The Nature Conservancy
Southeast Alaska Coastal Exposure Index, TNC, 2013
This coastal exposure index was published as part of a broader estuaries habitat classification framework in the journal Estuaries and Coasts: G.C. Schoch, D.M. Albert, and C.S. Shanley. 2013. An Estuarine Habitat Classification for a Complex Fjordal Island Archipelago. Estuaries and Coasts DOI 10.1007/s12237-013-9622-3. Online URL: http://link.springer.com/article/10.1007/s12237-013-9622-3.Description excerpt: Marine exposure changes with the degree of protection from the full force of open ocean waves. Wave exposure is often quantified as a function of fetch, orientation, and nearshore bathymetry, or on maximum fetch and wind forcing where wave exposure increases with increasing fetch distance and windspeed and duration. However, these estimates do not account for the cumulative effect of ocean swells including refracted, diffracted, and reflected waves. Estimates using fetch are only useful for estimating wave heights for protected embayments and inland shores subjected primarily to locally generated wind waves. We developed an estimate of marine exposure based on an index of the total area visible over water from shore, allowing for the penetration and effects of deep water waves. The marine exposure index was calculated as: lnSum6 i=1 pi ri where p=number of points visible at radius i, and r=distance in km of radius i. We first generated concentric buffers to seaward of the shoreline at distances of 1, 2, 5, 10, 20, and 100 km. These lines were then converted to points at 1-km intervals. We used the Viewshed tool in ArcGIS to identify the number of points at each radius visible from each segment along the shoreline. The distance-weighted index of marine exposure was calculated as the natural log of the sum of points visible at each radius multipled be the radius distance and catagorized by area of exposure.
Data and Resources
Start Date: 2011/12/31
End Date: 2012/12/30