Part 5 — Analyze Your Results

A close look at the sections of the full graph reproduced below reveal that the stream's response to precipitation is highly variable. In the image immediately below, the rain event of January 10 is accompanied by a moderate increase in stream discharge while the smaller rain event of February 24-25 is accompanied by a larger jump in stream discharge.

In the section below there is a similar discrepancy: the precipitation that occurs on April 21-23 totals approximately 2.75 inches but is accompanied by a much greater change in stream flow than the 4-inch rain of early June.

The fact that the Sudbury River's surface can freeze during the New England winters, and that the watershed is often covered in snow, are just two of the factors that combine to make the streamflow-precipitation relationship a complex one. This complexity, however, is not unique to New England. Every area of the country has its own set of factors — some natural and some that are directly related to human disturbances — that influence the streamflow-precipitation relationship.

Many factors influence the way a stream responds to a rain event. Some of them will vary across time within one watershed. For example:

• intensity of the rain event
• duration of the rain
• air temperature
• etc

Other factors will not vary across short periods of time, such as from week to week, but they will influence the precipitation-stream flow relationship. These factors will also vary from one watershed to another. They include:

• type of soil
• amount of vegetation on the ground
• presence of impervious surfaces
• etc.

What other factors can you think of that might influence the relationship between precipitation and streamflow?

Find out as much as you can about the Sudbury River and its watershed. As you conduct your research, try to figure out what factors play a role in the way the Sudbury River responds to precipitation throughout the year.

There are many sources available to you that will help you to investigate a watershed.

• The Web Form that you received from the National Climatic Data Center is one of them. Print this file and see if it holds clues to the way a stream responds to precipitation: the air temperature, or the presence of snow or ice on the ground, may help explain surprising jumps or drops in stream flow.

To learn more about soils, porosity, and the movement of water through soil, check the following resources:

• The Teacher's Guide on the Web site of the GLOBE Program has an extensive section about soils, and includes a variety of hands-on activities and tests students can perform.
• The Natural Resources Conservation Service, formerly the Soil Conservation Service, has a wealth of information about soil types. It has soils maps for at least some states, and there is an NRCS office in every state which can offer resources and help with questions related to the local soils. Browse the site for information of interest.
• The Groundwater Foundation: Kid's Corner has simple graphics and text, and may be more appropriate for younger students, but is listed on the DLESE website and is a Reviewed Resource. It is also an on-line store for groundwater related materials.

Print your graph and write an explanation to the question, "What factors influence the way the Sudbury River responds to precipitation?"