Geography 1: Physical Geography
Lab #5 (20 Points)
Chapter 16: Fluvial Systems
The US Geological Survey has established and maintained stream gages for over 100 years. This data is collected constantly from thousands of stream gages from across the country. These stream gages are permanent sites that record depth and speed of a stream’s water. By knowing the channel profile and speed, a volume is calculated: cubic feet per second, or CFS. This means that if a stream is at 10 CFS, there is ten cubic feet of water flowing by each second. Now, think about that. A cubic foot is a box with a foot in each dimension (like a box that a volleyball would fit into). 10 CFS is ten of those boxes passing by every second.
Each stream is unique in character – width, depth, and volume. Most streams are somewhat episodic, meaning that there are certain times when there is more water in the stream than is average. Imagine the Big Sioux in South Dakota in springtime. Most of the year, it’s pretty mellow, but when the snow melts and the spring rains come, there’s flooding all over the place. As you’ll read in Chapter 16, there are even some streams that don’t exist except for when it rains (called ephemeral).
Part I
On the USGS real-time water data website, find a stream gage that is close to where you live or work. Click on the state. Then hover over a couple of the gages to see if you can determine the location. The stream gage south of Brookings in South Dakota is site number 06480000.
When you find the site, an entire page comes up with data on that gauge. Make sure the box at the top of the page says “Time-Series: Current/Historical.” In the next box, where it says “Available Parameters,” “Output,” and “Days” change Days from 7 to 30.
The first graph is the discharge (in CFS).
In the sample graph above (from 2011), you can immediately see that the amount of water flowing past the stream gauge has gone down for the last 30 days (the blue line). One interesting thing they include on this graphic is the median statistics. This means that the discharge over the history of the station (57 years in this case) has had as many days over the triangle as below. So, for the last 57 years, there have been 28 years where water has been higher than the triangle, and 28 years when the water has been below the triangle on the same date.
- Copy and paste this graphic from your site here: (2 points)
- Explain the discharge curve and how it compares to the median values: (2 points)
The second graph (also from 2011) displays the actually height of the stream at the gage. This is the base information from which all the other data are derived.
The key information on this graph is how high the gage height is above the flood stage. This graph shows that while the stream height has been going down for the last 30 days, it is still almost a foot above the flood stage. The flood stage is the level at which the stream is officially considered flooded. The stream height can go up and down quite a bit and still be considered ‘normal.’
- Copy and paste your Gage Height graph here: (2 points)
- Explain how the current gage height relates to the flood stage: (2 points)
- In general, why do you think the graphs look this way for your site? Are you in a drought? Is it wetter than usual? (2 points)
Part II
- On the aerial photograph of the Cedar River in Iowa below: Please identify and name three major fluvial landforms present in this river valley (you may put numbers or letters in the image to identify the landforms). Also, explain how they were formed and what they can tells us about the geomorphic history of this valley. (5 points)
- From this ground photograph taken in northern Utah, please identify landforms A and B and as best as you can explain their genesis (draw a picture if you need to). (5 points)
