Point bar (foreground, right) and cut bank (foreground, left) along Camp Creek at Fort Harrison State Park in Marion County. Click for a larger image (IUPUI Earth Sciences).
You’ve heard words like river, creek, brook, bayou, and run and these words may bring to mind a body of water that is flowing in some direction. In fact, these words all fall under one category for geologists – streams. Streams are defined as any surface water whose flow is confined to a channel.
A drive around Indiana reveals that we have many, many streams running across our landscapes. You will observe the action of streams in each of your field trips; you will see how stream action has carved out canyons, you will see how streams travel along glaciated terrain, you will look at the deposits that streams leave behind, and you will see waterfalls created by a stream. This overview will have 4 sections:
• What is a Stream?
• Erosion by Streams
• Deposition by Streams
This overview is followed by directions for completing your workbook exercises.
Before completing the "Overview" sections of this lab, please read the following in your lab book:
Pages 153-156: Please read all the text on these pages, taking note of the bolded terms.
Pages 168-169: Please read the introduction and the discussion of flood frequency. You may stop reading at "Questions (Part A)".
What is a Stream?
A stream is a body of water that flows along a clearly defined natural passageway, called a channel. Streams are part of the Earth’s hydrologic cycle, the system where water continuously moves between oceans, lakes, glacier ice, streams, groundwater and the atmosphere.
A stream is fed by it’s drainage basin or watershed. A drainage basin is the area from which surface flow (from rain or snow) reaches a stream. A stream may collect water from water that runs directly on the ground surface or it may collect water from smaller streams called tributaries. A drainage basin is bounded by an area of higher topography called a drainage divide. On a very large scale, the Rocky Mountains are a drainage divide from water flowing towards the Mississippi River or to the Pacific Ocean.
When you hear people talk about streams, you may hear some of the following terms:
- Gradient: This is the vertical drop in elevation over a given distance of stream flow; the steeper the gradient, the more quickly the stream flows. This is often expressed in meters per kilometer or feet per mile.
- Velocity: This is the distance that a stream’s water travels in a given amount of time. This is often expressed in meters per second. This can vary with the gradient, the shape of the channel and the characteristics of the stream bed.
- Discharge: This is the volume of water passing a given point on the stream bank per unit time. It is usually expressed in cubic meters of water per second. Discharge is calculated by taking into account the stream’s width, depth, and velocity. Discharge is controlled by the amount of precipitation the stream’s drainage basin receives. For these reasons, the Mississippi River will have a much higher discharge than the White River.
If you were to fly across the U.S. on a clear day, you would most likely notice that streams have a variety of shapes including straight channels, channels with lots of bends, or places where it looks like there are several channels in one place. Straight channels are fairly rare and generally only occur in the places between curves. Curvy rivers are called meandering streams, and generally have a series of bends that look like S’s. Braided streams have several channels where water repeatedly divides and reunites.