ElevationBased EstuaryExtent

This project – History and Topography to Improve Decision-making for Estuary Restoration (HiTIDER) – sheds light on the current and past distribution of habitats in the nation’s estuaries. The habitat change analysis was conducted at each of the 30 NERRs, which are operated in partnership between the National Oceanic and Atmospheric Administration (NOAA) and state agencies. Although habitat change studies already exist for some reserves, we used new methods that can improve accuracy; and by applying the same methods consistently across reserves and their surrounding estuaries on all coastlines of the continental US as well as Alaska, Hawaii and Puerto Rico, we hope to facilitate nationwide comparisons and planning. HiTIDER has two main analytical components involving Geographic Information Systems (GIS): 1) Elevation-based mapping: NOAA-generated elevation models and tidal datums were used to estimate the areas within tidal range (the likely extent of the estuary, in the absence of barriers to tidal flow), applying the approach developed by Brophy and colleagues for the U.S. West Coast (Brophy et al. 2019, https://doi.org/10.1371/journal.pone.0218558). In Elkhorn Slough, the interpolated value is equivalent to approximately 2.15 m NAVD88. We compared estuary boundaries as estimated by elevation vs. by the National Wetland Inventory (NWI). Where the elevation-based map of areas within tidal range appears to approximate historical estuary boundaries, and where NWI accurately represents current boundaries, we combined these two datasets to estimate change from past to present. 2) Historical mapping: We used the best, oldest T-sheet (topographic map) or similar historical map to examine extent and distribution of habitats in one smaller area of interest on/near each reserve, and compared that to current mapping, highlighting losses of rare habitat types that could be restored. NOTE: This layer represents the approximate current and historical tidal wetland extent for Elkhorn Slough and adjacent tidal wetlands. See the Resource Lineage steps below for detailed information on how this layer was created. Also see the link to the published report.