Sea Level Rise Impact Calculator

Horizontal inundation is sea level rise divided by the tangent of the slope angle, and the tangent shrinks very quickly as the slope angle approaches zero — meaning the same amount of sea level rise divides by an increasingly tiny number on a very flat coast. That's why flat coastal plains and river deltas are disproportionately vulnerable to sea level rise compared to coasts with even a modest incline.

The Bruun Rule, published by coastal engineer Per Bruun in a 1962 ASCE paper, is a widely used formula estimating how much a beach retreats as sea level rises, based on the shape of the underwater beach profile. This calculator applies typical representative values for that profile's length, berm height, and closure depth rather than site-specific survey data, since those figures genuinely vary by beach and would need actual field measurements to model precisely for a real location.

It's a simplified geometric estimate — often called a bathtub model — that ignores storm surge, wave action, tidal range, sediment transport, and coastal defenses like seawalls or beach nourishment, all of which significantly affect real flooding. Use it to get a rough sense of exposure and compare scenarios, not as a substitute for a detailed engineering flood study before making decisions about a specific property or infrastructure.

Horizontal Inundation distance reflects how far flooding pushes inland at any single point along the coast, which is the figure most directly tied to whether specific structures or roads end up underwater. Total Inundated Area combines that distance with coastline length, which can look large simply because a long coastline is being analyzed, even if the actual inland flooding distance at any one spot is modest.