101 Summary — Physical Geology – 2nd Edition
The topics covered in this chapter can be summarized as follows:
| Section | Summary |
|---|---|
| 13.1 The Hydrological Cycle | Water is stored in the oceans, glacial ice, the ground, lakes, rivers, and the atmosphere. Its movement is powered by the sun and gravity. |
| 13.2 Drainage Basins | All of the precipitation that falls within a drainage basin flows into the stream that drains that area. Stream drainage patterns are determined by the type of rock within the basin. Over geological time, streams change the landscape that they flow within, and eventually they become graded, meaning their profile is a smooth curve. A stream can lose that gradation if there is renewed uplift or if their base level changes for some reason. |
| 13.3 Stream Erosion and Deposition | Erosion and deposition of particles within streams is primarily determined by the velocity of the water. Erosion and deposition of different-sized particles can happen at the same time. Some particles are moved along the bottom of a river while some are suspended in the water. It takes a greater velocity of water to erode a particle from a stream bed than it does to keep it in suspension. Ions are also transported in solution. When a stream rises and then occupies its flood plain, the velocity slows and natural levées form along the edges of the channel. |
| 13.4 Stream Types | Youthful streams in steep areas erode rapidly, and they tend to have steep, rocky, and relatively straight channels. Where sediment-rich streams empty into areas with lower gradients, braided streams can form. In areas with even lower gradients, and where silt and sand are the dominant sediments, meanders are common. Deltas form where streams flow into standing water. |
| 13.5 Flooding | Most streams have their highest discharge rates in spring and early summer. Floods happen when a stream rises high enough to spill over its banks and spread across its flood plain. One of the most significant floods in Colorado is the Front Range floods of September 2013. We can estimate the probability of a specific flood level based on the record of past floods, and we can take steps to minimize the impacts of flooding. |
Answers to Review Questions can be found in Appendix 2.
