Levees and Flooding
Another comment from a visitor to the website:
Here is another except from the same article you have posted on your web
blog, but the funny part of what these wetland environmentalist say is the levees they complain about were not even built till 1969, so what the heck caused the loses of wetlands from 1930 till 1969 if not natural conditions such as hurricanes and flooding?
"Sidney Coffee, executive assistant to the governor for coastal activities, said about 1,900 square miles of wetlands have disappeared from the area since the 1930s, and the receding continues at a rate of about 24 square miles per year"
Here's what I found on that:
Indians had lived along the Mississippi for hundreds of years, and apparently had not been bothered by the river's proclivity to leave its banks, or to wander to and fro in search of a speedier path to lower terrain. They simply moved their teepees when the blankets started getting wet. but, as one joker put it, "It's more difficult to move Baton Rouge."
As a river leaves its banks at flood stage, it quickly begins to slow and drop its sediment. The finer silt may be carried for some distance, but the heavier sands and small rocks will settle almost immediately. Thus, the Mississippi, a river prone to flooding throughout its history, had already built some substantial natural levees before the Europeans arrived on the scene.
This suggested to the new settlers that assisting nature by building the natural river walls even higher might offer some protection to them in the years when Montana and other upstream states had a very wet winter and spring, and they got the resulting runoff.
In New Orleans, a town where the majority of the first homes were built on the river's natural levees, an ordinance was passed in 1724 making each homeowner who lived along the river responsible for building and keeping in good repair an artificial levee. Not everyone bothered to construct a levee; indicating that even then they had the makings of fine American citizens, who today still balk when they are ordered by the government to do something for their own good. Those who did follow the ordinance constructed dirt and rock structures generally not more than three feet in height. In 1727, the New Orleans levee system was declared complete, and the city was considered to be flood proof.
No one informed the Mississippi, which proceeded to put New Orleans under water in 1735, and again in 1785. Levee building on both sides of the river now proceeded in earnest.
Levees became a business. By the time the War of 1812 erupted, there were levies along much of the river from New Orleans to the point where the California to Florida Bicycle Route crosses the Mississippi, a distance of more than 200 miles. Still the river flooded, and again the levees were built higher. By the time the Civil War broke out, the levees averaged nearly 6 feet in height, double the height of the initial New Orleans levees.
The river remained ignorant of the great pains the population was taking to keep it within its banks. In 1862, 1866, and 1867 it flooded; in dozens of places the levees failed and were rebuilt, and failed again.
In 1879, Congress got into the act and turned over the responsibility for flood control to the Army Corp of Engineers. After studying the problem, the Corp determined that the levees, if properly constructed and maintained, would do the job. They discarded alternate plans of tributary dams, spillways, and downstream reservoirs.
And so through the turn of the century the cycle continued, with higher and higher levees, and occasional pronouncements that the river was at long last under control. In 1884, 1890, 1891, 1897, 1898, 1903, 1912, 1913, 1922, and 1927 those pronouncements were drowned by the sound of rushing flood waters.
By 1928, with much of the 1,500 miles of levees now at eighteen feet or higher, someone finally asked, "How high is high enough?" The engineers worked their slide rules again, and this time arrived at a different, and very disturbing, answer: the levees would not fully solve the flooding problem, no matter how high they were built.
The Corp turned to "Plan B," essentially the system of flood ways, reservoirs, and control gates, it had discarded some 45 years earlier. Levees were not ignored as part of the solution; by the 1930s the average Mississippi levee was 30 feet high.
And still the river continued to flood. By the 1970s, it was time to try a new approach. The Corp decided to draw the battle line at Old River, where the Atchafalaya River and the Red River join the Mississippi.
Labels: History
posted by Slide @ 8:20 AM
