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Flood Control

Rivers bring both nurturing and devastation. They are definitely a mixed blessing to humankind. A raging river is fearsome, and trying to control nature for decades on end is a tricky business. This is true all over the world. Here is what a Japanese engineer writes,

The centuries-old traditional river management techniques, which had sustained both a dense farming population and abundant river and estuarine fisheries, were replaced by a river engineering ideology based on the notion that maximum public benefits could be achieved by controlling floods. As a result, today almost every river in Japan has now been embanked, channelized and dammed, creating an emerging ecological crisis due to the wholesale elimination of wetlands, floodplains and estuaries.

Rivers have been a mixed blessing to humankind, and that is why we have tried to tame them with technology. Our efforts, however, have created a new problem: we have been too successful, and have significantly disrupted the cycling of materials by rivers and damaged their ecosystems. Due to enormous dams, many rivers no longer flow naturally. Some rivers have gone dry and many banks are covered with concrete dikes. In short, many rivers have been turned into cold, uninteresting ditches detached from our lives.

From nature's point of view, flooding and the associated downstream movement of sand and earth are the natural workings of the river forming alluvial valley floodplains. Generally, floodplains offer favorable living conditions for human existence because water is easily available, the land is suitable for cultivation, irrigation is easy and navigation is available. The irony is that due to the very geographic characteristics that are a blessing to their inhabitants, alluvial valley plains are subject to frequent flooding. Without flooding, there could be no sand and earth brought down to enrich the land, so that these areas would not provide favorable conditions for settlement.

In the old days of the Edo era (1603-1868), people knew how to coexist with rivers. For example, by accepting occasional, inevitable flooding, they intentionally allowed the water to overflow in sections where relatively little damage would be done. In this way, overflow was avoided at locations where flooding could collapse the levee and cause great damage. Forest belts were laid along rivers to further reduce flood damage. In these buffer zones, special types of soil were employed as construction material while the surfaces of the levees were also carefully designed. When high water overflowed through it, the forest belt weakened the force of the flow and stopped debris, gravel, and large-particle sand and earth. As a result, the overflow, once out of the forest, contained only fine sediment and was slow moving. Although farmland was submerged, farmers in the Edo Era welcomed a flood if it occurred only about once a decade because the sediments it left enriched their fields.

(From http://www.irn.org/pubs/wrr/9701/japan.html)

Mississippi River Flood

The Great Mississippi Flood of 1927 killed many people and left thousands homeless. Levees were built to control the flow of water, and were considered protection from flooding. The levees in their turn have created issues that need to be dealt with. The unpremeditated consequence that the levees brought was to deprive southern Louisiana of its coastline (see the Environmental Issue for Venice, Louisiana)

As John M. Barry of the Tulane-Xavier Center for Bioenvironmental Research in New Orleans so beautifully writes in his article in the November 2005 issue of Smithsonian:

Since before the Civil War, the U.S. Army Corps of Engineers had regulated the Mississippi River, and since the 1880s had insisted upon a "levees-only policy"—that is, a belief that levees alone were all that was needed to control flooding. The corps believed that if the quantity of water in a river increases, the current will accelerate. This is generally true. The theory also assumed that a faster current would scour the riverbed more than a slower current, and thus deepen the river. This is also true. But the corps further concluded that such scouring would deepen the river enough to accommodate even a huge flood. This was not true. In fact, all the scientific data about the river up to that time—most of it collected by the corps itself—contradicted that assumption. Nonetheless, the corps opposed building spillways and floodways to let water out of the river, and it had closed off natural reservoirs to maximize the amount of water in the river.

Then, in 1927, the disaster that critics of the corps had long expected finally arrived.

When it was over, the Mississippi River and its tributaries had killed people from Virginia to Oklahoma, flooding the homes of approximately 1 percent of the U.S. population. At its widest point, north of Vicksburg, Mississippi, the river became an inland sea nearly 100 miles across. No one knows the death toll; officially, the government said 500 people died, but a disaster expert who visited the flooded area estimated that more than 1,000 perished in the state of Mississippi alone. The Red Cross fed roughly 650,000 for months, many for a year; 325,000 lived in tents for months, some of them sharing an eight-foot-wide crown of a levee—the only dry ground for miles, with flooded land on one side and the river on the other, their hogs, mules and horses in tow but not their dogs, which were shot for fear of rabies. The worst of the flooding occurred in April and May. Not until September did the floodwaters drain from the land.

The devastation left a legacy of change far beyond the flooded regions—changes that are still being felt today. The first involved the river itself. The 1927 flood ended the debate over the levees-only policy and forced engineers all over the world to look at rivers differently. Most recognized they could not dictate to a great river; they could only accommodate its awesome power.

(From: http://www.smithsonianmag.si.edu/smithsonian/issues05/nov05/presence.html)

Other Options

Research what other option there may be in working with rivers. One answer may be what European companies have begun: to use: removable floodwall protection. Used in Cologne Germany to protect the city from the Rhine River’s flooding these walls are used when it is important to preserve the natural river setting.

What other new inventions might be coming down the pike?

 

 

One River Mississippi

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

New Orleans : Environmental Issues

June 24
2006