What is a Watershed

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					          Hydrology: Water Quality
        “What is a Watershed?” Molly Crawford and Thomas Sobat, PIE scientists, Ball
        State University, Muncie, Indiana 47306


6.3.8      Explain that fresh water, limited in supply and uneven in distribution, is essential for
           life and also for most industrial processes. Understand that this resource can be
           depleted or polluted, making it unavailable or unsuitable for life.


Students will be able to:
    Reproduce a model that illustrates the general movement of water throughout the
    Recall pollutant sources found in their own watershed.
    Match land use activities with water pollutants.
    Compare/ contrast non-point and point source pollution.
    Predict the water quality of a water body when they are told what the local land use is.


Watershed model (stream table, kiddy pool or similar shallow container)
Cups, buckets, plastic containers to create topography
Mid-weight sheet of plastic (Large enough to amply cover pool)
Red, green and blue sugar drink mix powder
Cocoa powder (hot chocolate mix)
Vegetable oil
Spray bottle filled with water
Small child’s watering can
Dry erase pens three or four colors
One scrap piece of paper
One apple and a knife


       A watershed describes an area of land that contains a common set of streams and

rivers that drain into a single larger body of water, such as a larger river, a lake or an ocean.

A watershed can cover a small or large land area. Not only does water run into the streams

and rivers from the surface of a watershed, but water also filters through the soil.

These two processes, surface runoff and infiltration are important for a number of reasons.

       They can affect water quality. The water that runs off the surface of the Earth picks up

water pollution and deposits the pollution in streams and rivers as it drains the watershed.

Along with many different types of pollution that are carried by surface runoff, soil also

becomes a water pollutant as it is eroded from farm lands. Water that filters through the soil

can become contaminated with pollution that is left over from agricultural, industrial,

commercial, and other types of human activity.

       The network of streams and rivers that drain our watershed can carry water pollution

into larger bodies of water, such as lakes and oceans. As the larger rivers carrying water

pollution from the land flow into lakes and oceans all of the pollution that was in the rivers

now is concentrated into these other bodies of water. The oceans of the world become the

final resting place for tons of pollution. Through our watersheds, pollution is distributed far

away from its original source, and polluted water affects water quality.

1. In order to impress upon the children how much water there is on Earth; use an apple to

represent the Earth. Cut the apple into fourths. Three-fourths of the Earth is water; one-

eighth of the Earth is made up of water that supports life. Of this eighth, only a small amount

is fresh water. This may be represented by the apple peel. Three percent of the water on

Earth is fresh. Most of that is found in the frozen polar icecaps, unavailable for human use.

The amount of fresh water in lakes, streams and groundwater on Earth is represented by

1/1000th of the apple. Have the students estimate what is 1/1000th of the apple.

2. After establishing a perspective on the availability of fresh water on Earth, have the

students think of the ways that they use water in their daily lives. Next, discuss the

importance of keeping that supply of water clean and available for human use. It is important

to mention that the health of many plants and animals depend on clean water, and these

organisms directly affect the health and well-being of humans. Fisheries, agriculture and

recreational activities exemplify this.

3. Ask students which way water flows. Make sure that it is understand that cardinal

directions aren’t an accurate way to describe the general flow of water. show them that water

flows from high ground to lower ground. Inform the students that they are going to build a

watershed. A watershed is the catchment basin into which rainwater falls and then flows

downstream to form lakes and rivers. It’s like a large bowl. The bowl may be very shallow like

a dinner plate, or very deep like a mixing bowl.
4. Have students gather around the “watershed” model. One or two students should place the

cups and objects within the watershed model to form the topography. Spread the plastic over

the objects and explain that the model represents natural landforms and topography.

5. Have students come up with things that people might do in this watershed that might affect

the water (they inevitably come up with trash and litter). Use this as a starting point to

broaden their understanding of land use and how it affects water quality. Suggest that there

is a new building being built on a hill, and have them draw it on the plastic using dry erase

markers. There might be an agricultural field in one section of the watershed, roads

throughout, a neighborhood, and a factory of some kind (have them draw these as well).

6. Use blue colored drink mix to represent fertilizer used in agriculture, lawn care and a

component of wastewater. Use a red colored drink mix to represent pesticides, and cocoa to

represent soil from either field erosion or construction site run-off. Use vegetable oil to

represent petroleum leaks from vehicles on roads and parking lots. Use green drink mix to

represent a chemical in a spill at a factory. As students choose these sites in the watershed

and apply the “pollution,” explain the difference between these sources of pollution. The

colors of the pollutants in the watershed will help illustrate the difference. Blue, red, brown

and oil will be scattered, while the green will be in just one spot.

7. Have a student begin imitating a rain shower by spraying the watershed with a spray bottle

followed by the watering can. The students should observe where the water flows and what

results. Students can make observations, and formulate hypotheses regarding the quality of

the water in the section of river after the rain event.

The students can journal their observations and questions. Points can be assigned for

hypothesis development, and participation in creating the watershed.


This lesson can be used prior to a field trip to an aquatic habitat. If land use is explored prior

to the field exercise, students can develop hypotheses regarding the systems water quality.

Students could walk the banks, and map land use surrounding their sample station (see “Water Walk” hydrology learning activity). Students could regroup and

discuss the possible effects of what they have seen. If land use is agriculture one might

expect higher values from the transparency measurements than at a site that is forested or a

park with grass. Depending on the protocols used similar hypotheses could be tested

regarding dissolved oxygen, E coli, pH or nutrient profiles. In addition, relationships could be

explored that link the land use of a watershed, its water quality, and the subsequent effects

on the biota that lives in the aquatic systems ( and

have excellent protocols outlined for the collection and analysis of biotic sampling for