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Etudes

Lesson 8: Streams and Flooding

Roaring River, Kings Canyon National ParkThis week's lesson on streams and flooding is our third to focus on a specific geologic hazard. Streams—like the Roaring River, at right—are crucial to human agriculture and civilization. The can also be deadly, however, when rain or snowmelt bring more water to their channels than they can carry and produce swiftly moving floods that sweep out across the surrounding landscape. Like the volcanoes we studied last week, streams and flooding are also relevant to people's lives and livelihoods here in Siskiyou County. As some of you may remember, heavy rains in January 2006 triggered flooding on the Shasta River that swept away riparian fencing and vegetation and required tens of thousands of dollars for repairs that had to be undertaken before that year's irrigation and grazing season could begin. Agriculture in the Shasta Valley depends on the river, but is at its mercy as well.

In this week's lesson Keller begins with an introduction to the basics of streams—calculating their discharges, classifying their sediment loads, and recognizing their channel types—and then brings these ideas together in a discussion of stream dynamics that explains how streams respond to changes in these parameters. He then explores how we analyze flooding through the calculation of recurrence intervals, how we can mitigate its effects, and how human actions may change a stream's behavior. Finally, this week's exercise will help you learn how geologists measure the discharges of actual streams and give you and opportunity to measure the discharge of a virtual stream.

As you read through this chapter on streams and floods and work through the River Discharge exercise, it will be helpful to take detailed notes so that you can keep track of major points and have ready access to them when we refer back to them later in the semester. Be sure that you have completed this week's exercise on determining river discharge and are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.

Weekly Learning Objectives

Upon successful completion of this week's lesson, a student is expected to be able to:

Reading and Browsing Assignment

Exercise 8: River Discharge (Due by 9:00 AM on 10-Oct-2011)

In this week's reading from the textbook you learned that a stream's discharge is the product of its channel width times its channel depth times its velocity. Unless a channel has a simple rectangular cross-section, however, you could never determine a stream's discharge this way. Instead, this week's exercise will give you an opportunity to learn how geologists actually measure stream discharges.

Quiz 8: Rivers and Flooding (Due by 9:00 AM on 10-Oct-2011.)

After you feel you have met the learning outcomes outlined above, please complete Quiz 8 in the Etudes "Assignments, Tests, and Surveys" area. There are ten questions, each worth one point. If you can answer all of them correctly it means that you know your way around the basics of rivers and flooding pretty well and are ready to move on to a more detailed look at landslides and subsidence next week. Please contact me if you have any questions or there are concepts you're not sure about.