RISING TIDE: The Great Mississippi Flood of 1927 and How It Changed America.<i> By John M. Barry</i> .<i> Simon and Schuster: 524 pp., $27.50</i>

The sea is around us, T.S. Eliot wrote, but the river is in us. Flowing through Eliot’s mind was the majestic Mississippi on whose banks he was born; to him, it was a “strong brown God--sullen, untamed and intractable.”

Due in no small measure to Eliot, Mark Twain and Oscar Hammerstein, the Mississippi became the river of American consciousness and the river in us all. The passionate eloquence it has inspired in literature renders any attempt to add to the treasure a risk for only the best and boldest writers.

In “Rising Tide,” an ambitious history of the Great Mississippi flood of 1927, John M. Barry takes on the river once more from the muddy and treacherous ground of social and political commentary. And he ends up awash in the same raging waters of race that have kept Twain controversial for more than a century.

Not only does Barry provide a marvelous chronicle of the world’s greatest flood since Noah, he also meticulously mines the residue of its wake for both the relics of a society washed away and the roots of a new one spawned. The story that emerges is the unavoidable truth of the South--that throughout its history, both the great Mississippi and the issue of racial inequality have been an inseparable and insuperable divide.

To appreciate the magnitude of Barry’s challenge is to understand the magnificence of the river itself, (made possible through a superb recount of the battle between two 19th century engineers, James Eads and Andrew Atkinson Humphreys, over whether the river could best be controlled by levees and jetties to hold the water in or through cuts or crevasses that allowed it to escape.)

In 1927, The Mississippi River was 4,300 miles long. It snaked seaward through the American heartland in a continual series of S curves that sometimes approach 180 degrees. “The Mississippi River never lies at rest,” writes Barry. “It roils. . . . The collision of river and earth at these bends creates tremendous turbulence; currents can drive straight down to the bottom of the river, sucking at whatever lies on the surface, scouring out holes often several hundred feet deep.”

Among the river’s unique properties is that for the final 450 miles, the riverbed lies below sea level, in some places by as much 170 feet. This means the water at the bottom has no reason to flow at all, allowing the water above it to spill over itself, creating a wild and random tumbling effect that is magnified by high water. Held in place by the gorge in the Commerce hills that dissect Midwest America and by levees and artificial jetties at its mouth in the Gulf of Mexico, the Mississippi between these points “writhes like an imprisoned snake.”

The scientific struggle to control the river benefited mightily from the development of bridge-making technology and contributed to the popularization of steel construction techniques and the inspiration of Louis Sullivan’s form-follows-function architectural philosophy. But in spite of this technology, the Mississippi remained unchecked at the turn of the century. And as it rolled, speeding mountains of earth toward the Gulf of Mexico, depositing thick, heavy sediment along its twisting banks, it created natural levees--some 40 feet high--and, beyond them, the Mississippi Delta--”a lush saucer” of a flood plain, 7,000 square miles.

It was on this rich frontier--”wild as any jungle in Africa” and “lined with gold the color of chocolate, gold that was not in the earth but was the earth”--that the river and the people along its edge fought the epic and heretofore undocumented struggle that is this book’s reason for being. For there, in the heart of the delta, at the city of Greenville in Mississippi, the mighty Mississippi encountered and ultimately defeated its most stubborn and indomitable opponent: the family of William Alexander Percy, who had been both its enemy and lover for more than a century.

At 28, Percy had returned from the Civil War “white-haired aloof and steely-eyed” and bearing the nickname “the Gray Eagle.” While the rest of the nation enjoyed the gilded age of industrialization and vast Wall Street fortunes, Percy’s rural South remained largely poor and unsettled. White landowners had no cash, poor black laborers had no land and enmity simmered between them. But Percy saw in the rich soil of the levees the foundation for the reconstruction and economic salvation of the postwar South. He rebuilt the levees that had been cut by Ulysses S. Grant as a war tactic. And his “sharecropping” idea, in which white planters shared their crops with the black workers, brought blacks to the delta in droves and created the plantation economy.

In spite of his efforts to transform the regional economy, issues of race and the threat of a forever-unruly river still plagued the Percy family’s dream of a peaceful, elite-controlled, black worker-driven agricultural factory half a century later. With demagoguery and racial hatred on the rise, blacks were heading for Northern cities. Percy’s son Leroy, a former U.S. senator, saw this exodus of the only available labor as a death knell for Southern agriculture. His brave public demand for education and equality for blacks had a moral base, but the success of his idea stemmed from its economic practicality. The industrial development of the South, he argued, demands fair treatment of the Negro.

Although the Percys’ plantation society was doomed anyway by racial fear and hatred, it was swept to oblivion in a matter of days in the spring of 1927 by the greatest flood in the nation’s history. And from this enthralling account of the flood and a companion tale of how the New Orleans elite protected themselves by dynamiting the levees and flooding two poor nearby parishes comes Barry’s most important contribution to history and literature--an enhanced understanding of the role of both nature and government in the social and political development of man. The scope of the injustice is matched only by the magnitude of the disaster. At the peak of the big 1993 Mississippi flood, water flowed into the lower basin at the rate of 1 million cubic feet per second. But in the spring of 1927, the flood crest rushed toward the delta at 3 million cubic feet per second.

“There is no sight like the rising Mississippi,” writes Barry. “One cannot look at it without awe, or watch it rise and press against the levees without fear. It grows darker, angrier, dirtier; eddies and whirlpools erupt on its surface. It thickens with trees, rooftops, the occasional body of a mule. When a section of the riverbank caves into the river, acres of land at a time collapse . . . with the great cracking sounds of heavy artillery.”

In an effort to harness such power, the white delta establishment, under the tentative direction of Percy’s son Will, brutally rounded up and enslaved once more the black citizens of the South. Thousands were conscripted at gunpoint and trucked to the levees to fortify and raise them but to no avail. The power of a mass of water and debris several miles wide, 100 feet deep and moving at 9 mph punctured the levee at Mounds Landing, near Greenville, forming the largest single crevasse ever to occur anywhere on the Mississippi. It flooded an area 50 miles wide and 100 miles long with up to 20 feet of water, submerging houses 75 miles away in Yazoo City. Nearly 200,000 people were driven from their homes, many of whom never returned. Hundreds, mostly black men, died. And those who did not drown were put to work ferrying supplies to the white landed gentry and feed to their livestock.

The physical devastation was nothing, however, compared to the long-range political and social consequences of the flood. Herbert Hoover, secretary of commerce in the Calvin Coolidge administration, was placed in charge of the cleanup, the vast network of refugee camps set up by the Red Cross and the economic revitalization of the area. And the reputation bestowed upon him by an adoring press as “the great humanitarian” won him the Republican nomination for president a year later. But the reputation, Barry argues, was a fraud. And it was Hoover’s deliberate cover-up of the scandalous treatment of Mississippi blacks both before and after the flood that allowed him to defeat Democrat Al Smith in the 1928 election, an election aided by the support of black Republican voters and some of their most prominent leaders. Hoover had exploited Southern blacks in ways even more devious than the Percys had.

Ironically, Hoover’s federally guaranteed loan program for rebuilding the delta and the subsequent federal assumption of responsibility for controlling flooding along the Mississippi signaled a liberal change in direction in Washington that presaged the New Deal philosophy of Franklin Roosevelt as a means of dealing with the Great Depression.

These were small steps of change directly attributable to the flood, Barry concluded, but they were part of a far larger, more ambiguous and less tangible legacy. “Like the blues music born in the delta, languid and rolling at the same time, it penetrated to the core of the nation, washed away surface, and revealed the nation’s character. Then it tested that character and changed it” as it had the landscape, spreading one more layer of rich topsoil up on the land.

In no small measure, Barry has done the same, layering history with another rich deposit of passion and truth.