In the New World, man’s influence on the natural dynamics of flooding began in earnest
shortly after the pilgrim’s landing at Plymouth Rock. Settlers immediately began to alter the
landscape of their surroundings. Forests and native vegetation were cleared to make way for
agricultural fields. Trappers were one of the single most influential groups of pioneers. Beaver
populations, which had constructed and maintained millions of dams, were harvested en masse
for their pelts (Hey and Philippi, 1995). Empty dams were cleared to facilitate navigation and
lower surrounding water levels, thereby removing a powerful hydraulic control and huge
reservoir system. To compound the problem, land that was naturally inundated was cleared for
farming, further elevating conveyance rates. Structural flood control was used to protect newly
claimed lands and as a response to the artificially strengthened floods.
Today, anthropogenic influences are recognized to extend beyond the realm of flood
control structures. In many instances, man creates hazards that rival the most dangerous and
bizarre of natural flood conditions. Often man’s influences on natural systems are long-term and
go unrecognized until conditions gradually deteriorate to critical levels. Examples of this include
the transport of chemicals in floodwaters, creation or aggravation of extreme events, and dangers
associated with social works that are not related to aquatic systems.
Water quality is of key importance to man and nature. Flooding tends to reduce water
quality by introducing large amounts of eroded materials. By transforming low lying areas to
farm lands, man has removed much of the floodplain vegetation and wetland areas that act as
natural stilling ponds, sediment intercepts, hydraulic sponges, and erosion protection.
Compounding the problem, large quantities of chemicals are flushed into the surface water by
overland flows. Chemical loading and poor water quality can have long and short-termconsequences. Point sources for chemical introductions include inundated municipal and
industrial sites, including wastewater treatment plants, chemical processing and manufacturing
centers, and disposal or holding areas (Goolsby et al., 1993). The largest non-point pollution
source is runoff from agricultural land.