Scientists Release Flood of Analyses As Mississippi Waters Move North
BOSTON — AS colder weather spreads over the Midwest, the record-breaking Mississippi flood waters have receded. Along with the massive cleanup in eight states comes a different kind of flooding - an increase in the voices of scientific analysis explaining how and what the flood did to earth and people. This includes an answer to the question, ``Where did all that water go?''
According to scientists at the University of Miami, the muddied flood waters poured into the Gulf of Mexico and turned greenish. Measuring at one point 15 nautical miles wide and nearly 70 feet deep - the mass flowed past the Florida Keys on the current.
Narrowing and lengthening, the waters are now moving up the East Coast in the Gulf Stream and have been seen as far north as North Carolina.
``The flood waters also passed through the Keys,'' says John Wang, an applied marine physicist at the University of Miami in Coral Gables, Fla., ``and into Florida Bay. Whether this has ever occurred before, nobody really knows, but this is the first it has been observed. The flood waters stayed there about two weeks.''
How unprecedented was the volume of water that filled the Mississippi to overflowing? The official estimate of water flowing past St. Louis at peak was 1.8 million cubic feet a second.
Scientists don't know if any long-range effects might occur to marine life in Florida Bay or the Atlantic similar to what happens at the point where the nutrient-rich river enters the Gulf.
Every summer for years a hypoxic condition (decrease in oxygen) has existed at the mouth of the Mississippi, covering an estimated 2.4 million acres. Environmentalist call it a ``dead zone'' because ocean marine life can't survive in the sediment-heavy fresh water, which increases the amount of algae. This year scientists estimate that it is twice its usual size.
But all river water eventually becomes diluted by sea water. University of Miami oceanographer Rod Zika says initially the flood waters found off Florida had reduced the salinity of the seawater, carried freshwater microorganisms, and contained hydrogen peroxide (from fertilizers) at 300 percent higher than normal - all unusual conditions.
Meanwhile, at the annual meeting in Boston of the Geological Society of America, James Knox, a geographer at the University of Wisconsin at Madison, suggested that the flood was linked to the greenhouse effect.
``If current trends in emissions of atmospheric greenhouse gases continue,'' he says, causing modest changes in climate, ``the frequency and magnitude of floods [in the Mississippi Valley] could increase.''
His studies of geologic records of the Mississippi Valley indicate that small shifts in average temperature, of 1 degree centigrade or less, and changes in average annual rainfall of 10 percent to 20 percent, could drastically alter flood patterns.
``What I've found,'' he says, ``is that the probability of events being the same from year to year - a key assumption in standard flood-prediction methodology - is not very likely because of climate changes.''
If Mr. Knox and a handful of others are right, the flood statistics used by the government and insurance companies to calculate the risk of floods are inadequate in establishing probabilities because small climate changes - thought up to now nearly impossible to predict - are not included.
On flood control, Gary DyHouse, Army Corps of Engineers hydrologist, told a panel discussion at the annual meeting that the string of federally built levees along the Mississippi did not ``straitjacket'' the river and contribute to the flooding, as environmentalists have charged.
``They didn't fail,'' says Mr. DyHouse. ``They weren't high enough. Over 78 percent of the private levees were breached or topped,'' he says, ``and 17 percent of federal levees failed.''
He also said that even if the river had had more wetlands to soak up the water, the levees wouldn't have succeeded in reducing flood waters, as environmentalists have also maintained. But Timothy Searchinger, an attorney for the Environmental Defense Fund in New York said later DyHouse's assertions were more ideological than scientific.
``Much of this needs further analysis,'' he says. ``The Corps has a vested interest in levees. One of the reasons that fewer federal levees failed is that weaker, smaller levees failed first and took the pressure off the stronger ones.... As for wetlands, the loss over the years is as high as 85 percent in some areas. That is an enormous loss of storage capacity.''