Tidal Datums, Tidal Range, and Nuisance Flooding Levels for Chesapeake Bay and Delaware Bay

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Frequently anticipated questions:

What does this data set describe?

Title:
Tidal Datums, Tidal Range, and Nuisance Flooding Levels for Chesapeake Bay and Delaware Bay
Abstract:
This U.S. Geological Survey data release provides data on spatial variations in tidal datums, tidal range, and nuisance flooding in Chesapeake Bay and Delaware Bay. Tidal datums are standard elevations that are defined based on average tidal water levels. Datums are used as references to measure local water levels and to delineate regions in coastal environments. Nuisance flooding refers to the sporadic inundation of low-lying coastal areas by the maximum tidal water levels during spring tides, especially perigean spring tides (also known as king tides). Nuisance flooding is independent of storm event flooding, and it represents a cumulative or chronic hazard. The data were obtained by following a consistent methodology and at sufficient spatial resolution to resolve the distinct and complex features of each bay system. Tidal water levels were simulated by using the ADCIRC model system for the entire 2016 year. The year 2016 was chosen because it corresponded with the maximum magnitude of the combined 18.6-year and 4.4-year tidal modulations. The estuarine and bay areas were resolved with horizontal resolutions on the order of tens to hundreds of meters. The ADCIRC simulations provide time series of water levels at each computational point of an unstructured grid that covers the entire area of interest—from the open ocean to overland areas up to approximately 15 meters above the North American Vertical Datum of 1988. The water-level time series were analyzed to provide estimates of tidal range (great diurnal range and mean range of tide), tidal datums (mean high water, mean higher high water, mean low water, and mean lower low water), and nuisance flooding (highest astronomical tide and monthly mean high water). The resulting data are provided at all points of the computational grid for Chesapeake and Delaware Bays and the surrounding coastal area.
  1. How might this data set be cited?
    Aretxabaleta, Alfredo L., Defne, Zafer, Kalra, Tarandeep S., Blanton, Brian O., and Ganju, Neil K., 20211115, Tidal Datums, Tidal Range, and Nuisance Flooding Levels for Chesapeake Bay and Delaware Bay: data release DOI:10.5066/P9G7KGBF, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Aretxabaleta, A.L., Defne, Z., Kalra, T.S., Blanton, B.O., and Ganju, N.K., 2021, Tidal datums, tidal range, and nuisance flooding levels for Chesapeake Bay and Delaware Bay: U.S. Geological Survey data release, https://doi.org/10.5066/P9G7KGBF.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -77.511016
    East_Bounding_Coordinate: -74.000498
    North_Bounding_Coordinate: 40.233526
    South_Bounding_Coordinate: 36.701001
  3. What does it look like?
    Tidal_Datum_Inundation_FEMA_R3.png https://www.sciencebase.gov/catalog/file/get/61029353d34ef8d7055e38a4?name=Tidal_Datum_Inundation_FEMA_R3.png (PNG)
    Graphic showing maximum inundation by the tide in Delaware Bay.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2021
    Currentness_Reference:
    publication date, data are from a 2016 model simulation
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Point data set. It contains the following vector data types (SDTS terminology):
      • Entity point (1701465)
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0197549539. Longitudes are given to the nearest 0.0251133226. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is North_American_Datum_1983.
      The ellipsoid used is GRS_1980.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    Tidal_Datum_Inundation_FEMA_R3.shp
    Attribute information associated with tidal datums and tidal flooding for the Chesapeake and Delaware bays and surrounding coastal areas. The data are available in shapefile and CSV format. The attributes are the same except the shapefile specific attributes (FID, Shape) are not present in the CSV file. The dataset has 1701465 records. (Source: U.S. Geological Survey)
    FID
    Internal feature number. (Source: Esri) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: Esri) Coordinates defining the features.
    LON
    Longitude coordinate in decimal degrees, NAD83. Negative value indicates Western hemisphere (Source: USGS)
    Range of values
    Minimum:-77.511016
    Maximum:-74.000498
    Units:decimal degrees longitude
    LAT
    Latitude coordinate in decimal degrees, NAD83 (Source: USGS)
    Range of values
    Minimum:36.701001
    Maximum:40.233526
    Units:decimal degrees latitude
    GT
    Tidal Range; Great Diurnal Range (GT): The difference in height between mean higher high water and mean lower low water. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:0.000000
    Maximum:2.797186
    Units:meters
    MN
    Tidal Range; Mean Range of Tide (MN): The difference in height between mean high water and mean low water. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:0.000000
    Maximum:2.695798
    Units:meters
    HAT
    Maximum inundation by the tide (maximum nuisance flooding), also known as Highest Astronomical Tide (HAT): The elevation of the highest predicted astronomical tide at a specific point. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:-3.50176
    Maximum:1.754963
    Units:meters
    MHHW
    Mean Higher High Water: The average of the higher high water height of each tidal day. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:-3.521748
    Maximum:1.512122
    Units:meters
    MLLW
    Mean Lower Low Water: The average of the lower low water height of each tidal day. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:-3.595848
    Maximum:1.274278
    Units:meters
    MHW
    Mean High Water: The average of all the high water heights. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:-3.534599
    Maximum:1.44014
    Units:meters
    MLW
    Mean Low Water: The average of all the low water heights. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:-3.585806
    Maximum:1.274280
    Units:meters
    MMHW
    Monthly Mean High Water: The average of the higher high water height of each tidal month. It is also an estimate of nuisance flooding representing flooding occurring on the order of ten times per year. No data value is -9999. (Source: USGS)
    Range of values
    Minimum:-3.509139
    Maximum:1.753608
    Units:meters
    Entity_and_Attribute_Overview:
    In this dataset, tidal datums and tidal flooding for the Chesapeake and Delaware bays and surrounding coastal areas has been provided. Tidal datums are standard elevations that are defined based on average tidal water levels. Datums are used as references to measure local water levels and to delineate regions in coastal environments. Nuisance flooding refers to the sporadic inundation of low-lying coastal areas by the maximum tidal water levels during spring tides. In this product, tidal datums, tidal range and nuisance flooding are estimated from model simulations. Simulated water levels are analyzed and the different tidal datums are calculated and mapped.
    This metadata file has information for one shapefile (Tidal_Datum_Inundation_FEMA_R3.shp) and specific attributes are described.
    Entity_and_Attribute_Detail_Citation: USGS

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Alfredo L. Aretxabaleta
    • Zafer Defne
    • Tarandeep S. Kalra
    • Brian O. Blanton
    • Neil K. Ganju
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Alfredo Aretxabaleta
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-548-8700 X2204 (voice)
    aaretxabaleta@usgs.gov

Why was the data set created?

The tidal datum, tidal range, and nuisance flooding data were created to be used in evaluating the spatial variation of the response and resiliency of coastal environments to tidal flooding.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 01-Feb-2021 (process 1 of 3)
    This process step and all subsequent process steps were performed by the same person, Alfredo Aretxabaleta, unless otherwise stated.
    A model simulation of the ADCIRC (version 53.04, https://adcirc.org/home/documentation/users-manual-v53/; Dietrich et al. [2011]) modeling system was conducted for the entire 2016 year. The year 2016 is chosen because it corresponds with the maximum magnitude of the combined 18.6-year and 4.4-year tidal modulations. The simulation uses tidal forcing at the open-ocean boundary (at the 60 deg west meridian) from the TPXO-9 global barotropic tides (https://www.tpxo.net/; Egbert and Erofeeva [2002]).
    The ADCIRC unstructured mesh (FEMA_R3) covers the FEMA (Federal Emergency Management Agency) Region III (https://www.fema.gov/about/organization/region-3 ), which includes Chesapeake Bay and Delaware Bay, with high-resolution and is appended to a lower-resolution grid of the western North Atlantic and Gulf of Mexico. FEMA_R3 (https://sites.google.com/site/r3coastal/home/storm-surge-study/adcirc-mesh ) is an unstructured finite element grid that extends westward to the 60 W longitude, which covers the entire east coast of the United States and Gulf of Mexico, but with much higher resolutions in the coastal areas between North Carolina and New Jersey. The grid contains 1.88 million grid points resulting in horizontal resolutions as low as 30 m with most coastal grid elements in the FEMA Region III area being 50-150 m in size. The grid extends overland to approximately the 15 m elevation (NAVD88) to allow for inland flooding. The grid resolves major features such as inlets, main river courses and elevation landforms that were identified during grid creation based on NOAA charts, satellite imagery, and the base DEM (10 meter horizontal resolution, https://sites.google.com/site/r3coastal/home/storm-surge-study/dem-development ).
    The model was run initialized from rest starting December 15, 2015, but the initial 16 days of simulation was considered the spin-up period and were not used for the analysis. The hourly water levels were extracted and are available in the file fort.63.nc.zip.
    Many papers describe the development and usage of the ADCIRC computational model, but basic details can be found in Luettich et al. (1992) and Dietrich et al. (2011).
    References:
    Dietrich, J.C., Zijlema, M., Westerink, J.J., Holthuijsen, L.H., Dawson, C., Luettich Jr, R.A., Jensen, R.E., Smith, J.M., Stelling, G.S. and Stone, G.W., 2011, Modeling hurricane waves and storm surge using integrally-coupled, scalable computations. Coastal Engineering, Vol 58(1), pp.45-65.
    Egbert, G. D., and Erofeeva S. Y., 2002, Efficient inverse modeling of barotropic ocean tides. Journal of Atmospheric and Oceanic Technology 19.2 (2002): 183-204.
    Luettich, R.A., Westerink, J.J., and Scheffner, N.W., 1992, ADCIRC: An Advanced Three-Dimensional Circulation Model for Shelves, Coasts, and Estuaries; Report 1: Theory and Methodology of ADCIRC-2DDI and ADCIRC-3DL; Technical Report CERC-TR-DRP-92-6; U.S. Army Corps of Engineers, U.S. Department of the Army: Washington, DC, USA. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Alfredo Aretxabaleta
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-548-8700 x. 2204 (voice)
    aaretxabaleta@usgs.gov
    Date: 03-Jul-2021 (process 2 of 3)
    This process step was performed in Matlab (ver. 2016b).
    In order to estimate tidal datums at each grid point, the entire water level time series for 2016 is analyzed based on the following definitions: - The maximum inundation by the tide (Highest Astronomical Tide, HAT) is calculated as the elevation of the highest predicted astronomical tide at each specific point. - The Mean High Water (MHW) is calculated as the average of all the high water heights. - The Mean Low Water (MLW) is calculated as the average of all the low water heights. - The Mean Higher High Water (MHHW) is calculated as the average of the higher high water heights of each tidal day. - The Mean Lower Low Water (MLLW) is calculated as the average of the lower low water heights of each tidal day. - The Monthly Mean High Water (MMHW) is calculated as the average of the higher high water height of each tidal month. It is also an estimate of nuisance flooding representing flooding occurring on the order of ten times per year. - The Mean Range of Tide (MN) is calculated as the difference in height between mean high water (MHW) and mean low water (MLW). - The Great Diurnal Range (GT) is calculated as the difference in height between mean higher high water (MHHW) and mean lower low water (MLLW).
    The definition of high water and low water heights is based on a calculation of a change in the water height slope from positive to negative (high) or from negative to positive (low).
    The tidal datum definitions are based on the National Oceanic and Atmospheric Administration (NOAA) definitions (https://tidesandcurrents.noaa.gov/datum_options.html ), except the Monthly Mean High Water (MMHW) is based on a definition by Philip Orton (Stevens Institute of Technology; https://gacoast.uga.edu/wp-content/uploads/2019/07/05-Orton-CPASW19-ThursSession09-TidalFlooding.pdf ).
    Date: 24-Aug-2021 (process 3 of 3)
    To produce the final dataset, we eliminate the parts of the domain with lower resolution by only selecting tidal datums and inundation for the ADCIRC FEMA_R3 grid points inside the polygon (longitude, latitude): p=[ -76.9105 36.7010; -77.9757 37.5000; -77.9757 40.2500; -74.3623 40.2500; -74.2757 39.6104; -74.0000 39.6104; -74.0000 36.7010; -76.9105 36.7010]; using a Matlab code.
    In Matlab (v2016b), the function dlmwrite.m was used to export the data to CSV format. The shapefile was created in ArcMap (ver. 10.7.1) from the CSV file using the XY Table to Point function, no Z Field was used.
  3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    The tidal datums and inundation values represent model conditions simulated for a domain that includes Chesapeake Bay and Delaware Bay. Tidal boundary conditions (TPXO-9) used as forcing for the ADCIRC simulations could have inaccuracies due to resolution restrictions and physical processes misrepresentations. We take the ADCIRC simulation as our best guess for the tidal conditions in the area. The accuracy of the tidal model simulation is also limited by resolution and the choice of physical parameters. The model parameters were chosen following the expert opinion of the modeling group that conducts forecast simulations for the east coast of the United States on the same unstructured grid and that are used by FEMA for their flooding evaluations. Finally, a visual comparison between the current tidal analysis data and NOAA published results was conducted to qualitatively assure accuracy.
  2. How accurate are the geographic locations?
    The horizontal accuracy is inherited from the source model grid (ADCIRC grid FEMA_R3). During the process of grid development by the US Army Corps of Engineers modeling team several quality checks were performed including a visual comparison between grid elevations and the original maps or data. The complete check of the ADCIRC grid was conducted after development: 1) to make certain that elevations were properly captured; and 2) to check that morphological features (e.g., inlets, large rivers, barrier islands and canals) were properly represented in the model grid. According to the US Army Corps of Engineers development team (https://sites.google.com/site/r3coastal/home/storm-surge-study/adcirc-mesh ), the grid satisfied FEMA and industry standards.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    Tidal datums and range should not be extrapolated into areas with oceanographic characteristics different from the reference points. A detailed on-the-ground analysis of a single site may result in a different tidal range than established through this analysis.
  5. How consistent are the relationships among the observations, including topology?
    The data provided matches the tidal source information and falls within the expected ranges for tidal datums. The geospatial data were checked for integrity during the data field creation process and the model points were checked to ensure they match available horizontal datums. Possible data duplicates have been checked and eliminated.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
Use_Constraints:
These data are defined for scientific research purposes and should not be used as a sole source of reference for any regulations and policy making. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the source of this information.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    Attn: GS ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO
    United States

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? The dataset consists of one shapefile: Tidal_Datum_Inundation_FEMA_R3.shp and associated files. Additionally, there is one browse graphic file (Tidal_Datum_Inundation_FEMA_R3.png), one file describing the graphic file (Tidal_Datum_Inundation_FEMA_R3.docx), one ZIP file contains the model output (fort.63.nc.zip) and FGDC CSDGM metadata in XML format (Tidal_Datum_Inundation_FEMA_R3.xml).
  3. What legal disclaimers am I supposed to read?
    Although these data have been processed successfully on a computer system at the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 15-Nov-2021
Metadata author:
U.S. Geological Survey
Attn: Alfredo Aretxabaleta
Oceanographer
384 Woods Hole Road
Woods Hole, MA
US

508-548-8700 x. 2204 (voice)
aaretxabaleta@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P9G7KGBF/Tidal_Datum_Inundation_FEMA_R3.faq.html>
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