FLOOD03407

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Stormwater Management in the United States - A Study of Intsitutionl Problems, Solutions and Impacts
• Date: 9/1/1980
• Prepared By: Office of Water Research and Technology
• Floodplain - Doc Type: Educational/Technical/Reference Information

political and physical impacts of stormwater management programs and facilities
were to be identified, studied and evaluated.

The purpose of the study was to assemble, in a comprehensive report, information
that can be used by local public officials and management personnel for developing
and operating effective stormwater management programs and facilities. The study
goal was to provide insights into stormwater management processes, and provide some
of the knowledge needed to protect, preserve and enhance the man-made and natural
environments in urban and metropolitan areas.

Stormwater Impacts

Among the usual effects of urbanization are increases in both surface runoff
flows and volumes--the amounts being dependent largely upon the land uses before
and after the land is developed. For example, it would not be unusual for the peak
discharge from a small undeveloped catchment, say 100 acres, to increase by a factor
of six after development. Serious and costly damages and losses usually follow if
the excess flows are not carefully collected, transported and released without ex-
ceeding the capacities of downstream drainage systems. The physical problems re-
sulting--usually characterized by difficult and expensive solutions--can be grouped
in four categories: flooding, soil erosion, sedimentation, and pollution of land
and receiving waters. In places where groundwater constitutes the principal source
of municipal water supply, "interference with groundwater supplies" is a fifth
problem type.

The physical problems and physical impacts of stormwater can be attributed to
"Acts of God" combined with human ignorance, shortsightedness, greed and indiffer-
ence. Understandably, streams, lakes and oceanfronts provide many positive attri-
butes and advantages to homebuilders, homeowners, industry and commerce. However,
the human and economic losses of the last century could have been considerably less
had foresight and good judgement prevailed as towns and cities were established and
expanded.

Impact of Flooding

Since the start of the twentieth century, the greatest loss of life from
flooding in the United States occurred at Galveston, Texas (in the year 1900) when
an estimated 5,000 persons were killed in a hurricane. Eleven years earlier, in
1889, a flash flood in Johnstown, Pennsylvania claimed 2,209 lives. During ensuing
years, floodwaters have claimed huge numbers of lives, both human and animal, in
most parts of the Country. As recently as 1977, flash floods in Toccoa Falls,
Georgia and in a highly urbanized part of Kansas City, Missouri claimed 29 and 85
human lives, respectively.

Government estimates are that more than 35 million persons in the United States
either live in floodplains or are affected by floods in an area totaling about 50
million acres. This is equivalent to a strip of land 28 miles wide extending across
the Country, coast to coast. Much of this land is urbanized. Apparently, few local
governments maintain reliable records of damages, losses and costs. Although aver-
age annual flood damages in the United States are thought, by 1980, to exceed $4
billion dollars,(l) stringent and absolute prohibition against floodplain occupancy
and erection of permanent structures in flood prone areas are enforced in relatively
few urban areas. Accordingly, reduction of property values, other economic losses,
personal injury and loss of lives continue, relatively unabated, and the lessons
learned are usually soon forgotten--exept by those who suffered most. Besides

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