Frequently Asked Questions

The following is a list of common questions relating to the Coastal Flood Monitoring System. They include information on the operation of the website, data sources, interpretation of the data, terminology, and other topics. This page will be updated as we move forward. If you still have questions about the CFMS after reading this FAQ, please don't hesitate to contact us.

  • What is the CFMS?

    The Delaware Coastal Flood Monitoring System (CFMS) is a web-based tool and alert system designed to provide emergency managers, planners, and others the information on the extent, timing, and severity of upcoming coastal flood conditions.

  • Who manages the CFMS?

    The CFMS was initially developed by the Delaware Environmental Observing System (DEOS) and the Delaware Geological Survey (DGS), with support from DNREC Coastal Programs. It continues to be managed and operated by DEOS and DGS with participation and hosting from the Delaware Environmental and Analysis Center (DEMAC)

  • What is the intended audience of the CFMS?

    The targeted audience for the CFMS is state, county, and local emergency management personnel, researchers, planners, and others involved in the preparation and planning for severe flooding events. The CFMS is used by several state agencies including the Delaware Department of Natural Resources and Environmental Control (DNREC), the Delaware Emergency Management Agency (DEMA), the Delaware Department of Transportation (DelDOT), and the Delaware National Estuarine Research Reserve (DNERR). Moreover, the proposed system will have a direct impact upon the well-being of Delaware's coastal communities.

  • What communties are supported? What about Delaware communities that are not currently suported?

    The current version of the CFMS includes the coastal communities from the City of New Castle down to the City of Lewes. There were 15 communities identified in this area, approximately one location for every 3 miles of coastline. Each community is listed on the CFMS home page with its maximum forecasted water level as well as a community map page with 48-hours tidal forecasts and road elevation profiles. Each community also has configurable alerts, which means a user can set a threshhold value for any one of these communities and will receive an email or text message alert if a forecasted water level value crosses their threshhold.

    Areas to the north of New Castle (Piedmont region) and to the south of Lewes (Inlands Bays and Coastal Atlantic) are planned to be included in future versions of the CFMS.

  • Is there a User Guide for the CFMS?
  • How often is the CFMS website updated?

    Forecasts from the DBOFS model are produced every 6 hours at 00Z, 06Z, 12Z, and 18Z. Forecasts from these models runs are injected into the CFMS soon thereafter, usually an hour or two after the model run is complete.

  • How accurate are the flood inundation maps?

    The flood inundation maps are meant for planning purposes and provide a measure of where flooding could occur. They should not be viewed for absolute accuracy in depth of extent. Errors come from the uncertainty in the forecasts, the hydrologic connectivity of the low lying areas, and in the measurement of the land surface elevation. However, they do provide a realistic interpretation of inundated areas based on the selected water surface.

  • Where do your tide/water level forecasts come from?

    Water level predictions are provided by the National Oceanic and Atmospheric Administration (NOAA)'s National Ocean Service (NOS). The model operated by NOS is called the Delaware Bay Operational Forecast System (DBOFS), which provides high resolution hydrodynamic predictions of water level, water temperature, salinity, and water currents specifically for the Delaware Bay/Delaware River.

  • What Digital Elevation Model (DEM) data does CFMS use?

    Land-based elevation (topographic) datasets were produced for Delaware based on LIDAR. Sussex County was collected in 2005 through a contract with the U.S. Geological Survey and NASA to collect lidar using NASA’s Experimental Advanced Airborne Research Lidar (EAARL) system. New Castle and Kent Counties were collected in 2007 through a contract with Sanborn as part of their orthophotography acquisition. In 2009, DNREC Coastal Programs gathered up all mass point data for the 3 counties and sent them to NOAA Coastal Services Center for reprocessing as a statewide 2-meter grids. Accuracy of the mass points meets or exceeds FEMA Accuracy standard for use in flood mapping and remapping work. In New Castle and Kent Counties, 18.5 cm RMSE for well defined points, 37.5 cm for heavily vegetated areas. In Sussex County, 15 cm RMSE.

  • All of the data and maps on CFMS site are given in NAVD88 feet. What is NAVD88?

    NAVD88 is an abbreviation for the North American Vertical Datum of 1988. NAVD88 is the vertical control datum of orthometric height (i.e., elevation) established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988. NAVD88 is like NGVD29, the de facto standard for vertical elevation data in the United States prior to NAVD88, before it, but uses more factors to calculate a more accurate elevation for each location of the Earth's surface.

  • How are the tidal parameters (MHHW, MSL, MLLW) calculated?

    Tidal parameters (e.g., MHHW, MLLW, MSL) for each community were provided by the NOAA VDatum software package ( Note that these locations are not necessarily the same as the existing NOS tidal gages, even if they have the same name (both are named for the nearby community.) Therefore the parameters will be slightly different that reported values on the NOS tidal station's web page.

    From the NOAA website, "VDatum is designed to vertically transform geospatial data among a variety of tidal, orthometric and ellipsoidal vertical datums - allowing users to convert their data from different horizontal/vertical references into a common system and enabling the fusion of diverse geospatial data in desired reference levels."

  • What are DEOS Alerts?

    DEOS alerts are email or smartphone text messages based on observations from DEOS real-time monitoring network. Alerts can be configured based on each variable and station.

  • What are DEOS Forecast Alerts?

    DEOS Forecase Alerts are similar, in that they are configurable for individual variables and locations, but are based on model forecast fields rather than real-time observations. Currently, Forecast Alerts are available only for water levels along the Delaware Bay coast in communities supported by the CFMS.

  • What is the intended audience of the DEOS Forecast Alerts?

    At the present time, the CFMS ALERTS system is designed to aid coastal community emergency management personnel. If you represent a state/local agency or related organization responsible for planning or responding to coastal hazards, and would like to receive email or text alerts, please contact us.