MEA 200 Third Exam

Water Depth- Explain the differences between waves classified as deep or shallow water waves, including how the shape of the water particle orbital paths differ

waves are either only a function of L (or T), or only of depth, d i. Deep: When d > than or equal to ½ L, ocean waves are unaffected by water depth. The diameter of the orbital paths of water particles under these waves decreases as depth increases below the surface, and shrinks to zero at d = 1/2 L. Wave celerity is directly proportional to either wavelength or wave period, as shown below: C prop L (or T). This means that waves with longer wavelengths (or wave periods) will travel faster across the ocean surface than waves with shorter L or T ii. Shallow Water waves. When d < than or equal to 1/20 L, ocean waves are only under the control of water depth, and the orbits are elongated ellipses with a major axis in the horizontal direction and the minor axis in the vertical direction. Only the minor axis decreases as depth below the surface increases, so that near the bottom, the water motion is only horizontal and water particles move back and forth with the passage of a wave. Wave celerity is directly proportional to depth, This means that as water depth decreases, waves slow down,

Wave Classification

waves can be classified in at least 4 different ways: period of waves, water depth, method of generation, and relationship to the generating force

Long waves

waves with periods greater than 5 minutes, which are generated by intense storms and by earthquakes, and restored by gravity and the Coriolis force (ex: tsunamis and storm surges)

Equatorial Tides

where the two high and low tides have equal heights - as the earth rotates around its axis, someone standing on the equator would detect two high water levels (HW) and two low water levels (LW) with the same height and with a tidal period of 12 hrs

Mixed Tides Why can we also call them tropical tides?

where the two highs that occur each day do not have equal heights. Why can we also call them tropical tides

HW: To answer questions below about how the minimum fetch required for FD Sea is determined, note the set-up of the experiment shown in the figure above: the left half of the figure shows the placement of six wave gauges set at increasing distances (fetches) away from and perpendicular to the shoreline; and the right half is an x-y plot of the growth of the six wave-spectra for each of these wave-gauge fetches as a function of period (T) on the x-axis. Notice on the spectral plot that the wave spectra for wave gauges x5 & x6 are basically identical (same area under curves and same T). (1) How long would the wind need to blow before you start measuring wave growth at all gauges to determine minimum fetch? Why is that important? (2) What is the minimum fetch for this wind speed determined by this experiment? Include, in your answer a discussion of the progressive development of the wave spectra as a function of distance from shore (the fetch), including changes in the area under the curve of the spectrum and in the spectrum's peak period, T, as the sea builds toward FD. How do you know when FD has been reached? Explain.

(1) FD is a function of both fetch and duration, to to measure fetch, the wind must blow for at least as long as the theoretical minimum duration required for FD - only then would you be able to detect changes in the spectra as a function of fetch. (2) For any given wind speed there is a minimum fetch required for wind-waves to reach FD. In the experiment shown above, this occurs at the fetch of wave gauge 5, because even though the wind wave spectra progressively grow at gauges x1, x2, x3, x4 and x5 (both in the increase of the area under the curve - the total energy of all the waves in the development area, and in the lengthening of peak period) there is no appreciable change in the spectrum at fetch x6 when compared with x5. We conclude, therefore, that even though x6 is at a greater fetch than x5, the minimum fetch required for FD for the given wind speed is reached at fetch x5, because the spectrum doesn't get larger (in period and area under curve) for fetches longer than x5 (in fact the spectra will stay constant).

What are rogue waves? -causes

(with maximum heights of around 30 m or 100 ft, get their name from the sudden way in which they seem to appear - Rouge waves are thought to be caused by two different processes: Wave/Current Interaction and Constructive Interference, and that Global Warming may make them more common. -ocean waves whose height is more than twice the height of other waves in the area

compare narrow basins vs broad basins

- Nodal lines in narrow basins open to the ocean are near the open end of the basin. Therefore, the SW set up in these basins by a small-range ocean tide will produce SWs with antinodes at the closed end of the basin that are of much greater magnitude than for a similarly-dimensioned enclosed basin - If the basin is wide, the SW set up by the tidal forcing at the open end of the basin also will be subject to the CE (not an issue in narrow basins). Suppose you had a wide basin in the Northern Hemisphere opened to the ocean on its south side. As the tide in the ocean rises (bottom picture), the water moving into the basin from the south will be deflected to the right and piled up against the eastern boundary of the basin. This results in a slope down toward the west, so as water begins moving west under the influence of gravity, the CE deflects it right and piles it up against the northern boundary.This creates a slope toward the south, and as the water flows down the slope it also is deflected toward the right so that the water is piled up against the western boundary of the basin. Finally, the water flowing down the slope to the east will be deflected toward the right just as the ocean tide is again rising. overall movement of the highest side of the water (the antinode of the SW that has been set up) moves in a counter-clockwise direction and makes one complete cycle in one tidal period. instead of oscillating along a nodal line (as in a narrow basin), this SW moves around a nodal point (called an Amphidromic point - AP), with the period of the TPF.

distinguish between offshore, nearshore, and foreshore

- The Shore is subdivided into the --Backshore (from the Coastline to the Shoreline) and the --Foreshore (that part of the shore between the high-tide and low-tide shorelines that is submerged and uncovered repeatedly by the tides), also called the littoral or intertidal zone. - The Nearshore is the region between the low tide shoreline and the low-tide breaker line. -The Offshore is everything seaward of the low-tide breaker line.

What are wetlands and what is their relationship to estuaries?

- Wetlands in general (terrestrial and marine) are extremely important to the healthy ecology of our environment. They mitigate flooding by collecting runoff waters, but just as importantly, they remove inorganic nitrogen compounds and metals from groundwater polluted by land sources. As a result, on land, artificial wetlands have been used as the final stage of water purification from waste water plants,with resulting water being clean enough to drink. - Marine wetlands, which border estuaries and other shore areas protected from the ocean, are biologically productive areas delicately in tune with natural shore processes.

What does the theory predict about the movement and accumulation of water on the earth as a result of these bulges and the moon's movement around the earth?

- adding the vectors of G and Fc = tractive forces. these forces are in equilibrium and result in the TPF (inverse to distance between attracting masses). moon tpf is 2x the sun. - when G and G act together at any location on earth: i. The resulting tractive forces cause the water on our frictionless spherical earth to move toward both points N and Z, so we get TWO "bulges" on opposite sides of the earth ii. The bulge on the side of the earth nearest the moon (Zenith) is primarily the result of the moon's gravitational attraction, while the bulge on the opposite side of the earth (Nadir) is primarily the result of the centrifugal force of the earth-moon system.

How can this theory be used to explain diurnal tides (one high and one low each day) that have a period of 24 hr 50 min., something the Equilibrium Theory cannot?

- four partial tides with periods close to the semi-diurnal period and three partial tides with periods close to the diurnal period. - Diurnal will take twice as long as semidiurnal because semi have more than one HWs (high tide) and LWs (low tide) in a day where as a Diurnal only has one.

Standing waves - formation

- in lakes (enclosed basins) - can be enhanced to produce resonance standing waves - are produced by the passage of two progressive waves of the same period in opposite directions

What are the differences in vertical and horizontal water movement under nodal lines and antinodal lines in a standing wave?

- no net momentum is being carried by SW. - SWs oscillate but not in the same way as in a progressive wave. they have nodes in the center of the basin where all the particle motion is horizontal AND antinodes at each of 2 ends of the basin, where the surface of the SW and all the particle motion under the surface moves vertically. the particle motion is a combo of these 2 movements.

which of these two waves occurs most frequently and which does the most overall damage on an annual basis? tsunami or storm surge

- storm surge is much more frequent - storm surge is more damaging/ kills more people

How is the diurnal inequality of a tropical/mixed tide defined?

- there is an unequal high tide highest high water and the lowest high water - difference between the heights of the two hight waters (the HHW & the LHW) is called the Diurnal Inequality.

what causes a tsunami? what kind of wave is it? main requirement for their generation? whats the height and wavelength of a tsunami at sea? celerities? when do tsunamis get big?

- underwater earthquakes - they are surface waves/long waves - the full force of the impact is applied to and displaces the water surface -height of 0.5m (small) and long wave length. not noticable even though they have large celerities - when they shoal they are now able to be destructive. 30m height, 50 km/hr

What period and phase conditions between Tc and the TPF are required for the seiche to be enhanced to produce a free/forced standing wave called a resonance tide?

-Resonance SWs are a special combination of free and forced SWs. If a Seiche has been set up by the wind with a Tc very nearly the same as the period of the forced TPF SW AND, most importantly, if Tc and the period of the TPF are in phase, then a small amplitude Resonance SW may be set up in a basin. -In other words, the Resonance SW is a Seiche that is "boosted" at just the right moment by the TPF to enhance its motion and, as a result, cause it to last longer and/or be larger than a totally free SW not so enhanced.

What causes the brine pools in the Red Sea, and how does the circulation with the Indian Ocean contribute?

-The Red Sea is a flooded rift valley created by the movement of the African and Arabian plate -evaporation is very high -surface salinity is 42.5% very high but at lower depths 2000m it is over 250% salinity -These brine pools are so dense that they do not move from their location. However, heated water enters these pools through the porous crust and dilutes the brine so that it doesn't rise above 250 ppt

what are the 3 kinds of SWs set up in narrow enclosed basins

1)vforced sws set up by TPF (tide producing force, moon and sun) 2) free sws set up by winds (seiche) 3) free/forced SWs (resonance sws)

Differentiate between ebb, flood and slack tidal currents

1. At high tide, when the bay high water is the same height as the ocean tide, the tidal current is high water slack tidal current (zero speed) because the water levels in the ocean and the bay are the same. 2. Ebb: as the tide begins to fall in the ocean, a pressure head is formed within the bay that causes the water to flow out of the inlet as an ebb tidal current 3. At low tide, when the water levels in the ocean and the bay are again equal, there is a low water slack tidal current 4. Flood: As the ocean tide begins to rise, a pressure head is formed in the ocean that causes the water to flow into the inlet, which reaches its maximum velocity after 3 hours and then diminished as the tide in the ocean nears its highest point 5. Then we have high water slack tide current a gain and the process repeats itself

there are 2 different tides with 2 highs and 2 lows per day they are:

2 semi-diurnal tides - equatorial tides - and mixed tides-

HW Answer the following three questions about mixed tides using the Equilibrium Theory. a. Describe the characteristics of a mixed tide (the period, and the different kinds of high waters [HW] and low waters [LW]) and define the diurnal inequality.

A mixed tide has a semi-diurnal period tide, but its HWs and LWs are not of equal height. The diurnal inequality is defined as the difference in height between the adjacent HWs of a mixed tide (the highest HW (HHW), & lowest HW (LHW)). Note: in the 'real ocean', there also is a lowest LW (LLW) and a highest LW (HLW), but the equilibrium theory does not model this.

hw What is a seiche (define it) and explain how it is created

A seiche is a free SW generally set up in a narrow enclosed basin by the wind blowing along the long axis of the basin. Water is 'piled up' at one end of the lake by the wind and, when the wind stops blowing, the water runs back toward and reflects off the other end of the lake. This creates a seiche.

How does the wind set up a free standing wave (called a seiche) in this basin?

A strong wind blowing for a long period of time in a constant direction along the long axis of a narrow enclosed basin will push the water to one end. - This "wind set-up" is not large, but when the wind stops, the water at the high end of the lake will run in the opposite direction and, after reflecting off the other end, may create a small amplitude free SW.

Why are these equitorial tides produced when the moon is directly over the equator?

A twice daily Semi-diurnal Tide created when the moon's two "bulges" are over the equator, and which will have a period of 12 hr 25 min and equal high waters and low waters -- called the Equatorial Tide.

what are the general results predicted by the equilibrium theory

A twice daily tide with a Semi-diurnal Period of 12 hr 25 min (not 12 hr), because of the moon's orbit around the earth. A twice daily Equatorial Tide created when the moon's two "bulges" are over the equator, and have equal high waters and low waters. A twice daily Mixed Tide created when the moon's two "bulges" are at a 28.5 deg angle to the equator, and have unequal high waters -- also called the Tropical Tide. A twice monthly Fortnightly Tide created when the earth-moon "bulges" are combined with the earth-sun "bulges", which will result in a twice monthly change in the RANGE of the tides, with a period of a little more than 14 days (a fortnight) called Spring and Neap Tides.

explain the increase in wave height (h) for shoaling waves for waves breaking in the surf zone

According to linear wave theory, the total energy (TE) in a wave is equally partitioned between kinetic energy (KE) and potential energy (PE) in deep water, and wave energy travels at a group velocity. - KE is the energy of motion, and in an ocean wave KE prop C. - PE is the energy of position. PE prop H. -where the portion of the leading wave slows more near the bottom than the top portion does, and the wave eventually becomes too steep and breaks, creating "surf". We can represent this energy balance as: TE = KE (C) + PE (H) -Waves slow when they shoal (i.e., C decreases), and because KE prop C, KE also will decrease. Since TE is conserved (held constant), the decrease in KE results in a comparable increase in PE, so wave height (H) is increased.

How does this decrease and the resultant re-partitioning of energy from kinetic to potential, cause the wave height to increase?

According to linear wave theory, the total energy (TE) in a wave is equally partitioned between kinetic energy (KE) and potential energy (PE) in deep water, and wave energy travels at a group velocity. KE is the energy of motion, and in an ocean wave KE prop C. PE is the energy of position (think of lifting a weight and holding it above a bench -- its height above the bench is proportional to its PE and equal to the work required to lift the weight to that height) and in an ocean wave PE prop H.

Under what conditions are they formed with wave-current interaction? -rougue wave

According to non-linear ocean wave theory, large waves from storms that run directly into a strong oncoming current will steepen and actually gain energy from the current- so that waves with significant wave heights of 12 to 15 m can more than double in height. Also, according to theory, waves that run with a current will lose energy, and those that cross a current will be refracted, but will be otherwise unaffected.

Why is an ocean wave described as being an orbital progressive wave, and what is the path of water particles at and below the surface as this wave passes?

As the wave form passes a certain point, the water particles under the wave move with orbital paths. They are progressive because the wave form moves (progresses) horizontally from one location to another)

hw Explain how partial tides are combined to estimate the actual tide at any location along the coast? Hint: look at the figure above.

As you can see from the figure above, the four semi-diurnal partial tides and three diurnal partial tides when superposed (combined constructively and destructively) produce an actual tide (in this case a mixed tide).

In HW# 18, you explained how you could find the minimum fetch required for FD. Now, I want you to explain how you would set up an experiment to determine the minimum duration required for wind waves to reach full development (FD) for a constant wind direction and speed. Recall that both fetch and duration can limit FD of wind waves - therefore, since you want to find minimum duration, you want to chose a fetch that no longer contributes to wave growth. What fetch would that be and how is it related to the results of HW#18?

Because FD depends upon both fetch and duration, and we want to determine the minimum duration, we want to make sure our fetch is large enough so that it will not contribute to wave growth. Therefore, in this experiment we would choose a fetch that was already determined to be at or greater than the minimum fetch required for FD. If you recall the experiment for determining minimum fetch, this would be at a fetch greater than or equal to the fetch at wave gauge 5 - assume, therefore, that we put the wave gauge at fetch 6.

how do we monitor the growth of the sea

Because the 'sea' is made up of many component waves with different periods and heights (and not a single monochromatic or single period sine wave) we monitor the growth of 'seas' not by the growth of an individual wave, but by the growth of the sea's wave spectrum (a statistical property that describes ALL of the component waves present in the sea).

As waves shoal (enter increasingly more shallow water), why does wave celerity decrease?

Celerity for shallow water waves is directly proportional to depth

What are partial tides, and how do they compare with component waves found in "sea".

Component waves of different periods -4 partial tides with periods semi-diurnal -3 partial tides with periods diurnal

what are the determinants of wave erosion

Degree of exposure. Coastlines that are fully exposed suffer the most erosion. Tidal range. The smallest tidal range concentrates more wave energy and erodes more. Composition of bedrock. Sandstone and shale are more easily eroded than igneous rocks.

What is the relationship between beach slope and particle size on a beach?

Direct

What relationship do white-caps have to the energy put into the sea by the wind?

Energy must be dissipated - not caused by dec water depth like surf

When do "white-caps" (the breaking of waves in deep water) form during the growth of a fully-generated sea?

Even after the seas are fully developed, the wind may continue to transfer momentum to the ocean but, because the waves cannot grow any larger (i.e., they are fully developed), the EXCESS ENERGY supplied by the wind MUST BE DISSIPATED.

hw What is the definition of the Tc for a long narrow basin, and what dimensions of the basin dictate this definition?

Every narrow basin, when 'excited' by the wind in this manner, will produce a SW. This SW will ALWAYS oscillate with a fixed period that is characteristic of that basin - so we call it "the Characteristic period", Tc. Tc in a narrow basin is directly proportional to the length, and inversely proportional to the depth, of the basin.

why would we want to determine required minimum fetch and duration

Finding minimum fetch and duration are essential to oceanographers and engineers who want to forecast waves at any location in the ocean for use by sailors and fishermen who may want to 'go out next week'. They also are used by these same people to hind-cast waves (after the fact).

What do we mean when we say a sea is fully developed?

For a given constant wind speed, if the depth, fetch and duration are large enough (greater than the minimum required values of each), the waves that constitute the 'sea' will reach what is called "full-development" - where the largest of the waves in the "sea" (with period Tp) cannot grow and larger and its wave height and wavelength have reached their full potential. ii. So that means that if a sea is fully developed for a given constant wind speed, it CANNOT continue to grow, even if the fetch or duration is more than the minimum required for full development.

why are there two water "bulges" found on the earth in line with the position of moon above the earth?

Grav force point toward center of moon , pull water toward moon. points closest to moon have largest G Centrifugal force Fc are equal in length and point away from moon.

If you were on a tropical island in the middle of the Western Pacific Ocean and had no way to communicate with the outside world, how would you know (using only the concept of Wave Dispersion) that a Typhoon was heading toward your island? Hint: How would the period and height of the SWELL arriving from the storm at the island, change over time as the storm got closer?

I would know that a typhoon was headed toward the island if the incoming surf progressively increased in size and decreased in period. I would know that, in principle, because of the concept of wave dispersion. Because wave celerity is directly proportional to wave period, waves with longer periods would outrun the shorter waves. Therefore, the first waves to arrive at the island would be the longest and, as it got closer, the period of the waves would decrease and the wave height would increase (because more energy is being concentrated per unit area).

relationship between C and L,T,D

In general, wave celerity (C) is directly proportional to either L or T and to water depth (d), or in a proportional expression C prop L (or T); d and these waves are called transitional or intermediate depth waves.

what causes a storm surge?

Intense cyclones at sea have very low pressure centers around which the storm winds blow. This low pressure creates a "hill" of water on the surface under it, that moves with the storm. And as the storm moves across the ocean, this hill AND the water in the right front quarter of the storm being pushed by the winds in the same direction the storm is moving, create a high-water surge that can exceed 10 m (approximately 30 ft) for a very large (category 5) storm.

What is the major difference in the movement of water in a breaking wave as compared to water movement in the same wave before it breaks?

Just as it begins to break and the water particles changes from their orbital paths to a more horizontally-oriented translational path that hurls the water toward the beach as swash.

what is a long wave

Long waves are waves with periods greater than 5 minutes. -tsunamis -storm surges

High-high water (HHW), low-low water (LLW), high-low water (HLW), low-high water (LHW) for mixed or tropical tides:

Mixed tides also have two HWs and two LWs per day, but they are not the same height, so this tide has four tidal ranges and each HW and LW have different names

How does the sun's tide-producing force combine with the moon's tide-producing force to create this twice monthly tide?

Moon and the Sun in conjunction. When the sun and moon are lined up on the same axis through the center of the earth, either with the moon on the same side as the sun (a NEW MOON) or on the opposite side from the sun (a FULL MOON), the tides produced by each will be additive (they are in phase). This will produce a new bulge that is the sum of the moon's bulge and the sun's bulge, producing a maximum tidal range (between the highest HWs and lowestLWs)

What is the loop current in the Gulf of Mexico, and how is it associated with the Florida Current?

Much of the water that circulates through the American Mediterranean comes from the S. Equatorial Currents. It leaves the Caribbean and enters the Gulf of Mexico through the Yucatan Straits. Some of this water circulates in a clockwise gyre in the Gulf, and then joins other water flowing directly through the Yucatan Straits, and out through the Florida Straits as the Florida Current -The Florida Current joins with the remainder of the water from the N. Equatorial Current that flows east of the Caribbean in the Antilles Current to form the Gulf Stream

Why will the resonance tides produced in basins open to the ocean usually have larger ranges than those for lakes (think of Bay of Fundy)?

NARROW BASINS Nodal lines in narrow basins open to the ocean are close to the open end of the basin Therefore, the SW set up in these basins by a small-range ocean tide will produce SWs with antinodes at the closed end of the basin that are of much greater magnitude than for a similarly-dimensioned enclosed basin (where the nodal lines are more in the center of the basin), especially if the characteristic period Tc of the basin is close to the TPF

HW Explain the statement: "Partial tides are to actual tides as component waves are to the sea".

Ocean waves are made up of the superposition of many component waves of different heights and periods. Therefore, because tides are considered to be long waves, they also are made up of several component waves (but these component waves are called partial tides), so the statement "Partial tides are to actual tides as component waves are to sea" is a good analogy.

Why is there not an inequality for an equatorial tide?

Only has one tidal range

What are wave rays (also called orthogonals) and how are they oriented with respect to the wave-crest lines?

Orthogonal lines that are perpendicular to the crest-lines - refraction example (the arrows are the orthogonal lines/wave rays)

Explain why and how this process of shoaling increases the wave steepness parameter, H/L, and why we call H/L > 1/7 the breaking criteria?

Recall that the wave steepness parameter is H/L and the breaking criteria is H/L > 1/7. This means that wave steepness can increase if L decreases or if H increases (or both occur) Therefore, because H increases and L decreases, H/L will increase doubly fast, and in theory when the breaking criteria (H/L>1/7) is exceeded, the wave will break with its swash rushing onshore.

What are coastal waters?

Relatively shallow-water areas that adjoin continents of islands. Coastal waters are those adjacent to land and at the extremes of oceanic margins. They are influenced by continental processes more than their parent ocean because of this proximity, and because they are shallow. As a result, changes in the salinity and temperature structures of the coastal ocean are generally more rapid than in the ocean. -river runoff and the blowing of dry offshore winds from the continents may offset each other to produce isohaline condition throughout its depth

What is the force that drives these standing waves? consider SWs set up in basins that are open at one end to the ocean

Rising and falling tide in the ocean -these SWs are free/forced waves.

How are they formed by constructive interference of two or more wave trains? -rogue wave

Rogue waves are thought to occur when the period of arriving waves are harmonics (1/4; 1/2; etc) of the period of the predominate wave and when all the crests arrive together, suddenly producing a constructed wave that is the sum of the heights of all the waves that are interfering.

In what direction (clockwise or counterclockwise) do cotidal lines rotate in the northern hemisphere?

Rotates counter-clockwise around the AP

Define the Characteristic Period (Tc) for this type of basin (free-sw set up by winds seiche)

Tc is the characteristic period of the free SW -- this means that every time a basin is "excited" by the wind and a SW is produced, it will oscillate with the same characteristic period - TC PROP L, 1/h l is length of basin in meters,

What is a Kelvin Wave, and how is it produced in a broad basin?

The SW created by these processes in a broad basin open to the ocean. A Kelvin wave is a wave in the ocean or atmosphere that balances the Earth's Coriolis force against a topographic boundary such as a coastline -if we make this open-ended basin large enough with its opening toward the south, we can model the SW set up in the Northern Hemisphere and discover that the tides in the open ocean actually are Kelvin Waves

What is meant by the dynamic zone of the shoreline?

The dynamic zone of a beach includes all of the shore and coastal areas that are affected in any way by breaking waves, including those parts that are covered with water during a hurricane storm surge. -Dynamic zones, therefore, should contain no fixed structures. As humans have built more and more on our coasts (and particularly on our more fragile barrier islands and other locations near the dynamic zone of the beach), the effects of intense storms (with high winds and storm surge), wave erosion and the inevitable rise in water levels, have become more critical.

hw Finally, explain how mixed tides are created by the moon (according to the equilibrium theory) when the moon is at its maximum northern or southern declination angle. Hint: Where are the two tidal bulges when the moon is at its maximum declination, and describe the HWs that a person at, say, 28 N would observe during one lunar day. You may want to draw a picture on scratch paper to help you visualize your answer.

The equilibrium theory predicts the earth-moon system will produce two bulges of water on opposite sides of a spherical earth. When the moon is at its maximum northern declination, one bulge is centered at 28 deg. N and the other at 28 deg. S latitude (so you see that it doesn't matter whether the moon is at its maximum north or south declination). Now someone at, say, 28 N. latitude would record two HWs; the one directly under the bulge north of the equator would be the HHW, and the one about 12 hours later would also be a HW, but it would be lower (the LHW), because most of the water in that bulge is in the Southern Hemisphere.

How do the assumptions of dynamic theory differ from those of equilibrium theory

The key dynamic theory of tides is that the tides are really just very long waves. This means that we can treat tides as we would long waves and assume that the actual tide at a location is composed of a number of component waves of different periods called partial tides.

What are the 2 things that change sea level/shore line -tectonic forces -isostatic changes - density of water - glacial ice

The level of the shoreline can change by the vertical movement of continents or by an increase in the volume of water in the ocean -tectonic forces: earth quakes that uplift the coast -isostatic changes: the rebound of continents before during and after an ice age. -density of water: direction relationship between sea level and ocean water temp. for every 1C change in temp the sea level changes 2m. - changes in amount of glacial ice: during last ice age the sea level was at least 120 m below present shoreline due to changes in density but mostly due to freezing of ice.

How do dispersing waves sort themselves out, so that "order" is created from "chaos"? - aka what is wave dispersion

The longer waves outrun/travel faster the shorter waves and order is created out of chaos. This sorting of waves by wavelength is called wave dispersion.

hw What is the declination angle of the the plane that includes the moon's orbital path around the earth (inclined with respect to the equatorial plane)?

The moon orbits the earth in a plane that is inclined with respect to the equatorial plane by an angle of about 28 deg. (this is called the declination angle).

Sea

The ocean is quite chaotic and made up of many component waves of different periods and directions combining to produce what we know as "sea."

why are ocean waves hard to measure?

The sea is very confused and irregular, and most wave gauges only measure wave height (not direction).

What two forces are in equilibrium in this theory?

There are two forces in Newton's theory that, when in equilibrium at all locations on the earth, produce the observed tides; they are: i. Gravitational attraction: that the sun and moon have on the water of the earth (G prop to mass of moon and earth/distance between them2) ii. Centrifugal force: set up by the earth-moon system and earth-sun system each rotating around a common center of mass (Fc or C, equal everywhere on earths surface - ferris wheel)

Why is a seiche a free standing wave?

Therefore, these free SWs are "tuned" to their basin and, using the name given to such waves by the Swiss, are called Seiche.

Define and explain what is meant by the equilibrium of a beach?

This beach slope equilibrium is established when the sand moved up-slope in the swash establishes an equilibrium with the sand moved down-slope in the backwash (i.e., the backwash returns as much sand as that moved toward shore by swash).

What are the benefits of assuming that tides are very long waves (recall the earlier classification of waves by period and that tides were the two 'spikes' on the figure are near 12 hrs. and 24 hrs)?

This means that we can treat tides as we would waves and assume that the actual tide at a location (analogous to the "sea" in an active wind-wave generation field) is composed of a number of component waves of different periods called Partial Tides.

How are each of these currents (ebb flow, slack tidal) associated with ocean tides, and the subsequent rise or fall of water in the ocean

Tide is the sea level. Tide is the reason that the ocean would be higher than the basin and vise versa

Why is a Tsunami always a shallow water wave?

Tsunamis have such long wavelengths (average about 200 km) that they are always shallow-water waves. -The leading wave of the train created by the seismic event will move with a celerity proportional to the water depth and generally in excess of 700 km/hr (472 mph), and will arrive at distant locations within a few hours

how does a storm surge differ from a tides

Unlike regular waves that shoal, break and rush on-shore (swash), then retreat back down-shore (backwash),storm surge is more like a very fast rising and moving tide (and often called a storm tide) that moves toward land at the same speed the hurricane is moving, quickly reaches its peak as it shoals, and then stays there at that height and speed until the storm moves well onshore. -Tides - if you lay your blanket on the sand fairly close to the water at a low tide, after a few hours, you will have to move it to higher ground to keep from getting wet (and high tide would be reached after around 6 hrs). -Storm surge would advance at 7-10 mph, and if large (7-17 ft or 2 - 5 m) would submerge beaches and homes with water coming in so fast that you would be swept with it.

Define WAVE DISPERSION and explain why the wave Celerity (C) for a deep water wave is responsible for this dispersion. Hint: Write down proportional relationship between C and L or T and use it to get your answer.

Wave dispersion is defined as longer waves outrunning short wavers and the sorting of waves by wavelength. This occurs because the speed at which a wave crest moves (wave celerity, C) for a deep water wave is directly proportional to the length (L) or wave period (T). This means that longer waves travel faster than shorter waves.

How "big" are the waves when the sea is fully developed and in what way may the wave steepness parameter, H/L, be used to explain this bigness?

Wave steepness of an ideal wave is measured by the "steepness parameter"(H/L) which increases as H increases and/or as L decreases. According to linear wave theory, when H/L > 1/7, waves become too steep and unstable, so they break; therefore, H/L > 1/7 is called the "breaking criteria".

Wave dispersion is directly proportional to wave celerity. For deep water, therefore, does wavelength or water depth govern wave dispersion?

Wavelength

Explain why wavelength (L) also decreases during shoaling

Waves slow when they shoal, and because KE prop c, KE also will decrease. Since TE is conserved (held constant), the decrease in KE results in a comparable increase in PE, so wave height (H) is increased. - There is no change in the orbital progressive waves until the depth decreases below 1/2 their wavelength. Thereafter, however, as a train of waves shoal they will slow down (because they are now being affected by decreasing depth). The leading wave, being in the shallowest water, will slow before the wave just behind it, which will slow before the wave behind it, etc. Therefore, as the waves in the train shoal, they will begin to "crowd up", with the second wave closing on the first wave, etc., and the wavelengths (L) between successive crests will decrease. - race example: The first of the group to cross the finish line would slow, but the second runner would be running at full speed, so would close up on the first runner

After explaining this set-up, how would you determine the minimum duration? (b) Why do you want to start the experiment when the wind is zero, and how would you be able to tell, from the spectral plot, that the minimum duration required for FD had been reached?

We wait until there are no waves present and wait for a steady wind to begin to blow directly offshore. Then (since the variable is now time), we measure the progressive growth of the spectra as a function of time (say t1, t2, t3, t4, t5 & t6), not distance. Then we note that there is no difference in the spectra at, say, t6 & t7 (they have the same peak period and area under curve). We reason that the waves reach FD at t6, because even with the longer duration of t7, the wave spectrum did not grow. Therefore, we conclude the the minimum duration required for FD is t6.

a. Assume a steady wind blowing offshore and explain what we mean when we say that wind-waves are fully-developed (FD), and why "white-caps" are produced in a FD Sea.

When a constant wind blows over an unlimited fetch for an unlimited duration, wind waves build up and eventually reach a limit in steepness (measured by the steepness parameter, H/L) - at this point they are called fully-developed (FD) waves (i.e., the waves are 'as big and steep as they can get'). But even after FD, energy is still being put into the sea by the wind, and this excess energy must be released by turbulence - producing "white-caps".

What about a neap tide?

When moon and sun are 90 degrees out of phase and acting independently -When the moon is either in the 1st or 3rd quarter of its distance around earth and 90 deg. out of phase, the tides produced will have a minimum tidal range, because each tide "acts on its own" and, therefore, is not additive.

Swell

When the component waves do appear more as individual waves as in the case of the ocean "swell," their crests are more "peaked" and troughs more "cantilevered" than the ideal wave

What phase of the sun and moon will produce a spring tide?

When the moon and sun are aligned and tides are additive -When the moon is either in the 1st or 3rd quarter of its distance around earth and 90 deg. out of phase, the tides produced will have a minimum tidal range, because each tide "acts on its own" and, therefore, is not additive. - the max range rise is the SPRING tide

what is wind generated waves - the sea surface is made up of ____ waves with ____ ____ and ______

When wind blows over the ocean, surface waves are generated by transferring some of the wind's energy, in the form of momentum, from the air to the water. actual sea surface is made up of component waves with different periods and heights.

Tides with 12 hr 25 min. periods. Explain why the semi-diurnal period is not 12 hr (the earth rotates once around its axis in 24 hrs, doesn't it?)

While the earth was making one complete CCW revolution (in 24 hrs), the moon also was moving CCW around the earth (taking about 29 days to complete its orbit), So to 'catch up' with the moving maximum bulge, the earth has to rotate an additional 50 minutes to get back under it. Therefore, the lunar day has a diurnal period of 24 hr 50 min (and half of that is the semi-diurnal period of 12 hr 25 min)

Why is the Coriolis effect required to produce these Kelvin waves?

Will move left in the Southern Hemisphere. It's what causes them to rotate. only in broad basins (not narrow)

how big a wind wave gets is dependent on 4 variables

Wind Speed Wind Fetch (the distance over which the wind blows) Wind Duration (how long the wind blows) Water Depth

method of generation

Wind waves are generated when wind blows across the water surface and momentum is transferred from the wind to the water. Impact waves (such as Tsunamis) may be generated on the water surface by earthquakes or any other forms of impact (even, on a small scale, by a rock thrown into a pond).

Do both wind waves and impact waves disperse?

Yes

hw What two conditions between the Tide Producing Force (TPF) and Tc are necessary for this seiche to become a resonance standing wave (RSW)? Assume that a SEICHE HAS ALREADY BEEN CREATED in a long narrow lake and that it has a Characteristic Period (Tc) = 12.4 hr.

You already know that the semi-diurnal tidal period created by the TPF is equal to 12.4 hrs. Since the Tc of the basin also is given as being equal to 12.4 hrs, the Seiche may be 'boosted' by the TPF to produce a resonance SW, if and only if Tc and the TPF ARE IN PHASE. -if Tc is equal to and in phase with the TPF its a Resonance Standing Wave. -Therefore (and this is important), there are TWO conditions for a resonance SW to be produced: 1. The Seiche Tc = 12.4 hrs AND 2. the Seiche is in phase with the semidiurnal TPF.

Wind wave

are generated when wind blows across the water surface and momentum is transferred from the wind to the water

Standing waves in an enclosed basin

basin only for the longest east-west oriented lakes may the moon and sun produce a measurable astronomical tide as a result of the tide-producing force (TPF)

The Equilibrium theory

cannot be used to explain diurnal tides (that have only one high and low per day ), but it can give us insight into tides that have two highs and two lows in a day, and into combined tides produced by the sun and the moon:

A twice daily Mixed Tide

created when the moon's two "bulges" are at a 28.5 deg angle to the equator, and which also will have a period of 12 hr 25 min, but with unequal high waters -- called the Tropical Tide.

equilibrium theory concerning the changes in the tidal range

diff in water height between a HW and an adjacent LW that occurs with a periodicity of about 2 weeks (a fortnight). this results when we combine the tides produced by the moon and the sun.

in the full-development table: as wind speed increases what else increases - what limits full development

fetch, duration, height, length, and period all increases. - For full development, fetch and duration must be greater than or equal to the minimum required for full development. fetch and duration are less than the minimum and, therefore, "limit" full development

How does the wave spectral-peak period, and the area under the curve of a wave energy spectrum (where wave energy is plotted as a function of wave period), grow as the wind speed and duration increase?

first that you place a single wave gauge at a fetch that is greater than or equal to the minimum required fetch (in our example above, either fetch 5 or 6). -we have to hold fetch 'constant', so we chose the fetch that is at least the minimum required for FDS - this way fetch does not contribute to the increase in the spectra. -initially, there is no wind and no resulting waves, and that the experiment begins when the wind begins to blow offshore and after it reaches a constant speed. -As before, you would plot spectral growth, but NOW as a function of time, not distance (as you did in the fetch experiment). Look at the spectral plot above and think of the numbers 1-6 as being time (duration) measurements rather than distance (fetch) measurements. ***so how will you know when you have reached the min duration required for FDS? SEE HW BELOW

how big is the tidal range in this standing wave enclosed basin?

for forced SWs set up by TPF - its insignificant and measured in CENTIMETERS

Will a sea that is fully developed for a given wind speed, remain that way if the wind speed increases?

full development at a given wind speed will not remain fully developed if we increase wind speed

Why is a SW produced by the TPF called a forced wave?

gravity is necessary to keep them going

Why is a tide produced by the TPF called a forced wave? - forced SWs set up by TPF

gravity is necessary to keep them going. In the largest and longest east-west oriented lakes, the Tide Producing Force (TPF) may cause very small-amplitude, forced SWs with semi-diurnal periods. these forced SWs are insignificant (with a range usually measured only in centimeters)

Wind duration

how long the wind blows

Wave energy spectrum

i. A statistical property that describes all of the component waves present in the sea ii. Total energy in the sea and the predominate wave in a sea (period of the peak of the spectrum (Tp))

Why do we need at least a year-long tidal height record at a particular spot in the coastal ocean before we can determine the importance of the partial tides present at that location, and be able to accurately predict future tidal heights at that location.

i. Conditions during any one month would not be representative of the seasonal conditions found and averaged over a year; ii. Seasonal variations from year to year could affect how the partial tides are added together and, therefore, the importance assigned to each partial tide; Therefore, with longer term collections, these short term variations would be filtered out, and you get a much better determination of the partial tides at that location. The height-time record you make at your site is then subjected to something called a harmonic analysis, that will identify the most important partial tides by period and determine their relative weight (or importance) at that location. These weighted partial tides are then used as input in a computer program to make predictions about the actual tides at your location for anytime in the future.

Relationship to Generating Force after Generation: What relationship do free waves and forced waves have to their generating force, and under what conditions may each of these classes of waves be found?

i. Free waves: run independent of their generating force (such as impact waves and swell) ii. Forced waves: are dependent upon their generating force for their continued existence (tides) iii. Free/forced waves: are those being actively generated (in an intense storm, for instance)

How does wave interference occur, and what is the difference between constructive and destructive interference?

i. In a large storm, component waves of many different wavelengths and directions are being generated simultaneously and they combine, by the process of interference, to create "sea," a very chaotic state of the sea surface that has no discernible organization. Over time, the energy from the storm generates larger and larger waves that begin to gain some organization as they disperse away from the active generation area as "swell. ii. Destructive: where crests and troughs arrive out of phase, canceling each other out only to reappear iii. Constructive: where crests and troughs are in phase and reinforce each other. they have same wavelength and add together, making a period that is the the height of the 2 periods added. can cause a rogue wave

What part do swash and backwash play in this relationship?

i. Large-grained/coarse sand: Some of the sand moved up the beach by the swash stays there- it is not moved back in the backwash, and a larger equilibrium slope must be established before an equal amount of sediment can be returned in the backwash (VOID SPACE) ii. Very fine sand: All the water from the swash returns in the backwash and the equilibrium of the beach establishes a very small slope (NO VOID SPACE)

Who formulated this equilibrium theory and what are the theory's simplifying assumptions?

i. Newton ii. Unrealistic assumptions (a perfectly spherical earth covered with water, but with no basins nor continents, nor bottom friction)

Contrast and compare the way that waves change direction during reflection, refraction and diffraction

i. Reflection: Waves that encounter a solid vertical surface (such as a seawall) will abruptly change direction, and if they hit at an angle, without much loss of energy. - Angle of incidence "Xi" is equal to the angle of reflection "Xr" - When angle is zero, reflection may generate standing waves that are the product of two waves with the same period traveling in opposite directions - Can create dangerous conditions ii. Diffraction: also involves bending of wave rays, but now that bending is around corners or edges of solid objects. - When striking the edge of a solid surface, any point on a wave may be the source from which energy can propagate in all directions iii. Refraction: Waves also may bend as they shoal (because C prop d) if they approach the beach at an angle - At some distance away from the coast the crest-lines may approach at an angle of more than 45 degrees, but as they get closer to shore they appear to bend so that the crest-lines are more parallel with the coastline by the time they reach the surf zone - Sometimes bend around a point of land - involves wave rays/orthogonal lines

Period of waves: how are waves classified by period and what are their principle generating and restoring forces?

i. Ripples (capillary waves): <0.1 second; generated as the wind begins to blow, the surface is restored by surface tension if wind stops because these are very small ii. Gravity waves (most common): 1-30 seconds; generated by the wind and storms and restored by gravity iii. Infra-gravity waves: 1 minute; generated by strong storms and restored mostly by gravity iv. Long waves: 5 minutes; generated by intense storms and by earthquakes, restored by gravity and the Coriolis Force v. Tides (longest wave): 12-24 hours: generated by the sun and the moon and restored by bottom friction and the Coriolis Force

Contrast and compare sea and swell:

i. Sea: The ocean is quite chaotic and made up of many component waves of different periods and directions combining to produce what we know as "sea." ii. Swell: When the component waves do appear more as individual waves as in the case of the ocean "swell," their crests are more "peaked" and troughs more "cantilevered" than the ideal wave. - think of a marathon. starts and all in a group, hours later the group is dispered into a long string with the fastest in the front. this is the process that makes a swell and leaves behind a confused sea

How does a coastline differ from a shoreline (and coast)

i. Shoreline: water's edge which moves back and forth, up and down the shore, with the tide. ii. Coastline: demarcation line (the landward limit) of the effect of the highest storm waves on the shore - terrestrial flora and fauna -The Coast is everything landward of the coastline that has only terrestrial flora and fauna. Sometimes the coastline is half-way up a steep cliff (as shown below and described in the next section). Primary Coasts are those shaped primarily by non-marine processes. You can think of these coasts as being relatively new (e.g., volcanically or seismically generated) and unmodified by ocean waves and other marine processes, or those older coasts that are not exposed to the full effects of ocean waves (e.g., drowned river basins). Secondary Coasts are those in which exposure to the action of ocean waves have changed their characteristics and structure (e.g., wave cut cliffs).

Identify the parts of an ideal (sinusoidal) ocean wave (height (H), length (L), trough, crest, period (T)), and define what is meant by wave celerity (C)

i. Sinusoidal: with crests and the troughs having identical shapes and the wave having one fixed wavelength Spatial scale: ii. Height (H): the vertical distance from the top of the crest to the bottom of the adjacent trough iii. wave Length (L): the horizontal distance between two adjacent crests (or troughs, for that matter) iv. Trough: bottom of the wave- between crests v. Crest: top of wave Temporal scale: vi. Period (T): the time that it takes for two consecutive crests to pass a fixed point. - the inverse of the period 1/T is the wave frequency (f) which is a measure of the number of times one complete wave will occur per unit time. One cycle per sec = 1 Hz vii. Wave Celerity (C): the speed with which a wave crest moves horizontally across the ocean surface

Which of these tides (spring or neap) has the maximum, and which the minimum, tidal range?

i. Spring: maximum ii. Neap: minimum

In how many ways does a storm surge differ from a tsunami?

i. Storm surges are not as spectacular, but far more damaging ii. Occur far more frequently than tsunamis

In what way are amphidromic points in wide basins comparable to nodal lines in narrow basins?

i. The SW moves around a nodal point (called an AP), with the period of the TPF ii. He drew a representative co-tidal line that extends out from the AP to the antinode of the SW iii. Co-tidal lines show the times of the phases of the SW

How do these man-made structures affect the movement of sand and change the erosion or deposition of sand in the dynamic zone?

i. Therefore, any structure in the dynamic zone that interrupts this natural flow will create problems downstream. Note that as the longshore drift is interrupted, sand accumulates on the upstream side of the jetties, but erodes on the downstream side. ii. The erosion on the downstream side results because the sand moved away from that part of the beach by a wave's action is not replaced by sand from the normal upstream flow.

In what zone (and how close to shore) are longshore currents found, and how are they created by ocean waves?

i. Waves that approach a shoreline at an angle and then break in the surfzone will produce a longshore current 1. When waves break and the water continues to rush u the beach as swash, but when it stops, the water runs back down the beach along the greatest slope as backwash, being pulled back by gravity. This swash/backwash motion will result in a zigzag movement of the water with a net direction that is the same as the approaching waves which will produce a longshore current

For a given wind speed, how can wind duration and wind fetch limit the sea from reaching full development?

i. When fetch and/or duration are large enough for a sea to be fully developed for a constant wind speed (i.e. their min fetch/duration), there will be no additional growth in the wave spectra, regardless of whether fetch or duration increase beyond that point. you would have to raise wind speed to get additional wind speed and new FDS. ii. The other important concept is that full development depends on two variables (fetch and duration) so, to determine the effect that one of those variables has on full development, we have to 'neutralize' the other (hold it constant) - If our goal is to measure the minimum fetch required for a FDS, we must wait for the wind to blow at least as long as the theoretical minimum duration required for a FDS so that duration will not have an effect on the spectrum). If our goal is to measure the minimum duration required for a FDS, we must placeour wave gauge at a distance at least as great as the theoretical minimum fetch required for FDS (so that fetch will not have an effect on the spectrum).

Why is it necessary for the moon to be at the maximum declination angle?

i. When the moon is inclined with respect to the equator at its maximum declination in either the northern or southern hemisphere, you will notice that one bulge is primarily in the Northern Hemisphere while the second bulge on the opposite side of the earth is primarily in the Southern Hemisphere. ii. If you were standing on the earth at 28.5 deg N, in one complete rotation of the earth, you would see two highs, but these highs would not be the same height because of the location of the two bulges are not in the same hemisphere

What is longshore drift, and how is it related to longshore currents?

i. most of the sediments are distributed in the surf zone by waves as Longshore drift ii. his wave action also will pick up sediment that will be moved by the longshore currents - the movement of sand by these currents is called longshore drift.

Updrift and downdrift compare to upshore and downshort

if the current is flowing south for example, updrift would potentially occur in the opposite direction (northernmost part of the barrier) and the downdrift would occur the southernmost part of the barrier - upshore is literally upshore, the top in the direction it is flowing. this is the area that has the most sand. the downshort part on the other side of the groin is downshore and has least sand

What is the major difference in the movement of water in a breaking wave as compared to water movement in the same wave before it breaks?

just as it begins to break and the water particles change from their orbital paths to a more horizontally-oriented translational path that hurls the water toward the beach as swash.

component wave

longer waves travel faster than shorter waves. This has some interesting consequences. As a first example, suppose you tossed a large rock into a pond. The immediate result of this is a turbulent splash and the creation of many impact waves of various wavelengths all mixed up together (called component waves ). After just a few seconds, however, if you look closely, you will see concentric rings of waves propagating away from the center and you will note that the longest waves are out in front of the next longest wave, which is out in front of the third longest wave, etc.

Impact wave

may be generated on the water surface by earthquakes or any other forms of impact (even, on a small scale, by a rock thrown into a pond)

During the passage of the moon

moon in its orbit around the earth, the tides may alternate between being equatorial tides and tropical tides.

What is an estuary and what relationship does it have to movement and interaction of ocean water and fresh water?

o An estuary is a semi-enclosed basin of water in which fresh water mixes with, and significantly dilutes, coastal ocean water. Classified by origin and degree of mixing

What are the names of the four major classes of estuaries (by origin), and what are their characteristics?

o Coastal Plain Estuaries: These estuaries were formed at the end of the last ice age when rising seawater flooded (or "drowned") existing river valleys. The Chesapeake Bay is an example of this estuary o Fjords are glaciated, U-shaped valleys with steep walls. Usually, the glacial deposit pushed ahead by the advancing glaciers creates a shallow sill near the ocean entrance. Fjords are common along Norwegian and Canadian coasts. o Bar-Built (Barrier Island): These most commonly are barrier islands that are separated from land by a shallow lagoon. They are formed by the creation of sand bars parallel with the shore, usually adjacent to slow flowing rivers that discharge freshwater into the coastal waters. Wave action plays a pivotal roll in the creation of these sand bars, but their existence also may be caused by some chemical interactions between the salt water and the fresh water that aid in the bonding (flocculation) of fine particles in the water that then fall to the seafloor as they accumulate size and mass. The Outer Banks of NC are an examples of this estuary o Tectonic: These are caused by earthquakes, where folding or faulting may create bays with narrow inlets to the sea. San Francisco Bay is an example of this estuary

What is the "American Mediterranean"

o Marginal sea: The American Mediterranean includes the four basins of the Caribbean Sea and the Gulf of Mexico

Contrast and compare salt marshes and mangrove swamps.

o Salt marshes are filled with a variety of grasses and are found from the equator to as high as 65 deg. latitude. o Mangrove swamps are restricted to latitudes below 30 deg. Once mangrove swamps colonize an area, they normally outgrow and replace marsh grasses.

What are near-shore coastal geostrophic currents (cgc) and how do they compare to well established ocean currents further offshore?

o These CGC's also are driven by a density-induced sloping sea surface, but the cause of the slope is quite different than for the ocean geostrophic currents o Look specifically at the Davidson Current. This current flows north off the Oregon coast, between and opposite to the southward flowing eastern boundary California Current offshore. it is produced by freshwater flowing into the ocean that flows to the right from coriolis effects.

What two ways can the density slope that drives the davidson current be established?

o When strong southerly or southwesterly winds blow north along the Oregon coast, Ekman Transport toward shore causes water to pile-up along the coastline, creating a slope gradient toward the ocean - this alone could cause this current. o During the rainy season, runoff from major rivers in that region, swollen by heavy precipitation west of the coastal range of mountains, can create a freshwater wedge that also alone could cause this current -Combined, these processes create a strong low density slope that extends away from the coastline toward the ocean, with the Davidson Current as the result.

Orbital Progressive Waves

ocean waves are this (not transverse, longitudinal or standing waves) - they move in orbital paths. the orbit extends below the surface of the water because radius of orbits dec with depth. -the wave form moves/progresses horizontally from one location to another

High water/low water for diurnal tides

only have one HW and one LW per tidal day

what is an internal wave?

orbital progressive waves to be generated and propagate along density interfaces under the surface of the ocean. a strong pycnocline is such an interface. - The difference between the densities on either side of the pycnocline is not very large, certainly not as large as at the interface between water and air. Therefore, these internal waves will not propagate with nearly as much energy, even though their heights are above 100 m -propagate at slower speeds than surface waves but longer periods and wavelengths - made by undersea earthquakes or turbidity currents, or movement of ships.

Free wave

run independent of their generating force (such as impact waves and swell)

what kind of tide does newtons equilbrium theory of tides explain

semi-diurnal not diurnal tide

How does the wave spectral-peak period, and the area under the curve of a wave energy spectrum (where wave energy is plotted as a function of wave period), grow as the wind speed, fetch - minimum wave fetch/wind speed

six wave gauges (numbered 1 through 6) are located at increasing distances (fetches) away from a straight coastline -in the wave energy plot on the right above that, as the fetch increases (labels 1-5), the spectral peak for each fetch shifts right toward longer periods and the total amount of wave energy (the area under the curve) increases. This continues until the spectral plot for wave gauge 6, which we observe (to the limits of such measurements), has the same spectral peak period and the same amount of wave energy as wave gauge 5 (i.e., for all practical purposes,fetches 5 and 6 have the same spectra). We conclude that full development and the minimum fetch required for a FDS were BOTH REACHED AT FETCH 5, because there was no further growth in the spectrum at a longer fetch 6. i. The spectra will not continue to grow for any fetches longer that the minimum required for full development. And it also will NOT decrease for fetches longer than the minimum required for full development.

define celerity

swiftness of movement - the speed the wave propagates

How long do these davidson currents last?

the Davidson Current is NOT permanent. The dominant wind is usually from the northeast, creating upwelling, and only during the rainy season do you get significant runoff. so the conditions for this current are not often or persistent.

the first swell to arrive at some distant point will be the _____ and as a storm gets closer, the wavelength (or period) of the arriving swell will _____ and wave height will _______

the FIRST SWELL to arrive at some distant point will be the LONGEST, and as the storm gets closer, the WAVELENGTH (or period) of the arriving swell will DECREASE and WAVE HEIGHT will INCREASE (because as the progressively shorter waves arrive, the energy per unit area increases - the wave energy is concentrated in a smaller area between crest lines and wave rays

Tidal Range:

the difference in water height between HW and an adjacent LW - lunar hours because its more than 24 hours

Wind fetch

the distance over which wind blows

Gravity waves

the most common waves; have periods between 1-30 seconds (with the most energy centered around 8 seconds), are generated by the wind and storms, and are restored by gravity

Capillary waves

the smallest waves (ripples); have periods < 0.1 second and are the first to be generated as the winds begin to blow, but because they are so small (on a molecular scale), if the wind stops they don't last long- the surface is restored by surface tension

define period and range in tides

the time between two adjacent HWs or LWs is called the tidal Period and is equal to one Tidal Day. The difference in height between a LW and an adjacent HW is called the tidal Range.

Tidal Period

the time between two adjacent HWs or LWs is called the tidal period

How do actual ocean waves differ from ideal waves

they do have a sinusoidal shape and rarely are found with a single wavelength or wave period. -sea -swell

Under what depth and shoreline conditions are wave rays focused by refraction and toward what shoreline depth do the wave crest-lines (or wave rays) bend?

this is for an irregular coast line! - the portion of the wave train that first encounters the shallow water of the headland will slow and both the crest-lines and the wave rays will turn toward the headland and the waves will quickly break in the headland surf zone i. Wave rays will bend "toward" shallow water (toward the headlands), but also as shown, "away from the bay" ii. During this refraction into the bay, the area between two wave rays and two adjacent wave crests increases. Therefore, the wave energy per unit area is greatly decreased when the train enters the surf zone of the bay.

Contrast and compare artificial barriers: jetties, groins, breakwaters and seawalls?

this is to protect beaches from erosion. HARD STABILISATION (extend out from land into the long shore drift) i. breakwater Jetties: artificial barriers attached (anchored) to, and extending out from land to the longshore drift ii. tethered float Breakwaters: made of rock rick-rack (or other surfaces with large void spaces and surface areas) that cause incoming waves to break and dissipate their energy. A breakwater interrupts the longshore drift and prevents the movement of any sand directly along the beach at its location. iii. Groins, low-lying structures (may be long cylindrical sandbags) that stick out into the ocean and interrupt, but do not prevent the movement of all sediment -- they usually are designed so that some of the sand moves over its top. Help counter erosion by trapping sand from the current. accumulate sand on updrift side, erosion is worse on downdrift side (deprived of sand) SEA WALLS iv. Seawalls are rigid and solid structures generally built parallel with the shoreline, and are used as a last act of desperation when everything else has failed. temporary protects property, increases beach erosion by deflecting wave energy onto sand. IMPORTING SAND: best response to erosion, dredged sand, expensive, but dredged sand erodes more quickly because its finer sand.

How do partial tides combine to produce the actual tides observed, regardless of the tide's actual period?

to understand how these seven partial tides act constructively and destructively to produce the actual tide, just as component waves produced a sea.

Surf

wave breaking

Distinguish between wave erosional coasts shoreline features (sea caves, sea arches, stacks and wave-cut bench or terrace) and wave depositional shoreline features (delta, barrier islands, bay barrier, spit, lagoon, and Tombolo).

wave erosion = rocky coasts. has irregular coastlines with headlands (extend into ocean) and bays (semi enclosed part of coast between headlands) headlands will erode to produce in this order: i. Sea caves: the initial burrowing into rock on the side of headland ii. Sea arches: when caves on both sides of headland meet iii. Sea stacks: when arch collapses iv. Bench: waves may cut out a bench that underlies the sand of the beach and shore regimes, creating "wave-cut terraces" DEPOSITIONAL COASTS - Delta, where sediment from rivers sink to the bottom and spread out into ocean -Sand Spit, where sediments are deposited from a jutting point of land along the direction of the longshore drift, v. Bay barrier: if the spit spans between two jutting sides of an embayment vii. Tombolo: when a spit extends between an island and the land vi. Barrier island: when sediments are deposited parallel with the shoreline (our coastline) -Lagoon - behind the barrier island