Surf zone dynamics during upwelling on the Oregon coast

Abstract

A 45-day time series study was conducted along the central Oregon coast during July and august 1973. The North Pacific Subtropical High dominated the weather pattern with strong north winds and coastal upwelling. Waves were 1–3 m high with periods of 6 to 9 s. The upwelling was interrupted when low pressure systems passed over the coast. With the low pressure, the wind shifted to the southwest, and the wave height increased. Rip currents and southward longshore currents in the surf zone reached 90 cm s −1 . The mixed diurnal—semi-diurnal tide along the coast had a spring tide range of 4 m. Three beaches were mapped at low tide once every three days. At South Beach, Oregon, 2 sets of bars advanced shoreward at I to 5 m day −1 and expanded to the south at 5 to 15 m day −1 . A longshore trough and rip channel system which was active at mid-tide separated the bars. At Beverly Beach, a basalt ridge formed an island 400 m long and 730 m offshore. The island functioned as a detached breakwater and formed a protuberance on the beach. Sand bars and rip channels built up on the protuberance and migrated 200 m to the south. At Gleneden Beach, cusps with a wavelength of 40 m were formed on the steep foreshore. Rhythmic topography formed by bars and rip channels with a wavelength of 300 m developed on the nearshore. The bars advanced across the rip channel at 5 m day −1 and welded onto the foreshore.