Atchafalaya and Mississippi

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Assignments

John McPhee, The Control of Nature, Part 1 Complete Chernicoff, Streams and Rivers, ch. 13.

Reminders

Journals due Friday should include 5 weather observations and one geology reflection (no homework). The Mars Show is presented every Friday night at 8 p.m. If you can't make this regular evening time then let me know whether you could make it Monday April 6 from 10:00 to 10:45 a.m. Saturday April 4th is movie night in the planetarium! Attendance is entirely optional, and will not count for extra credit. At 6 p.m. sharp we will begin with Twister, then follow it with Dante's Peak. If you haven't seen these movies the planetarium provides a great opportunity. Perhaps they will stimulate your next geology reflection. If you can, please bring refreshments, preferably finger foods that can be eaten in the dark without being messy. (Nutritional items, not just sweets, will be needed since everyone will be hungry for supper at 6 p.m.) A sign-up sheet will be available in class; reservations are necessary in order to determine whether there will be enough room to invite guests.

Chernicoff Review Questions

The following questions relate to material covered in chapter 13 of Chernicoff that is especially pertinent background information for McPhee's account of the Atchafalaya and Mississippi rivers.

1. The difference between alluvial fans and deltas is that:
   1. deltas are formed of larger particles
   2. alluvial fans are formed of heavier particles
   3. alluvial fans are deposited on land; deltas are deposited in water
   4. deltas are triangular in shape; alluvial fans are oval in shape

    

2. True or False? Due to the gradually decreasing gradient of older distributaries, new distributaries continually develop, shifting stream flow along more direct routes to the sea.

    

3. Study pages 264-268. We will discuss it along with Part 1 of McPhee's The Control of Nature, which provides a detailed case study of the lower Mississippi and the Atchafalaya.

    

McPhee Focus Questions

Read the entire Part 1 of McPhee's The Control of Nature. Then go back and review by focusing your attention on the following questions for discussion. (Page numbers in parentheses are approximate; most questions are discussed in many places throughout the reading.)

1. McPhee claims that the Mississippi River has created most of Louisiana. Explain how the mouth of a river, with its distributaries, reworks a delta in general, and how the Mississippi delta in particular has been reworked to create southern Louisiana. (5 ff; compare with Chernicoff)

    

   • Natural levees are ridges of silt and sand naturally deposited along a river's banks during a flood. With each flood, they are raised up higher above the backswamp or lowland beyond, and sediment raises the riverbed higher as well. Eventually, the river will jump its banks and find a new way through the lowland to the sea. This results in building up the floodplain through widespread deposition; or, near the sea, the fan-shaped deposition of deltas.

      

   • The Greek historian Herodotus referred to one ancient civilization as the gift of a river. Can you guess which civilization, and which river he was referring to? (Cf. p. 54)

    

2. What you learned from Chernicoff about headward erosion and stream capture pertains to the Atchafalaya river. Explain how these processes provide the setting for McPhee's narrative about the attempt to "preserve 1950."

    

3. From the juncture of the Mississippi and the Atchafalaya rivers, which takes the longer path to the Gulf of Mexico: the Mississippi or the Atchafalaya? (6)
   1. Which takes the steeper path? (6)
   2. What major river, once a Mississippi tributary, has already been captured by the Atchafalaya? (7)

    

4. Old River
   1. A 7-mile meander bend, once the mouth of the Red River, is now known as Old River. What was built across Old River in the early 60's? (7 ff)
   2. Why is water sometimes let through Old River now? (9-10)
   3. A sill or weir, 566 feet long with 11 gates, was built near Old River in the early 60's to control latitude flow from the Mississippi through Old River. Explain how its purpose is "to hold the Mississippi in place." (10 ff)
   4. All 11 gates of Old River Control were kept wide open during the 1973 flood. Where did they see fish unexpectedly? (pp. 29 ff and top of p. 50)

    

5. What are the different water resource needs of farmers, fishermen, navigators, municipal officials and industries, and how are these various interests adjudicated in southern Louisiana? (21ff)

    

6. Define the following colloquial terms for river snags: (34)
   1. Planter
   2. Sawyer
   3. Preacher

    

7. Who was James Eads? (38ff)
   1. How did he dredge the mouth of the Mississippi?
   2. Compare the quote from Eads on pp. 38-39 with the last paragraphs of the excerpt from Mark Twain's Life on the Mississippi (assigned for last time).

    

8. Compare what has happened to the level of the Mississippi riverbed in New Orleans (McPhee, pp. 61 ff) with the Po river in Italy.
   • Supplemental note on the Po river: A major Italian river arising from a multitude of mountain tributariess, the Po has changed course often, even on a human time scale. As early as the middle ages, people constructed banks to control the river and keep it from changing its course. What might be the effects of increasing the riverbed height upon the following: water velocity, river erosion and transport capacity, rate of delta formation, and the rate of the silting up of river bed?
   • In some places now the river is higher than the roofs of houses, much like old Roman aqueducts.
   • Explain how this same process has occurred in the lower Mississippi.

    

9. Which is lower, the bottom of the Mississippi riverbed in southern Louisiana, or sea-level? (91)

    

10. To what extent is the Army Corps of Engineers in control of nature with the Atchafalaya and Mississippi rivers?