CHAPTER 1: INTRODUCTION- HAZARDS-OCEANS-WAVES

CHAPTER 1: INTRODUCTION- HAZARDS-OCEANS-WAVES
NATURAL HAZARDS: FLOODS VOLCANIC ERUPTIONS HURRICANE DROUGHT EARTHQUAKES

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

NATURAL HAZARDS: FLOODS:
Floods are the most common and widespread of all natural disasters--except fire. Floods have been an integral part of the human experience ever since the start of the agricultural revolution when people built the first permanent settlements on the great riverbanks of Asia and Africa.

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

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

NATURAL HAZARDS: Effects of volcanic eruptions:
1) pyroclastic eruptions can smother large areas of landscape with hot ash, dust, and smoke within a span of minutes to hours; 2) red hot rocks spewed from the mouth of a volcano can ignite fires in nearby forests and towns, while rivers of molten lava can consume almost anything in their path as they reshape the landscape; 3) heavy rains or a rapidly melting summit snowpack can trigger lahars-sluices of mud that can flow for miles, overrunning roads and villages; and 4) large plumes of ash and gas ejected high into the atmosphere can influence climate, sometimes on a global scale.

1) pyroclastic eruptions can smother large areas of landscape with hot ash, dust, and smoke within a span of minutes to hours;

1) pyroclastic eruptions can smother large areas of landscape with hot ash, dust, and smoke within a span of minutes to hours; 2) red hot rocks spewed from the mouth of a volcano can ignite fires in nearby forests and towns, while rivers of molten lava can consume almost anything in their path as they reshape the landscape;

1) pyroclastic eruptions can smother large areas of landscape with hot ash, dust, and smoke within a span of minutes to hours; 2) red hot rocks spewed from the mouth of a volcano can ignite fires in nearby forests and towns, while rivers of molten lava can consume almost anything in their path as they reshape the landscape; 3) heavy rains or a rapidly melting summit snowpack can trigger lahars-sluices of mud that can flow for miles, overrunning roads and villages; and

1) pyroclastic eruptions can smother large areas of landscape with hot ash, dust, and smoke within a span of minutes to hours; 2) red hot rocks spewed from the mouth of a volcano can ignite fires in nearby forests and towns, while rivers of molten lava can consume almost anything in their path as they reshape the landscape; 3) heavy rains or a rapidly melting summit snowpack can trigger lahars-sluices of mud that can flow for miles, overrunning roads and villages; and 4) large plumes of ash and gas ejected high into the atmosphere can influence climate, sometimes on a global scale.

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

NATURAL HAZARDS: DROUGHT:
Many different climatic events can trigger crop failures including excess rainfall leading to flood damage or crop disease, heat waves, drought, fire, unexpected cold snaps, severe storms, climate-related disease outbreaks, and insect invasions. Nationwide losses from the U.S. drought of 1988 exceeded $40 billion,. In the Horn of Africa the 1984–1985 drought led to a famine which killed 750,000 people.

NATURAL HAZARDS: Drought can be defined as;
Meteorological drought is usually based on long-term precipitation departures from normal, but there is no consensus regarding the threshold of the deficit or the minimum duration of the lack of precipitation that make a dry spell an official drought.

Meteorological drought is usually based on long-term precipitation departures from normal, but there is no consensus regarding the threshold of the deficit or the minimum duration of the lack of precipitation that make a dry spell an official drought. Hydrological drought refers to deficiencies in surface and subsurface water supplies. It’s measured as stream flow, and as lake, reservoir, and ground water levels.

Meteorological drought is usually based on long-term precipitation departures from normal, but there is no consensus regarding the threshold of the deficit or the minimum duration of the lack of precipitation that make a dry spell an official drought. Hydrological drought refers to deficiencies in surface and subsurface water supplies. It’s measured as stream flow, and as lake, reservoir, and ground water levels. Agricultural drought occurs when there is insufficient soil moisture to meet the needs of a particular crop at a particular time. A deficit of rainfall over cropped areas during critical periods of the growth cycle can result in destroyed or underdeveloped crops with greatly depleted yields. Agricultural drought is typically evident after meteorological drought but before a hydrological drought.

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

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

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

Tectonic Activity Map of the Earth

OCEANS

OCEANS cover about 70% of the Earth's surface
contain roughly 97% of the Earth's water supply moderate the Earth's temperature by absorbing incoming solar radiation

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

OCEANS Ocean Area (square miles) Average Depth (ft) Deepest depth (ft)
Pacific Ocean 64,186,000 15,215 Mariana Trench, 36,200 ft deep Atlantic Ocean 33,420,000 12,881 Puerto Rico Trench, 28,231 ft deep Indian Ocean 28,350,000 13,002 Java Trench, 25,344 ft deep Southern Ocean 7,848,300 sq. miles ( million sq km ) 13, ,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 3,953 Eurasia Basin, 17,881 ft deep

OCEANS Pacific → the most active tsunami zone, according to the U.S. National Oceanic and Atmospheric Administration (NOAA). But tsunamis have been generated in other bodies of water, including the Caribbean and Mediterranean Seas, and the Indian and Atlantic Oceans. The Caribbean has been hit by 37 verified tsunamis since 1498.

OCEANS WAVES

1.3 WAVES, CLASSIFICATION, TRANSFORMATIONS
BASIC WAVE PARAMETERS wave amplitude or wave height wave period or wave length water depth.

WAVES, CLASSIFICATION, TRANSFORMATIONS
BASIC WAVE PARAMETERS wave amplitude or wave height wave period or wave length water depth.

WAVES BASIC WAVE PARAMETERS wave amplitude or wave height
wave period or wave length water depth.

WAVES 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

WAVES wave amplitude, wave height wave period, wave length water depth

WAVES Wave profile (η) Wave crest Wave trough Wave amplitude (a)
Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth.

Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth. Mean Sea Level MSL

Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth. L

Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth. T

WAVES f= 1/ T Wave profile (η) Wave crest Wave trough
Wave amplitude (a) Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth. f= 1/ T

WAVES k= 2  / L Wave profile (η) Wave crest Wave trough
Wave amplitude (a) Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth. k= 2  / L

WAVES = 2  / L Wave profile (η) Wave crest Wave trough
Wave amplitude (a) Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth. = 2  / L

WAVES C= L / T Cg = Group Velocity Wave profile (η) Wave crest
Wave trough Wave amplitude (a) Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth. C= L / T Cg = Group Velocity

Wave height (H) Wave length (L) Wave period (T) Wave frequency (f) Wave number (k) Angular wave frequency (σ) Wave celerity (C): (C=L/T). α and β: horizontal and vertical water particle displacements respectively, and functions of time and depth.

WAVE LENGTH AND WAVE CELERITY
Relation between wavelength, wave period and water depth is Wave celerity is equal to the ratio of wavelength to wave period as C=L/T (3). Thus; →

Wave Classification (Ippen 1966)
CLASSIFICATION OF WAVES ACCORDING TO PERIOD (SHORT, INTERMEDIATE AND 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 Trajectories
Water Particle Trajectories for Long, Short and Intermediate Waves as A Function Depth

How Water Moves in a Wave

WAVE BEHAVIOR IN SHALLOW WATER
Near shore Wave Processes

CLASSIFICATION OF WATER WAVES
Classification of Water depth Classification of Wave Height Classification of Height, Length and Depth

WAVE REFRACTION Wave Refraction in a bay

WAVE REFRACTION Top View of Refraction Phenomenon

WAVE REFRACTION Wave Refraction at Headland

WAVE DIFFRACTION

WAVE BREAKING

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

WAVE BREAKING The separation of water particles from the wave under the action of gravity is known as wave breaking. Wave breaking process causes energy dissipation by turbulence.

WAVE BREAKING The separation of water particles from the wave under the action of gravity is known as wave breaking. Wave breaking process causes energy dissipation by turbulence. Breaking is always a nonlinear phenomenon and is therefore extremely difficult to describe analytically

WAVE BREAKING

Types of Wave Breaking Plunging and Collapsing Breaker Surging Breaker
Spilling Breaker Surging Breaker

LONG WAVE AND ABNORMAL WAVES

1.4 LONG WAVES and ABNORMAL WAVES IN NATURE
TIDAL WAVES SWELL WAVES SEICHES (RESONANCE OF BASINS) FREAK WAVES

1. TIDAL WAVES Tides are the alternating rise and fall of the surface of the seas and oceans. They are due mainly to the gravitational attraction (pull) of the moon and sun on the rotating earth. Two high and two low tides occur daily and, with average weather conditions, their movements can be predicted with considerable accuracy.

1. TIDAL WAVES 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.

1. TIDAL WAVES 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.

1. TIDAL WAVES The General characteristics of tides in different locations are shown below: Wind waves: T<20sec, H<20 m Tidal waves: T=24 hours, diurnal type T=12 hours, semidiurnal type H=1-6 m. in Pacific Ocean Mombasa:Kenya 6 m. Rio: 1.6 m. Tokyo: 1.6 m. England: 6 m. La Haye (Den Haag)=2.5 m. Black Sea: H<0.20 m. The Sea of Marmara: H<0.30 m. The Mediterranean Sea: H<0.40 m.

SWELL WAVES

2. SWELL WAVES a wave system not raised by the local wind blowing at the time of observation, but raised at some distance away due to winds blowing there, and which has moved to the vicinity of the ship, or to waves raised nearby by winds that have since died away travel out of a stormy or windy area and continue on in the direction of the winds that originally formed them as sea waves may travel for thousands of miles before dying away Its length increases until it is approximately from 35 to 200 or more times its height. normally come from a direction different from the direction of the prevailing wind and sea waves at the time of observation

Difference Between Sea (Wind) and Swell Waves:
"Sea (Wind) Waves" are produced by local winds and measurements show they are composed of a chaotic mix of height and period. In general, the stronger the wind the greater the amount of energy transfer and thus larger the waves are produced. As sea waves move away from where they are generated they change in character and become swell waves. "Swell Waves" are generated by winds and storms in another area. As the waves travel from their point of origin they organize themselves into groups (Wave trains) of similar heights and periods. These groups of waves are able to travel thousands of miles unchanged in height and period. Swell waves are uniform in appearance, have been sorted by period, and have a longer wave length and longer period than sea waves. Because these waves are generated by winds in a different location, it is possible to experience high swell waves even when the local winds are calm.

3. SEICHES Seiches are periodic oscillations of water level set in motion by some atmospheric disturbance passing over a Great Lake. The disturbances that cause seiches include the rapid changes in atmospheric pressure with the passage of low or high pressure weather systems, rapidly-moving weather fronts, and major shifts in the directions of strong winds. Seiches exist on the Great Lakes, other large, confined water bodies, and on partially-enclosed arms of the sea. The intervals (or periods) between seiche peaks on the Great Lakes range from minutes to more than eight hours. The term was first promoted by the Swiss hydrologist François-Alphonse Forel in 1890, who had observed the effect in Lake Geneva, Switzerland. The word originates in a Swiss French dialect word that means "to sway back and forth", which had apparently long been used in the region to describe oscillations in alpine lakes.

RESONANCE OF BASINS

RESONANCE OF BASINS Resonance may be described as the coincidence of natural period of oscillatory motion of a system with the period of external effect on this motion and the resultant increase in the magnitude of motion. This oscillatory motion-not exactly motion actually- may be caused by sound, magnetic effects, waves etc. A swing example: Ti → free oscillation period of swing. Text → another oscillation period added on the system by pushing the swing from back (external effect on this motion) → If (Ti) = Text, speed of this system gains an unexpected increase in its magnitude!! This concept is called resonance, and the corresponding period is called resonance period (free oscillation period).

RESONANCE OF BASINS From coastal engineering point of view, every closed basin also has its own free oscillation period. Determination of these oscillation periods is considerable since incoming waves with this oscillation periods make effect within basin higher than expected. When a wave enters a closed basin (harbor, bay etc.), surface fluctuations occur within the basin which affects coastal infrastructure, navigation of marine vehicles, public safety etc. Thus, magnitudes of these fluctuations are significantly important and they depend on 2 basic parameters: Boundary conditions of the system and incoming wave properties.

Wave resonance in a basin (harbor,bay)
Text Ti Ti Ti = Text 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 1.4.5.2: Map of the Rectangular Basin
Figure : The Shapes of Two Different Impulse Waves Figure : Map of the Rectangular Basin

Figure 1.4.5.4: Spectrum Curve of the Rectangular Basin for Point 1.
Figure : Water Surface Fluctuations of the Rectangular Basin for Point Figure : 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) 93.6 99.9 31.2 33.3 18.7 19.3 20.0 13.7 14.3 10.6 11.1 9.5 - 8.6 9.1 8 7.9 7.4 7.3 7.7 9 6.4 6.7 10 5.6 5.9

Figure 4.1 Map of the Sea of Marmara
ISTANBUL N Figure 4.1 Map of the Sea of Marmara

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

Figure 4.3 Initial wave profiles, Test 1 and Test 2

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. 23.41, 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 absorber After entering wave absorber

4. FREAK WAVES Freak, rogue, or giant waves correspond to large-amplitude waves surprisingly appearing on the sea surface (“wave from nowhere”). Such waves can be accompanied by deep troughs (holes), which occur before and/or after the largest crest. Very often the term “extreme waves” is used to specify the tail of some typical statistical distribution of wave heights (generally a Rayleigh distribution); meanwhile the term “freak waves” describes the large-amplitude waves occurring more often than would be expected from the background probability distribution. Its height should exceed the significant wave height in 2–2.2 times. In particular, twenty-two super-carriers were lost due to collisions with rogue waves for 1969–1994 in the Pacific and Atlantic causing 525 fatalities. At least, the twelve events of the ship collisions with freak waves were recorded after 1952 in the Indian Ocean, near the Agulhas Current, coast of South Africa.

CHAPTER 1: INTRODUCTION- HAZARDS-OCEANS-WAVES

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