A Case Study in Jetty Maintenance, Tillamook Bay, Oregon

Abstract

The north and south jetties at the entrance to Tillamook Bay, Oregon have experienced damage to both jetty heads as well as areas along the trunks. The deterioration of the jetties has been more pronounced in the last 7 years. There is concern that the receding jetty heads will contribute to already hazardous navigation conditions over the ebb tidal shoal and within the navigation channel. Navigating the channel becomes even more dangerous because of remnant jetty stone that lies under water just seaward of the exposed end of the south jetty. Erosion of the shoreline along the north jetty is a major concern in terms of a potential break at the jetty root. A recent apparent increase in the Pacific Ocean wave climate has exposed both jetties to more extreme storm waves, especially the south jetty which is more exposed to southwesterly storm events. Increasing wave heights and aging structures has led to a need for major repairs to these and other jetties along the Oregon coast. This paper looks at the issues that are dealt with when evaluating jetties for repair.