SEICHE WAVE MODEL
FACTILIATION GUIDE
This project was brought to you by the LakeViz project and
funded by the National Science Foundation
Table of Contents
Overview and Background . . . . . . . . . . . . . . . . . . . . . . 2
Learning Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Preparation and Procedure . . . . . . . . . . . . . . . . . . . . . 8
Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
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OVERVIEW
This facilitation guide is intended
for educators who plan to give
demonstrations to public visitors
and school-aged children who visit
a museum or science center.
Overview to
Facilitation Guide
and Background
This guide includes instructions on how to introduce the activity, set
up the demonstration, and facilitate visitor questions. In addition, this
guide provides some background content about lake science, possible
extensions to activities, and links to additional resources.
BACKGROUND INFORMATION
If you’ve ever gone swimming in different lakes, you may have noticed
some are warm and others are cold. Why is this? A lake’s temperature
is affected by its size and shape, the change of seasons, and the climate
where the lake is found.
We’ll explore what happens under a lake’s surface, including how
changes in temperature and density lead to an important process called
lake mixing. Density measures how heavy something is compared to how
big it is. Denser water has more water molecules squeezed into a given
amount of space. Denser water always sinks while less dense water rises.
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Lake Stratification
Ice Formation
As the seasons change from
winter to spring and then
summer, lake water separates
into different temperature layers
from top to bottom. This is known
as stratification. In summer, the
Sun heats the lake’s top layers,
while the lake’s bottom layers
stay cold (warmest layer on top).
When the winter air temperature gets very
cold ice can form at the lake’s surface, while
warmer water stays below the ice. Why does
that happen? Why doesn’t the lake freeze all
the way through, or from the bottom up?
Stratification happens because
the warmer water at the surface
has a lower density than the cool,
deeper water and literally floats
on top of it. The lake’s top water
layer, or epilimnion, is always
less dense than the bottom
water layer, or hypolimnion. The
water layer in between them,
the thermocline, is where water
temperature changes a lot even
though lake depth changes very
little.
Water is an unusual substance when its
temperature falls below 4 degrees Celsius (or
39.2 degrees Fahrenheit). As water cools below
4 ºC it starts to become less dense (lighter).
And so as the surface of the lakes continues to
lose heat and cool, the cold surface water now
floats on top of the warmer 4 ºC water below
it. When that surface water freezes (which
occurs at 0 ºC), it stays floating on top of the
water – it is less dense than liquid water. That’s
why ice floats in a glass of water and on a lake’s
surface. This layer of ice acts as insulation on
top of the 4 ºC water below it.
Lake Mixing
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Lake mixing is a progressive
process. As we move from
summer to fall, and then winter,
the water at the very top cools,
becomes denser and then mixes
with the layer immediately
underneath it. This will often
continue until this mixing has
reached the very bottom and
“lake overturn” has occurred.
Now water temperature and
density are the same throughout
the lake.
Photo courtesy of Lake George Association
How Mixing and Stratification Affect Lake Life
When a lake is stratified, algae in the surface layer can consume all the life giving nutrients,
and then sink to the bottom of the lake. This leaves the surface layer starved of nutrients, and
creates the conditions for harmful phytoplankton that can produce their own nutrients. When
lake turnover occurs, it brings nutrients back to the surface, which increases growth of algae, a
food source for many aquatic animals. Turnover also moves oxygen from the surface to deeper
waters, supporting aquatic life throughout the lake. If lake mixing didn’t bring oxygen to the
organisms living in the bottom of the lake and nutrients to the organisms in the top of the lake,
they might not be able to survive!
Stratification affects where fish and other organisms live within the lake. In summer most
living things, including fish, hang out in top layers of the lake where it’s warmer and there is
more sunlight and available food. In winter, fish tend to stay near the lake bottom where the
temperature is warmer. Some even burrow into the lake’s muddy bottom.
Water’s interesting physical properties make it possible for animals to survive the winter in a
frozen lake. Because ice is less dense than liquid water, the ice stays at the top of the lake. The
ice insulates the water below from the cold winter air—this keeps the whole lake from freezing
like a Popsicle, and the fish and other organisms from freezing in it!
Density/Stratification Model
This model can be used to explain “lake physics” or “lake hydraulics”, and can include topics like
lake stratification, lake mixing, and seiche (internal) waves.
This graph is helpful in explaining why the cold water sinks to the bottom of the model while
the warm water goes to the top. It is also helpful in explaining why lakes like Lake Tahoe don’t
freeze during the winter.
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Learning Goals
This activity models density stratification, lake mixing, and seiche waves by
showing how water moves in model “deep lake cross-section”, using containers
with different shaped bottoms and plastic and rubber partitions to model waves
in lakes. Visitors can also compare what happens in the various models, to see
how lake shape can impact how water moves and flows.
The key ideas that visitors should take away is that lakes vary in size, depth,
shape and that physics control water movement within the lake and affect water
quality by the distribution of dissolved substances, nutrients, microorganisms
and plankton. Large-scale water motions include changing water levels, seiche
waves, currents, waves and turbulence. Wind, solar radiation, stratification, and
earth’s rotation are important forces causing water movements of lakes.
Photo courtesy of ECHO Lake Aquarium and Science Center
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Detailed List:
• Model Tanks (plastic model with
divider)
- Flat Bottom (1)
- Sloped Bottom (1)
- Curved Bottom (1)
• Tank Partitions
- Acrylic - for Flat Bottom Tank
9.5” x 3.25” (3)
- Rubber (3)
• Fluorescent Light - 18” (1)
• Wooden Supports for Fluorescent
Light (2)
• Thermometers (3)
• Suction cups for securing
Thermometers (6)
• Rubber stoppers (3 in sizes: 00, 2,
and 2)
• Drain hose assemblage (1)
• Stir sticks (3)
• Pitchers or thermos with at least 2
liter capacity (3)
• Various colors of Liquid Watercolor
Paints or Food Coloring (1 set,
preferred colors blue and yellow)
• Clear Plastic Tubing with at least
30 cm length (1) or Blow dryer
• Funnel (1)
• Coffee Urn with at least 30 cup
capacity (1)
• Water Cooler with at least 2 gallon
capacity (1)
• Cooler (1)
• Ice
• Straws to simulate wind
• Waste Bins - if a drain is not easily
accessible
Materials
Simple List:
• Plastic model with plastic divider
• Hot water
• Ice cold water
• Yellow food coloring
• Blue food coloring
• Blow dryer or straws
• Waste water bucket if planning
to do the demonstration multiple times
For Extensions:
Optional Materials:
- Dry Erase Marker (1)
- Container of Salt (1)
Photo courtesy of Lindsay Chan
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Photo courtesy of 3dh2o.org
The plexiglass container,
divided into two sections
by a partition (rubber or
plastic), is filled with colored
water (red and blue or yellow
and green). After the water
has been added to each
compartment, the partition
between the containers is
removed to allow mixing.
This experiment can be done
in many ways: where both
sections have water at the
same temperature; where
the sections have different
initial temperatures; etc.
A tube can be used to add water of a different temperature to the “lake” to mimic
“stream insertion” (yellow and green water, stream in red). Visitors can see how
different temperatures and types of water mix. Visitors can also add ice and observe the
depth the ice sinks to, and how the water from the melting ice mixes. Furthermore, dye
representing point source pollution or invasive species can be introduced, observed, and
compared between models. The flow of the brightly colored fluids, due to differences
in temperature or salt content, helps visitors visualize important concepts including
lake currents, wind effects on mixing, and thermoclines. Water can drain through a
tube at the bottom of the tank to start over.
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Photo courtesy of UC Davis Tahoe Environmental Research Center
PREPARATION
Before the demonstration:
1. Obtain hot water. Dye the hot water
yellow. Make sure it stays hot until
you do the demonstration or else it
will not work.
2. Obtain ice cold water. Dye the ice
cold water dark blue. Remove the
ice from the water just before the
demonstration.
3. Put empty plastic model tank in
the location you wish to do the
demonstration and make sure the
center divider is in place.
PROCEDURE
1
Introduce the topic of lake
physics which describes how
water moves within a large, deep
lake. The main topics within lake
physics we’re going to look at are
lake stratification, lake mixing,
and seiche (or internal) waves.
With younger audiences, you
might have to explain what
stratification is.
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Preparation and
Procedure
3
4
Introduce the demonstration. Tell the
students you’re going to add warm
yellow water to one side of the model
and cold blue water to one side of the
model and remove the divider. We’re
going to observe how the two different
temperatures of water interact. Ask the
students to make a hypothesis of what
they think is going to happen when you
remove the divider. Have a few students
share their ideas with the group.
Make sure you press down firmly
on the center divider as you
add the cold water to one side
of the model and warm water
to the other side of the model.
(Note: It works best to add equal
amounts of water on each side
of the divider at the same time.)
Remind the students to observe
what happens when you remove
the divider. Remove the divider.
Give the model a minute to settle
after you remove the divider and
ask the students to share their
observations. What happened?
Why did this happen? There
is one key factor that causes
the two different temperature
waters to separate, does anyone
have an idea what that factor is?
Explain how the warm water has
a much lower density than the
cold water. You can reference
a laminated copy of the graph
given above to show students
that cold water really is denser
than warm water.
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5
Explain how stratification like
this actually does occur in large,
deep lakes like Lake Tahoe. Ask
the students how they think the
top layer of the lake might warm.
Explain how the sun heats the
top layer of the lake and that the
intensity of the sun is different
in each season (most intense in
the summer, least intense in the
winter) which leads to different
stratification levels in the lake
throughout the year. (Test tubes
filled with blue water and olive oildarker yellow/canola oil-lighter
yellow are useful to illustrate
the cold and warm layers in the
different seasons as shown to the
right.)
In the spring the water on the
surface of the lake starts to warm,
during the summer the warm
layer gets deeper due to the
more intense heat from the sun,
in the fall the warm layer begins
to lose heat to the air above the
lake as the air begins to cool for
the season, and in the winter the
air above the lake is cool enough
and the intensity of the sun is low
enough that the lake becomes a
uniform temperature at about 39
degrees F (refer to the first graph
for the reasoning behind this).
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6
Lake Mixing: When the lake
is at a uniform temperature
and density from top to
bottom (during the winter), it
can achieve full lake mixing,
bringing oxygenated water
from the surface to the bottom
of the lake and cycling nutrient
rich water from the bottom to
the surface of the lake. This
natural cycle is essential for
the health of the lake and the
organisms living in it.
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Seiche Waves: Now you can talk about seiche waves. Seiche waves are
internal waves that occur beneath the surface of the lake due to forces like
wind and tectonic activity.
Photo courtesy of UC Davis Tahoe
Environmental Research Center
These waves usually do not
show on the surface of the
lake. While the water in the
model is still stratified you
can demonstrate the effect
of wind on seiche waves in a
lake. Using either a straw or
a blow dryer you can apply a
“wind force” laterally across
the surface of the lake. Before
you do the demonstration,
ask the students to make a
hypothesis of what they think
is going to happen when you
apply the wind to the model.
As you do the demonstration, the students should see the cold blue water from the
bottom of the model begin to move upward toward the surface as the yellow warm
water is pushed by the wind away from the source in the direction the wind is going.
During this demo you don’t want to cause too much turbulence on the surface of the
water. You can explain that while seiche waves cause movement to happen within a
lake, they don’t cause the lake to mix fully from top to bottom – for that to happen you
need the lake to have a uniform density.
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Photo courtesy of UC Davis Tahoe
Environmental Research Center
End with a recap
of Lake Physics and
the topics that you
covered,
including
density stratification,
seasonal changes, lake
mixing, and seiche
waves.
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Credits
This project was supported by the National Science Foundation under
grant number DRL1114663. Any opinions, findings, conclusions, or
recommendations expressed in this program are those of the author
and do not reflect the views of NSF.
This project was created as part of the LakeViz project funded by
the above-named grant. Content provided by ECHO Lake Aquarium
and Science Center. Find out more at www.lakeviz.org for an archive
of learning resources related to 3D visualizations and freshwater
ecosystems.
The collaborating institutions include the ECHO Lake Aquarium and
Science Center, the University of California at Davis Tahoe Environmental
Research Center, and the Lawrence Hall of Science at the University of
California, Berkeley.
www.nsf.gov
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