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M. Lorraine Tighe, PhD
M. Lorraine Tighe, PhD
Dr. Tighe has a Ph.D. in Earth Sciences, a graduate degree in Remote Sensing and GIS, and a B.Sc. in Physics and Geology. Dr. Tighe has delivered lectures ranging from a half day workshop to a 4 week training program to over 2000 participants in USA, Canada, Jamaica, Brazil, Ecuador, Honduras, … More »

Accuracy of Flood Modeling?

November 12th, 2013 by M. Lorraine Tighe, PhD

Flood inundation models provide predictions of the depth and extent of a potential flood. This information is then used in the assessment of risk to life and property in the floodplain (e.g. creation of hazard and risk flood maps), and to develop mitigation and restoration strategies. We have seen over the past decade significant advances in flood inundation modeling due to advances in hydrological modeling software coupled with the availability of more accurate elevation data. But how is the accuracy flood hazard and risk maps established?

The data requirements for any flood inundation model start with a digital elevation model that represents the elevation of bare ground features and is often referred to as a digital terrain model or a DTM. The vertical accuracy of DTMs is often used as a data requirement for use in flood hazard and flood risk assessments. Different nations have different accuracy requirements for DTMs to be used in flood modeling.

Using guidelines put forth by FEMA, Intermap Technologies® has been able to establish the regions where the NEXTMap® data meet FEMA requirements as a DTM dataset to be used for floodplain mapping across continental USA. NEXTMap DTMs satisfies FEMA’s Risk MAP requirements for the majority of the United States lower 48 states. In accord with FEMA’s standards for LiDAR and other high-quality digital topography datasets, the NEXTMap DTM data meets the decile requirements for accuracy and density for the low and medium decile watersheds, as illustrated in this map.

Flood Mapping

The NEXTMap DTM is hydro-enforced to ensure structures over water bodies (such as bridges) are removed, water surfaces are flat, and watercourses flow downstream. These DTMs are then used to derive:

    • county or statewide watersheds
    • flood risk areas surrounding critical floodplains
    • isolated areas that largely have low flood risk, but may have population clusters with significant risks
    • other areas in critical need of map updates where funding is limited

But what are the standards for elevation data used in the creation of flood maps in other parts of the world? How do we properly validate flood maps in other parts of the globe?

To read FEMA’s Procedure Memorandum No. 61 – Standards for Lidar and Other High Quality Digital Topography, visit:

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