West Coast USA Current and Historical Estuary Extent

Accurate mapping of tidal wetlands is vital for effective conservation and restoration of these valued habitats, and good mapping is key to strategic planning for coastal resilience. Tidal wetlands are defined by regular inundation by the tides; therefore, mapping of tidal wetlands should be based on knowledge of tidal water levels and the land areas inundated by the tides. We developed this tidal wetland mapping following that principle.

Briefly, we used a method developed in Oregon that combines NOAA's extreme water level models ( https://tidesandcurrents.noaa.gov/est/ ) with high-resolution LIDAR digital elevation models (DEMs) to map areas subject to tidal inundation. We refined the mapping using additional data sources such as the National Wetland Inventory, local knowledge, and aerial photo interpretation. Detailed information on the Oregon methods can be found here: http://www.coastalatlas.net/documents/cmecs/EPSM_CoreGISMethods.pdf

Our mapping includes areas currently inundated by the tides -- "current tidal wetlands" -- from ocean to head of tide, including the freshwater tidal zone. To assist restoration planning, our mapping also includes "historical tidal wetlands" -- areas that were historically inundated by the tides, but are no longer inundated by the tides due to human alterations to the landscape such as dikes and tide gates. Although the mapping does not yet distinguish current from historical (disconnected) tidal wetlands, a future mapping phase (currently in the data development phase) will provide that information.

Note: This subset of data represents the approximate extent of current and historical tidal wetlands for PMEP’s 444 estuaries, excluding “unassociated extents” and “mouth connection areas”.