Lab 6: Tides and Coastal processes Goals: 1. Understand what causes tides. 2. Understand how deep-ocean waves change and break when they reach a coastline. 3. Understand how shoreline transport of sediment occurs and how it is affected by human activities. Tides Tides are actually waves that move through the oceans and large lakes. In the oceans, they have periods of several hours and wavelengths of 1000s of kilometers. Depending on the wave period that dominates in different parts of the world, some places have only one high and one low tide a day (diurnal tides), whereas others have two high (about equal to each other) and two low tides (also about equal to each other) known as semidiurnal. A third type is mixed tides with two highs and two lows a day with different heights, (a high high, a low high, a high low and a low low). California, as the rest of the west coast has mixed tides. The gravitational pull of the Sun and the Moon causes tides on Earth. The gravitational influence of an object is directly related to its mass and its distance from another object. So even though the Sun has much more mass than the Moon, it is over 380 times farther away from the Earth than the Moon. Therefore, our little Moon wins out and has the most influence on the tides on Earth. As the Earth spins about its axis, centrifugal force keeps water balanced on all sides of the planet. However, the Moon's gravitational forces disrupt this balance by pulling the water towards the Moon. A double "bulge" is formed—one side pulling toward the Moon and the opposite side pulling away from it, just like swinging a water balloon causes it to stretch both toward AND away from your hand. The areas where the bulging occurs experience high tides. Tides are predictable, but their periods do not coincide with the 24 hour Earth day. The Moon takes about 24 hours and 50 minutes to line up again exactly with the same point on the Earth. Therefore, the timing of the tides shifts almost an hour a day. Because the relative positions of the Sun, Earth and Moon change over the course a day, a month and a year, the absolute heights of diurnal, semidiurnal and mixed tides vary over these periods. For example, even within the same ~25 hour period, the heights of the semidiurnal tides are not exactly the same, although they are close. Even more significant changes are seen over a monthly cycle, with higher-than-normalspring tides (not named for the season but because the water "springs" higher than normal) and the lower-than-normalneap tides. Exercise 1. Let's investigate the causes of spring and neap tides. Go to this websitehttp://aspire.cosmic-ray.org/Labs/Tides/tides_simulator.html . Pick the student version because the teacher version has an annoying note in the middle of the simulation screen—the teacher version will not give you any more information than the student version to answer these questions. Click on the tide simulator. Click the box to turn on spring/neap ...

1. Lab 6: Tides and Coastal processes
Goals:
1. Understand what causes tides.
2. Understand how deep-ocean waves change and break when
they reach a coastline.
3. Understand how shoreline transport of sediment occurs and
how it is affected by human activities.
Tides
Tides are actually waves that move through the oceans and large
lakes. In the oceans, they have periods of several hours and
wavelengths of 1000s of kilometers. Depending on the wave
period that dominates in different parts of the world, some
places have only one high and one low tide a day (diurnal
tides), whereas others have two high (about equal to each other)
and two low tides (also about equal to each other) known as
semidiurnal. A third type is mixed tides with two highs and two
lows a day with different heights, (a high high, a low high, a
high low and a low low). California, as the rest of the west
coast has mixed tides.
The gravitational pull of the Sun and the Moon causes tides on
Earth. The gravitational influence of an object is directly
related to its mass and its distance from another object. So even
though the Sun has much more mass than the Moon, it is over
380 times farther away from the Earth than the Moon.
Therefore, our little Moon wins out and has the most influence
on the tides on Earth.
As the Earth spins about its axis, centrifugal force keeps water
balanced on all sides of the planet. However, the Moon's
gravitational forces disrupt this balance by pulling the water

2. towards the Moon. A double "bulge" is formed—one side
pulling toward the Moon and the opposite side pulling away
from it, just like swinging a water balloon causes it to stretch
both toward AND away from your hand. The areas where the
bulging occurs experience high tides.
Tides are predictable, but their periods do not coincide with the
24 hour Earth day. The Moon takes about 24 hours and 50
minutes to line up again exactly with the same point on the
Earth. Therefore, the timing of the tides shifts almost an hour a
day. Because the relative positions of the Sun, Earth and Moon
change over the course a day, a month and a year, the absolute
heights of diurnal, semidiurnal and mixed tides vary over these
periods. For example, even within the same ~25 hour period, the
heights of the semidiurnal tides are not exactly the same,
although they are close. Even more significant changes are seen
over a monthly cycle, with higher-than-normalspring tides (not
named for the season but because the water "springs" higher
than normal) and the lower-than-normalneap tides.
Exercise 1.
Let's investigate the causes of spring and neap tides. Go to this
websitehttp://aspire.cosmic-
ray.org/Labs/Tides/tides_simulator.html . Pick the student
version because the teacher version has an annoying note in the
middle of the simulation screen—the teacher version will not
give you any more information than the student version to
answer these questions. Click on the tide simulator. Click the
box to turn on spring/neap tides. Keep the particle number the
same because it helps you to see what the oceans look like
during different times of the month. As the simulation
progresses, put the cursor over the stop button and when you
see "neap" appear, stop the simulation and look at the position
of the earth, sun and moon. Do the same with "spring." Try it
enough times so that you are confident of the positions of the
three astronomical bodies that cause the spring and neap tides.

3. Question 1. Draw two different pictures of the sun-earth-moon
system that produce a spring tide. Label each of the
astronomical bodies and show the envelop of the ocean water
(the blue dots in the simulation). Move the circles around until
they are in the places that you want them. The big circles are
the sun, the medium size circles are Earth, and the small circles
are the Moon. The blue oval is the water.
Question 2. Draw one picture of the sun-earth-moon system that
produces a neap tide. Label each of the astronomical bodies.
Move the circles around until they are in the places that you
want them. The big circle is the sun, the medium size circle is
Earth, and the small circle is the Moon.
Question 3. Let the simulation run and watch the month on the
right and the neap and spring labels.
How many neap tides are there in a month? ______________
How many spring tides are there in a month? _____________

4. Question 4. Go to the National Oceanic and Atmospheric
Administration (NOAA) tide predictions website for Santa
Monica, California:
http://tidesandcurrents.noaa.gov/noaatidepredictions/NOAATide
sFacade.jsp?Stationid=9410840
Change the time range to monthly to see the tides from June 1-
30, 2013. Fill in the first three columns of the chart using the
information from this website.
How to find spring tides: Look for the dates that have not only
high heights (add the two highs together), but also the a large
difference between high and low tides. Make the best decision
that you can using both factors. The two spring tides cannot be
within the same week.
How to find neap tides: Look for smallest differences between
the two high tides and smallest differences between high and
low tides. Make the best decision that you can using both
factors. The two neap tides cannot be within the same week.
Go to http://www.farmersalmanac.com/calendar/moon-phases/
and change the date to June, 2013. Mouse-over the dates that
you chose to get the phases of the moon and add to the last
column.
Date
combined spring tide heights of the day AND max difference
between high and low tides (both in feet)
combined neap tide heights of the day AND max difference
between high and low tides (both in feet)
phase of the moon

5. You have now discovered the relationship between phases of the
moon and spring and neap tides!
Your biggest spring tide is unusually big! A special
astronomical event occurred on this date.
http://www.scientificamerican.com/article.cfm?id=supermoon-
to-rise. Re-read paragraph 2 under Tides on p. 1. Explain why
this event would cause the spring tide to be larger than normal.
Interaction of the Ocean with Coastlines
This section of the lab looks at the interaction of the ocean with

6. coastlines, particularly the development of longshore transport
and what happens when human development along coastlines
interacts with longshore transport. Although the video that you
will be watching is quite old, it is still one of the best for
illustrating coastal processes in southern California. Watch the
video and answer the following questions. The Beach- A River
of Sandhttp://www.youtube.com/watch?v=FqT1g2riQ30)
1. Where does sand that forms beaches in southern California
come from and how does it get to the coast?
2. Along many California beaches, there is a big difference in
appearance between winter and summer.
A. During which season is wave energy smallest?
1) winter 2) summer
B. Smaller waves move sand:
1) toward the beach (onshore) 2) away from the beach
(offshore)
C. Is this picture typical of a summer or winter beach? 1)
winter 2) summer
3. Most waves approach and strike the coast at an angle. Chose
the picture that correctly shows the correct relationship between
the direction of approach of the waves and the movement of
sand in the surf zone and along the beachface.
(
waves
waves
waves
) a. b. c.

7. 4. Man-made structures rock groins and jetties interfere with the
flow of sand generated by the longshore current, causing
deposition of sand on one side and erosion of sand on the other.
Based on this knowledge, which picture correctly shows the
direction of longshore current?
a. b.
4. Breakwaters are built to provide quiet water for marinas
where small boats can be safely harbored. What happens when
the longshore transport of sand encounters the breakwater at the
Santa Barbara marina? If this situation was just left alone, what
would happen to the marina? What does the City of Santa
Barbara do to prevent this?
5. At several places along the coast of southern California,
beaches come to an end and only rocky shores continue for a
portion of the coast. Why do the beaches end? What happens to
the sand?
6. How does the building of dams affect the supply of sand
along the beach?