[EM GIS Interest Group] Real-Time Flood Mapping Info Results

[STOELB Daniel * OEM]

Good morning EMGIG,

As a follow-up to our request we had last month, I did want to share with you what we'd heard from you all regarding a flood mapping capability. As some of you may know, we were taking a look at a possible solution regarding real-time flood mapping - to where we can view real-time estimations of flooding extents. Prior to going further down this road, we did want to see what you were all using for solutions to address this for your agencies/jurisdictions. We have consolidated the responses to these questions based upon which agencies had an existing capability. Please see below results (in red) from our survey (and web links for reference):


  *   Do you currently model flood extents outside of the typical FEMA national flood hazard dataset for active flooding?
     *   Salem: yes, we have some static flood inundation maps outside the FEMA NFHL for various flood return intervals (10, 25, 50 year) that are based on a 48 hour design storm rainfall distribution.
     *   National Weather Service: the NWS is slowly rolling out new flood inundation services for the whole continental US (info link<https://www.weather.gov/news/232609-experimental-flood-inundation-maps>). NWS Portland and NWS Pendleton are part of the group of offices for which flood inundation mapping will be implemented by fall 2024 (storymap link<https://storymaps.arcgis.com/stories/c7ae8422207241b5873fff38a22cf66b>). Inundation layers will be generated near real-time for observed and forecast river levels at or near flood stage and higher. Inundation modeling will be based on streamflow forecasts either from the Northwest River Forecast Center or the National Water Model. Flood inundation maps will be available to view on the new National Water Prediction Service (what is replacing the Advanced Hydrologic Predication Service, scheduled to be operational in late March 2024) and will also be served as GIS layers.
     *   US Army Corps of Engineers: the Corps has a suite of models for streams that are regulated by reservoir operations and can offer modeling capabilities for other non-regulated streams. USACE run scenarios from bankfull/non-damaging floods up to a large flood. Work is not necessarily tied to FEMA datasets but can lead to updates if desired.
     *   If so, what modeling do you have access to and how do you formulate those boundaries?
        *   Salem: we have a HEC-HMS model for a few of our more impactful streams. The model inputs included antecedent stream levels and rainfall, and quantitative precipitation forecasts. Model outputs include a project hydrograph, peak flow rates, and timing. These outputs are then used to determine the appropriate static flood inundation map (or set of maps)
        *   National Weather Service: the NWS is slowly rolling out new flood inundation services for the whole continental US (info link<https://www.weather.gov/news/232609-experimental-flood-inundation-maps>). NWS Portland and NWS Pendleton are part of the group of offices for which flood inundation mapping will be implemented by fall 2024. Inundation layers will be generated near real-time for observed and forecast river levels at or near flood stage and higher. Inundation modeling will be based on streamflow forecasts either from the Northwest River Forecast Center or the National Water Model. Flood inundation maps will be available to view on the new National Water Prediction Service (what is replacing the Advanced Hydrologic Predication Service, scheduled to be operational in late March 2024) and will also be served as GIS layers.
        *   US Army Corps of Engineers: We have a range of models available and modelling capabilities available. Available models include:
           *   Willamette from the federally authorized dams down to the mouth of the Columbia. We have some modeling for a handful of non-regulated streams.
           *   Ability to develop models using modelers available at the Corps.
  *   Would pre-event forecasting information be beneficial to you?
     *   All partners said yes to this question
     *   US Army Corps of Engineers: with all the maps available, there has been some interest in hosting a map to include API calls for inundation mapping.
  *   Do you perform any post-event analysis to determine the extent of the flooding for given areas?
     *   Salem: yes, but not to formulate boundaries but rather to identify discrepancies between xpstorm modeled links and nodes outputs (used to create our inundation maps) and areal flooding. This is done to QC our static inundation maps, identify shortcomings with the maps, and to identify conveyance issues (excessive aggradation, culvert blockage, etc).
     *   US Army Corps of Engineers: we sometimes map inundation mapping for big events, we sometimes collect high water marks to calibrate our models.
     *   If so, what modeling do you have access to and how do you formulate those boundaries?
        *   US Army Corps of Engineers: we will run our models for each forecast, we coordinate with the National Weather Service in creating models and inform forecasts. We will create inundation maps in real-time or rely on static maps we already create.

At this point in time, we are not looking at purchasing any data services and will be evaluating the information that we have received from our partners. We're sharing this information for your awareness. Please feel free to reach out with any questions that you may have. Thank you all for helping respond to our request for information!

[cid:image001.png at 01DA6E12.C0AE0E30]<https://www.oregon.gov/oem>
Daniel Stoelb | GIS Program Coordinator
Response Section
Oregon Department of Emergency Management
Office 503-378-3234
Cell 971-719-0917
daniel.stoelb at oem.oregon.gov<mailto:daniel.stoelb at oem.oregon.gov>
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OEM GIS Hub: https://oregon-oem-geo.hub.arcgis.com<https://oregon-oem-geo.hub.arcgis.com/>

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