Today’s blog post is brought to you by Xander Kalna.
Now that you have learned the basics of erosion and deposition in streams, let’s look at the bigger impacts of these processes. Streams make up a network that drains an area of land, this area is called a watershed. Watersheds are areas in which all the precipitation that lands in the watershed drains to a common point. Imagine a bathtub. Everywhere inside the walls of the bathtub flows to the drain at the bottom. Water that falls outside the bathtub does not drain to the same point as water in the bathtub. The edges of the watershed are usually the highest points that allow water to flow to a common point such as mountains (or even very small hills where rain drains to different points on either side).
Streams form when enough water follows the same path, causing the soil there to erode and creating a stream channel. The channel becomes larger in areas with more water moving through there as the additional water causes additional erosion. If you look at mountains and hills, they often have areas called draws. Draws are formed on mountains and hills between two areas of higher elevation. Draws are lower than the areas on both sides of them, causing water to drain into the draw. Many draws have intermittent streams (streams that flow seasonally, not year-round). These streams are evidence of the power that water has in eroding landscapes. As water falls on top of the mountain, or when snow melts, it drains into draws. This causes the draws to experience more erosion than the rest of the mountain, meaning that draws will continue to get wider and deeper until the water reaches the ground around the mountain. This phenomenon can continue as long as there is water falling on land! The Grand Canyon is an example of this. The Colorado River and its tributaries have been flowing over the area that would become the Grand Canyon for so long that it has slowly eroded out what you see now as the Grand Canyon! Watch it here!
Once the stream has formed, it can begin to meander. Meanders are wavy paths. Meandering streams and rivers have an incredible impact on the land. They slowly move across the land; washing away plains, exposing bluffs, and creating lakes. See it here! Meanders are created when water flowing through a stream hits one bank and erodes some of the soil. When this happens, the water on the opposite side of the stream usually slows down, causing deposition. As this occurs, the stream starts to eat away at one bank while leaving sediment along the opposite bank, creating bars. Eventually, trees and other plants begin to grow on these bars. This vegetation helps deposit additional sediment and the bar to be stabilized. Once this occurs, the stream may have eroded away so much of the opposite bank that it is like the stream was never near that bar to begin with!
Sometimes when streams and rivers meander, they curve so much that their meanders meet. When this happens, the two meanders join and become the main channel of the stream. The old meander that was left behind oftentimes becomes an oxbow lake. Horseshoe Lake near Granite City is an example of this! Sometimes though, these oxbow lakes dry up and remain as meander scars: a crescent shaped cut in the land from a stream or river meander. You can see many of these in the photo posted above!
One final landscape that streams and rivers often expose are bluffs. Bluffs are basically natural rock walls like a cliff. With the large Mississippi, Illinois, and Missouri rivers near us, bluffs are all around! Here are some near Grafton, Illinois. Rivers and streams expose bluffs by slowly eroding away softer sediment and rock until they run into bluffs. Bluffs are usually made up of harder rock that does not erode as fast as the materials that the rivers took away. Streams and rivers have such a large impact on the natural environments and the built environments people construct around them. And they have so much more going on inside of them that we have yet to talk about! Learn about stream features like habitat next time!
USGS Watersheds and Drainage Basins: https://www.usgs.gov/special-topic/water-science-school/science/watersheds-and-drainage-basins?qt-science_center_objects=0#qt-science_center_objects
National Parks Service:
JC Wise Project: http://www.jcwise.hk/gis/landforms.php?lang=en
MIssissippi Historical Paths
Photo from fyfluiddynamics.com