From
Gristmill to Hydro Power:
Virginia's Dams
Virginia’s
relationship with its dams has come full circle.
While the 19th and 20th centuries saw a flurry of
dam building in the Commonwealth, the 21st century
is more likely to see a few dismantled.
In
fact, on February 23, 2004, thousands watched as
almost 650 pounds of explosives blew a 40-meter hole
in the Embrey Dam on the Rappahannock River near
Fredricksburg. Officials had decided the dam was too
expensive to maintain and blocked fish migration to
spawning grounds (“Tales of the Undamned, Removing
Barriers Doesn’t Automatically Restore River
Heath,” Science News, April 10, 2005.) The Embrey
is just one of about 500 small dams that have been
removed across the U.S. in the past three decades.
Such structures are usually dismantled because of
safety concerns, high maintenance costs or
environmental issues.
Dam
removal is a fairly recent trend in the U.S. and a
far cry from the glory days of the controversial
Tennessee Valley Authority. The federal agency began
building dams in the 1930s and 1940s, for flood
control and to bring electricity to the then-rural
South. Two of the TVA’s 49 dams, Beaver Creek and
Clear Creek, are located in the southwestern corner
of our state. Both were built in the 1960s.
Dam
building actually began in the Commonwealth in the
early 1800s, according to George Mason University
geography teacher, Charlie Grymes (Virginia
Places). The structures provided waterpower for
gristmills and factories. Such water-powered mills
helped transform Richmond into a major exporter of
flour in the Old Dominion’s early days. At one
time, five major dams existed on the James River. As
such structures developed, they served several
different purposes. Dams created canals for
transportation; harnessed hydropower for industries;
or provided drinking water for towns, cities or
counties.
Today,
there are more than 1,300 state-regulated dams in
Virginia, according to an April 2005 “Report of
the Ad Hoc Dam Safety Study Committee” submitted
to the Virginia Soil and Conservation Board. Most
are small; many are on private land. This number
does not include larger federal dams, such as the
TVA projects or the John H. Kerr and Philpott dams,
both run by the Southeastern Power Administration.
The John H. Kerr Dam is located on the Roanoke River
in Mecklenburg County and was built in 1952. The
Philpott Dam, built one year later, is on the Smith
River in Henry and Franklin counties. Both use
turbines to transform their impounded water into
electrical power.
Thanks
to Hurricane Katrina, we’ve learned a lot about
how water barriers are engineered and constructed.
Just as the levees of New Orleans were built to
withstand certain weather conditions (which
unfortunately proved inadequate for Category IV
Katrina), Virginia’s dams are judged on their
ability to withstand damage from extreme weather and
the dangers posed should they fail.
The
benchmark in dam safety is “probable maximum
storm,” which is a storm so intense it would
happen only every 500 to 10,000 years. For example,
Hurricane Floyd in 1999 created half of a
“probable maximum storm” by dropping 24 inches
of rain in 30 hours in the Franklin area. But even
experts can’t predict the consequences of severe
weather on dam structures. Katrina forced the
Association of State Dam Safety Officials, those who
inspect and certify the safety of our nation’s
dams, to move its September national convention from
flooded New Orleans to Orlando.
Virginia’s
regulated dams fall into four categories based on
their threat to surrounding communities should they
fail. A Class I dam would cause probable loss of
life and excessive economic loss downstream; a Class
II, possible loss of life and appreciable economic
loss; a Class III, no loss of life expected and
minimal economic loss; a Class IV, no economic loss
to others and no loss of life expected. As of a 2004
inventory, the bulk of the Commonwealth’s dams –
over 900 – were rated as Class III, although
as rural areas become more populated, they may be
reclassified Class II or Class I structures as more
and more people choose to live in harm’s way.
Dam
safety is serious business in Virginia. The Virginia
Department of Conservation and Recreation
administers a dam safety program mandated by the
1982 Virginia Dam Safety Act. It ensures that dams
are designed, constructed and maintained safely.
Another organization, the Virginia Lakes and
Watersheds Association even offers a Dam Awards
program in such categories as “Best Operated and
Maintained” or “Best Rehabilitated.”
Still
the state of Virginia’s state-regulated dams
garnered national attention several years back. At
the time, 40 dams needed repairs. According to an
article in a professional journal, U.S. Water
News, the director of Virginia’s dam safety
program was concerned that many individuals did not
know they were living or buying a home in dangerous
locations below dams. He explained that individuals
tend to adopt a “dry-weather mentality” and
don’t realize how dangerous a flood can be. A
probable maximum storm, he explained, “is a big
storm, but it’s a very realizable storm, and
that’s what worries me.” ("Virginia
Dams in Distress and Need of Repair,"
January 2002.)
Three
years later, a tsunami, hurricanes Katrina and Rita
and mudslides in Guatemala and New Hampshire have
proved the improbable does happen. Dismantling a dam
doesn’t seem so odd anymore.
NEXT:
Breaking the Codes: Virginia’s Multiplying Numbers
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October 3, 2005
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