the magnitude of motion.the magnitude of motion.

• This oscillatory motion-not exactly motion actually- may be This oscillatory motion-not exactly motion actually- may be

caused by sound, magnetic effects, waves etc.caused by sound, magnetic effects, waves etc.

• A swing example:A swing example:TiTi →→ free oscillation periodfree oscillation period of swing of swing. . TTextext →→ another oscillation period added on the system another oscillation period added on the system by by pushing the swing from backpushing the swing from back ( (external effect on this motionexternal effect on this motion))→→ If (If (Ti) Ti) = = TTextext, speed of this, speed of this system gains an unexpected system gains an unexpected increase in its magnitudeincrease in its magnitude!!!! This concept is called This concept is called resonanceresonance, and the corresponding , and the corresponding period is called period is called resonance periodresonance period (free oscillation (free oscillation period)period). .

RESONANCE OF BASINSRESONANCE OF BASINS

• From coastal engineering point of view, every closed basin From coastal engineering point of view, every closed basin also has its own free oscillation period. Determination of also has its own free oscillation period. Determination of these oscillation periods is considerable since incoming these oscillation periods is considerable since incoming waves with this oscillation periods make effect within basin waves with this oscillation periods make effect within basin higher than expected. higher than expected.

• When a wave enters a closed basin (harbor, bay etc.), When a wave enters a closed basin (harbor, bay etc.), surface fluctuations occur within the basin which affects surface fluctuations occur within the basin which affects coastal infrastructure, navigation of marine vehicles, public coastal infrastructure, navigation of marine vehicles, public safety etc. safety etc.

• Thus, magnitudes of these fluctuations are significantly Thus, magnitudes of these fluctuations are significantly important and they depend on 2 basic parameters: important and they depend on 2 basic parameters: Boundary conditions of the system and incoming wave Boundary conditions of the system and incoming wave properties. properties.

Wave resonance in a basin (harbor,bay)

Ti = Text

Resonance period of a basin depends on:

- geometry

- depth profile

- reflection & dissipation characteristics

Boundary conditions

* The greater a basin is, the higher resonance periods it has.

Analysis & Discussion on

Harbor Resonance

- Long waves& earthquake region Resonance studies

- Accurate studies * Selection of initial period of impulse

* Detailed grid maps* Sufficiently long runs

in order to resolve each resonance period

The periods of fee oscillations (Tn) inside a

closed basin (the boundaries are vertical, solid, smooth and impermeable) is in general

where l is the length in the direction of wave and

h is the depth of the basin,

n is integer number represents each mode.

n=1, 2, 3, ……..

If the basin is semi enclosed (one of the boundaries is open boundary) then the periods of free oscillations become

n= 1, 2, 3, ……

where l is the length in the direction of wave and h is the depth of the basin, n is integer number represents each mode.

Modes of Free Oscillations in Semi-enclosed Rectangular Basin with Horizontal Sea Bottom

Figure 1.4.5.1: The Shapes of Two Different Impulse Waves

.105 km .

d = 500 m .

Figure 1.4.5.2: Map of the Rectangular Basin

0.0 25.0 50.0 75.0 100.0 125.0 150.0

T im e (m in.)

-10.00

Point 1

Figure 1.4.5.3: Water Surface Fluctuations of the Rectangular Basin for Point

0.000 0.005 0.010 0.015 0.020

Frequency (1/sec.)

Point 1

Figure 1.4.5.4: Spectrum Curve of the Rectangular Basin for Point 1.

Table 1.4.5.2: Periods of Free Oscillations of Rectangular Basin (in minutes)

MODE 1 2 3 4 5 6 7 Bruun (1981)

1 93.6 93.6 93.6 93.6 93.6 93.6 93.6 99.9

2 31.2 31.2 31.2 31.2 31.2 31.2 31.2 33.3

3 18.7 19.3 19.3 19.3 18.7 18.7 19.3 20.0

4 13.7 13.7 13.7 13.7 13.7 13.7 13.7 14.3

5 10.6 10.6 10.6 10.6 10.6 10.6 10.6 11.1

6 9.5 - - - - 9.5 - -

7 8.6 8.6 8.6 8.6 8.6 8.6 8.6 9.1

8 7.9 7.4 7.3 7.3 7.3 7.3 7.3 7.7

9 6.4 6.4 6.4 6.4 6.4 6.4 6.4 6.7

10 5.6 5.6 5.6 5.6 5.6 5.6 5.6 5.9

26.50 27.00 27.50 28.00 28.50 29.00 29.50

2 3 4 56

7 8910

Figure 4.1 Map of the Sea of Marmara

ISTANBUL

26.50 27.00 27.50 28.00 28.50 29.00 29.50

Test 1, in itia l im pulse

26.50 27.00 27.50 28.00 28.50 29.00 29.50

Test 2, in itia l im pulse

-0 .80

-0 .70

-0 .60

-0 .50

-0 .40

-0 .30

-0 .20

-0 .10

Figure Initial impulses, Test 1 and Test 2, (plan view)

Test 1 (section A-A)

0 2000 4000 6000 8000

North South

Test 2 (section B-B)

0 2000 4000 6000 8000

West East

Figure 4.3 Initial wave profiles, Test 1 and Test 2

Tekirdağ

0 30 60 90 120 150 180 210 240 270 300

time (min)

Çınarcık

0 30 60 90 120 150 180 210 240 270 300

time (min)

Tekirdağ

0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

k (1/sec)

)Yenikapı

0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

k (1/sec)

Çınarcık

0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010

k (1/sec)

The numerical tests on the Sea of Marmara show that

The waves with periods 14.89, 13.65, 11.70, 10.57, 9.36, 8.86, 6.43, 5.75, 4.62, 4.49, 4.15, 3.95, 3.68, 3.45, 3.12 minutes cause resonance in North-South direction.

The waves with periods23.41, 13.10, 10.24, 8.19, 7.45, 6.97, 6.55, 6.13, 5.85, 4.89, 4.75, 4.26, 3.86, 3.68, 3.56, 3.34, 3.15, 3.03 minutes cause resonance in East – West direction.

Energy dissipators

* A wave is the superposition of several waves.

* Cr= Hr /Hi

* Wave agitation up to 50 cm. is allowed in harbours.

Standing waves – Full reflection

* Cr = 1

* E = 0* Nodes & antinodes form.

Partially reflected waves

* Cr < 1

* E > 0* Shape of reflection envelopes change.

Wave energy

Wave energy: E = ρ. g. H2 / 8 ..........E α H2

Reflection coefficient: Cr = Hr / Hi

Energy loss: ∆E % = ((Hi)2 – (Hr)2 ) / (Hi)2

Instead of vertical walls, surfaces able to dissipate wave

energy are required.

Don Carpenter, Detroit, USA

Before entering wave absorberAfter entering wave absorber

4. FREAK WAVES4. FREAK WAVES

• Freak, rogue, or giant waves correspond to large-amplitude Freak, rogue, or giant waves correspond to large-amplitude waves surprisingly appearing on the sea surface (“wave from waves surprisingly appearing on the sea surface (“wave from nowhere”).nowhere”).

• Such waves can be accompanied by deep troughs (holes), Such waves can be accompanied by deep troughs (holes), which occur before and/or after the largest crest. which occur before and/or after the largest crest.

• Very often the term “Very often the term “extreme wavesextreme waves” is used to specify the tail ” is used to specify the tail of some typical statistical distribution of wave heights (generally of some typical statistical distribution of wave heights (generally a Rayleigh distribution); meanwhile the term “a Rayleigh distribution); meanwhile the term “freak wavesfreak waves” ” describes the large-amplitude waves occurring more often than describes the large-amplitude waves occurring more often than would be expected from the background probability distribution. would be expected from the background probability distribution.

• IIts height should exceed the significant wave height in 2–2.2 ts height should exceed the significant wave height in 2–2.2 times. times.

• In particular, twenty-two super-carriers were lost due to In particular, twenty-two super-carriers were lost due to collisions with rogue waves for 1969–1994 in the Pacific and collisions with rogue waves for 1969–1994 in the Pacific and Atlantic causing 525 fatalities. At least, the twelve events of the Atlantic causing 525 fatalities. At least, the twelve events of the ship collisions with freak waves were recorded after 1952 in the ship collisions with freak waves were recorded after 1952 in the Indian Ocean, near the Agulhas Current, coast of South Africa. Indian Ocean, near the Agulhas Current, coast of South Africa.

CHAPTER 1: INTRODUCTION- HAZARDS-OCEANS-WAVES NATURAL HAZARDS: FLOODS FLOODS VOLCANIC ERUPTIONS...

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