12.1: Introduction

Module 12

Streams and Floods

Figure 1. Delta Ponds in Eugene, Oregon Delta Ponds is a 150-acre waterway site consisting of numerous ponds, channels, wetlands, and associated riparian areas. Up until the late 1800s, the Delta Ponds area was part of a river floodplain network of side channels, sloughs, and tributaries that provided a rich habitat well-suited for many native fish and wildlife species. Over time, flood control management, urbanization, and land use practices changed the area dramatically. The ponds, peninsulas and islands that are present today at Delta Ponds were formed by gravel extraction operations that took place in the 1950’s and 60’s. Perhaps the biggest change to the area was that following gravel mining, this former side-channel of the Willamette River became disconnected from the river. -Rick Obst

Introduction

Think about how many times a day you take water for granted— you assume the tap will be flowing when you turn on your faucet, you expect rainfall to water your lawn, and you may count on water for your recreation. Not only is water necessary for many of life’s functions, it is also a considerable geologic agent. Water can sculpt the landscape dramatically over time both by carving canyons as well as depositing thick layers of sediment. Some of these processes are slow and result in landscapes worn down over time. Others, such as floods, can be dramatic and dangerous.

What happens to water during a rainstorm? Imagine that you are outside in a parking lot with grassy areas nearby. Where does the water from the parking lot go? Much of it will run off as sheet flow and eventually join a stream. What happens to the rain in the grassy area? Much of it will infiltrate, or soak into the ground. We will learn about both surface water and groundwater in the next two modules. Both are integral parts of the water cycle, in which water gets continually recycled through the atmosphere, to the land, and back to the oceans. This cycle, powered by the sun, operates easily since water can change form from liquid to gas (or water vapor) quickly under surface conditions. Both surface water and groundwater are beneficial for drinking water, industry, agri- culture, recreation, and commerce. Demand for water will only increase as population increases, making it vital to protect water resources both above and below ground.

Select an image to view larger

Figure 2. Chesapeake Bay Virginia National Estuarine Research Reserve. Aerial view of Taskinas Creek area showing the very low gradient, meandering tidal streams.

Figure 3. Looking down a waterfall in Pant Glas, Scotland. The constant flow of water has cut the rock smooth and created small stepped pools.

Figure 4. Flash floods, like this one in the Gobi Desert of Mongolia, are common across the Southern United States, as well.

Figure 5. A weir was built on the Humber River (Ontario) to prevent a recurrence of a catastrophic flood.

Figure 6. Flooded street in Cedar Rapids, IA

Figure 7. USGS personnel monitoring flood waters in Waverly, Iowa.

Module Objectives

At the completion of this module you will be able to:

1. Explain the hydrological cycle and residence times of water in its various compartments.
2. Describe a drainage basin and different types of drainage patterns.
3. Explain how streams form, how they are graded, and how flow velocity and sediment size are related to erosion and deposition in a stream channel.
4. Describe the process of stream evolution and the types of environments where one would expect to find straight-channel, braided, and meandering streams.
5. Describe examples of processes that lead to flooding.

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Activities Overview

See the Schedule of Work for dates of availability and due dates.

Be sure to read through the directions for all of this module’s activities before getting started so that you can plan your time accordingly. You are expected to work on this course throughout the week.

Read

Physical Geology by Steven Earle

• Chapter 13 (Streams and Floods)

Module 12 Assignment: Calculating and Assessing Flood Recurrence Intervals

10 points

After you complete the reading, you can start working on Module 12 Assignment – Calculating and Assessing Flood Recurrence Intervals

Module 12 Quiz

10 points

Module 12 Quiz has 10 multiple-choice questions and is based on the content of the Module 12 readings and Assignment 12.

The quiz is worth a total of 10 points (1 points per question). You will have only 10 minutes to complete the quiz, and you may take this quiz only once. Note: that is not enough time to look up the answers!

Make sure that you fully understand all of the concepts presented and study for this quiz as though it were going to be proctored in a classroom, or you will likely find yourself running out of time.

Keep track of the time, and be sure to look over your full quiz results after you have submitted it for a grade.

Your Questions and Concerns…

Please contact me if you have any questions or concerns.

General course questions: If your question is of a general nature such that other students would benefit from the answer, then go to the discussions area and post it as a question thread in the “General course questions” discussion area.

Personal questions: If your question is personal, (e.g. regarding my comments to you specifically), then send me an email from within this course.