MEA Test 3

What are wetlands and what is their relationship to estuaries?

Wetlands mitigate flooding by collecting runoff waters and REMOVE INORGANIC NITROGEN COMPOUNDS AND METALS FROM GROUNDWATER POLLUTED BY LAND SOURCES. Marine wetlands, (border estuaries and other shore areas protected from the ocean) are biologically productive areas delicately in tune with natural shore processes. The key to the effectiveness of marine wetlands is the natural circulation and flushing provided by the tides.

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

When the moon is either in the 1st or 3rd quarter of its distance around the earth and 90 deg out of phase, the tides produced will have a minimum tidal range, because each tide 'acts on its own' and is not additive. We call the maximum range tide spring tide (when moon and sun are aligned and tides are additive)

salt-wedge estuary

deep estuaries with a large volume of fresh water

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?

1. Free waves - run independent of their generating force (such as impact waves and swell) 2. Forced waves - are dependent upon their generating force for their continued existence (such as the tides). 3. Free/forced waves - are those being actively generated (in an intense storm for instance)

tidal range

The difference in hight between a LW and an adjacent HW

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

direct relationship

impact wave

(such as Tsunamis) may be generated on the water surface by earthquakes or any other forms of impact.

How does a coastline differ from a shoreline?

The shoreline is defined as the water's edge, which moves back and forth, up and down the shore, with the tide. The coastline is the demarcation line (the landward limit) of the effect of the highest storm waves on the shore (and in which marine flora and fauna are found)

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

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.

What part do swash and backwash play in this relationship? What part does grain size play in this relationship (think void space)?

long grain sand - have a lot of void spaces, making sand more porous, so some of the water (especially in the backwash - because the water comes to a stop before running back down the beach) percolates beneath and moves back toward the ocean under the surface of the beach. This means that 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 very fine sand - no appreciable void space - so all of the water and the vast majority of sand that runs up the beach in the swash, runs back down the beach in the backwash on top of the surface, and the equilibrium of the beach establishes a very small slope

Partially mixed estuary

relatively shallow, moderately high-volume estuaries in which the salinity increases from the head to the mouth at any depth

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. In an ocean wave, KE prop C and PE prop H. An energy balance can be expressed as: TE = KE (C) + PE (H). 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 is increased.

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.

Conditions during any one month would not be representative of the seasonal conditions found and averaged over a year and seasonal variations from year to year could affect how the partial tides are added together and the importance assigned to each tide. SO for the longer term, these short term variations would be filtered out, so you get a much better determination of the partial tides at that location.

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

Crest lines of the advancing wave train, but also orthogonal lines that are perpendicular to the crest-lines. We call these orthogonal wave rays (they are an artifact used in drawings that show refraction, but a very useful one for understanding how wave energy is focused and spread ou).

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

CGC's are also driven by density - induced sloping sea surface, but the cause of the slope is quite different than for the ocean geostrophic currents.

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

Celerity for shallow water waves is directly proportional to depth or change in the orbital progressive waves until the depth decreases below 1/2 their wavelength. Thereafter, as a train of waves shoal they will slow down. 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.

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 any larger and its wave height and wavelength have reached their full potential. This 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.

high water/low water for diurnal tides

Diurnal tides have one HW and one LW per tidal day Semi-diurnal (semi-daily ) tides - There are two semi-diurnal tides and both have 2 HWs and two LW per tidal day. The period and range in these tides have the same definition for that of the diurnal tides, but the period is half as large.

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

For full development, fetch and duration must be greater than or equal to the minimum required for full development. If water is too shallow, the wave steepness will grow more than is warranted by the fetch and duration, and the breaking criteria will be reached before the waves are fully developed.

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, or duration increase?

Total wave energy in a sea is represented by the area under the spectral plot. This total energy is a measure of the energy of all waves of any size that make up the 'sea'. The predominant wave in a sea is represented by the period of the peak of the spectrum (Tp).

Why is a Tsunami always a shallow water wave?

Tsunamis have such long wavelengths that they are always shallow-water waves. The leading wave of the train created by seismic event will move with a celerity proportional to the water depth and generally in an excess of 700 km/hr, and will arrive at distant locations within a few hours. Since Tsunamis are surface waves, the main requirement for their generation is that the full force of the impact is applied to, and displace the water surface. At sea, Tsunamis have wave heights of only about 0.5 m. With such small heights and long wave lengths, Tsunamis are not noticed by someone on a ship in deep water.

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

Wavelength

Contrast and compare salt marshes and mangrove swamps

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

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

sea caves - the initial "burrowing into rock" on side of headland sea arches - when caves on both sides of the headland meet stacks - when arches collapse wave-cut bench or terrace -underlies the sand of the beach and shore regimes barrier islands - when sediments are deposited parallel with the shoreline and which produces a Lagoon bay barrier - if the spit spans between two jutting sides of an embayment spit-where sediments are deposited from a jutting point of land along the direction of the longshore drift which may eventually result in a bay barrier Tombolo - when a spit extends between an island and the land

Wind fetch

the distance over which the wind blows

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?

If Seiche has been set up by the wind with a Tc very nearly the same as the period of the forced SW (TPF) 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, 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.

During the passage of the moon in its orbit around the earth, the tides may alternate between being equatorial tides and tropical tides. How does the theory explain these changing tides and there different heights?

The changes in the tidal range (the difference in water height between HW and an adjacent LW) that occurs with a periodicity of about 2 weeks ( a fortnight). These tides result when we combine the tides produced by the moon and the sun.

The wave celerity of each of these two types of waves is a function of different variables - what are they?

Celerity is directly proportional to either L or T and water depth.

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

Difference between the heights of the 2 hight waters (the HHW and the LLW)

Vertically mixed estuary

Generally shallow, low-volume estuaries that are well mixed vertically, and stratified horizontally

Highly -stratified (fjord) estuary

deep estuaries with net flows much like that of the slightly stratified estuary, but where the mixing is from the deeper ocean water up into the surface water, which creates a horizontal surface water salinity gradient that increases toward, and equals that of the ocean at the head.

wind wave

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

An ocean wave with a length of 800 m will first be considered a deepwater wave at what depth? Hint: remember L and d relationship for deepwater waves.

400m

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

7. Notice the location of the AP in the North Atlantic and the co-tidal lines of the M2 (main lunar) tide as it rotates counter-clockwise around the AP. Note also that none of the AP's in any ocean are in the middle of their basin, and that the South Indian Ocean and South Pacific Ocean have two AP's -- consequences of the actual shape and size of ocean basins and allowed by the Dynamic theory.

FULLY DEVELOPED SEA: Define a Fully Developed Sea (FDS) and explain how fetch and duration may limit this full development.

A fully developed sea is when the waves are growing due to the wind and it begins to reach its limit of steepness and how big it is. Fetch and duration may limit this full development as full development rely on the fetch(wave distance) and duration(time). As the wind speeds increase, the waves are going to require a larger fetch and duration in order to reach full development before breaking at H/L>1/7.

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.

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. Hint: Recall that both fetch and duration can limit FD of wind waves - therefore, if you already know the minimum fetch required for FD, you want to chose a fetch that is no longer limiting (i.e., 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.

BEACH EQUILIBRIUM SLOPE. Explain why a coarse grain beach has a steeper slope than a fine grain beach (include a definition of equilibrium slope, how sand and water are moved both up and down the beach, and how this differs for coarse grain and fine grain sand).

Coarse grain beach has a steeper slope than fine grain as coarse grain beaches have more air voids. For the equilibrium slope of the coarse grain beach, the sand and grain are swashed up the beach but then very little is swashed back into the ocean due to the air voids. This is why the slope is steeper than fine grain since more grain is accumulating on the coarse grain beach and its not back washing into the ocean. For fine grain there are very few air voids so the swash and backwash are able to push grain up the beach but also pull it back into the ocean. With very little grain accumulating the slope of fine grain beaches are less steep.

Contrast and compare the beach equilibrium process and resulting slope for coarse-grain granules and very fine sand particles. Hint: What is different about the water movement during the swash and backwash for coarse-grain beaches compared to very fine sand beaches, and how does that affect the slope for each.

Coarse grain sand has relatively large void spaces, so some of the water being moved in the surf zone percolates and moves below the surface. The beach slope is larger because the swash is 'driven' by a breaking wave and has more energy than the backwash (which is 'driven' only by the down slope gravity), so more sand is moved onto the beach above the surface (with less time for percolation) than for the returning sand. Therefore, a greater slope is required to achieve the equilibrium of sand moved up the beach with that moved back down. Fine grain sand, on the other hand, is closely packed with little void space, so there is very little or no percolation, and the amount of sand moved up the beach in the swash is just slightly more than the amount moved down the beach in the backwash.

b. 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 SWELL arriving from the storm change at the island, 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).

What is a Kelvin Wave, and how is it produced in a broad 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. Suppose you had a wide basin in the N Hemisphere opened to the ocean on its south side. As the tide in the ocean rises, 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 the 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. The overall movement of the highest side of the water (the antinode of the SW that has been set up) moves in a CCW direction and makes one complete cycle in one tidal period. This SW moves around a nodal point, with period TPF. The SW created by these processes in a broad basin open to the ocean is called the Kelvin wave.

After the wind begins to blow steadily offshore at a constant speed, the waves arriving at the wave gauge at fixed intervals of time (t) are measured. Assume that the plot shown above is of spectral growth as a function of time (so that the numbers, t=1 through t=6, are time measures, not distance measures). Explain, using this spectral plot, why you know minimum duration has been reached at t=5. Be specific.

In order to find minimum duration we need to find the maximum fetch needed in order for there to be no wave growth. From looking at the plot shown above we know that the maximum fetch would be at time of 5. The fetch grows from t=1 to t=4 and it does not grow any more after t=5 so the maximum fetch is going to equal t=5. We know the minimum duration has to be t=5 since the maximum fetch is t=5.

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

Note from the figure that the 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. Furthermore, 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.

DYNAMIC THEORY OF TIDES. What are partial tides and how are they used to estimate the observed (actual) tides at a specific location on a coastline? EXPLAIN IN DETAIL.

Partial tides are used to combine smaller tides to form bigger ones. Partial tides are used to estimate actual tides as 4 semidiurnal and 3 diurnal tides are used to compose an actual tide

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)?

The Bay of Fundy has a narrow basin open at one end to the Atlantic Ocean and its Tc is very near that of the semi-durnal TPF, so a resonant SW is produced when a forced SW, created by the rising and falling ocean tide at the open end , is propagated into the bay. Because the bay narrows and shoals, the amplitude of the resonance SW increases as it moves toward the north end of the bay and reaches a max height of 17m.

FULLY DEVELOPED SEA: The left hand side of the picture below is a PLAN VIEW (looking down upon) of an experimental setup to determine the minimum fetch required for a sea to reach full development. On the right hand side is an xy plot of wave energy versus wave period (T) for different fetches, where we found from the lesson that full development was reached at wave gauge 5. But now I want you to tell me how to find MINIMUM DURATION. a. Assume that no wind is blowing and that no waves exist at the beginning of the experiment. At what fetch would you place your wave gauge to be able to find minimum duration? Explain why you chose that fetch.

The fetch that I would place my wave gauge in order to find minimum duration is at gauge 5 since the fetch is increasing from gauges 15. At fetch 6 the gauge has no change in energy so in order to find the minimum duration the fetch would be at gauge 5 since it is where it has the most energy.

How are each of these currents associated with ocean tides, and the subsequent rise or fall of water in the ocean.

The ocean tide is responsible for these tidal currents, causing either a flooding tide when it rises and an ebbing tide when it falls. Maximum tidal currents occur about halfway between the slack tides.

What is the force that drives these standing waves?

The rising and falling tide in the ocean provides the driving force for SW, so these SWs are free/forced waves.

RESONANCE STANDING WAVE (RSW). Assume that a Seiche (with a Characteristic Period Tc) ALREADY HAS BEEN CREATED by wind setup in a long, deep, enclosed and narrow lake. What TWO conditions must be present for a RSW to be created in this narrow basin as this Seiche interacts with the astronomical tide producing forces (TPF)? Be specific; and remember that the Seiche already has been created, so don't tell me how it was created - focus on the two conditions for resonance

The two conditions that must be present for a RSW to be created in this narrow basin is first Tc has to equal 12.4 hrs and second the seiche has to be in phase with the semi diurnal wave of the tide producing forces.

What are cotidal lines and how are they related to the phase of the tide at a particular location in the ocean?

They extend out from the Ap to the antinode of the SW and connects all points along that line (which occur simultaneously) and defines a 'ridge' (or phase line) of the SW. The co-tidal lines show the times of the phases of the SW.

Define WAVE DISPERSION and explain why the wave celerity for a deep water wave is responsible for this dispersion.

Wave dispersion is the concept of longer waves "outrunning" shorter waves. This dispersion happens because wave celerity (speed at which a wave crest moves) for a deep water wave is directly proportional to wave period

(1) After explaining this set-up, tell me how you would determine the minimum duration? What is the variable (distance or time) you will use to find minimum duration, and why would you start with a wind speed of zero to begin plotting the growth of the spectra for this time variable? (2) How would you 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

FULLY DEVELOPED SEA: What specific function do whitecaps serve in a FDS? EXPLAIN in detail

When a wave is fully developed it can no longer receive any energy but the sea is still receiving energy due to the wind. So the energy is released by turbulence which are whitecaps.

DAVIDSON CURRENT. What two conditions (together or alone) could produce the density slope away from the shoreline toward the ocean that creates a Coastal Geostrophic (Davidson) Current off the coast of Oregon? How is the slope produced from these conditions, and what is the direction and relative width of the current? (0 OF 5 POINTS)

When strong south or southwest winds blow North water starts to pile up along the coastline. The slope gradient that is created starts at the coastline and extends away toward the ocean. This is one condition that can create a Davidson current. The other occurs during the rainy season when runoff from rivers enters the ocean and creates a wedge layer on top of the salt water. This also can create a Davidson current. Together however these conditions create a low density slope that is stronger than when just one condition is occurring.

WAVE DISPERSION. Suppose you live on an island in the Western Pacific Ocean and have NO telephone or radio communications with the 'outside' world, and that a : : Typhoon is 1500 km from your island. Using only the change in the swell arriving at the island, explain conceptually how you would know the storm was moving toward the island. You don't have to see the storm on the horizon use the principle of wave dispersion (and don't confuse the Typhoon with a Tsunami).

You would know the storm was moving toward the island if you looked out at sea and saw that the wave height was increasing while the wave period was decreasing. With the principle of wave dispersion the first waves that come to shore should be the longest waves and as more waves come the wave heights would be increasing while the wave periods would be decreasing.

a. What is a seiche (define it) and explain how it is created (don't define Tc yet - do that in b. below).

a. 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 SW called a seiche

a. Define the process called beach equilibrium of sand being moved by the swash and backwash (don't worry here about differences in grain size; that will be considered in part b. - just define BEACH EQUILIBRIUM SLOPE).

a. Beach equilibrium is the condition in which the amount of sand moved up the beach by swash equals the amount of sand moved down the beach by backwash.

H/L increases toward 1/7 for a shoaling wave and eventually breaks, because as the leading wave in the wave train slows: Hint: Look for how H and L change in a way that will cause become steeper (i.e., H/L 1/7).

a. L decreases and KE is converted to PE

Beach erosion and man-made structures. Suppose you had a barrier island on the North Atlantic coast that was oriented on a NW-SE line, an inlet perpendicular through that island oriented on a NE-SW line, and a longshore drift that was moving generally toward the SE. Hint: Draw this picture on a piece of paper to help you visualize conditions, and use this figure in the next three questions. a. Because of the SE direction of the longshore drift, explain how the inlet itself (its location on the coast and the areas of the islands both north and south of the inlet) may change under these conditions. Could the inlet itself move - if so, in what direction?

a. Longshore drift moves sand along its path. When an inlet is encountered, the current 'slows' down as it turns in or out of the inlet and begins dropping some of its sand. A good proportion of that sand will be moved into the inlet by flood tidal currents, and some will also be moved out by ebb tidal currents, but these two amounts may not be the same over time. This means that the required supply of sand downstream on the beach front south of the inlet will not be available and that portion of the beach will erode; the beach north of the inlet will gain sand. During other seasons longshore drift may be in the opposite direction, mitigating somewhat the erosion. Over time, however, the beach front on the north side of the inlet opening will begin to grow into the inlet itself, while the beach front on the south side of the inlet will erode - i.e., the inlet will migrate toward the south.

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

a. 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.

Which statement below is correct concerning free and/or forced waves? Caution: part of some of the statements may be true, so chose only the one where everything in the statement is true.

a. Swell is an example of a free wave that exists only when the generating force is present. b. A rock thrown into the water will create free waves that radiate out from the point of impact. c. Tides are free waves created by the interaction of the moon's and sun's tide producing force. d. A forced wave runs free of the generating force

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.

a. 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".

b. Explain how partial tides are used to estimate the actual tide at any location along the coast? And in particular, a Mixed Tide. Hint: look at the figure above.

b. 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).

From the list below, pick the generating force/restoring force of a Tsunami wave, in that

b. Earthquake/surface tension

b. What is the definition of Tc and what dimensions of the basin dictate this definition?

b. 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.

b. 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). So 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.

b. 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).

Where (and why) along a rocky coastline would you want to anchor a boat during a storm if you could not get into port?

b. Near shore in the middle of a bay, between two headlands because wave energy per unit area is decreased there

An example of a Tectonic estuary is

b. San Francisco Bay

b. 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)? As a result of this declination, therefore, what is the path of the moon's orbit around the earth during its 29 day period?

b. 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).

b. If breakwater jetties were built that extend out more than one-half mile on each side of the inlet (as has been proposed for Oregon Inlet in NC outer banks), how would this change the movement of sand in the longshore drift above and below the inlet?

b. To counter this migration of the inlet many propose erecting breakwater jetties anchored to the beach front on both sides of the inlet and extending out to sea for 1/2 to 1 mile. What usually happens in this situation is that the sand accumulates first against the northern jetty, forming a wedge-shaped beach, then sand will again be moved to the end of the jetty and be subject to the same flood tidal currents as before, but now the sand will accumulate in the inlet all along the length of the jetties. This deprives the beach south of the inlet from its supply of sand and, therefore, that beach will have an accelerated erosion.

c. Why do you need several years of tidal records to determine which of the partial tides are the most important? Explain.

c. Based on a harmonic analysis of many years of actual tidal records at any location on the coast, each of these 7 partial tides are 'weighted' for that location, so the actual tides predicted using these weighted partial tides at this location will be unique and quite accurate. You will need many years of actual tidal data to give you good estimates of the real partial tidal components

c. Would sand be deposited in the inlet between the jetties, and what piece of equipment would likely have to be provided year round in the inlet if these jetties are constructed?

c. Dredges will need to be kept permanently in the inlet, otherwise even less sand will be available to re-nourish the beach front to the south of the inlet. Usually, this is an expensive solution that makes the problem worse.

c. Finally, explain how mixed tides are created by the moon (according to the equilibrium theory) when it is at its maximum northern or southern declination angle. Include the two tidal bulges of the tide in your answer and describe the HWs 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.

c. 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.

With the tide RISING in the ocean, in what direction does water flow through an inlet that connects the ocean and an estuarine basin and what is it called?

c. Water flows into the estuary as a flood tide

c. 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 hrs.

c. 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. 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.

● A mixed (or tropical) tide is created, according to Newton's equilibrium theory of tides,

c. when the moon is at its maximum declination with respect to the earth.

A standing wave (SW) set up in a broad semienclosed basin open to the ocean in the NORTH ATLANTIC has ALL BUT ONE of the following characteristics: a. Answer not given. b. It is called a Kelvin wave c. Its node is an Amphidromic point. d. The SW crest (antinode) and cotidal lines move around the basin in a clockwise direction

d. The SW crest (antinode) and cotidal lines move around the basin in a counter clockwise direction

The Characteristic Period (Tc) of a Seiche set up by the wind in a narrow enclosed basin is the:

d. period that the Seiche will always have when it is created in that basin

Wave reflection involves the

d. the bending of wave rays around the corners of solid objects, such as harbor entrances.

Differentiate between ebb, flood and slack tidal currents?

high water slack tidal current - beginning at high water in the ocean and the bay, because the water levels in the ocean and bay are the same. Low water slack tidal current - when the water levels in the ocean and the bay are again equal. 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, which reaches its max velocity after 3 hrs and then diminishes as the tide in the ocean nears its lowest point. Flood tidal current - as the ocean tide begins to rise, a pressure head is formed in the ocean that causes the water to flow into the inlet as a flood tidal current, which reaches its max velocity after 3 hrs and diminishes as the tide in the ocean nears its highest point.

What about a neap tide?

minimum range tide (when the moon and sun are 90 deg out of phase and acting independently)

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

An estuary is a semi-enclosed basin of water in which fresh water mixes with, and significantly dilutes, coastal water.

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

Any structure in the dynamic zone that interrupts this natural flow will create problems downstream. As the longshore drift is interrupted, sand accumulates on the upstream side of the jetties, but erodes on the downstream side. 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.

There are two different tides with two highs and two lows per day -- They are: Equatorial Tides - where the two high and low tides have equal heights. Why are these tides produced when the moon is directly over the equator?

As the earth rotates around its axis, someone standing on the equator would detect two high water levels (HW) and 2 low water levels (LW) with the same height and with a tidal period of 12 hrs. 25 minutes.

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

As you watch the moon rotate around the earth in its 29 day orbit, you see that the plane of its orbit is inclined with respect to the earths equatorial plane at an angle of 28.5 deg (declination angle). When the moon is inclined with respect to the equator at its max declination in either the N or S hemisphere, one bulge is primarily in the Southern hemisphere. This means that if you were standing on the earth at 28.5 deg N, 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.

Explain how you would set up an experiment to determine Min. Duration for a fixed wind speed.

If our goal is to measure minimum duration required for full development, we must place our wave gauge at a distance at least as great as the theoretical minimum fetch required for full development. Assume first that you place a single wave gauge at a fetch that is greater than or equal to the minimum required fetch. Assume, initially there is no wind and no resulting waves and that the experiment begins when the wind begins to blow offshore and reaches a constant speed. You also would plot spectral growth, but NOW as a function of time, not distance.

Contrast and compare jetties, groins, breakwaters and seawalls?

Jetties - artificial barriers attached ("anchored") to, and extending out from land into the longshore drift and include: breakwaters - made of rock rick-rack 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, groins - low-lying structures that stick out into the ocean and interrupt, but do not prevent the movement of all sediment tethered float breakers - dissipates wave energy without interrupting the flow of sand. sea walls - are rigid and solid structures generally built parallel with the shoreline, and are used as a last act of desperation when everything else had failed.

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

The Gravity force vectors point directly toward the center of the moon with magnitudes that are inversely proportional to the square distance from those points to the center of the moon and will tend to pull the water toward the moon. Therefore, at all points on the earth closest to the moon will have the largest G, and those farthest from the moon will have the smallest G. The centrifugal force vectors are all equal in length and are pointing in the same direction away from the moon. By vector addition, we end up with short vector tractive forces on the surface of the earth that point both toward z on the moon side of the earth-moon axis and toward N on the opposite side of the earth from z. These forces are in equilibrium and together result in TPF. TPF is inversely proportional to the cube distance between the attracting masses, the distance between masses becomes more important than the size of the masses. The closeness of the moon the the earth means that the moon's TPF is twice that of the sun. THE RESULTING TRACTIVE FORCES CAUSE THE WATER ON OUR FRICTIONLESS SPHERICAL EARTH TO MOVE TOWARD BOTH POINTS N AND Z, SO WE GET 2 "BULGES" ON OPPOSITE SIDES OF THE EARTH. The bulge on the side of the earth nearest the moon (zenith) is primarily the result of the moon's gravitational attraction. The bulge on the opposite side of the earth (N) is primarily the result of the centrifugal force of the earth-moon system.

Contrast and compare sea and swell.

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).

Dynamic Theory How do the assumptions for this 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 differences in vertical and horizontal water movement under nodal lines and antinodal lines in a SW in this basin?

The node (or nodal line for a narrow-width basin) is where all the particle motion is horizontal (no vertical movement of surface); The antinode (or antinodal line for narrow-width basin) is where the surface of the SW and all the particle motion under the surface moves vertically. Between these two extremes, the particle motion is a combination of both movements.

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

The tide producing force may cause very small-amplitude forced SWs with semi-diurnal periods. Most of these are insignificant (with a range usually measured only in centimeters). Free - A strong wind blowing for a long period of time in a constant direction along the long axis of a narrow enclosed basin (such as a continental lake) will push the water to one end. this wind set up may create a small amplitude free SW.

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. When H/L > 1/7, waves become too steep and unstable, so they break; therefore, H/L>1/7 is called the breaking criteria. As wind speed increases, full development results in larger and larger values of H and L and requires longer and longer minimum fetches and durations. For full development, fetch and duration must be greater than or equal to the minimum required for full development. Full development at a given wind speed will not remain full developed if wind speed increases.

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

Waves that approach a shoreline at an angle and then break the surf zone will produce a longshore current. It is created when these waves break, and the water continues to rush up the beach (at the same angle as the wave's approach) as swash, but when it stops, the water runs back down the beach along the greatest slope as backwash, being pulled 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 and which will produce a longshore current.

Combined Effects of the Moon and Sun (with fortnightly period of 14 days). How does the sun's tide-producing force combine with the moon's tide-producing force to create this twice monthly tide?

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. 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.

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?

When wave trains approach an irregular coastline, 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. that portion on either side of the headland will continue for some time at its deeper water celerity without refracting. Often, there are bays between two headlands. Note that if we advance the waves toward shore, the wave rays will bend "toward" shallow water (toward the headlands) and away from the bay. 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.

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: 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?)Use example given in lessons about why lunar tide is 24 hrs 50 min (and divide it by half)

While the earth was making one complete CCW revolution (24 hrs in solar day), the moon also was moving CCW around the earth, so to come again under the moving maximum bulge, the earth has to rotate an additional 50 minutes - the lunar day (and half of 24 hr 50 min is 12 25).

wind duration

how long the wind blows.

What two forces are in equilibrium in this theory?

1. Gravitational attraction - the moon and the sun have on the water of the earth. G, the moon's gravitational force, will attract every part of the earth's surface depending on the distance of the moon from that part with G vectors on the earth pointing toward the center of the moon. The magnitude of the vector forces are inversely proportional to the square of the distance from those points to the center of the moon, and will tend to pull the water "toward the moon". 2. Centrifugal force - set up by the earth-moon system and the earth-sun system each rotating around a common center of mass. Created when a mass moves around a center of rotation. It is equal at all points on the center of the earth.

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?

ocean surface waves propagate horizontally along the air-sea boundary. They are orbital because, as the wave form passes a certain point, the water particles under the wave move with orbital paths. They are are progressive because the wave more moves (progresses) horizontally from one location to another.

What is the "American Mediterranean"?

Marginal sea. It includes the four basins of the Caribbean sea and the Gulf of Mexico. The Caribbean Sea is set off from the Atlantic ocean by an island arc called the Antillean Chain. 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 north of around Jacksonville, FL. Sometimes, the flow through the Yucatan Straits forms a CW looping current in the eastern end of the Gulf of Mexico. Occasionally, this Loop Current will intensify and turn with such a sharp curve as the current approaches the Florida Straits, that a clockwise rotating rig and warm core eddy is broken off.

Explain how you would set up an experiment to determine Min. Fetch. for a fixed wind speed

If our goal is to measure the minimum fetch required for full development, we must allow the wind to blow at least as long as the theoretical minimum duration required for full development. To see how this is done for wave fetch, consider the following set-up. The figure on the left is a plan view of the coast and the ocean. The figure on the right is a plot of the progressive growth of the wave spectra for a n increasing fetch. As you can see, six wave gauges (1-6) are located at increasing fetches away from a straight coastline. Then, for a steady wind that blows directly offshore for a long period of time, we measure wind-wave growth at each gauge and compare their wave-energy spectra, where the numbers correspond to the wave gauge from which the measurements are being made. The spectra will not continue to grow for any fetches longer than the minimum required for full development. And it also will NOT decrease for fetches longer than the minimum required for full development.

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

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 0 this alone could cause this current. During the rainy season, runoff from major rivers in that region, swollen by heavy precipitation west of the coastal rang of mountains, can create a freshwater wedge that could also alone cause this current. combined, these processes create a stronger low density slope that extends away from the coastline toward the ocean

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

when the sand moved up-slope in the swash establishes an equilibrium with the sand moved down-slope in the backwash (ie the backwash returns as much sand as that moved toward shore by swash)

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

1. Coastal plain estuaries - formed at the end of the last ice age when rising seawater flooded existing river valleys. Ex: Chesapeake bay 2. Fjords - 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. 3. Bar -built or barrier island estuaries - 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. The Outer banks of NC 4. Tectonic estuaries - caused by earthquakes, San Francisco bay

Explain the differences between waves classed as deep or shallow water waves, including how the shape of the water particle orbital paths differ.

1. Deep - (d>= 1/2 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 0 at d=1/2L. Wave celerity is directly proportional to either wavelength or wave period. Waves with longer wavelengths will travel faster than waves with shorter L or T. 2. Shallow - (d<=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.

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

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. Also, according to the theory, waves that run with a current will lose energy and those that cross a current will be refracted, but will otherwise be unaffected.

Define the Characteristic Period (Tc) for this type of basin?

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.

How long do these currents last?

The Davidson current IS NOT permanent. The dominant wind usually from the northeast, creating upwelling, and only during the rainy season do you get significant runoff

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

These open-ocean, deep-water breakers are NOT caused by decreasing water depth, but because the waves have reached full development and are already as steep as they can be, so the excess energy must be dissipated.

high-high water, low-low water, high-low water, low-high water for mixed or tropical tides

They are found when the moon is around 28 deg above or below the equator. Mixed tides also have 2 HWs and 2 LWs per day, but they are not the same height. This tide has four tidal ranges and each HW and LW have different names.

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.

How do dispersing waves sort themselves out, so that "order" is created from "chaos"?

Longer waves run faster than shorter waves ( because celerity of a deep water wave is directly proportional to length or period). Longer waves outrun the shorter waves and order is created out of chaos. This sorting of waves by wavelength is called wave dispersion.

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

Near-shore currents may distribute some of this sediment to the edge of the shelf break and onto the slope, but most sediments are distributed in the surf zone by waves as longshore drift. Much more important for understanding marine depositional coasts, is that wave action also will pick up sediment that will be moved by the longshore currents. The movement of sand by these is called longshore drift.

Who formulated the Equilibrium theory and what are the theory's simplifying assumptions

Newton. A perfectly spherical earth covered with water, but with no basins nor continents, nor bottom friction)

How are they formed by constructive interference of two or more wave trains.

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.

What are Rogue waves?

Rogue waves are unpredictable and very damaging. With maximum heights of around 30 meters, or 100 ft), they get their name form the sudden way in which they seem to appear. They are thought to be caused by wave current interaction and constructive interference.

Explain why wavelength (L) also decreases during shoaling.

Shoaling waves crowd up and L decreases.

Which of these two waves occurs most frequently and which does the most overall damage on an annual basis?

Storm surges occur more frequently and are more damaging.

tidal period

The time between two adjacent HWs or LWs

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

The basin that forms the Red Sea is being created by the separation of the Arabian Peninsula from the African mainland because of plate movement (that also created the great African Rift Valley). It is separated from the Gulf of Aden and the Indian Ocean by a narrow strait and a shallow sill of only 125 m in depth, but has a depth of over 2300 m at its deepest point.

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.

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

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 refraction (Xr). Sometimes reflection can crated dangerous conditions when the reflected waves interferes constructively with an incoming wave, creating a wedge with nasty characteristics. Very large waves, may reflect a good portion of their energy off the continental shelf and slope, even though the wave also will break as surf in shallow water. Diffraction - Involves bending of wave rays, but now that bending is around corners or edges of solid objects such as breakwaters, other harbor structures, or islands, and is not the result of changes in wave celerity as a result of changes in depth. 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. 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 they bend (refract) around a point of land, because the portion of a crest-line that reaches shallow water first is slowed (remember c prop d), but the portion still in deeper water continues at its regular celerity .

What is the loop current in the Gulf of Mexico, and how is it associated with 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 north of around Jacksonville, FL. Sometimes, the flow through the Yucatan Straits forms a CW looping current in the eastern end of the Gulf of Mexico. Occasionally, this Loop Current will intensify and turn with such a sharp curve as the current approaches the Florida Straits, that a clockwise rotating rig and warm core eddy is broken off. This Loop Current was the source of very warm water continually supplied to the easter portion of the Gulf that allowed hurricanes crossing west over Florida to explode from a Category 2 to a Category 5 storm in 12-16 hrs.

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

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. Destructive interference - where crests and troughs arrive out of phase, canceling each other out Constructive interference - where crests and troughs are in phase and reinforce each other.

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

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.

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.

Distinguish between offshore, nearshore, and foreshore

foreshore = the part of the shore between the high-tide and low-tide shorelines that is submerged and uncovered repeatedly by the tides) Nearshore - region between the low tide shore line and the low-tide breaker line offshore - everything seaward of the low-tide breaker line

Antillean chain

includes islands of Cuba, Hispaniola, Puerto Rico, Jamaica, and the Greater and Lesser Antilles).

How are waves classified by period and what are their principle generating and restoring forces? (5)

The principle generating forces and principle restoring forces change as the period of waves increase. Principal generating forces: moon and sun, earthquakes, volcanoes, landslides, storms, wind. Restoring forces: Coriolis/friction, gravity, surface tension 1. smallest waves - capillary waves (period <0.1 seconds). The surface is restored by surface tension. They are generated as the wind begins to blow. 2. Gravity waves - (T = 1 - 30 seconds). Generated by wind storms and restored by gravity. 3. Infra-gravity waves - generated by strong storms and restored mostly by gravity. Period around 1 min. 4. Long waves - (period > 5 min). Generated by intense storms and by earthquakes, and restored by gravity and the Coriolis force. 5. tides - (periods 12 - 24 hours). Generated by the sun and moon and restored by bottom friction and Coriolis force.

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 (they are fully developed), the excess energy supplied by the wind MUST BE DISSIPATED. This is accomplished through the turbulent breaking of the waves, which dissipates the excess energy and creates "white caps."

In how many ways does Storm Surge differ from a Tsunami?

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 that moves with the storm. This hill and the water in the right front quarter of the store being pushed by the winds in the same direction the store is moving create a high water surge that can exceed 10m. Storm surge is more like a very fast rising tide, that quickly reaches its peak and then stays there until the storm moves well onshore.