Silting Situations

SILTING SITUATIONS

Barry L. Witten
Western Illinois University
Macomb, Illinois

Overview:
One of the major problems with the lakes of the Kansas-Lower Republican Basin is the fact that they silt in after a number of years. This teaching strategy was designed to illustrate sedimentation in a simple but effective manner. Students will be able to see that silting can be a long process, but it can also occur where runoff erodes the soil rapidly, as in a flood.

Grade Level: 5-8

Time Needed:
One 30-45 minute lesson with several additional time slots over the next several days.

Geographic Themes:
Location, Place, Human/Environment Interaction, Movement, & Region

Kansas Social Studies Standards for Benchmarks, Grade Levels 8-K:
The students will understand the connections among people, places, and environments in the local school and community, Kansas, the U.S., and different nations of the world.

The students will understand the effects of economics, science, and technology in the local school and community, Kansas, the U.S. and different nations in the world.

National Geography Standards, Grades 5-8:

#7 The geographically informed person knows and understands the physical processes that shape the patterns of Earth’s surface.

#14 The geographically informed person knows and understands how human actions modify the physical environment.

#16 The geographically informed person knows and understands the charges that occur in the meaning, use, distribution, and importance of resources.

#18 The geographically informed person knows and understands how to apply geography to interpret the present and plan for the future.

Outcomes:

Students will understand how sedimentation effects the life of a man-made lake in the Kansas-Lower Republican Basin.
Students will understand how sedimentation occurs and how the process can be accelerated during a flood.
Students will project what can be done to reduce sedimentation and extend the life of a man-made lake:

Performance Objectives:

Students will list and describe the purposes of man-made lakes in the Kansas-Lower Republican Basin.
Students will define and describe the concept of sedimentation.
Students will demonstrate the process of silting and explain how the life of a man-made lade is shortened.
Students will hypothesize how silting can be limited, attempt to prove their hypothesis, and explain the results of their design.

Vocabulary Terms:

Silting Flood Control

Sedimentation Conservation

Kansas-Lower Republican Basin Recreation

Materials Needed:

1 paint tray with a hole in the deep end to serve as the reservoir.
a container with a hole near the bottom to serve as inflow for the reservoir.
a container to be placed below the paint tray to catch water ‘released from the reservoir.’
a small container of dirt to be mixed with water which will flow into the reservoir.
access to water or a five gallon jug of water.

Procedures:

1. To introduce the topic discuss the purposes of man-made lakes in Kansas. Follow up this discussion by defining and describing the concept of sedimentation, how it occurs, and its effects. Emphasize that it is a natural process, but when silting occurs in man-make lakes the dam stops the silt, trapping it behind the dam, eventually filling the lake with silt, which limits its uses, especially for recreation.

2. Set up the paint tray (lake) on a table and fashion your inflow (water container) so that water can flow into the shallow end of the paint tray. Add three to five table spoons of dirt to each gallon of water to simulate erosion. Fashion another container to catch the water after it has gone into the lake and has drained through the hole (release tube) in the deep end of the paint tray (dam). Put five gallons of water through the paint tray (lake), drain it , and evaluate what has happened to the bottom of the paint tray. Keep track of the amount of water that you put through the process and the amount of dirt that you add to the water. Note- it may not be necessary to add dirt to the inflow (water container) with each gallon of water. You can continue this process over the next several days if you wish to show what happens to a lake over a long period of time.

3. Ask the students to evaluate what happens when you put more dirt in the water that goes through the paint tray. When does this generally happen? Will lakes silt in more quickly in agricultural areas where erosion can occur more readily? How can silting be reduced, or is this something that is going to happen to all lakes eventually?

4. As an optional activity have one paint tray every three students and let them experiment how to increase or reduce the silting process. Vary the amount of dirt given to each group to show various degrees of sedimentation.

Assessment:
Students are to write a 2 page essay addressing the following points: Why were the man-made lakes in Kansas built? What is silting and how does it occur? What effect does it have on man-made lakes? What did you learn from the activity demonstrated in class? What are some possible solutions to this problem?

Resources:

Hilbert, K. (1997). An analysis of suspended concentration in the Republican River between Harlan County Dam, Nebraska, and Clay Center, Kansas. Unpublished mater’s thesis, Kansas State University, Manhattan, KS.
Martin, C.W. (1997, June). 1997 Kansas Geographic Alliance Summer Institute: Kansas River Valley Field Trip. Paper presented at the Kansas Geographic Alliance Institute, Manhattan, KS. (for a copy write to Dr. Martin at : KSU, The Department of Geography, Dickens Hall, Manhattan, KS 66506)

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e-mail: pphillip@fhsu.edu irc staff / jh 03/16/98 (updated kn 06/23/99) Disclaimer

#7	The geographically informed person knows and understands the physical processes that shape the patterns of Earth’s surface.
#14	The geographically informed person knows and understands how human actions modify the physical environment.
#16	The geographically informed person knows and understands the charges that occur in the meaning, use, distribution, and importance of resources.
#18	The geographically informed person knows and understands how to apply geography to interpret the present and plan for the future.

Silting	Flood Control
Sedimentation	Conservation
Kansas-Lower Republican Basin	Recreation

1.	To introduce the topic discuss the purposes of man-made lakes in Kansas. Follow up this discussion by defining and describing the concept of sedimentation, how it occurs, and its effects. Emphasize that it is a natural process, but when silting occurs in man-make lakes the dam stops the silt, trapping it behind the dam, eventually filling the lake with silt, which limits its uses, especially for recreation.
2.	Set up the paint tray (lake) on a table and fashion your inflow (water container) so that water can flow into the shallow end of the paint tray. Add three to five table spoons of dirt to each gallon of water to simulate erosion. Fashion another container to catch the water after it has gone into the lake and has drained through the hole (release tube) in the deep end of the paint tray (dam). Put five gallons of water through the paint tray (lake), drain it , and evaluate what has happened to the bottom of the paint tray. Keep track of the amount of water that you put through the process and the amount of dirt that you add to the water. Note- it may not be necessary to add dirt to the inflow (water container) with each gallon of water. You can continue this process over the next several days if you wish to show what happens to a lake over a long period of time.
3.	Ask the students to evaluate what happens when you put more dirt in the water that goes through the paint tray. When does this generally happen? Will lakes silt in more quickly in agricultural areas where erosion can occur more readily? How can silting be reduced, or is this something that is going to happen to all lakes eventually?
4.	As an optional activity have one paint tray every three students and let them experiment how to increase or reduce the silting process. Vary the amount of dirt given to each group to show various degrees of sedimentation.