Engineering Inc - January/February 2018 - 19

The federal standard for gauging the protection level of a
dam or levee is whether it can withstand a 100-year flood or a
1-in-100 chance of failure in any given year. That standard was
established 1973 when the National Flood Insurance Program
(NFIP) was mandated by the Federal Emergency Management
Agency (FEMA) to map all the floodplains in the U.S.
Yet there's an important nuance that goes beyond the physical
integrity of dams and levees and takes into account factors over
the lifespan of aging structures,
especially increased development
downstream and improved data
predicting natural disasters such
as hurricanes, floods and earthquakes, as well as national security
threats.
"Many dams were designed for
low-hazard or significant-hazard
potential," says Mark Ogden, a
technical specialist for ASDSO,
"but development has occurred
downstream since and now they're
high-hazard potential and need
to be upgraded to a different
standard."
The same situation exists with
many levee systems, says Steve
Verigin, a senior principal at GEI
Consultants, Inc. "It only takes
one point of weakness for a levee
to fail," he says. "Many started out
as low structures that protected
agricultural land and, over time,
have become higher structures that protect greater lives and
property and have not been reassessed to structurally meet those
demands."
The historic flooding in Houston from Hurricane Harvey
is a poignant, and painful, example of expanding urban development. The Buffalo Bayou is a 52-mile river that flows east
through the city and surrounding Harris County. The bayou's
flood control system is highlighted by the Addicks and Barker
dams. The reservoirs they created were cresting during Harvey,
forcing USACE to release water, which inundated surrounding neighborhoods. And even though the dams held up then, a
2009 report by the Houston Press found that Addicks and Barker
are the most dangerous dams in the U.S.
"There are 1 million people in the floodplain below the
Addicks and Barker dams," Halpin says. "When we built those
dams 70 years ago, there were about
10,000 people so that has to be part
of the discussion moving forward."
Much of that discussion will be
spearheaded by Houston's Storm
Water Action Team, reports Steve
Costello, an engineer who retired
from Costello, Inc., in 2015 and is
now the city's chief resilience officer,
or "flood czar," as he's often called.

As of October
2016, the U.S.
Army Corps
of Engineers
listed
90,580
dams, with
an average
age of 56
years, though
around 4,400
are over 100
years old

"The city has been experiencing stress-related redevelopment,"
says Costello. "We advocate for densification of the city, and
when you densify an existing area, you strain the infrastructure."
That infrastructure has required updating for years, and though
several initiatives have addressed needs, more needs remain, raising
vital questions around ongoing development. "Should developers
participate in improving the existing drainage problem, over and
above just the mitigating of this project?" Costello says. "Ideally,
the city would have money in advance to invest in infrastructure
for redevelopment, and we wouldn't have this issue." But the public funds aren't there, he says, and developers balk at footing the
bill. "We hope the redevelopment task force will address some of
these issues moving forward," Costello says.
A similar situation confronts communities around Sacramento, California, where a 42-mile levee system controls the
confluence of the Sacramento and American rivers. New Orleans
used to top the list of U.S. cities most at risk from river flooding, but it's been replaced by Sacramento, as noted in a recent
news report from National Public Radio (NPR). The risk in
the region is so great that in 2008, federal officials mandated
a building moratorium until the city worked on its levees. "It's
pretty scary when you think about it," Rick Johnson, director
of the Sacramento Area Flood Control Agency, tells NPR. "We
have more than 100,000 people living out there."
The cost of upgrading Sacramento's levees has been estimated
at $4.4 billion and would take nearly a decade more. Instead
of waiting on federal funds, the city tapped into state coffers
and raised local taxes. So far, 18 miles of the levees have been
improved, and the building moratorium has been lifted.
That solution exemplifies what's become a bizarre incentive to
continue urban development in flood-risk areas throughout the
country. This points to a basic problem the nation faces, says Jim
Murphy, a water resource project director for AECOM. "It may
appear that we reduce risk, but we do not eliminate it. By allowing development, it actually increases risk. Thus, we still build
where we shouldn't build," he says.
The reality, however, is that development is going to continue,
so efforts must continue to mitigate the risks of inevitable future
floods not only by investing to improve dams and levees but
also by addressing non-structural floodplain management. For
instance, FEMA has only mapped about a third of the floodplains in the country, which means that many people aren't
aware they live in a flood zone and thus don't purchase policies
from NFIP.
Communities and individuals need to better understand
their risk and what they can do to reduce the chance of
flooding, says Jeff Sparrow, senior vice president at Michael

"It only takes one point of weakness
for a levee to fail."
STEVE VERIGIN | GEI CONSULTANTS

JANUARY / FEBRUARY 2018

ENGINEERING INC.

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