## Activity Source:

Source: American Geophysical Union.

Watersheds can be as small as a lake or thousands of square miles. The natural or human-made surface of the land and the sediments and rocks below are all part of a watershed. Rainfall
supplies watersheds, and water moves across the surface or infiltrates and moves through the ground.

In this activity you will use a computer model to explore the movement of water within your watershed.

## Materials

• Computer with internet

## Procedure

1. Getting to know your watershed: Geometry and scales of streams.
• Open Model My Watershed: https://wikiwatershed.org/model/.
• Navigate to your local area.
• Click “Select by boundary.” Choose USGS Watershed unit (HUC-10).
• In the Layers list, select “Continental US Medium Resolution Stream Network.”
• Zoom out. Identify your local watershed. Which rivers are familiar?
• Double click a river to bring up the “Analyze” section for Stream Network Statistics.

### Discuss:

• Describe the pattern of the stream network.
• What is meant by stream order? Describe the results for stream order.
• Which stream would carry the most water following a major rain event that covers the entire watershed? Explain.

2. Where does the rain go? Exploring evapotranspiration, runoff, and infiltration and how they vary with rainfall.
• Click “Model” in the top left of the screen.
• Select “Site Storm Model.”
• Before experimenting with different precipitation amounts, record your hypothesis about the impact that increasing the precipitation amount in a 24-hour period will have on the relative amounts of evapotranspiration, runoff, and infiltration.
• Set the precipitation amount in the top right corner of the screen.
• The model will show the amounts of evapotranspiration, runoff, and infiltration as a result of the rain event based on the landcover, soil, terrane, etc. as shown in the “analyze” tab.
• Vary the amount of precipitation. Record the results in a data table.

### Discuss:

• What happens to the relative amounts of evapotranspiration, runoff, and infiltration as the amount of rainfall increases?
• Is there a point at which this relationship breaks down? Explain.

3. Water quality: Impacts of rainfall, suspended solids, nitrogen, and phosphate.
• Click the “Water Quality” tab.
• Set the precipitation amounts to those used above.
• Record the values of total suspended solids, nitrogen, and phosphorus for each precipitation amount.

### Discuss:

• In which fraction, evapotranspiration, runoff, or infiltration do you think the suspended solids, nitrogen, and phosphorus would be found? Explain.
• What happens to the amounts of each as precipitation increases? Why?
• Describe possible effects of changes in the amounts of total suspended solids, nitrogen, and phosphorus?