Mapping Non-Levee Embankments in IndianaPosted on Aug 28, 2015
The Geoinformatics team at The Polis Center is renowned for its expertise in hazard risk mapping, analysis, and mitigation planning. Over the years, we have successfully developed GIS based Risk Assessments and DMA 2000 Mitigation Plans and led FEMA Risk MAP planning and mapping activities throughout Indiana. These projects identified flood risks often associated with dams and “levee like” structures.
We’re excited to share that we are getting ready to wrap up a multi-year project, “Mapping Non-Levee Embankments in Indiana.” This project is a joint effort between the Indiana Silver Jackets, IMAGIS/Indy GIS, Indiana Department of Natural Resources, and SIU Geography. Recently one of our GIS analysts, Matt Riggs, shared a presentation on mapping non-levee embankments during FEMA’s CTP training. FEMA selected this research as a “best practice” and will soon feature it on the CTP website.
What are Non-Levee Embankments? (NLEs)
- NLEs are elevated linear features adjacent to waterways and within the floodplain.
- They are typically man-made and include agricultural embankments built by landowners and road and railroad embankments banks.
- They are levee-like structures, but are not certified or engineered to provide flood protection.
The National Committee on Levee Safety estimates that the location and reliability status of 85% of the nation’s non-levee embankments is unknown. In Indiana, majority of NLEs are unidentified and not maintained. NLEs impose lateral constraints on flood flows, reducing the floodplain storage capacity and increasing the flood velocity. As a result, downstream flooding and the potential for stream erosion can increase. As such, NLE’s can give a false sense of security and protection to the people residing near NLEs. For these reasons, it is extremely important to map where these features are located.
It was important to accurately map the levees and non-levee embankments across Indiana. The team performed a literature review on existing approaches and developed new approaches before narrowing the methods to manual digitization, a semi-automated slope-derived method, and a semi-automated maximum curvature method. The team developed a set of characteristics that helped define NLE and distinguish them from natural berms or spoil banks.
- Within or partially within the buffered 100 year floodplain (DFIRM)
- At least 100 yards (300 ft.) in length
- At least 1 meter (3 feet) in height
- At least 20 degrees of slope on either face
Thankfully a statewide LiDAR dataset existed making this project possible. The high-resolution LiDAR data was used in conjunction with multiple GIS data layers including digital elevation models (DEM) and slope maps. This allowed for accurate measurement of potential embankments to determine whether they met the minimum characteristics. These were then assigned attributes that included their type, height, length, elevation and slope.
Mapping NLEs generated valuable data that is helpful in providing a holistic view of flood problems in Indiana. The data collected is being used by the Indiana Department of Homeland Security, and Indiana Department of Natural Resources to analyze flooding problems and identify mitigation strategies. To request data or more information about the project, please contact John Buechler at firstname.lastname@example.org.