ESC Lab – Sketching Assignment
All responses must be red or underlined. Also leave a space between the question and answer.
River Drainage Basins
River systems are composed of a trunk stream joined by several tributaries. The drainage basin (also called the watershed) is defined by the area encompassing all the tributaries of the river. The rivers feeding individual tributaries compose sub-basins. The ridge separating to drainage basins or sub-basins is a drainage divide. Precipitation that falls anywhere within a drainage basin will contribute to the flow at the mouth of the basin. In general therefore, the larger the drainage basin, the larger the flow in the river.
Figure 4 shows the major rivers in the Continental US along with the topography. Using this map, do the following:
1) The largest river is the Mississippi which flows into the Gulf of Mexico at point A. Starting at point A, use a red line to sketch the Mississippi drainage by drawing a line the encompasses all its tributaries.
Use the color topography as a guide.
2) The western boundary of the Mississippi drainage basin matches the continental divide, the drainage divide which divides water flowing east into the Atlantic and west into the Pacific or into internal drainage in the Great Basin. Using the rivers and topography as a guide sketch in green the continental divide from the top to the bottom of the map
3) The two largest tributaries of the Mississippi are the Ohio River which joins the Mississippi at point B and the Missouri River which joins the Mississippi at point C. Using the method in question 1, sketch in blue the Ohio River and Missouri River sub-basins.
Figure 4. Major rivers of the US#
#
#
A
B
C
Livingston
Omaha
Pierre
Memphis
Billings
Bismarck
Vicksburg
St. Louis
Williston
Sioux City
New Orleans
Kansas City
The Longitudinal Profile
In all river systems, both the elevation and the gradient decrease from the headwaters to the mouth.
This characteristic of river systems is shown graphically in the form of the longitudinal profile, a graph of river elevation versus distance from the headwaters. Table 5 shows elevations and distances of selected locations along the Mississippi river system.
Table 5. Elevation and distance of points along the Mississippi River system
Site # Location River Elev (m) Distance (km)
1 Continental Divide, WY Yellowstone 3353 0
2 Yellowstone National Park, MT Yellowstone 2357 87
3 Livingston, MT Yellowstone 1356 243
4 Billings, MT Yellowstone 945 431
5 Williston, ND Missouri 560 950
6 Bismark, ND Missouri 494 1308
7 Pierre, SD Missouri 433 1688
8 Sioux City, IA Missouri 329 2202
9 Omaha, NE Missouri 291 2385
10 Kansas City, MO Missouri 220 2733
11 St. Louis, MO Mississippi 120 3336
12 Memphis, TN Mississippi 56 3957
13 Vicksburg, MS Mississippi 16 4431
14 New Orleans, LA Mississippi 1 4946
15 Mouth of Mississippi Mississippi 0 5119
4) Using this data, plot the longitudinal profile on Figure 5. Label each of the points with the site #.
Figure 5. Longitudinal profile of the Mississippi system
5) The gradient is the slope of the stream and is calculated by dividing the change in elevation by the change in distance. Using the graph or the data in Table 5, calculate the stream gradients in meters per km for the following locations:
- a) Continental Divide, WY (#1) to Livingston, MT (#3) ___________________ m/km
- b) Williston, ND (#5) to St. Louis, MO (#11) ___________________ m/km
- c) St. Louis, MO (#11) to the Mouth of the Mississippi (#15) ___________________ m/km
6) Describe the general shape and characteristics of the longitudinal profile. Include words such as concave, convex, upward, or downward if necessary
7) The base level is the elevation in the profile where the gradient approaches zero (horizontal). Indicate the base level on the profile. What is its elevation?
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Elevation in m above sea level
Distance from the Continental Divide in km
ESC Lab – Sketching Assignment
Changes in stream valley cross sections
Along with the river elevation and gradient changing along the longitudinal profile, the shapes of rivers valleys also change in cross profile. Figure 6 shows cross sectional profiles across the river valleys of the Yellowstone River in the high Rocky Mountains, the Missouri River in the high plains near Williston, ND, and the lower Mississippi River, near Vicksburg, MS.0 50 100 150 200 250
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Distance Along Profile (km)
Elevation (m)
100x VE
Vicksburg, MS
Williston, ND
Yellowstone, NP
Figure 6. Cross Profiles of river valleys in the Mississippi, Missouri, Yellowstone River systems.
Profiles are plotted at 100x vertical exaggeration (VE).
