Lesson 1: Watersheds and Natural Boundaries

Lesson 1:
Watersheds and Natural Boundaries

The objective of this lesson is to introduce the concepts of watersheds as natural boundaries.

In the last lesson, you looked at the location of Fort Collins within the context of political boundaries.
Now we'll look at the location of Fort Collins within the context of natural boundaries - watersheds.

STEP 1: First let's talk about watersheds.

Have you ever heard of a watershed?
Do you know what a watershed is?
Are you in a watershed now?

A watershed is an area in which all of the rainfall flows to one point. Imagine a bathtub. No matter where you dump a cup of water in the tub, it will all flow to the drain.
The bathtub is like a watershed. Watersheds are defined by a point... a point that collects all the water from the area above it.

Let's try an exercise to help explain watersheds.

Get a piece of paper and fold it the long way.
Imagine that this paper is a valley with a stream flowing down the middle.
If you choose a point in the middle of the stream, about half of the area of the paper would flow downhill to the stream and downstream to that point.
If you choose a point at the downhill side of the stream, almost the whole paper would flow to that point.

Think about the following questions.

Where would the watershed boundary occur?
Well, where would water flow in a different direction?

Remember the bathtub...

Where would water not flow to the drain?
How about if you dumped the cup of water on the floor?
It wouldn't flow into the tub drain, would it?

The edge of the bathtub is the watershed boundary.

STEP 2: Where would the watershed boundary be in the natural landscape?

Think about the top of a ridge. If a raindrop falls on the ridge, it will flow down one side or the other.
Thus, ridges are watershed boundaries.

Have you ever heard of the Continental Divide?
What is it? It occurs along the top of the Rocky Mountains.

Rain that falls on the western side of the divide flows to the Pacific Ocean.
Rain that falls on the eastern side, flows to the Atlantic Ocean.

Now that you know what watersheds are, do you think you are in a watershed now?

Yes, everywhere is in a watershed.

STEP 3: Now let's take a look at some watersheds.

Open ArcView, click "open existing project," and click "ok."
Open "Lesson1.apr." The view shows a map of the U.S.A.
"Fortcollins Collins" and "USA (Lower 48)" are turned on.

Does this view look familiar? It's similar to the introduction, but there are different themes in this view.

Zoom to all of Colorado. Remember how to do this?
Click on the "zoom button", , and click and drag a box around Colorado.

Now you can see Fort Collins.

What is the main river that flows through Fort Collins?
It's the Cache la Poudre.

Turn on "Poudre Watershed" by putting a checkmark in the box next this theme in the Table of Contents.

What you're seeing is the watershed of the Cache la Poudre River. Fort Collins is totally within this watershed.
What does that mean? All of the rain that falls in Fort Collins will eventually drain to the Poudre River.

Zoom out to all of the US.

How much of Colorado is drained by the Poudre? Only a little bit.
Does the Poudre River flow directly into the ocean? Nope.
What river does it flow into? If you said the South Platte, you're right.

Turn on "S. Platte Watershed" Notice that the Poudre watershed is part of the South Platte Watershed.

How much of Colorado is drained by the South Platte? Almost one-fourth of the state.
The South Platte River flows in to the Missouri, which flows into the Mississippi River.
The Mississippi flows into the Gulf of Mexico.

Turn on "Missouri Watershed" and "Mississippi Watershed."

These are the Missouri River Watershed and the Mississippi River Watersheds. We are increasing the scale of the watersheds that we are looking at.

Look how much of the U.S.A. flows into the Mississippi.
What is the last city that the Mississippi River flows through before it reaches the Gulf of Mexico?
It's New Orleans.

That means that the rain that falls on almost half of the U.S.A. will eventually flow through New Orleans.

Turn on "Mississippi River System" These are the major rivers within the Mississippi Watershed.

In the last lesson, we learned that Fort Collins was within Larimer County, which was within Colorado, which was within the U.S.A.
These are political boundaries.

In this lesson, we see that in the context of natural boundaries, Fort Collins is within the Poudre Watershed, which is within the South Platte Watershed, which is within the Missouri Watershed, which is within the Mississippi Watershed.

Close ArcView by clicking "exit" from the File menu.
Click "No" when asked to save changes.

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Lesson 1 Worksheet

Lesson 2