Zone A Floodplains Suck
April 15th, 2015
“Your floodplain maps are wrong. They are likely so wrong that they are either costing you money or they are weakening your negotiation position when looking to buy or sell land.” said Andy Carter, co-founder of CivilE, LLC. “Review of a recent project showed 37.6 acres within the limits of the effective FEMA floodplain. A simple hydrologic and hydraulic analysis by CivilE revealed that only 17.6 acres were truly within the limits of the 100 year floodplain. This effort empowered the developer to proceed with closing on the land, knowing that he could produce the desired single family yield”
Floodplain maps provided by FEMA are used to determine flood insurance requirements and potential development restrictions. In the central Texas area, the designated 1% annual chance (100 year) flood zone primarily come in two flavors. The first is a ‘Zone AE’ floodplain which is established through the creation of a detailed engineering model. From this model, base flood elevations are determined and mapped showing the anticipated water surface elevation of the flood.
The second type of flood zone is ‘Zone A’ which is delineated on the published FEMA maps without the aid of a detailed analysis. Zone A floodplains are typically determined in just a few minutes by analysts working as FEMA contractors. The approximate Zone A floodplains are typically found on virgin lands in rural areas or the fringe of developing areas.
These quickly and sometimes crudely drawn ‘Zone A’ floodplains often incorrectly show the limits of the land encumbered by floods. Advances in technology including terrain modeling and model extraction can allow engineers to develop floodplain models to quickly determine the true location of the floodplain.
“In a typical 8 hour workday, CivilE leveraged LiDAR terrain data to develop a hydrologic model of a 1 square mile basin and develop a floodplain map of 1 mile of stream,” stated Mr. Carter. “Utilizing custom software written by our staff, we determined the Zone A floodplain was wrong and over 20 acres was actually out of the floodplain.” To revise the floodplain and remove flood insurance requirements, a LOMA (Letter of Map Amendment) request is still required to be submitted to FEMA. However, securing an engineer versed in floodplain modeling is advised when a property is under contract and encumbered with Zone A floodplain.
About the Firm
CivilE was founded by Larry Hanrahan, PE and Andy Carter, PE in September of 2013. Mr. Hanrahan received his B.S. in Civil Engineering from the University of Illinois at Urbana-Champaign, a Master of Science in Engineering, and an MBA from the University of Texas at Austin. He has more than 28 years of experience pertaining to site development and subdivision civil engineering in central Texas. Mr. Carter received his B.S. in Civil Engineering from the University of Texas at Austin. He brings 16 years of site design experience and was awarded "Young Engineer of the Year" in 2007.