Level 8 Guiding Question: Does a watershed change?
Young StageThis stage represents the early stages of a stream where most of its energy is used to downcut, or erode, a narrow V-shaped valley.
This is a valley whose typical cross-section is shaped like a 'v'(a cross-section is the shape that you would walk if you walked down one side of a valley and up the opposite side). A V-shaped valley has steep sides and a narrow floor. Vertical erosion by the stream deepens the valley floor. Weathering and gravity cause material to be worn away and tumble down the valley side. During this stage the ground over which the stream flows has a steep slope with many abrupt changes in elevation resulting in waterfalls and rapids.A waterfall is a steep drop in the bed of a stream causing the water in the stream to fall vertically. Waterfalls occur where a band of harder rock crosses the path of a stream. The stream is less able to erode this harder rock and leaves it as a step in the stream's long profile. Due to the steep gradient of this stage water velocity is very fast. Fast moving water can carry larger sized sediments like boulders and cobbles. |
Mature StageFurther downstream, water added to the stream from tributaries and from ground water increases the size, or width, of the stream. The slope during this stage decreases and so does the velocity of the water flowing through the stream. Since the water velocity has decreased the stream no longer has enough energy to carry boulders and cobbles. The largest sediments the stream can now carry are pebbles and sand. Due to the increase in width, the stream begins to shift its course in a series of bends or turns called meanders. As the water flows down a stream, its speed is faster on the outside of the meander causing erosion and slower on the inside of the meander resulting in deposition. This is how meanders are created. During times of flooding, when the stream overflows its banks, it deposits, or releases, sediments. Each time this occurs a thin layer of fine material is laid down on both sides of the river forming a flood plain (Fig. 3). During this stage a very narrow flood plain forms.
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Old Age StageA stream greatly slows down in its oldest stage and begins to cut, or erode, a very wide valley and an equally wide flood plain. Since the water velocity has further decreased from the previous stage it no longer has enough energy to carry pebbles and sand. Now it can only carry smaller sized sediments like silt. This stage also possesses meanders which curve even more than in the mature stage. Due to the larger size of these meanders ox-bow lakes are often seen. An ox- bow lake is a horseshoe lake found on the flood plain of a stream
Meanders may form a loop so that only a narrow neck of land separates their outer banks. In a heavy flood the stream cuts through this neck leaving the loop as a cut-off. This cut-off section becomes an ox-bow lake. During this older stage the stream usually comes to an end when the flow enters a sea or lake. This is known as the mouth of the stream. Where a river meets the sea or a lake the ground is virtually flat so its speed slows down and it deposits, or releases, all of the sediments it was carrying. This leads to a fan-shaped deposit extending out to sea called a delta. |
Stages of a Stream
You will be placed on a team of 3-4 and together you will assembly a stream table and perform three different stages of a creek; the young, mature and old age stages. Once you have completed all three you will present it to another table where they will grade your team based on a rubric provide below. The directions for how to build it are included in a small manual that came with your kit, entitled, "Earth Science Stream Table". You will also receive a packet of information about the 3 stages.
Level 8 Investigation: Changes in watershed mean impact
City to Farm
On the stream table, build a city along the stream and create a farm downstream of the city along the stream. The city and/or farm can be built on both sides of the stream with a bridge connecting the two halves. Obtain a copy of the handout, CITY TO FARM STUDENT ACTIVITY SHEET. Set up one or more of the scenarios on the sheet, each of which reflects some ways in which the city might change the flow of surface and/or groundwater and affect the farm downstream. When you have completed this activity enter into the form below. |
Farm to City
On the stream table, you are to create a farm along the stream and build a city downstream of the farm along the stream. The farm and/or city can be built on both sides of the stream with a bridge connecting the two halves. Please get a copy of the FARM TO CITY STUDENT ACTIVITY SHEET. You and your team must set up one or more of the scenarios on the sheet, each of which reflects some ways in which the farm might change the flow of surface and/or groundwater and affect the city downstream. When you have completed this activity enter into the form below. |
Level 8 Videos: Helpful VDOs
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Level 8 Elaborate: Making a VDO of your stream table.
Once you have completed your lab on the Farm to City and City to Farm you and your team will have an opportunity to film one concept your learned today about changing watersheds. The VDO will be between 1-2 minutes in length. You can do a VDO on watershed stages or on what you learned about water movement or give us a run down on your recommendations for improvements in your watershed. Email your VDO to your instructors address remember under 2 minutes is essential for successfully sending it.
Level 8 Review: Read the chapter take the practice tests and watch the VDOs.
After reading the chapter click on the assessment icon to take practice tests.
Level 8 Summary: Unit Test
To take the test click on the download button.