Ice-Floe Impact with a Rubble-Mound Causeway at the Port of Nome, Alaska

Abstract

The Port of Nome, Alaska, contains a structure unique for coastal areas subject to large, wind-driven ice sheets or floes. The structure, an almost kilometer-long rubble-mound causeway, stretches perpendicularly out from the coastline to form the main stem of the port’s outer harbor. This paper presents findings from a case study that reconciles results from a somewhat uncommon combination of ice-tank tests and field observations of the causeway’s performance in floe-prone waters. The ice-tank tests, done more than 35 years ago, show that wind-driven ice floes could ride up and overtop the causeway, although without dislodging armor rock sized to withstand design-wave attack. Thirty years of observations, including several ice ride-up events, confirm that the causeway has indeed remained structurally sound, without loss of armor rock to wave or ice loads. A rock breakwater built to the east of the causeway now shields the causeway from floes moving from the east but aggravates ice problems at the entrance to and within the port.