ESR: Lesson - Watersheds (Topic 4.6) 📖

⏳ Estimated Reading Time: 4 - 6 minutes

Learning Objective

Describe the characteristics of a watershed.

 

Watersheds

A graphic of a watershed, showing springs, tributaries, and the main river channel flowing to the mouth of the river and into the estuary. When tributaries join the main river, it is called a confluence.
The Chattahoochee River basin covers about 8770 square miles in Georgia, Alabama, and Florida. It originates in the Blue Ridge Mountains and empties into the Gulf of Mexico.

According to the United States Geological Service, a watershed is “an area of land that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir, mouth of a bay, or any point along a stream channel.”

Watersheds can be thousands of square miles in an area like the Mississippi River watershed or simply a mountain meadow. All land areas are a part of a watershed.

Characteristics of watersheds include area, length, slope, soil, and vegetation types.

An image of a pool cover loosely covering a pool.The low areas of the pool cover are filled with water. Orange arrows point from the high points of the pool cover to the low points filled with water, showing how a watershed directs water to low-lying areas.
A watershed is like a loose pool cover - the fabric directs precipitation to the lowest points of the pool cover.

An interesting way to visualize a watershed is to imagine a pool cover on a swimming pool. When it rains or snows, the blue fabric directs all of the water towards the lowest point (orange arrows on the image) which, in this case, happens to be the middle of the cover on top of the pool water. This is similar to what happens when precipitation falls on land areas. The water follows gravity and flows to the lowest point and continues to flow until it reaches its final destination.

The final destination for flowing water may be a lake or the ocean and a lot can happen to the quality of the water during its journey to that final destination.

Watersheds are separated by divides, or high points. Perhaps the best-known divide in North America is the Continental Divide. This divide runs the length of the Rocky Mountains from the southern part of the United States all the way up into Canada.

Precipitation that falls on the east side of the Continental Divide runs to the Atlantic Ocean while the precipitation that falls on the west side of the divide runs to the Pacific Ocean.

The map below shows all of the rivers in the United States and the major watersheds:

A map of the United States depicts rivers resembling veins on a leaf against a dark background. Major watersheds like the South-Atlantic Gulf, Lower Mississippi, Great Lakes, and others are labeled.
This map shows all of the rivers in the United States and their watersheds.

 

Essential Knowledge

Characteristics of a given watershed include its area, length, slope, soil, vegetation types, and divides with adjoining watersheds.

 

Human Impacts on Watersheds

Streams, lakes, rivers, groundwater, and the ocean are interconnected by the flow of water into, through, and out of watersheds. Under normal conditions, dissolved nutrients and minerals move along with the water and these help to nourish aquatic ecosystems.

When humans introduce pollutants in the form of industrial waste, excess fertilizer, pesticides, animal waste, or runoff from roadways and parking lots, the pollution also moves along with the flow of water.

The graphic depicts a forest, tributaries, and a river. A city with roads, homes, and a factory is on the left, while agricultural fields and a cow farm are on the right. Pink arrows illustrate water flow from these sources to the river, showing how pollutants can enter waterways.
You can see a sampling of the sources of water pollutants in this image. Water on land, and any associated pollutants, flow into waterways as runoff.

The pollution from a watershed can have long-lasting impacts on the aquatic ecosystem into which it empties. 

A satellite image of the United States, with agricultural areas highlighted bright green and major cities highlighted in red. All flow into the Mississippi river, which flows into the Gulf of Mexico, creating a dead zone, shown in yellow and blue.
Green areas indicate agricultural land currently in production and the red areas are large cities. Each of these entities contributes to the formation of the “dead zone” in the Gulf of Mexico (yellow/blue area).

The huge Mississippi River watershed empties into the Gulf of Mexico. Any human activity that creates pollution on land can eventually impact the Gulf. Scientists have detected a significant “dead zone” just offshore in the Gulf in which pollution has reduced the dissolved oxygen to extremely low levels. The lack of oxygen and the presence of other pollutants decreases life in this zone, hence the name “dead zone.”

Because of the runoff of pollutants from various watersheds, the Environmental Protection Agency (EPA) has created the Healthy Watersheds Program (HWP) to raise awareness about watershed pollution.

The Healthy Watershed Program (HWP) cycle involves collaboration with partners to identify available data and assess the watershed scale. The EPA synthesizes this data by evaluating six healthy watershed components, integrates results to identify healthy watersheds, and evaluates vulnerability. Then implement strategic watershed protection priorities through outreach and continual monitoring.
The Healthy Watershed Program (HWP) takes a holistic approach to managing the health of our nation's watersheds.

The goal of the HWP is to prevent water pollution in watersheds by involving local and state governments along with citizen-based efforts in protecting watersheds. This holistic approach to watershed protection is gaining traction nationwide.

Everyone can help protect the health of the nation’s watersheds.

Here are some things that you can do to help protect the watershed in your area:

  • Minimize the use of chemicals and fertilizers in and around your property.
  • Keep your vehicle in good shape to avoid fluid leaks.
  • Recycle as much as possible and avoid littering.
  • Never pour anything down a storm drain.
  • Volunteer to clean litter and other items from your local watershed.
  • Research local governmental candidates and vote for those that support protecting the health of our watersheds.

If everyone works together, the health of watersheds can be protected for future generations.

 

AP Exam Tip

You should know how humans affect watersheds.

 

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