1. Hook Your Students: What is a watershed?

Ask students to remember the last time it rained. Did the rainwater stay exactly where it fell on the ground? [No, it moved somewhere.]

Where did the rainwater go? [It went into the ground or ran off the pavement into a storm drain, lake, or river. Rainwater runs downhill, from higher elevations to lower elevations, eventually reaching a body of water, like a river or lake.]

Ask students to write down a definition of the term “watershed.” Watch the first segment (~3 minutes) of the After the Storm DVD and discover the definition of ‘watershed.’ During this segment a reporter asks several adults and children to define the term “watershed.” After viewing, ask the students to re-write their definition. Discuss what is a watershed with the class.

A watershed is the entire land area that drains runoff to a common lake, stream, or river. This area is called a drainage basin. The boundaries of a watershed are called the drainage divide. These are high points in the landscape (hills and ridges) from which water flows downhill to the river, stream, or lake. Drainage divides separate adjacent watersheds. Every body of water is surrounded by a watershed.

Think of your bathtub as a watershed. Imagine a stream flowing down the middle of the tub. The drain is the mouth of the stream as it empties into a river, lake, or the ocean. The rim of the tub is the drainage divide. Water that falls on the outside of the tub does not flow down the drain. The water that falls on the inside of the tub runs into the drain (mouth) at the bottom of the tub.

Display the overhead transparencies Diagram of a Watershed, Aerial View of a Stream and Stream Channel Profile to show the parts of a watershed and stream channel, and introduce new vocabulary.

2. Demonstrate a 3-D watershed model. (Outdoor Connection)

Make a model of a watershed on your classroom floor (or outdoors) by laying a sheet of plastic or a tarp over newspaper wads to create a U-shaped ridgeline as shown in these photos (exact shape is not essential). If available, the model can be placed into a child’s swimming pool or large, shallow plastic container.

Have the class gather around, as you demonstrate the movement of water and parts of a watershed using your model. Spray blue-colored water (or use the rain cups) to demonstrate rainfall and runoff on the watershed model. The water will flow downhill, with several small streams coming together to form a main channel that eventually empties into a lake (if necessary, elevate the headwater end of the model). Ask students to predict what will happen when water falls on the top of a ridge. [Some water will run off one side of the ridge into one stream, and some will run off the other side of the ridge into another stream.] The ridge between the two streams is called the drainage divide—it is the highest point of land between two bodies of water. Water falling on the other side of the drainage divide will run off into a different watershed.

Distribute the overhead transparency watershed labels amongst the students for them to place in the appropriate places on the watershed model:

• Drainage divide – higher elevation (ridge) between two watersheds

• Floodplain – a flat area adjacent to a stream channel that is periodically covered by flood overflows

• Headwaters – the source or beginning of a river

• Main channel – the largest channel into which smaller streams flow

• Mouth – outflow of river into large river, lake, or ocean

• Tributary – small stream entering main channel

• Meander – curve in river

• Streambank – the sides of the channel

• Direction of flow – water flows down gradient from headwaters to mouth

• Sub-watershed – land area surrounding a tributary

• Upstream – towards the source of stream or river

• Downstream – towards the mouth of a stream or river

3. Explore Michigan’s watersheds.

Students apply their understanding of watersheds to Michigan’s watersheds illustrated on Michigan’s Water World poster. Distribute one laminated Michigan’s Water World poster, one Michigan highway map, the Michigan’s Water World student activity page, and a set of washable markers to each small group of students.

Orient students to the highway map by finding their hometown and several of Michigan’s largest cities. Note the rivers nearby. Next, orient the students to the Michigan Water World poster by helping them to locate their own watershed.

Allow groups time to complete the Michigan Water World student activity page. Review the correct answers with the class using the Michigan’s Water World overhead transparency to guide the students through the questions on the student activity page. Be sure to have students wipe the posters clean at the end of class, so they are ready to use again.

Use the overhead transparency Great Lakes Watershed and Political Boundaries to show students the watershed for each of the Great Lakes. These watersheds are sub-watersheds of the Great Lakes watershed or Great Lakes basin, with the Atlantic Ocean as the final destination. Each of the boxes represents a different county. Point out the county in which the school is located.

4. How is streamflow measured in Michigan streams?

Streamflow is the volume of water in a stream passing a specific point during a specified period of time (usually expressed in cubic meters per second).

The U.S. Geological Survey (USGS) measures streamflow at gaging stations established on rivers throughout Michigan and the United States. The USGS first began measuring stream discharge in 1900. Some rivers have 50 or more years of data. Large rivers, like the Saginaw, Muskegon, and Grand Rivers, have several gaging stations placed along the river’s length from headwaters to mouth.

Today, many streams are equipped with a continuous, real-time recorder that allows the USGS to gather streamflow data without having to visit the stream to manually collect the data. Real-time data is recorded every 15-60 minutes, stored onsite, and transmitted to USGS offices every 4 hours. Streamflow data are available for viewing within minutes of data collection. This USGS website displays real-time data from 176 stream gaging sites in Michigan: http://waterdata.usgs.gov/MI/nwis/current/?type=flow.

The USGS website Surface Water Sampling and Methods has illustrations of equipment used to measure stream discharge (http://ga.water.usgs.gov/edu/picturesmw.html) and How Streamflow Is Measured contains a detailed explanation of how stream measurements are made by a hydrologist (http://ga.water.usgs.gov/edu/watermonitoring.html).

Many factors affect the amount of streamflow:

• Size of the watershed

• Steepness (gradient or slope) of the land

• Soil saturation (runoff increases if the soil is saturated or frozen and no more water can infiltrate)

• Weather and climate

• Season

• Type of land cover (see table below) (discussed further in Lessons 4 and 8)

A stream hydrograph is a graph that shows streamflow (in cubic feet or cubic meters) through time, usually daily, monthly, or annually. The USGS website Streamflow in Michigan will automatically graph this data and provide presentation quality printouts (http://mi.waterdata.usgs.gov/nwis/current/?type=flow).

Display the overhead transparencies Stream Hydrographs and Stream Hydrograph Data for several Michigan streams.

Discuss the following questions to encourage students to carefully examine the hydrographs and the varying streamflows for the different rivers.

How do the sizes of the drainage basins of these rivers compare?

Which river has the largest streamflow?

Which year had the highest peak flow?

Which year had the lowest flow?

Why might the streamflow vary from month to month?

Why might the streamflow vary from year to year?

Why do we need to know how much water is

flowing in a stream or river?

By knowing streamflow, we can:

• Predict flooding and potential threats to human health, property, and safety

• Identify streams with adequate year-round streamflow to support different species of fish

• Identify appropriate building sites that won’t be damaged by flooding

• Aid navigation

• Determine potential for different forms of recreation

• Predict potential for pollution impacts

5. Tying it all together.

Review the following concepts:

What is a watershed? [An area of land that drains water into a river or lake = drainage basin.]

To what body of water do (almost) all watersheds flow in Michigan? [Great Lakes.]

What determines the amount of water in a river? [Size of watershed, amount of precipitation, whether ground is frozen or saturated.]

What do I want to know about my watershed? [Responses may vary. The types of land uses in the watershed and the water quality of the streams or lakes in the watershed.]