Technical Report

Development and erosion history of Bayocean Spit, Tillamook, Oregon

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  • Bayocean sand spit lies along the northern Oregon coast approximately 70 miles south of the Columbia River. Work was begun on the construction of a large recreational resort on the spit in the early 1900's. At the outset, the resort appeared to have a promising future. However, a three-year delay in the completion of the railroad to Tillamook created financial instability and lawsuits which continued up to the depression of the early 1930's. There soon followed severe erosion of Bayocean spit leading to its breaching in 1952 and forcing the abandonment of the deteriorated resort. The erosion appeared to have been initiated by the construction and subsequent lengthening of a north jetty to the Tillamook Bay channel. Rapid sand deposition north of the north jetty indicated that the structure had blocked a predominant north to south longshore sand transport, thus depriving the spit of sand and resulting in erosion. Similar occurrences have been documented at other coastal locations. However, analysis of historical shoreline changes and aerial photographs taken in 1971, 1972, and 1973 show that sand eroded from beaches to the north and to the south of the jetty has been transported and deposited immediately adjacent to both sides of the structure. This symmetrical pattern of erosion and deposition on both sides of the jetty indicates a reversing longshore sand transport with a near zero net annual drift. The shoreline conditions at Bayocean demonstrate that beach erosion can result from the construction of a jetty transverse to a seasonally reversing longshore sand transport with a near-zero net drift.
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  • Master files scanned at 600 ppi (256 Grayscale) using Capture Perfect 3.0 on a Canon DR-9080C in TIF format. PDF derivative scanned at 300 ppi (256 Grayscale), using Capture Perfect 3.0, on a Canon DR-9080C. CVista PdfCompressor 3.1 was used for pdf compression and textual OCR.



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