LESSON
INTRODUCING WATERSHEDS AND HYDROLOGY
OBJECTIVES
Students will understand how and where water is distributed throughout the
earth; the relationship between groundwater and surface water; how a
watershed is relevant to a stream; and how hydrographs are created and what
they can tell us. They will know how to create hydrographs online using data
from the USGS; compare differences in streamflow between geographical sites;
and correlate discharge to precipitation and weather patterns.
METHODS
Part 1: Instructor uses PowerPoint to lead a discussion: Where are the earth’s
water resources? How does water in Montana, in the Clearwater basin, and in
Morrell Creek fit into the world’s water? What is a watershed? What is the
water cycle? What are the properties of water and why are they important?
How is surface water measured and monitored?
Part 2: Students use the USGS online streamflow data to produce and investigate
hydrographs of local streams, and compare them to online precipitation
(SNOTEL) data.
MATERIALS
o Access to the internet (for obtaining additional data on
streamflows)
o Student pages for this lesson
o H2O PowerPoint
BACKGROUND
Grade level: 9-12
Subject Areas:
Biology, Earth
Science, Physics
Duration: 1 class
period
Setting:
Fresh liquid surface water makes up a tiny fraction of all the water
Classroom
found on earth, and yet it is an irreplaceable resource for humans
and other organisms. Hydrology is the study of water’s properties,
quantities, distribution, movement, and the hydrologic cycle. Hydrologists also
collect and analyze the data needed to predict how much water is available from
local supplies and whether it will be sufficient to meet the area’s projected future
needs.
A watershed is an area of land that drains all the streams and rainfall to a
common outlet such as a larger stream, lake, reservoir, or an ocean. (The word
watershed is sometimes used interchangeably with drainage basin or catchment.)
Ridges and hills that separate two watersheds are called the drainage divide.
Properties of a watershed help determine the quantity and quality of water in the
streams and lakes within it.
Streamflow or discharge can be recorded and represented over time using
hydrographs. Data on streamflow are collected at streams all over the U.S. and
are accessible to the public in an online database at the U.S. Geological Survey
(USGS) website at http://waterdata.usgs.gov/mt/nwis/rt. Users of this site can
generate hydrographs for different streams for a chosen time period, using these
to compare flows throughout seasons, among years, between streams and more.
PROCEDURE
Use the H2O PowerPoint and accompanying notes to introduce students to
concepts related to global water distribution, the water cycle, watersheds,
hydrology, and hydrographs. Near the end of the PPT, they will need to go
online to the USGS website, where they will generate hydrographs and answer
questions about their discoveries as they proceed.
Student Pages
Montana Streamflow Data and Hydrographs
1. Go to http://waterdata.usgs.gov/mt/nwis/rt .
2. Click on the map of % of normal streamflow data. This will open a page with a larger,
interactive version of this map. The circles on this map represent locations where the
USGS (U.S. Geological Survey) collects streamflow data in Montana. Look carefully at
the map and read the table below it. If you hold your cursor over the Explanation table,
you will be able to read a description of what the different colors of the circles mean,
A percentile is a value on a scale of one hundred that indicates the percent of a distribution that is equal to or
below it. For example, on the map of daily streamflow conditions a river discharge at the 90th percentile is equal
to or greater than 90 percent of the discharge values recorded on this day of the year during all years that
measurements have been made. In general,
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A streamflow which is greater than the 75th percentile is considered above normal
A streamflow which is between 25th and 75th percentiles is considered normal
A streamflow which is less than the 25 percentile is considered below normal
The flow category “Low” indicates that the estimated streamflow is the lowest value ever measured for the day
of the year. Similarly, the flow category “High” indicates that the estimated streamflow is the highest value ever
measured for the day of the year.
"Not ranked" indicates that a flow category has not been computed. Common reasons for a "Not ranked"
category are insufficient historical data or no current streamflow estimates.
similar to this:
3. Looking at the map of Montana streamflow data, what is your general impression?
4. Are most current flows within the range of normal? Are there very many below normal?
How about above normal?
5. Compare those in the Much Above Normal category to the Much Below Normal
category. Which are there more of?
6. Do you see any geographic patterns in where streams are at, above, and below normal
(e.g., are some parts of the state generally experiencing higher or lower than normal
flows?) Describe any patterns you see.
7. How do you think people who use water in Montana—irrigators, river guides and
outfitters, fishermen, floaters, fisheries biologists and managers, city water suppliers
and managers, manufacturers, ranchers, and other landowners—might use streamflow
information like that on this map?
8. Now look carefully at the map your teacher has projected and click on the dot that the
arrow points to. A small pop-up window will appear with a few tabs; the Summary tab
will be open. Define each of the terms below in your own words:
Drainage area:
Discharge:
Stage:
Percentile:
% normal (median):
% normal (mean):
9. Now click on the Hydrograph tab. You will see a hydrograph of your stream; click on it
for a larger image to open in another tab. This page should have at least 2 graphs (you
may need to scroll down a little to see them.) Find the Discharge graph.
What is the time period shown on this hydrograph?
10. What is the trend in streamflow, or discharge, in your stream during this time? Does it
rise, fall, or stay flat? What factors do you think may influence this trend?
11. Scroll down (or up) the page to the other graph(s). What types of information do these
graphs show? How do trends in these graphs compare to the graph of discharge? Why?
12. Above the discharge graph near the top of the page is a table that allows you to create
graphs with different lengths of time. Enter 365 days and see what your hydrograph
looks like now (you’ll be re-directed to another page; go ahead and click on the data
link). What trend(s) do you see in this graph?
13. Now go back to the tab with the map and click on a dot that is yellow, brown or red and
follow the same steps to get to the hydrograph page. How does the information for this
site compare to that for the first dot you clicked on?
14. Now you’ll go to http://www.wcc.nrcs.usda.gov/gis/precip.html. This site gives you
access to precipitation data collected at SNOTEL and other sites around the state
(SNOpack TELemetry is an extensive system of automated sites that collect precipitation
measurements around the west).
Look at the table of links on this page. In the right hand column titled Water Year to
Date you’ll see a box under % of Normal where you can select a state from a drop-down
menu. Select Montana.
What does this map show?
15. Do you see any patterns in these data across the state? How does it compare to the
streamflow map of Montana? Explain.