Erosion, sediment transport, and streams lab

Instructions: Answer the questions below based on careful analysis of the topographic maps and review of related material in the text and your notes. Reports will be graded on content (geology), organization and clear presentation of ideas. Two people may work together on one report.

Materials: 100 Topographic Maps and aerial photographs (provided).

For each map considered below, start by carefully considering the landscape setting. You should think about location, topography, elevation, and any features that help describe the local landscape (e.g. steep hills, many lakes, few streams, steep streams, canyons, etc.).

(1) Page 42. Campti, Louisiana (and color-infrared aerial photograph).

Passoit Lake and "Old River" (just NW of map center) are the same type of feature.

(a) What are these called?
(b) How did these features form?
(c) Where is the next one of these features likely to be created?
(d) What usually happens to these floodplain lakes, over long periods of time?
(e) Where is there an example of one that has already undergone much of that process?

Note the curved features on Smith Island (inside "Old River"). These occur near other meander bends on the map and are particularly apparent on the photos.

(f) How were these formed?
(g) Were these features on Smith Island formed before or after the Old River was cut off?

Visualize the future of this river.

(h) How permanent do you think its present course is?
(i) What implications does this have for human activity on river floodplains?

(2) Compare the Red River (p.42) with the streams on the Strasburg, VA map (p.100).

(a) What are the major similarities and differences between these two landscapes? Consider geologic materials, river form, and associated stream features.
(b) How can you explain the regular pattern of the meander bends in the Strasburg streams?
(c) Note also the similar pattern of the Conodoguinet Creek (see the large geologic raised-relief map on the classroom wall). Would you expect the meanders of Conodoguinet Creek to migrate more slowly or more quickly that those on the Red River in Louisiana? Why?

(3) Page 64. Bottomless Lakes, New Mexico.

(a) How would you describe the channel pattern of the Pecos River? (Note all of the side channels, not just the main channel.)
(b) What is the likely reason for the stream taking this form?
(c) Compare the Pecos River with the Red River at Campti, Louisiana (p.42): describe differences in sediment size, dominant type of sediment transport, bank material cohesion, and discharge variability for these two streams.

(4) Page 58. Ennis, Montana.

Examine the large alluvial fan that occupies much of the map.

(a) How large is the fan? (Quickly approximate its size by counting the numbered squares ("sections") which are one square mile each.)
(b) What is the fan's relief? (Calculate the elevation difference between the fan's apex and base.)
(c) Would you characterize the stream courses flowing across the fan as fairly permanent or fairly frequently changing? (Provide some explanation or support for your answer.)

(5) Examine the topographic map of the Mississippi River on page 107 (and also examine the aerial photograph composite available in class).

This map depicts two differing reaches of the Mississippi River: one above Lock and Dam No.4 (center of map) which creates a reservoir, and one below the lock and dam which reflects the more natural (pre-dam) river features.

(a) What characteristics of the pre-dam river (as seen below the dam) illustrate the kinds of difficulties that would have been encountered in trying to navigate with large boats?
(b) Examine the Zumbro River, a tributary flowing into the Mississippi from the west, and the area to the north and south of the Zumbro. This area can also be examined on the aerial photograph composite. What features can you identify on the map (or the photos) that are indications that this river and its surroundings have been altered through engineering modifications? (You need to consider almost all the land to the west of the Mississippi on this map.)

Additional Practice (not required)

Page 13. Bright Angel, Arizona (Colorado River).

(a) Which was there first the canyon or the river?
(b) Does the canyon determine the river and stream course of does the river determine the canyon formation? How and why?
(c) What type of landscape is primarily in this map?
(d) How does the Colorado River keep its course?
(e) What type of rocks does it dissect?

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