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

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.

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 ).

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.

Changed a thesaurus name from Common geographic areas to None since two of the three terms were not valid for the specified thesaurus (20240709).