Jonathan C. Allan

Storm Surge Magnitudes and Frequency on the Central Oregon Coast

There has been little documentation of storm surges along the coast of the U.S. Pacific Northwest (PNW), generated by extratropical storms. A 44-year record of measured tides on the central Oregon coast has been analyzed to determine the hourly non-tidal residuals, which were further analyzed to separate the storm-surge component from the enhanced winter water levels of the seasonal cycle, which can amount to 0.5 m during El Ninos. The results document that surge levels have reached 1.4 m, with as many as 15 significant occurrences during a winter, having been greatest during the late 1960s and early 1970s. Although storm intensities and measured wave heights have been increasing over the decades, there has not been a corresponding increase in surge levels and frequencies. Although small compared with surges generated by eastcoast Northeasters, the PNW surge events can produce 10s of meters of dune retreat, representing a significant erosion hazard.

Incorporating Uncertainty Associated with Climate Change into Coastal Vulnerability Assessments

An approach is developed for performing probabilistic coastal vulnerability assessments. By exploring a wide range of possible climate futures, coastal change hazard zones of arbitrary confidence level are developed using a suite of simple models. Exposure analyses are performed by superimposing relevant socio-economic data, such as locations of structures and roads, on the hazard zones. The approach allows for quantitative assessments of the impact of climate change uncertainty on possible future coastal configurations. Here we use the simplest coastal change models available, but the approach is developed modularly in that more sophisticated models can replace the simple models when appropriate (e.g., when more detailed results are needed).

Increasing Wave Heights along the Shores of the United States: Climate Controls and Hazards

Progressive increases in storm intensities and the heights of their generated waves have occurred along the Atlantic and Pacific shores of the United States, spanning at least the past 35 years. Those increases include the waves generated by hurricanes in the Atlantic and extratropical storms in the northeast Pacific. The increases in hurricane intensities and waves can be attributed to global warming, the elevated water temperatures being the fuel engine of tropical cyclones. The extratropical storms also appear to be intensified by global warming, but are significantly affected by climate cycles such as the range from El Ninos to La Ninas. It is important to account for these climate controls in models directed toward coastal-hazard assessments, so that future changes in storm intensities and wave heights are included, in addition to the projected accelerated rates of sea-level rise.

Earth's Changing Climate and Enhanced Erosion of the U.S. Pacific Northwest Coast

The goal of our 3-year program of research on the coast of the U.S. Pacific Northwest (PNW) is to document the climate controls on the ocean processes that are responsible for its erosion and flooding hazards. The review presented in this paper focuses on the climate and tectonic controls on the alongcoast variations in sea levels, the multidecadal increase in deep-water wave heights and its effects on coastal wave-breaker heights and swash runup elevations at the shore, and the multiple processes connected with strong El Ninos that are important to episodes of major coastal impacts. These multiple processes are being integrated into PNW management programs, involving applications of models that calculate total water levels and their potential impacts to shore- front properties, with the results used to project hazard zones (setbacks) that account for Earths evolving climate.