The SVI assesses a site’s vulnerability to submergence due to sea-level rise, which results from the feedbacks between flooding regime, surface elevation and surface accretionary processes. The SVI incorporates several parameters representative of soil building processes and elevation change dynamics to determine the vulnerability of a site to submergence. Surface elevation change, vertical accretion, and water elevation measured at each site are used along with regional estimates of global eustatic sea-level rise to make direct comparisons of wetland surface elevation to local relative water- level trends.

A site is scored (0-100) according to the position of the projected wetland elevation relative to the projected hydrologic frame using the following equation:

P_n= 100/N * (n-1/2)

where n is the rank of value of the projected wetland elevation within the projected hydrologic frame, that contains N total observations. Sites with more frequent flooding receive lower scores and are considered more vulnerable to submergence, whereas sites that are flooded less frequently receive higher scores and are considered less vulnerable to submergence.