General Topics

The Great Flood of 1993

With over $12 billion in damages, 50 human casualties, and over 20 million affected acres of land, the Great Flood of 1993 is the largest flood ever seen in the United States. Over 500 stream gauging stations along the Mississippi River flooded, along with 150 of its tributaries. Damages were immense, including 50,000 destroyed houses, disrupted industry in affected areas, reduced water quality, and over 1,000 damaged levees, all of which led to the immense cost of the flood.

Because the rivers were already saturated from snowmelt at the start of the summer of 1993, there was no buffer to contain the immense rainfall that summer. Hot, humid air from the south met cool air from the north and stalled over the region, leading to over 20 days of rain in some states. The immense quantities of water from both snowmelt and rainfall led to the flooding, with a record setting flow of 1 million cubic feet per second. Flooding started in the North and eventually made its way down the Mississippi.

The government responded with extensive data collection, forecasting, flood-control efforts, and rescue and evacuation efforts. The response cost topped $4.2 billion. FEMA spent $1.14 billion in responses. Most of FEMA’s money went to protecting hazardous sites from being flooded (Holmes).

Streamflow-gauging stations and U.S. Army Corps of Engineers collect data to determine patterns and potentially prevent another disaster. They also use this data to determine when to release reservoir water. Forecasting is a prime tool in evacuation and eventually saving lives (Holmes).

Floodplain environments should be protected, and many people became aware to this fact because of the flood. The floodplain preservation idea then benefited wildlife and ecosystems. So the flood was beneficial to nature in this respect (Theiling).

A perfect storm situation where the water just kept building up was ultimately the straw the broke the camel’s back. There were 5 distinct stages: buildup, transition, sustained precipitation, extended phase, and intermittent events (Theiling).

The effects were separated into the human and the ecological perspective. From the human perspective there were no positive outcomes except for future awareness and prevention. Social problems such as substance abuse and family deterioration were some negative outcomes that are often overlooked. These were due to the hardship people had to go through in the aftermath to just survive and find the basic necessities of life. In some parts a strong sense of community blossomed as a result of the flood. The flood negatively affected humans in the form of property damage, crop loss, and infrastructure damage (Theiling).

One of the negative ecological effects due to the flood was pollution and water quality degradation. Fish populations flourished because aquatic insects were abundant after feeding on the decaying herbaceous matter (Theiling).

Chemical pollution and water quality issues were most concentrated on shorelines and probably negatively affected the Gulf more than the rivers (Theiling).

Sediment redistribution and erosion were significant. More deposition occurred than erosion, though. Most plant beds recovered after the flood but experienced species changes. Some plants grew longer stems to reach the light in deeper water levels. Larger trees fared better than smaller in surviving the flood. Densities of macroinvertebrates declined probably due to fish population rise and concentration as flood waters receded (Theiling).

The number of species of fish increased after the flood, probably due to the expanded water area that let migratory fish move around where they previously were blocked by dams. Fish levels increased in most parts during the flood but the levels decreased back to average in a few years at most (Theiling).

Snakes weighed less in subsequent years because much of their prey base was gone due to the flood. It was concluded that the main way to prevent another event in the future is to manage and protect floodplain environments (Theiling).

Flood Effects on Snakes

A study was done on 8 species of snakes in St. Charles County. The study took advantage of the flood conditions that occurred in the 1990’s, since these events can yield interesting results and aren’t always studied. Different food sources that declined because of the flood seemed to have negatively affected the snakes (Sexton).

Snake samples were collected by catching them with “hands” as well as setting up boards that the snakes took refuge under. The flooding period was broken into the pre-flood (1990-1993), inter-flood (1994-1995) and post-flood (1996-2000). Species diversity declined after the flood and the 2 rarest species of snake were not observed again. Species evenness increased slightly. 23 snake species have been observed in St. Charles County (Sexton).

It was predicted that larger snakes would survive the flood and indeed 71% of the snakes captured after the flood were of larger than median size. Flooding reduced populations of five snake species by nearly 70% and reduced the other 3 species so much that they were not observed again (Sexton).

Snake populations in the area were affected by human settlement by reducing or eliminating habitats which might have served as corridors, modifying the habitat, reducing or eliminating the availability of sites which might serve as temporary refuges in times of flooding, and increasing the frequency and extent of flooding events (Sexton).

Constructing refuges or islands would help protect snake species from flooding. They would act as a lifeboat that would serve as temporary shelter for resident species until the flood receded and to act as a landfall for individuals of both resident and non-resident species swept down from upstream locations. These would serve to reduce the loss in population size and as corridors of sorts to increase species diversity for snakes that would get washed down stream but land on the islands (Sexton).

General Flood Patterns

Flooding can occur anywhere, but a lot of research has gone into how and where floods form. It was found that smaller streams flood a lot quicker than larger rivers. When further looked at, it was found that a huge problem with flooding was man-made construction that limits the spread and diffusion of water. In comparing Image 1 and Image 2 (appear below) we can clearly see the difference the limitation of where the water can sprea

In Image 1 we see the man made construction of a sewage system that blocks off the natural path of water. After heavy rain the water can only move in one direction, up, and flood. In contrast, Image 2 shows a natural stream that has long banks that will soak up any over-flowing water. This, natural stream is a lot less likely to flood than the sewer in image 1.

From this we can conclude that flash-flooding is more man-made than natural. These floods are very dangerous and can cause a lot of damage.

References

Holmes, Robert R. Jr. Johnson, Gary Waite P. Loyd A.  “The Great Flood of 1993 on the Upper Mississippi River – 10 Years Later.” USGS Fact Sheet May 2004. Web.

Sexton, Owen J. Drda, Wayne J. Sexton, Kenneth G. “The Effects of Flooding Upon the Snake Fauna of an Isolated Refuge.” Natural Areas Journal 27.2 (2007) : 133-144. Web.

Theiling, Charles. “The Flood of 1993.” UMESC Report Chapter 15. 1999. Web.

Images from http://mo.water.usgs.gov/

Black River Float Trip: http://www.missouricanoe.org/river-maps/black.html & http://mdc.mo.gov/your-property/greener-communities/missouri-watershed-inventory-and-assessment/black-river

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