88 Chapter 13 Streams and Floods
Introduction
Learning Objectives
After reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:
- Explain the hydrological cycle and its relevance to streams and what residence time means in this context
- Describe a drainage basin and explain the origins of different types of drainage patterns
- Explain how streams become graded and how certain geological and anthropogenic changes can result in a stream losing its gradation
- Describe the formation of stream terraces
- Describe the processes by which sediments are moved by streams and the flow velocities that are necessary to erode them from the stream bed and keep them suspended in the water
- Explain the origins of natural stream levées
- Describe the process of stream evolution and the types of environments where one would expect to find straight-channel, braided, and meandering streams
- Describe the annual flow characteristics of typical streams in Canada and the processes that lead to flooding
- Describe some of the important historical floods in Canada
- Determine the probability of a flood of a particular size based on the flood history of a stream
- Explain some of the steps that we can take to limit the damage from flooding
![Figure 13.1 A small waterfall on Johnston Creek in Johnston Canyon, Banff National Park, AB [SE]](http://opentextbc.ca/geology/wp-content/uploads/sites/110/2015/08/Johnston-Creek-.jpg)
Streams are the most important agents of erosion and transportation of sediments on Earth’s surface. They are responsible for the creation of much of the topography that we see around us. They are also places of great beauty and tranquility, and of course, they provide much of the water that is essential to our existence. But streams are not always peaceful and soothing. During large storms and rapid snowmelts, they can become raging torrents capable of moving cars and houses and destroying roads and bridges. When they spill over their banks, they can flood huge areas, devastating populations and infrastructure. Over the past century, many of the most damaging natural disasters in Canada have been floods, and we can expect them to become even more severe as the climate changes.
