Oregon Coast Shoreline Changes Due to Jetties

Patterns of beach erosion and accretion due to jetty construction are examined for the Oregon coast which has a seasonally reversing littoral drift with a zero or near zero net drift. Thus the shoreline changes do not result from the jetties blocking a net drift. Shoreline accretion took place adjacent to the jetties, both north and south, filling the embayments formed between the jetties and the prejetty shoreline. The amount of accretion depended on the size of the embayment created. Sand for this accretion was supplied by beach erosion at greater distances from the jetties. In the case of the jetties at Tillamook Bay, the erosion was sufficiently severe to breach Bayocean Spit. A computer model is developed to simulate shoreline changes that occurred following construction of the Siuslaw River jetties. The model demonstrates deposition next to the jetty and erosion at greater distances, showing good agreement with the actual shoreline changes.