Rivers of Water

From Experiment Central, published by U·X·L

The Carson begins in California, rushing northward from the headwaters on Sonora Peak in the Sierra Nevada Mountains, then rambling through gorges and alpine meadows. After leaving California, its next destination is the desert plain of Nevada. The Carson is a river, a main course of water into which many smaller bodies of water flow. The longest river in North America is the Mississippi. At 2,280 miles (3670 kilometers), it's the tenth longest on Earth. The Nile River, the world champion in length, winds 4,145 miles (6670 kilometers) from the equator to the Mediterranean Sea.

First things first

The source of a river's waters, in fact, all the waters of the world, is the hydrologic cycle, which circulates and distributes the fresh water on Earth. To examine this cycle, we might begin with the sea. The Sun warms the ocean water, causing some of the surface water to evaporate and rise into the air as water vapor. Upon meeting cooler air above, this water vapor condenses and forms rain droplets, or it freezes into ice crystals. The droplets or crystals eventually fall again as precipitation: rain, snow, or hail. Some precipitation falls back into the sea, while some falls on land where it sinks into the ground, or runs into rivers, lakes, ponds, and streams.

French scientist Claude Perrault was one of the first to describe the hydrologic or water cycle. In 1674, he measured the precipitation that fell into the upper Seine River's basin and compared it with the estimated amount of water flowing into the Seine from streams and smaller rivers. The precipitation added about six times as much water as the streams. This was a significant discovery because previously scientists had thought that all rivers were fed by underground springs.

Mapping out the journey

Rivers begin in mountains as several streams. These streams are formed from runoff consisting of rain, melted snow, sleet, and hail, as well as underground water that rises to the surface. Smaller streams gather into larger streams until they form a river. The river makes its home in a channel, a shallow trench carved into the ground from the pressure, volume, and movement of the water.

The journey of a river is rarely straight. Wide, shallow rivers with pebbly islands in the middle are called braided rivers. The islands split the river into many streams, which then come together again, just like braided hair. Lowland rivers that twist and turn before flowing to the sea are called meandering rivers. The term originated from the Latin word maeander. For example, the Menderes River in Turkey is famous for its windy course. Scotland's Deveron River meanders 26 miles (42 kilometers) back and forth across the land, but its actual straight-line length is only 6.5 miles (10.5 kilometers).

The power of water

Where does a river's energy come from? The elevation of the land triggers its push, even in areas where the slope is gentle. The speed and volume of a river descending a steep slope can reshape Earth's surface, picking up soil and rocky debris and then dropping it when the water slows down and loses some of its energy. Rivers have gouged out canyons, built mud and stone landforms, and sculpted solid rock into pillars and arches.

An example of how powerful a river's force can be is the Niagra River, which runs through Canada and the United States. As it courses downslope on its 35-mile (56-kilometer) trail, the water pounds everything along its way. The cliff that creates its falls is a ridge made of dolomite, a very tough limestone. The river has worn down the ridge's overlying rock, creating a lower area that focuses the fall of the water.

In the following experiment, you will explore ways that water changes the shape of our environment. The experiment will help you appreciate how rivers and streams have influenced the shape of your own community.

Weathering Erosion in Glaciers: How does a river make a trench?

Purpose/Hypothesis

In this experiment you will investigate the effects that glaciers, rivers of ice, have on the landscape, such as forming trenches and moraines, arc-shaped ridges of rocky debris. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of glaciers. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:

• the topic of the experiment
• the variable you will change
• the variable you will measure
• what you expect to happen

A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: "Ice flow causes sediment erosion."

In this case, the variable you will change is the presence of an ice flow, and the variable you will measure is the movement of soil in the ice flow's path. You expect the ice flow to cause erosion.

As a control experiment, you will set up one tray of sand with no ice flow in it. That way, you can determine whether the sand moves even with no ice flow. If the sand moves under the ice flow, but not in the control tray, your hypothesis will be supported.

What Are the Variables?

Variables are anything that might affect the results of an experiment. Here are the main variables in this experiment:

• size of the ice flow
• size of pieces of sediment
• temperature surrounding ice flow
• duration of the experiment

In other words, the variables in this experiment are everything that might affect the sediment erosion. If you change more than one variable, you will not be able to tell which variable had the most effect on erosion.

Level of Difficulty

Moderate.

Materials Needed

• 10 pounds (4.5 kilograms) play sand for sandboxes
• 24-inch (60-centimeter) square of window screening
• two 8 x 24-inch (20 x 61-centimeter) plastic trays (Liners for window boxes are ideal.)
• water
• freezer
• ruler
• bucket

Approximate Budget

$15.

Timetable

30 minutes to set up; 5 minutes a day to add water over a 30-day period.

Step-by-Step Instructions

1. Place the screening over the bucket and sift the sand by pouring it through the screen. Save any sand that remains on the screen. Discard any sand that goes through the screen.
2. Pour the sand that remained on the screen into both plastic trays.
3. Using the side of the ruler, smooth the surface of the sand in the trays and measure the depth of the sand. Make sure the sand is the same depth in both trays.
4. Using your finger, make a well in the sand at one end of both plastic trays.
5. Place the trays inside the freezer and prop up the ends with the well about 1 inch (2.5 centimeters).
6. Pour 0.25 cup (60 milliliters) of water into the well of one tray (the experimental tray) and close the door. The control tray will have no water---and thus no ice. Add another 0.25 cup (60 milliliters) of water to the experimental tray daily for 30 days.
7. After 30 days, record the length of the ice flow that formed in the experimental tray.
8. Carefully remove both trays from the freezer.
9. Allow the ice flow to melt 6 to 12 hours.
10. Diagram the pattern the ice caused in the sand; describe the sand pattern in the control tray.
11. Measure the depth of the sand in the trench and at the end of the ice flow in the experimental tray. Measure the sand depth at both ends of the control tray. Record your findings.

Summary of Results

Organize your data on a chart that shows the sand levels in both trays at the beginning and the end of the experiment. Compare your end results. Did the ice flow move sediment? Did erosion take place in the control tray? Write a paragraph summarizing what you found.

Troubleshooter's Guide

Here is a problem that may arise during this experiment, some possible causes, and ways to remedy the problem.

Problem: After 10 days, there is no ice accumulation near the well in the experimental tray. All the water flows quickly through the sand to the bottom of the tray.
Possible causes:

1. The angle is too steep. Lower both trays to a very gentle slope.
2. The sand is too coarse. Try a finer mesh screen and use smaller grains of sand.

Change the Variables

You can change the variables in this experiment by using different soils. You might try top soil or a more rocky soil. Also, you can change the angle of the slope and see how the depth of the trench is affected. Gravity plays a large role in soil movement. The steeper the slope, the greater the pull of gravity.

Recording Data and Summarizing the Results

It is important that your data be kept organized in graphs or charts. When you finish your experiment, you must summarize the data and record your results. Reflect on the original question you wanted to answer. Write a paragraph explaining what happened and why so others can learn from your research.

Related Projects

To develop an experiment on this topic, think about a question that you want answered. Where does the water flow the fastest? What is the largest size rock that can be carried by a river? Where does the water come from and go to? Investigate ways to measure and analyze rivers in order to answer your questions.