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

Erosion and Sedimentation Problems

In some urban places, erosion of land by stormwater runoff, and the accompany-
ing sedimentation, are serious and costly problems. Runoff flowa denude valuable
land and huge quantities of sediment are often deposited regularly on downstream
floodplains and in receiving streams. In the Potomac River at Washington, D.C., 20
percent of the total sediment is said to come from upstream "urban" areas that com-
prise only two percent of the total upstream tributary drainage area.

Fairfax County, Virginia is an example of an urban county where such problems
are prevalent and serioua. Eroded soil from Fairfax County produces sediment in
the Occoquan River, the County's principal source of municipal water supply. The
sediment is also deposited in the Potomac River and Chesapeake Bay, causing naviga-
tion problems and water pollution. Statistics indicate that farm land near Washing-
ton, D.C. having an annual soil loss of 50 tons per square mile can increase to
50,000 tons annually when the same land is developed.O)

Pollution Problems from Combined Sewers

Many metropolitan areas in the United States experience serious pollution and
flooding problems from combined sewer overflows and treatment plant by-passes.
Chicago's 4,200-mile combined sewer system, serving all of the City and several out-
lying cities, produces overflows frequently--sending sewage waters into basements,
streets, local waterways and Lake Michigan.

San Francisco's combined sewer system, serving 24,000 acres of the City and
County, has about 46 "overflow-days" per year. Estimates of overflow volumes show
that about 4 billion gallons of raw sewage are spilled into San Francisco Bay
annually, and about 2 billion gallons are discharged into the Pacific Ocean. A
masterplan(2) has been prepared to decrease the volumes and frequency of spills,
and initial construction work has begun.

Boston is another ocean city that has an extensive combined sewer system. About
17,000 acres of the City and 6,700 acres in neighboring communities spill untreated(3)
sewage into Boston Harbor and Dorchester Bay. Preliminary plans have been prepared
for the construction of a system of deep, underground tunnels for collecting sewage
and piping excess flows 45,000 feet out to sea, during wet weather. The 20-foot
diameter conveyance pipe would discharge the sewage at its terminus, through diffu-
ser pipes, into the ocean. The 200:1 dillution ratio is deemed satisfactory for
meeting water quality standards.

Cleveland, Ohio is another large City that has serious problems with combined
sewer overflows. Like many cities on the Great Lakes, Cleveland has much heavy
industry. Lake Erie has been the principal victim of Cleveland's wet-weather sewage
discharges. Beaches had to be closed to body contact, and commercial fishing had
to be prohibited in the 1960's because of the human health problems associated with
eating Lake fish. The Lake was practically devoid of many species of fish, and Lake
Erie was termed a "dead" lake. However, with progress made by Cleveland and other
American and Canadian cities bordering this fresh water body, fish life has reap-
peared and some commercial fishing is now permitted. But, Cleveland and other
cities around Lake Erie face huge tasks in planning, engineering, construction and
financing to restore the Lake to an acceptable condition.

Cincinnati, Ohio is an example of a large, inland, "river" city having an exten-
sive system of combined sewers with the associated water pollution problems. Efflu-
ent from the sewage treatment plants and sewage overflows pollute the Ohio River

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