Expand the WATERSHEDS AND DRAINAGE DENSITY folder.
A drainage basin is an area of land in which a stream receives water, predominately by surface runoff, through flow, and groundwater flow. Drainage basins are topographically divided from each other by the highest points of elevation, so that all water from the ridges and hills flow into a given drainage basin and thereby into a given stream. This topographic delineation is commonly referred to as a watershed (the drainage divide between two drainage areas), although many in the United States use the term watershed interchangeably with drainage basin or catchment.
A large drainage basin can contain several smaller drainage basins or sub-basins. The nested nature of these sub-basins is determined by topography as well as where the water flows out of the drainage area, known as the outflow point. In Figure 1, the red lines demarcate the watersheds of the tributary streams, while the yellow lines delineates the watershed of the larger drainage basins for the larger streams, which includes the smaller tributaries and their sub-basins.
Understanding watersheds are important because stream flow and water quality are influenced by the nature of and changes in the drainage basin. We can determine what is happening in our river basins by examining the water flow and water quality from a river’s outflow point. Changes to water flow or water quality in rivers could be due to either natural events (such as lightning induced forest fires increasing soil erosion) or human modifications (such as agricultural practices increasing pollution).
Double-click and select Columbia River Watershed. The Columbia River watershed encompasses 258,000 square miles (approximately the size of France), with 220,000 square miles in the U.S. and 38,000 square miles in Canada. The length of the river is approximately 1243 miles, making it the 15th longest river in the United States. Uncheck Columbia River Watershed. Check the Columbia River Sub-basin US only folder. Click on each sub-basin in the Google Earth map pane to identify its name. Question 10: How many sub-basins in the United States are displayed on the map? Uncheck Columbia River Sub-basin US only. Expand the Columbia River Watershed - Fly Over folder. The Google Earth flying simulation of the Columbia River shows how the basin is a multi-use watershed. Do the following steps to reduce confusion for the duration of the simulation:
1. Uncheck all the check boxes in the Google Earth’s Places and Layers panes.
2. Check only the Enable this check box for the tour check box to display the text in the simulation.
3. Double-click here to view the tour (Running Time: 2:06).
When the simulation stops, close the simulation control panel:
Question 11: What water uses did you see as you traveled upstream on the Columbia River? Uncheck Columbia River Watershed - Fly Over. Expand the Stream Order folder.
Stream Order
Stream order is a measure of the size of a stream based on a hierarchy of tributaries. Using the Strahler stream order method, the smallest tributaries are assigned the value of 1. When two streams with different order numbers join, the resulting stream is assigned the value of the higher order numbered stream.
In Figure 2, two streams with an order number of 1 join to form a stream with an order number of 2. However, when one stream with an order number of 1 joins a stream with an order number of 2, the stream remains a 2. Large river systems typically have a higher stream order. The Mississippi River for example has a stream order of 10. The Strahler stream order number for a given stream is dependent on the scale as which one views a stream network. A stream with an order number of 3 on a 1:24,000 map, for example, might have an order number of 1 on a 1:1,000,000 scale map, as fewer rivers are displayed on a smaller scale map.
Double-click and select the Willamette River folder. In this particular map, the Willamette River has a Strahler stream order of 5. Though not all streams are labeled with their order, you should be able to determine how the stream ordering system works. You might have to zoom in to see the labels clearly. Double-click and select the Snake River folder. For Questions 12 to 15, identify the stream order number for rivers A, B, C, and D: Question 12: A: Question 13: B: Question 14: C: Question 15: D: Uncheck the Stream Order folder. Stream Density Double-click and select the Stream Density folder.
Notice the two sub-basins that are highlighted. The smaller one is the Willamette River watershed and the larger one is the Snake River watershed. The drainage density of a basin measures how well a watershed is drained and depends largely on the underlying bedrock and topography of the basin. Basins with high relief and exposed bedrock tend to have a higher drainage density.
Use the following formula to calculate the stream density of each sub-basin (show your work):
drainage density = total length of all streams / area of the drainage basin
Willamette River watershed:
The area of the Willamette River sub-basin is 11,500 square miles.
The total length of all streams in the Willamette River sub-basin is 12,800 miles.
Question 16: What is the stream density of the Willamette River sub-basin?
Snake River watershed:
The area of the Snake River sub-basin is 108,000 square miles.
The total length of all streams in the Snake River sub-basin is 138,000 miles.
Question 17: What is the stream density of the Snake River sub-basin?
A large drainage basin can contain several smaller drainage basins or sub-basins. The nested nature of these sub-basins is determined by topography as well as where the water flows out of the drainage area, known as the outflow point. In Figure 1, the red lines demarcate the watersheds of the tributary streams, while the yellow lines delineates the watershed of the larger drainage basins for the larger streams, which includes the smaller tributaries and their sub-basins.
Understanding watersheds are important because stream flow and water quality are influenced by the nature of and changes in the drainage basin. We can determine what is happening in our river basins by examining the water flow and water quality from a river’s outflow point. Changes to water flow or water quality in rivers could be due to either natural events (such as lightning induced forest fires increasing soil erosion) or human modifications (such as agricultural practices increasing pollution).
The Columbia River watershed encompasses 258,000 square miles (approximately the size of France), with 220,000 square miles in the U.S. and 38,000 square miles in Canada. The length of the river is approximately 1243 miles, making it the 15th longest river in the United States.
Question 10: How many sub-basins in the United States are displayed on the map?
The Google Earth flying simulation of the Columbia River shows how the basin is a multi-use watershed. Do the following steps to reduce confusion for the duration of the simulation:
Question 11: What water uses did you see as you traveled upstream on the Columbia River?
Stream Order
In Figure 2, two streams with an order number of 1 join to form a stream with an order number of 2. However, when one stream with an order number of 1 joins a stream with an order number of 2, the stream remains a 2. Large river systems typically have a higher stream order. The Mississippi River for example has a stream order of 10.
The Strahler stream order number for a given stream is dependent on the scale as which one views a stream network. A stream with an order number of 3 on a 1:24,000 map, for example, might have an order number of 1 on a 1:1,000,000 scale map, as fewer rivers are displayed on a smaller scale map.
In this particular map, the Willamette River has a Strahler stream order of 5. Though not all streams are labeled with their order, you should be able to determine how the stream ordering system works. You might have to zoom in to see the labels clearly.
For Questions 12 to 15, identify the stream order number for rivers A, B, C, and D:
Question 12: A:
Question 13: B:
Question 14: C:
Question 15: D:
Stream Density
Use the following formula to calculate the stream density of each sub-basin (show your work):
drainage density = total length of all streams / area of the drainage basin
Willamette River watershed:
Question 16: What is the stream density of the Willamette River sub-basin?
Snake River watershed:
Question 17: What is the stream density of the Snake River sub-basin?