Freeing the Elwha (What is a Watershed?)
OverviewHealthy watersheds are vital for a healthy environment and economy. How can understanding watersheds and particularly the Elwha watershed help you protect the water and other natural resources?
A watershed is an area where all precipitation either drains on the surface or underground into an outlet stream or river. Watersheds can vary by scale, with a large watershed containing many smaller ones. In addition to surface waters, much of the precipitation filters through the soil and bedrock into the aquifer.
Aquifers are bounded by impermeable layers and once water reaches those, they begin to flow more horizontally. Groundwater flows along the rock layers until it reaches a surface point that is below the water table. Then, the water reemerges as springs or seep that flow over the surface.
- Precipitation: Any form of water, such as rain, snow, sleet, or hail, that falls to the earth's surface.
- Watershed: The drainage basin where all precipitation (snow and rain) on the surface or below ground, drains into a single river or lake on the way to the ocean or to an endorheic basin.
- Basin: A catchment area where water drains into a depression.
- Infiltration: The seeping of surface water into the soil and down into the aquifer through the porous spaces between rock particles.
- Aquifer: Underground water flow formed by the infiltration of precipitation from the surface. It flows through a permeable substrate and is contained by impermeable layers below it. They are often the source for springs, where the topography drops below the elevation of the water table.
- Water Table: The horizontal depth of the top of the aquifer. Where the surface elevation drops below the water table elevation, surface water in the form of lake.
- Permeable layer:Surfaces that contain pores or spaces which liquids can pass through and into.
- Impermeable layer: Surfaces that lack pores or spaces and do not allow liquids to penetrate.
- Springs: A place where water comes from below ground to run on the surface. Often these are the headwaters from streams.
- Seeps: A place where groundwater percolates to the surface or through cracks in the strata. They can form small wetlands that trickle into streams.
- Groundwater: Water that collects or flows beneath the Earth's surface, filling the porous spaces in soil, sediment, and rocks. Groundwater originates from rain and from melting snow and ice and is the source of water for aquifers, springs, and wells. The upper surface of groundwater is the water table.
- Substrate: An underlying layer.
- Lesson 2- What is a Watershed.pptx
- Lesson 2a- What is a Watershed.pdf
- Lesson 2 Demonstration/Lab Activity Sheet.doc
- 4-5 clear jars
- A small measuring cup or spoon
- An eyedropper or siphon for water removal
- A small quantity of small gravel, clay or hardened mud, potting soil
- A bucket full of sand
- A slab of sandstone
- Stream Table
- Reflection Journal Pages (Printable Handout)
- Vocabulary Notes (Printable Handout)
Have students take a minute to write in their reflection journals. Ask them to talk about what they've written.