Unit 5_Lab_StreamErosion (1)
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Broward College *
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Geography
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Dec 6, 2023
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Name ___________Tyler Hope____________
Date ____________9/27/23____________
Class Day/Time _______ESC1000L_________
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.
Starting in the youth stage of the stream, the stream's velocity was fast, as it was on a steeper slope, and a more rounded bed. It starts to carve a a wider area due to its high energy flow, which
allows it to carry more sediment. As we get to the mature stage, we can see that the stream has a calmer flow, and a gentler slope with a more widened bed. The velocity of the stream has carved a bend into the shape of the stream itself. The highest velocity stream flow occurs on the outside of this bend, or meander. During the old stage, the stream now begins to slow, and cut a very wide valley. A delta also begins to form where sediment has been placed in a larger body of water.
Part 2: Anatomy of a Stream
Draw a diagram with labels that display the major parts of a stream, using the stream table
demonstration as a guide.
Meander
Delta
water flows slowly
Floodplains
Erosion
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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.
________The higher the slope and water volume the higher the velocity of the stream and the lower the slope the slower the velocity will be. _____________________________________________________________________
_____________________________________________________________________________
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
1.00s
1.04s
1.18s
Low Water Volume
1.02s
1.07s
1.44s
Data Analysis
1.
Create a table to calculate the velocity of the streamflow for each of the 9 trials below.
Water Volume/Slope
Distance Traveled
Time Traveled
Velocity cm/s
High Water Volume/10
Slope
70cm
0.86s
81.3 cm/s
High Water Volume/5
Slope
70cm
1.02s
68.6 cm/s
High Water Volume/1
Slope
70cm
1.16s
60.3 cm/s
Medium Water Slope/10
Slope
70cm
1.00s
70 cm/s
Medium Water Slope/5
Slope
70cm
1.04s
67.3 cm/s
Medium Water Volume/ 1
Slope
70cm
1.18s
59.3 cm/s
Low Water Volume/ 10
Slope
70cm
1.02s
68.6 cm/s
Low Water Volume/ 5
Slope
70cm
1.07s
65.4 cm/s
Low Water Volume/1
Slope
70cm
1.44s
48.6 cm/s
2.
Discuss the outcome of the experiment in terms of the data collected. Which factors impacted the streamflow most significantly? The least? There were not many discrepancies between the different water volumes when it came to a high slope. However, having a low water volume did result in the slowest velocity for each slope. The slowest being the low slope with low water volume. The slope of the stream impacted the velocity of water more than the volume of water. 3.
Describe other variables that you would test to determine how those variables impact streamflow. Make predictions for those variables with expected outcomes.
Another variable that could be tested would be the depth of the stream. As the depth of the stream increases, the radius in which the water is allowed to increase allows it to flow freer. This would increase the stream's velocity. The widht of a stream channel would also determine how fast a stream flows too. A narrower channel would yield a higher flow, as there is a less friction
between the water and the stream bed, unlike a wider channel, which would result in more friction, and a slower flow.
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