Background:
The natural beauty of Connecticut is partly due to the variation in its relief or patterns of hills and valleys, traprock ridges and plains. What you see as you ride along a highway is not what you would have seen if you were traveling 100 million years ago, one million years ago, or even 50,000 years ago. Connecticut's surface is constantly changing. During the past 10,000 years Connecticut's surface has been relatively quiet: There are no new mountains forming, nor are parts of Connecticut faulting and sinking from being stretched, as happened in the past. Glaciers are not covering our land.
The Connecticut of the distant past can still be imagined, though, by observing what still remains. Today you can see remnants of the immense mountains that once grew here. You can also observe features from the glaciers that flowed over Connecticut as recently as 12,000 years ago. The changes occurring in Connecticut today are due to less spectacular forces than that of mountain building and glacial activity. They are chiefly due to slow, steady erosion made by water moving along Connecticut's surface.
Erosion produced by rivers today is related to Connecticut's geologic past. Water must always flow downward and down is a direction that is determined by the shape of the land. If you observe the shape of Connecticut's streams and how small streams connect to larger ones, you will notice how the shape of the stream is dependent on the shape of the land.
All of the land that is drained by a particular river and its tributaries ( A tributary is a small stream that flows into a larger one.) is called that river's drainage basin, although sometimes the older term "watershed" is used. The Connecticut River drainage basin, for example, includes not only the area immediately surrounding the Connecticut River, but also all of the land drained by all of its tributaries (and the tributaries of the tributaries!). The shape of entire drainage basins is also the result of the topography and the kind of rock at the surface. Soft rock, for example, wears down faster than harder, more resistant rocks. High areas generally are made of hard bedrock, while soft bedrock produces low areas that become major stream valleys.
Because water always flows downward, you should be able to figure out where the high areas are in Connecticut even with a simple road map. Major rivers, for example, should be the lowest areas on the map since all the tributaries drain into them. If you see streams flowing in one direction in one place and in the opposite direction in a location nearby, you can visualize that high land must exist between the two sets of tributaries since the water always moves from a higher area to a lower area. Such high areas are divides that separate one river's drainage basin from another.
The largest and most obvious divide in the United States is, of course, the Great Continental Divide of the Rocky Mountains. All of the streams west of the Rocky Mountain's peaks travel westward, which is downhill; likewise all of the streams east of the peaks flow down in an easterly direction. But even a state like Connecticut, with mountains so eroded that they are little more than hills, has divides that can be easily spotted using a map.
Objectives:
In this investigation you will use an unlabeled stream map of Connecticut to:
Figure 1. Hypothetical stream system, showing main stream and branches.
Two main stems begin in small lakes (the source). The stream ends in the ocean
(the base level for this stream system).
Procedure:
1. On
your stream map locate the Connecticut River.
Trace the path of the Connecticut
River in a bright color of your choice. Then find all of the streams that flow
into the Connecticut River and trace those also in the same color. Continue by
tracing the second order tributaries
(those that flow into the first
order tributaries you just colored), then the third
order tributaries and so on, until all of the water that eventually flows
into the Connecticut River is traced in the same color as that of the
Connecticut River.
2. Follow
the same procedure for the Housatonic River and the Thames River, using a
different color for each of these river systems.
3. In
pencil, lightly separate the three river systems from each other. The line you
sketch must not cross any streams because each stream is completely in only one
drainage basin. The lines you draw are the divides between the watersheds.
4. Notice
that a number of smaller streams are not part of the three major rivers. These
rivers geologists group separately as the coastal
rivers. With a pencil, separate the coastal rivers from the Housatonic,
Connecticut and Thames watersheds.
5. Neatly
label each river system with its name in large letters and provide a color key
at the bottom of the map with each system’s name.
6. The source
or head of a stream is the place the stream begins. It has the highest
elevation of any place along the stream and is often a spring or an outlet from
a lake. Find the sources for the Housatonic River, the Connecticut River, the
Thames River, and for the river that is closest to your school and/or home.
Since some of the preceding rivers do not originate in Connecticut, you will
need to use a map that shows the New England states. If a river does have its
source in Connecticut, find the source on your Connecticut map, draw a small
circle over the source and print a S
in the circle to symbolize source.
7. Eventually
every river reaches a location where the water can no longer go downward. That
location is called the river’s base
level and it also marks the end or mouth
of the river. If a river flows into the ocean, its base level is sea level
or 0 feet. If a river flows into a lake or into a larger river, its base level
is whatever the elevation of the lake or larger river is. Find the base level of
each of the streams you worked with in the previous question. Then mark the base
level for each on your map with a circle. Print a BL in the circle to symbolize
base level.
Analysis and Conclusion:
1.
Describe the pattern made by the major rivers on the Connecticut map.
2.
Describe the pattern made by the coastal rivers on the Connecticut map.
3.
Are the patterns described in answers to questions one and two different? If so, explain how.
4.
In what general direction do Connecticut’s streams flow?
5.
Write a hypothesis explaining why you think Connecticut’s streams flow
in this direction. (Consider Connecticut’s geologic history.)
6.
Which river(s) does (do) not originate in Connecticut? Where is this
these) river’s source(s)?
7.
Do any of the rivers flow northward? Is it possible for a river to flow
northward? Explain.
8. What could be the sources for various small streams in Connecticut?