Hydrology and its effects on distribution of vegetation in Congaree Swamp National Monument, South Carolina

Congaree Swamp National Monument preserves a large stand of old-growth southern bottomland hardwood forest on the flood plain of the Congaree River. The distribution of vegetation types in the Monument is controlled by duration of saturated soil conditions during the growing season, which is related to duration of inundation by the flooding river. During dry periods upland streams fed by seepage from shallow and deep aquifers supply water to the flood plain, and the potentiometric gradient in the flood plain slopes toward the river. During floods river water flows into the flood plain through breaches in the natural levee, inundating as much as 90 percent of the Monument an average of once per year. During floods the potentiometric gradient briefly slopes away from the river. The frequency of large floods has decreased slightly since completion of Lake Murray Dam in 1929.