Adding to the Toolbox for Tidal-Inundation Mapping in Estuarine Areas
Citation:
Flitcroft, R., P. Clinton, AND K. Christiansen. Adding to the Toolbox for Tidal-Inundation Mapping in Estuarine Areas. Journal of Coastal Conservation. EUCC - The Coastal Union, Leiden, Netherlands, 22(4):745-753, (2018). https://doi.org/10.1007/s11852-018-0605-1
Impact/Purpose:
Estuaries provide enormously important ecosystem services. Often referred to as the “nurseries of the sea” providing habitat and shelter for the young of many recreationally and commercially valuable species. Estuarine habitats are protective of water quality and serve as buffers against natural hazards such as flooding and erosion. They provide many recreational opportunities and often shelter commercially important ports. The economic and environmental benefits of healthy estuaries cannot be overstated. There are over 150 estuaries on the West Coast of the United States alone. The conservation and restoration of estuarine habitats are a priority of coastal planners, resource managers, stake holders and scientists. One key to understanding the dynamic biophysical condition of any given estuary is its tidal regime. Such information lends insight to intertidal ecology, storm hazards and the possible effects of sea level rise. Many estuaries have established tidal datums, vertical geodetic control points linked to local tide level cycles. Unfortunately, many of these have not been surveyed with respect to terrestrial elevation datums such as the National Vertical Datum of 1988. The result is that vertical datum transformation tools such as VDATUM are generalized, relying on tidal datum in estuaries that do have established links to terrestrial vertical datums. This in turn leads to generalization in regional topobathy elevation models, elevation models that provide a seamless link between bathymetry and topography. The resolution of these topobathy models are also generalized, at least in comparison to high resolution LiDAR based elevation models. Such generalizations hinder the precision of site specific studies. Fortunately, nearly the entire US coast has been surveyed in recent years high precision aerial LiDAR, yielding very high resolution elevation models. We have developed a simple GIS method to link tidal datum geodetic points to these terrestrial LiDAR surveys. This transformation method brings the high resolution and precision of LiDAR to the study of site specific estuarine biophysical conditions in systems without links to tidal regimes and terrestrial elevations.
Description:
In estuaries, land-surface and tidal elevation conspire to influence the amount of salt-water inundation in a specific location, ultimately affecting the distribution of estuary vegetation. Plants vary in their tolerances to salinity and inundation. Understanding even small changes in land-surface elevation at a site scale provides relevant information to managers seeking to design effective long-term restoration projects. Restoration of estuary habitats has been identified as a tool to mediate some anticipated effects of climate change, including flooding from sea-level rise, precipitation regimes, and storminess. Further, habitat restoration that is effective in the face of climate uncertainty is critical to the sustainable production of seafood and maintenance of ecosystem functions. We offer a simple method that links tidal elevations to upslope topography, allowing managers to determine where tidal inundation of upslope areas may occur. This method does not require complex modeling, rather we combine existing high accuracy tide-gage information with LiDAR imagery. However, we found that if LiDAR is not flown at low tide, or at consistent tidal heights, it poses significant challenges in the interpretation of tidal elevations. Where LiDAR is consistently collected at low tide, this method of linking the tidal datum to upslope topography is not data-intensive, and does not require long-term data collection. Along with locally specific information, the types of map products that can be developed using this method should identify places that may be potentially vulnerable to salt-water inundation, along with places that may be effective migration corridors for marshes and other habitats.
