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The NSM is a computer simulation of how water flowed in South Florida before man intruded. In a system as vast as the Everglades, where a change in one place can have dramatic repercussions elsewhere, the only way to understand the impact of proposed engineering projects is by using such models. The NSM tries to answer three central questions about the Everglades as it was 100 years ago: How much water flowed? What was its path? How deep was the water in different parts of the system at certain times of the year? Policymakers presenting the plan to Congress hope that returning the water to century-old patterns will restore the ecosystem of that time as well.
But the modelers fear their creation is being misused to compensate for a lack of information and to dodge hard truths about what needs to be done. Some scientists, environmentalists, and hunters believe the current plan pays more attention to water levels than to the way the water should flow. They believe the flow of water at specific times of the year is the key to a thriving wildlife population. They argue that policymakers are really concerned about water supply and development, and not actually about restoring the Everglades.
"They are not thinking of it as an ecosystem," complains Jack Moller, a board member of the sportsmen's group the Florida Wildlife Federation. "It is all highly speculative." Moller thinks planners have not allowed sufficient land for water storage at the top of the remaining Everglades.
Even the model's original inventor is troubled.
"The Natural System Model was designed as a compass, not a blueprint," insists Tom MacVicar, who largely created the first version of the NSM while a senior engineer with the water management district in 1988.
The glowing computer screen pulsates red and blue. The colors expand and contract as they wash over identical maps of South Florida that flank either side of the monitor. In the middle a display steadily ticks through the months of each year beginning in 1965 up to 1995, and then over again in an endless loop. A pause at any given date freezes the ebbs and flows of this bizarre form of time-lapse imaging.
The colors on the two maps identify water (and its depths) as it flows from Lake Okeechobee south to the Florida Bay. The map on the left is version 4.5 of the Natural System Model. It shows how water would move in South Florida with the topography and vegetation of a hundred years ago -- in other words, with no human impact -- but using the rainfall patterns of the past 30 years. (Modelers can't estimate what rainfall amounts and frequencies were, consistently, throughout the system a century ago.)
On the right side of the screen, the map shows South Florida as it stands today, cities, canals, and levees included. This is the model of the current managed system. The South Florida Water Management District uses this modern-day tool of hydrologists to determine how water gets distributed throughout South Florida.
In both systems different volumes of water move through the Everglades depending on whether it is the wet or dry season. The water's movement in the model makes the system appear to breathe. But the real Everglades does not move as quickly as the pulsations on the screen. And before canals hurried water out to sea, the flow of what Marjory Stoneman Douglas called the "river of grass" was so slow and languid through the saw grass prairies as to be almost imperceptible.
The elevation of Lake Okeechobee at the top of the Everglades was about twenty feet above sea level. On its 100-mile journey down to the tip of the peninsula, the land sloped, on average, only about two inches per mile. (Imagine a long pane of glass tilted slightly with a thin sheet of water flowing down it.) During each wet season, rainfall increases water levels. The Natural System Model shows that in the untouched Everglades, water from one wet season reached Florida Bay just as the next year's wet season was beginning. The result was constant water movement, and in most years, constant water coverage. Today the water is largely funneled or trapped, and not allowed to flow in one uninterrupted sheet as it once did. The Everglades is now frequently drier in the dry season and wetter in the wet season.
The two representations of the river of grass are running on the desk of Jayantha Obeysekera, the water management district's chief modeler. Obeysekera oversees a staff of roughly 25 hydrologists, mathematicians, and engineers. The computer is one of two in his corner office in the warrenlike maze of rooms and cubicles in West Palm Beach. On the wall in back of his desk is a quotation from Albert Einstein: "Equations are more important to me, because politics is for the present, but an equation is something for eternity."
The Natural System Model is unique, and Obeysekera and his crew are on the frontiers of the science of computer modeling. Most models are designed to show decision-makers how the future might appear, not resurrect the past.