Unit 5_Lab_StreamErosion
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Geography
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Dec 6, 2023
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Lab 5: Stream Erosion
Streams are extremely powerful erosional agents that sweep vast quantities of sediment
and other materials from the land surface to oceans every year. The result of running
water throughout history has been the development of systems of canyons and valleys,
which can be observed across the globe.
Today we are going to look at characteristics of streams, and how various environmental
factors change them. In addition, we are going to look at the interactions and
development of landforms due to stream activity. Models are used extensively in science
to accurately depict processes that cannot be observed directly. Stream tables are used to
display the ways that streams change over time.
Watersheds
The term stream
morphology (or fluvial geomorphology) is the study of how the watershed and stream
channel change, both in terms of time and space. A watershed is an area of land that
drains streams or rainfall into a common outlet. The map displayed in this lab of North
America shows the watershed boundaries that exist across our region. Between various
watersheds are often ridges or hills that separate them. These features are referred to as
the drainage divide. The watershed itself may consist of surface water located in streams,
reservoirs or lakes, wetlands, and all groundwater that underlies the area.
Watersheds serve as precipitation collectors. Once water enters a watershed, a few things
may occur. Some of the water infiltrates into the soil, where it may continue to move
deeper into groundwater aquifers or may remain near the surface. The water that remains
near the surface will gradually move downhill, through the soil and then enter streams
through seepage into stream banks.
The Life Cycle of a Stream
Streams experience a life cycle that consists of three main stages. The first stage is the
“youth” stage, which consists of a stream that is usually small and flows down steep
slopes with lots of energy. Some features found in the youthful stage of a stream include
the formation of V-Shaped Valleys (narrow banks steep sides and very narrow
streambeds), Interlocking Spurs (high ground that juts out on both sides of the valley),
and Potholes (hollows that form in the streambed from the movement of pebbles and
other bedload).
The second stage of
the stream life cycle is the mature stage. In this stage, the slope becomes gentler, the
stream widens and meanders form. Meanders are bends or curves formed in the river. On
the outside of a meander, water velocity is higher and erosion takes place. On the inside
of a meander, conversely, deposition occurs.
The last stage in the life cycle is the Old Age stage. The stream, at this time, will be at it’s
widest and the land will be at its flattest. The main agent at work during this time is
deposition. During this stage, Oxbow Lakes (lakes that form from meanders that are cut
off from the main streamflow) form and Floodplains (areas around streams where
overflow from the stream floods the land) become prevalent. Another feature that is likely
to form at this time is a delta, which is a triangular area of land that has been forms by a
stream that is depositing its load as it enters a larger body of water (a sea, etc.) A delta can
only form when a stream has been carrying a large load of alluvium (sediment) that is
being dropped off faster than currents or tides can take it away in the larger body of
water.
Part 1: Basic Stream Observations
Using both the reading section and visual observations in the stream table
demonstration, discuss how the stream changed over time. Explain where the
highest velocity streamflow occurs.
According to the readings and visual observations, stream started as a small,
narrow stream with strong flow in youth stage. Then, when it comes to mature stage,
outside banks becomes widens because of erosion, inside banks accumulated silt
due to deposition. This situation happened is because water velocity in the outside
banks is higher than in inside banks. This is also where the stream is flowing at its
highest velocity.
Part 2: Anatomy of a Stream
Draw a diagram with labels that displays the major parts of a stream, using the
stream table demonstration as a guide.
Part 3: Stream Velocity Experiment
There are several factors that impact streamflow velocity – channel size, slope, volume of
water, etc. Today, we are going to conduct an experiment with two variables to determine
how stream slope and water volume play a role in changing the velocity of moving water
in a stream.
Write a hypothesis, predicting the outcome of the experiment based on the two variables
we are observing.
Slope and volume will determine how fast the stream can flow
Carefully watch the stream table demonstration and record data from the experiment in
your data table below. Then, analyze your data using the questions as a guide.
10˚ Slope
5˚ Slope
1˚ Slope
High Water Volume
0.86s
1.02s
1.16s
Medium Water
Volume
1s
1.04s
1.18s
Low Water Volume
1.02s
1.07s
1.44s
Data Analysis
•
Create a table to calculate the velocity of the streamflow for each of the 9 trials
below.
Distance
70cm
Trail 1
70cm
0.86s
81.3
Trail 2
70cm
1s
70
Trail 3
70cm
1.02s
68.6
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Time/s
Trail 4
70cm
1.02s
68.6
Trail 5
70cm
1.04s
67.3
Trail 6
70cm
1.07s
65.4
Velocity
=distanc
e/time
Trail 7
70cm
1.16s
60.3
Trail 8
70cm
1.18s
59.3
Trail 9
70cm
1.44s
48.6
•
Discuss the outcome of the experiment in terms of the data collected. Which
factors impacted the streamflow most significantly? The least?
Based on the data, slope impact the streamflow most and water volume
impact the least.
•
Describe other variables that you would test to determine how those variables
impact streamflow. Make predictions for those variables with expected outcomes.
Other variables I would test is the shape and width of stream. The narrow,
more circular the stream, the faster water velocity would be.