14.4.2015 | Floodplain mapping
Putting risk on the map
Large and complex floodplains can now be mapped accurately
and cost-effectively in minutes – revolutionizing a job that once
took weeks.
The United States National Flood
Insurance Program (NFIP) provides
coverage for more than 5.5 million
policyholders and protects assets
worth an estimated $1.2 trillion.
Launched in 1968, it is one of
the biggest insurance programs
in the world.
As well as offering a lifeline to
millions of homeowners (standard
domestic insurance policies in
the US do not cover flood losses),
the NFIP plays a vital role in flood
prevention. To qualify for coverage,
participating communities must
agree to adopt planning policies
to reduce the risk of flooding.
Pinpointing where flood risks lie
depends on accurate mapping.
Production of flood maps –
known as FIRMs (Federal Insurance
Rate Maps) – is the responsibility
of the US government’s Federal
Emergency Management Agency
(FEMA). FIRMs carry statutory
weight and are used extensively
by local, state, and federal
government agencies, as well
as by insurance companies,
businesses, and property owners.
Mapping is carried out on a vast
scale; since the creation of the
NFIP, FEMA has undertaken more
than one million miles of mapping.
Atkins has played a leading role
in the NFIP since 1999, as a map
coordination contractor, mapping
contractor, and production and
technical services contractor.
Mapping the unknown
Flood hazard mapping is a complex
business. Unlike conventional
cartography, which deals with
visible and easily-measured
landscape features such as roads
and hills, flood mapping is
concerned with transient, relatively
rare events. FEMA’s benchmark is
the 100-year flood – a flood that
has a one percent chance of
being equaled or exceeded in
any given year. In many cases,
the areas being mapped have not
experienced such a major flood
in living memory.
To determine the extent of the
floodplain, engineers must carry
out a detailed analysis using a
range of data sets. These include
14.4.2015 | Floodplain mapping
discharge rates (the volume and
speed of water moving through a
river), river channel characteristics,
and topography. By combining
this and other data, it’s possible
to plot the floodplain with a high
degree of accuracy. But it’s
painstaking work that involves
enormous amounts of data.
“Conventional mapping tools
are accurate, but they’re not
quick,” explains Leo Kreymborg,
senior engineer at Atkins. “A lot
of the steps have to be done by
hand, so you’re bringing layers in
one at a time and entering data
manually. It’s a very timeconsuming process.”
Two major policy changes
governing the way US flood
maps are produced and supplied
brought the need to find a quicker
and more accurate floodplain
mapping method into focus.
The first was FEMA’s Flood
Map Modernization program,
a presidential initiative that
heralded the shift from paper
to digital maps. This provided
an opportunity to not only
upgrade the way maps were
stored and shared, but also to
extend coverage and to review
the accuracy of the information
held on existing maps.
The second was the adoption
of a stringent new accuracy
requirement known as the
Floodplain Boundary Standard
(FBS). Introduced in 2005, the FBS
imposed strict new rules on the
agreement between topographic
data and the floodplains derived
from that data. “The FBS
effectively eliminated several
previously common and acceptable
methods of creating flood maps,
and required vast amounts of
modelling and re-modelling of
floodplains,” says Michael DePue,
vice president at Atkins.
Back in 2005, digital techniques had
already transformed conventional
mapmaking, but little progress had
been made in streamlining the
floodplain delineation process.
The tools available for flood
mapping still required considerable
engineering setup and analysis time
for each mile studied.
Could there be a better way to
create flood maps? Kreymborg
believed there was. He set about
creating a tool to carry out simple
floodplain analysis using higher
levels of automation.
The result – the Rapid Floodplain
Delineation (RFD) tool – was a
game changer. “Once we had
RFD, we were several times faster
overnight – doing not only the
same quality of work, but a better
quality of work,” says DePue.
“The technology jump with RFD
was really substantial.”
Kreymborg’s next move was to
devise a method for calculating
ineffective flow areas on the fly and
to modify them through a series of
increasingly accurate computations
– a feature of RFD that remains
unsurpassed to this day.
RFD’s capabilities soon began
to attract attention. Following
discussions with FEMA Regions
and the States of Michigan,
Minnesota, and Georgia, the RFD
tool was used to map thousands
of miles of floodplains. “Today, if
you are looking at a flood map in
any of these states, there is a high
probability that the data on that
map was developed with RFD,”
says DePue.
Mapping for growth
As well as delineating floodplains
faster, RFD is bringing down the
cost of mapping. Atkins’ figures
– based on similar contracts
carried out before and after RFD
was adopted – suggest that the
cost of floodplain mapping with
RFD is between 50 and 75 percent
lower than it would be using
conventional methods.
RFD’s low cost puts accurate
flood mapping within the reach
of previously uncharted regions.
An early demonstration project
covering the Murray-Darling
basin in southeastern Australia
underlined the ability of RFD
to provide cost-effective results.
“Large parts of the world have
flood analysis needs, but relatively
low population densities, making
it is difficult to justify the return
on investment,” says DePue.
“Prior to RFD, you didn’t have a
lot of good choices in areas like
that, whereas now you’re really
using the same method as
you would in a very densely
populated area, just with a
lower level of input information
and for a fraction of the cost.”
This matters because a lack of
information about flood risk means
14.4.2015 | Floodplain mapping
that in many parts of the world,
potentially viable areas, are
effectively off limits from an
economic development perspective.
Without reliable data about flood
risk, insurers won’t insure, lenders
can’t lend, and businesses are left
wringing their hands.
“By using RFD, you would be
able to create a defensible and
measures that aim to capture
and retain urban rainwater
runoff before it reaches rivers.
Atkins recently completed such a
project for the US Environmental
Protection Agency (EPA).
“We were able to make some
assumptions about how green
infrastructure would affect the
runoff and then plug those new
“Conventional mapping tools
are accurate, but they’re not
quick. A lot of the steps have
to be done by hand, so you’re
bringing layers in one at a time
and entering data manually”
scientific basis for providing
insurance,” notes DePue. “You
would also be able to identify
new areas for investment.”
As well as charting new areas
quickly and accurately, RFD
can be used to get more out of
existing investments in mapping.
numbers into the hydraulic
models to get floodplains,”
explains Kreymborg. “So we’d
have a before and after floodplain,
with green infrastructure and
without. By comparing those two
floodplains, we were able to come
up with estimates of flood hazard
losses avoided in large events.”
“For FEMA, we’re reexamining
existing studies to determine
whether they’re still valid or not,”
says DePue. “The speed of RFD
allows you to look at ‘what if’
scenarios. What if the discharge
were to drop 20 percent? What
would that do to the floodplains?
Over large areas, that’s usually
very difficult to calculate, but
RFD makes it much easier.”
RFD represents a major technical
achievement, and its contribution
to the understanding of floodplains
is significant. Kreymborg, though,
is modest about his brainchild.
RFD’s what-if capabilities are
also helping to evaluate green
infrastructure – anti-flooding
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“We had work that needed
to be done, and it seemed like
it was taking too long,” he says.
“So we came up with a better
way to do it.”