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14 Apr 2015
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.
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 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 time-consuming 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.
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 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 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.
“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’s what-if capabilities are also helping to evaluate green infrastructure – anti-flooding 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 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.”
RFD represents a major technical achievement, and its contribution to the understanding of floodplains is significant. Kreymborg, though, is modest about his brainchild.
“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.”
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