What is a watershed?

A watershed is an area of land where all the water is fed into one body of water. Small watersheds combine to create large watersheds and networks of streams, rivers, lakes, and oceans. Everywhere you go you are within a watershed and the boundary of each watershed is determined by the hills and mountains surrounding it (because the water coming off a ridge top will flow in different directions – to different watersheds).

Check your understanding

To understand this better, take a piece of paper and crumple it up into a small ball.  Now lightly uncrumple it so that it isn’t in a small ball but it isn’t flat – you want some “relief” (high and low places).  The low places are now your valleys, the high places are ridges (hills and/or mountains), and the wrinkles are streams and rivers (you might even have some lakes form!). 

With a blue washable marker, draw on the paper where you think a stream might form.

Now place your paper on a tray and use a spray bottle to make it rain on your model!  Be sure to spray every place evenly until you have water running.  What where it goes – did you draw the streams in the right places?  Did you create a lake?  Is the water running in different directions? 

Try a second time but this time add pollutants with different colors.  Maybe brown for farms (herbicides, pesticides, fertilizers) and red for cities (car exhaust, oil, trash, fertilizer, etc.). 

What happens to the water now?  Does it change color as it flows?  What does that mean about the water that flows through our watersheds in real life?

Forests

Forests are important to watersheds because they maintain stream health by slowing down the runoff water, absorbing it into the soil to be filtered and used by plants, and improving drainage of the soil. 

Take a cup of water and pour it onto your sidewalk.  Does it absorb?  No!  Think about what happens when there is a huge rainstorm.  The storm drains get full and clogged with debris including our trash.  Now pour a cup of water on soil.  As it runs it may pick up a few pine needles, but it quickly absorbs into the soil.  Think about it – if everywhere you are is within a watershed, that means that the water (rain, streams, lakes, etc.) is always going to flow downhill until it gets to the ocean.  By absorbing this water, we are filtering out pollutants such as pesticides, herbicides, and fungicides, as well as preventing flooding, erosion, stream widening, loss of fish habitat and water quality, and pollution running into our streams and Puget Sound.

Our watershed

Within the Puget Sound watershed, Bridle Trails State Park is located in the Lake Washington/Cedar River Watershed.  Depending on where you live you may be within another, smaller watershed!  For example, if you live just east of the park you are actually in the Lake Sammamish watershed, and perhaps the Sammamish river watershed within that. 

In our watershed, the Bridle Trails forest helps in many ways.  Since we are surrounded by a heavily inhabited urban area, there are many pollutants.  The plants in the park help to filter out air-borne auto pollution from nearby highways, balance out the heat reflected by pavement, and filter water runoff.

More information:

For educational and age-specific home lessons developed by Nature Vision, check out their Watershed, Ecological Impacts, Humans and Water, or Water Quality packets here.

For a more in-depth and educational version of the watershed activity above, check out this write-up from NatureBridge.