Name: _______________________________________________ Section:_______________________

part 1: river terraces: snake river, Wyoming

Use the topographic map of Moose, Wyoming (Figure 20.3) to answer the questions below.

1. Construct a topographic profile between points A and B on the topographic map of Moose, Wyoming. Graph paper has been provided and the vertical axis has been labeled. For this profile to show the necessary detail, all of the contour lines must be used. Using just the index contour lines will not suffice.

2. Label the following features on the topographic profile:

· the channels to the Snake River

· the width of the current floodplain

· river (alluvial) terraces

· terrace scarps

3. Do the terrace elevations on the west side of the river match the terrace elevations on the right side of the river? Yes; there are very minimal differences

4. Based on the number of terraces evident, how many episodes of down-cutting occurred in this area? Two

5. On the topographic map, mark the edges to the current floodplain in red.

6. Calculate the width of the present floodplain, in miles, along the profile line. This may be measured on the map or on the profile; the scale is the same for both. Please show all your work. Conversion factors: 12 inches = 1 foot 5280 feet = 1 mile

((1.95"(24000))/63360= 0.74 MILES

7. The Snake River eventually flows into the Columbia River and out to the Pacific Ocean. How high above base level is the Snake River channel where you drew your profile?

6565’ above sea level

8. What type of channel pattern does the Snake River have along the stretch shown here? BRAIDED

FIGURE 20.3 USGS Topographic map

Moose, Wyoming

Original was1:24,000

contour interval = 20 feet

Name: _______________________________________________ Section:_______________________

part 2: landforms of meandering rivers

Use the map of Campti, Louisiana (Figure 20.4) to answer the questions below.

1. Highlight two or three examples of the following fluvial landforms on the map of Campti, Louisiana. Use the boxes provided below to create a key for your map, using either different colors or symbols for each feature listed.

Point bar deposits or areas of expected deposition along the Red River

Areas of expected erosion along the Red River

Oxbow lakes

Meander scars

Yazoo streams

Location of the next meander cutoff and formation of a new oxbow lake

2. Although bar and swale topography exists on the point bar deposits shown on this map, the contour lines do not show the bars and swales on the majority of these point bars due to the scale of the map. There is, however, one location where the contour lines actually show the bars and swales; where is this example of bar and swale topography?

Smith Island

3. What is the technical name for the semi-circular feature called "Old River"?

oxbow lake

4. Question 1 asked you to label the location of the next meander cutoff. Why did you choose this location? DEEP BEND; LOW ELEVATION NECK OF UNCONSOLIDATED ALLUVIUM THAT IS EXPOSED AND READILY ERODABLE; OFTEN PRE-EXISTING MEANDER SCARS INDICATED BY RED POLITICAL BOUNDARY LINES

5. a. Using variations in topography and elevation, estimate the approximate location of the edges (northern and southern) of the floodplain and highlight them on the topographic map. Only portions of the floodplain edge are visible.

b. A straight line appears on the map just to the west of the town of Campti, running from the north side of the map to the south side of the map. What is the width of the floodplain along this line, in miles? Use the ratio scale. Please show all your work. Conversion factors: 1 foot=12 inches 1 mile =5280 feet

(6.41” x 62500)/63360 = 6.32 MILES

6. The Red River flows into the Mississippi River very close to the Gulf of Mexico. How high above base level is the Red River? ~115’

7. a. How does the width of the Red River floodplain compare to the width of the Snake River floodplain (from Part 1)? wider

b. Is this what you expected? Why or why not? YES; SNAKE IS YOUTHFUL-MATURE STAGE; RED IS AN OLD AGE RIVER

8. Figure 20.5 is a 1998 air photo of the region shown on the Campti topographic map. The topographic map was made in 1957.

a. Locate Old River and Smith Island and highlight them on the air photo. These will serve as reference points to help you relate what you’re seeing on the photo to what the topographic map shows.

b. How has the Red River changed to the north and west of Smith Island in the time interval from when the map was made and the photo was taken? The river has cut off the meander southwest from Bright Morning Star Church.

c. Locate the city of Campti on the air photo. How has the river changed to the south of Campti? The river has cut off the meander in Questions 1 and 4. There is a new island in the channel at the next meander downstream.

FIGURE 20.4 USGS Topographic map

Campti, Louisiana

Original was1:62,500

contour interval = 20 feet

d. Locate two new oxbow lakes or incipient oxbow lakes on the air photo and highlight them.

9. Compare the length of the Red River on the topographic map to its new length on the air photo.

a. Use a piece of string or a map measurer to measure the length of the river in miles. Note that the scale for the air photo is not equal to the scale for the topographic map.

River length on topographic map (miles): 20.76 miles

River length on air photo (miles): 15.38 miles

b. Assuming the elevation of the river at its northern-most point on the map and air photo has not changed over time, and assuming the elevation of the river at its southern-most point on the map and air photo has not changed over time, how will this change in length affect the river gradient? The gradient will steepen (the same relief divided by a shorter distance)

c. What impact should this change in gradient have on flow velocity and on the river’s ability to transport sediment? Should there be more erosion or more deposition in 1998 than at the time the map was made? Explain. Since the same volume of water will have less channel volume to occupy, the flow velocity will have to increase if the water remains in the channel, and so the competence, erosion, and sediment load will increase.

However, if the river overflows its banks (“floods”), then the water spreads over greater volume of space so that the velocity and competence will decrease, and sediment deposition will increase.

Figure 20.5 Air Photo of Campti, Louisiana – 1998