Rock Creek EarthCache

Background:
It is important to classify streams because by knowing their form, you can reasonably predict their behavior. In other words, streams with similar form will function similarly. And when you can predict what kind of stream it is, you can predict the kinds of wildlife and vegetation you might find inhabiting in or around the stream. Water quality and ecology is monitored throughout the park by projects, including many supported by the Murie Science and Learning Center and Discover Denali (link: http://www.murieslc.org/static/377/denali-national-np-and-p).

The most widely used system in the United States for stream classification is the Rosgen Classification Method. It states that stream stability is achieved over time by developing a profile and pattern that doesn’t change due to degradation (erosion) or aggradation (deposition).

There are four levels to the Rosgen method: Level I (a geomorphic characterization using topography, landform, and valley morphology), Level II (morphological descriptions based on field observations), Level III (stream condition related to stability, response, and function), and Level IV (measurements made to verify processes).

For classifying Rock Creek, we’ll stay more basic and use Levels I and II. You can determine criteria for Level I using aerial photos and maps, but you need to get in the field to determine the criteria for Level II.

Using the Rosgen method to classify Rock Creek:

You won’t be directly measuring Rock Creek as intended by the Rosgen method. Instead, you’ll estimate the required components to come up with a reasonable guess using the following trickle-down chart. All the following graphics are from Rosgen and Silvey (1996).

1. Rock Creek is a single-thread channel, to get you started on the chart.

2. Entrenchment ratio: Measures how flood-prone the stream is based on how high the channel is. A high ratio (>2.2) indicates slightly entrenched rivers, or rivers that easily flood. A low ratio (1-1.4) indicates highly entrenched streams, or streams that would have trouble escaping their banks.

3. Width/depth ratio: The active channel width divided by the depth. A low W/D is a narrow, deep stream, and a high W/D is a wide, shallow stream.
4. Sinuosity: This is how much the stream twists and turns. Low sinuosity is straighter, while a high sinuosity curves more frequently.
5. Once you’ve narrowed this down, you’ll know the stream type (A, B, C, E, F, or G).
6. Slope: It’s a mountain stream, so the slope is probably pretty high…

7. Channel material: No bedrock is visible at this location. So how big or small is the dominant material in the stream bed?
8. Now you have the complete stream type classification number!

How to access this EarthCache:
Hike the Roadside Trail from either Park Headquarters or the Denali Visitor Center to the Rock Creek footbridge.

Please remember to practice Leave No Trace ethics to preserve this experience and environment for future visitors:

-Hiking off-trail is not required at this EarthCache.
-Collecting samples is not allowed in National Parks.
-You can do the cache right from the footbridge.

To log this EarthCache, please email me the following answers:

1. What color is the stream? How transparent or opaque is it?
2. What do you think influenced the condition of the creek at the time you visited?
3. What do you think the Rosgen classification is for Rock Creek?
4. Based on your classification, what sort of erosional and/or depositional environment would you expect at Rock Creek? Use http://www.fgmorph.com/fg_6_5.php, http://www.fs.fed.us/r6/frewin/projects/watershed/sycan/images/rosgen.htm and subsequent pages to find your classification.

Sources:

“Fundamentals of the Rosgen Stream Classification System.” Environmental Protection Agency. 1 June 2010. .
Karle, K.F., and Sousanes, P.J., 2000. Stream channel reference sites for long-term monitoring, Denali National Park. In proceedings: American Water Resources Association 2000 Annual Spring Speciality Conference: Water Resources in Extreme Environments. Anchorage, AK. May 2000.
“Rosgen Classification of Detailed Stream Type.” 1 June 2010. .
Rosgen, D.L., and Silvey, H.L., 1996. Applied River Morphology. Wildland Hydrology Books, Fort Collins, CO.
“Upper Sycan Watershed Analysis.” U.S. Forest Service. 1 June 2010.

This EarthCache was created by the Geological Society of America summer 2010 GeoCorps intern at Denali National Park and Preserve.