Part 4—Rainfall and Streamflow: How Do They Relate?
Step 1 – Compare Streamflow in the Three Largest Watersheds
In Part 2 you identified and became familiar with the three largest watersheds in the Santa Catalina Mountains, including Sabino Canyon. Next, you will examine the relationship between rainfall and streamflow in each of the creeks that drain these watersheds. You will learn what may be considered "normal" responses to rainfall in a watershed. You may discover that streamflow varies both among the watersheds and within each watershed over time, and that it does not always adhere to a pattern. This investigation will allow you to dig deeper and discover why.
- If necessary, launch My World and open the sabino_watershed.m3vz project file. The Precipitation and Catalina Watersheds layers should be on.
- Turn on the Streams and Gauging Stations layers.
- Activate the Gauging Stations layer.
- Select the Get Information Tool and click on each of the three gauging stations on the map to identify and familiarize yourself with their names and the names of the creeks in which they measure streamflow.
- When you are done reading, close the Get Information window.
- Select the Link Tool, and click the base of the flag at each of the gauging stations, then select the link name in the pop-up window.
- Once you have opened all three windows, arrange them on your screen so you can view all of them at once.
- With the graphs open, answer the following questions:
Most of the flood events seem to be responding to above-normal precipitation received in a particular month.
- Describe the pattern of precipitation between 2000 and 2007. Has it generally been above-normal, below-normal, or has the pattern changed over time? Generally, precipitation has been below-normal between 2000 and 2007. However, there are more months with extreme above-normal precipitation in recent years (specifically in 2005, 2006, and 2007).
- Which of the three watersheds experienced the largest flood event between 2000 and 2007? In what year did this large flood occur, and what was the highest discharge measured? (Note: The scales of the y-axes are different for each graph.) Tanque Verde Creek experienced the largest flood event in August 2006. The highest flow measured was approximately 175 cubic meters per day.
According to the graphs, what causes most of the flood events in the gauging station records? (Hint: What do these flood events seem to be responding to?)
- Are the responses in stream discharge always proportionate to the precipitation record? For example, are there instances where there is high discharge, but a lack of above-normal precipitation, or vice versa? In what years do these flood events occur? Yes, there are several flood events at each gauging station where there is average or slightly above-normal precipitation, from 2003 to present. In the cases of above-normal precipitation in 2005, 2006, and 2007, the discharge response is much greater than the response to even higher precipitation in 2000.
- Describe the pattern of precipitation between 2000 and 2007. Has it generally been above-normal, below-normal, or has the pattern changed over time?
- Click the Show Table of Layer button at the top of the Layer List.
This table shows the elevation (in meters) and the drainage area (in square kilometers) that each gauging station represents.
- Which gauging station measures discharge draining from the greatest land area, in square kilometers? The Canada del Oro gauging station measures discharge from 660 square kilometers of land.
- How does the drainage area of Sabino Creek gauging station compare to those of Tanque Verde Creek and Canada del Oro? The Sabino Creek drainage is much smaller than the other two, draining only 91 square kilometers.
- Which gauging station measures discharge draining from the greatest land area, in square kilometers?
- Close the Table of Layer and all three linked graphs when you are finished viewing them.
The top graph in each window is the same for all three watersheds. It shows the departure from normal monthly precipitation (in centimeters) for the Tucson area between 2000 and 2007in other words, it illustrates how far above or below-normal the precipitation measured for each month. A bar that is above zero implies above-normal precipitation for that month. A bar that is below zero implies below-normal precipitation for that month. The bottom graph in each window shows the streamflow, or discharge, in m3/day for each creek that flows from one of the three largest watersheds you previously identified. These discharge data are displayed over the same period as the top precipitation graph for purposes of comparison.
Step 2 – Compare Streamflow between Gauges within Sabino Canyon
- Select "Sabino Canyon" from the Map View drop-down list in the upper-right corner of the map. Now, only the Sabino Canyon watershed should be visible on your map.
- Turn on (show) the Precipitation (cm/yr) and Streams layers.
- Where does the majority of precipitation fall within the Sabino Creek watershed? The majority of precipitation falls near the top of the watershed.
- Where does the majority of precipitation fall within the Sabino Creek watershed?
- Show and activate the Sabino Creek Gauging Stations layer.
- Use the Get Information Tool to learn more about each of the two Sabino Creek gauging stations to determine their drainage areas.
- What is the drainage area, in square kilometers, of the (a) Upper Sabino Creek gauging station and (b) Lower Sabino Creek gauging station?a. 8.3 square kilometers
b. 91 square kilometers
- Which stream gauge in the Sabino Creek watershed do you predict would measure higher discharge during a rainy season? Explain. Answers will vary. Generally, the bottom, or outlet, of a watershed will experience the highest discharge during wet periods, because all surface water will eventually converge and exit the watershed at that location. Therefore, the Lower Sabino Creek stream gauge would measure higher discharge.
- What is the drainage area, in square kilometers, of the (a) Upper Sabino Creek gauging station and (b) Lower Sabino Creek gauging station?
- Close the Get Information window.
- Turn off (hide) the Precipitation (cm/yr) layer.
Step 3 – Save the Project File
Now that you have worked to make selections, you may want to save your project file. Save the file with a new name, such as "Sabino watershed part 4" or other unique name of your choice.
If you were unable to complete the steps in this part, or would like to start the next section with a completed file, you may download this completed, and saved, file. Sabino_watershed_part_4.m3vz ( 14.4MB May8 11)