Seasonal variation in beach erosion and sedimentation on the Oregon coast

Abstract

A study of the relationship between climate and beach erosion was conducted on the Oregon coast from June 1973 through May 1974. The climatic year on the Oregon coast can be divided into two major seasons, the summer upwelling season, extending from early April through late September, and the winter storm season, from October through March. The summer upwelling season, dominated by the North Pacific high, is characterized by north winds, coastal upwelling, frequent fog, and low waves. The winter storm season is marked by strong southwest winds, heavy rain, and high waves. During the upwelling season, north winds were 0 to 15 m/s, and waves were 1 to 3 m high. Two sets of sand bars formed in the intertidal zone and advanced up the beach at 1 to 5 m/day and expanded to the south at 5 to 15 m/day. Topographic maps of the beach and intertidal zone were surveyed at low spring tides at South Beach, Oregon. There was a net deposition of 15,100 m 3 of sand on the beach from July 4 through August 12, 1973. In the winter storm season, the wind shifted to the southwest and increased to 22 m/s, and waves reached more than 5 m in height. Sand was stripped from the beach by longshore currents and backwash from waves during storms and returned to the beach in large bars between storms. The total volume of sand involved in the exchange was about 54,000 m 3 or 110 m 3 per linear metre of beach.