South Beach, Yaquina Bay South Jetty

South Beach, Yaquina Bay South Jetty

by | Dec 12, 2021

South Beach is a state park south of the jetty protecting the mouth of Yaquina Bay and extending for 1 mile (1.6 km) along the Pacific coast, about 12 miles (19 km) north of Waldport and 2 miles (3.2 km) south-southwest of Newport, Oregon. The beach continues south beyond the park for another 7 miles (11 km) to Seal Rock. The park lands were acquired by gift, exchange, and purchase between 1933 and 1970, and combined two areas once separately maintained, South Beach Wayside and South Newport State Park. Gifted lands were received from Edith M. Bowman, Robert and Cherie Kiewel, Lincoln County, and W. J. and Janet Wineberg. The lands were obtained to protect the south shore of the Yaquina Bay bridge area from encroachment and also to provide public access to the beach. The entrance to Yaquina Bay is one of the oldest navigation projects on the Oregon coast, which includes two entrance jetties and several dredged channels inside the bay. The Yaquina north jetty was constructed from 1889 to 1896 to a length of 7,000 feet, and then extended in 1966, and repaired in 1978, 1988, and 2001. The south jetty was completed in 1896 to a length of 8,600 feet and then extended another 1,800 feet in 1972. Jetties are sediment control structures placed adjacent to tidal inlets and harbors to control sand migration and minimize sediment deposition within the entrance channel where dangerous sand bars can otherwise develop. However, jetties can significantly destabilize the natural coastal sediment transport regime necessary to prevent erosion as well as unnatural sand accumulation. Along much of the Oregon coast, erosion is an issue affecting both artificial and natural structures. Beach sand is typically removed and transported parallel along the shore by energetic winter storm waves and subsequently moved onshore and deposited by lower-energy summer waves. This dynamic is different at jetties which act as a barrier to alongshore sediment transport and sand is almost continually building up against the barrier. At South Beach, the sand is trapped against the jetty, and once the sand is deposited on the beach, the prevailing onshore winds transport the sand up the beach slope to create dunes that are eventually stabilized by beach grass.

There are about 314 miles (505 km) of the Pacific coastline in Oregon, and 195 miles (314 km) contain some form of dune activity. Inventories done in the early 1970s showed 125,400 acres (50,748 ha) of dunes of various types and 38,980 acres (15,775 ha) of associated wet interdune areas. There are three sources of sand available to form dunes along the Oregon coast including 1) erosion of coastal rock formations, coastal terraces, spits, and dunes, 2) sand supplied by rivers, and 3) offshore sand on the wave-cut platform of the continental shelf that is brought landward by currents. Winter storms create large high energy waves that provide a seasonal nearshore sand supply, and lower-energy waves and currents, which occur on a continual basis, transport the near-shore sand to beaches and tidal inlets. Early in the 20th century, jetties were constructed at many inlets along the Oregon coast that resulted in a realignment of some shorelines. The observed patterns of change suggest that even though there is a seasonal reversal in the alongshore transport of sand on Oregon beaches, the net transport averaged over several years is effectively zero. This is due to a geomorphological configuration peculiar to the Oregon coast where beaches are isolated between large rocky headlands, and contributions of new sand to the beaches are small. The absence of a net coastwide alongshore sand transport has spared the Oregon coast the types of problems found elsewhere. However, human intervention into the Oregon coastal dune process, and associated vegetation changes, started at the time of jetty construction. Jetties caused the embayments at the mouth of rivers to fill in with sand, and beaches to the north and south of the jetties rapidly prograded seaward. This accreted sand blew eastward across older dunes, and filled lakes, rivers, and wetlands, as well as buried road and railroad infrastructure.

Local communities became concerned about the sand accumulation, and stabilization work started. From 1897-1899, the Oregon Railway & Navigation Company was responsible for some of the earliest dune stabilization work on the coast, and a few years later, between 1910 and 1916, the U.S. Forest Service directed the planting of trees, shrubs, and European beachgrass. In 1935, the U.S. Soil Conservation Service and the Civilian Conservation Corps started testing various species of beach grass for dune stabilization. European beachgrass, American dune grass, and American beachgrass were the primary grasses tested. Based on the field trials, European beachgrass was recommended for sand stabilization because it transplanted more successfully and had more vigorous growth than native grasses. Because the sand accumulation associated with jetty construction created such a high wind hazard, by the early 1930s it was essential to reduce wind damage as fast as possible. Therefore, a grass was needed that could be successfully transplanted in very high wind energy and sand supply environments, and European beachgrass was selected. In 1937-1938, areas of blowing sand were stabilized with a combination of sand fences and planted European beachgrass. Herbaceous and woody vegetation was established one to two years after beachgrass was planted. The European beachgrass spread naturally from the planted locations, and this resulted in beachgrass eventually creating stable dunes along about 76 miles (122 km) of the Oregon coast by the early 1970s. Today, most of the stable dunes on the Oregon coast can be attributed to the introduction of European beachgrass, and this had a profound effect on subsequent land use. Stabilizing a low dune allowed for more development near the beach, and unfortunately, minimal consideration was given to the potential wind erosion, water erosion, or ocean flood hazard that might be associated with the development on the dunes. Read more here and here. Explore more of South Beach and Yaquina Bay South Jetty here:

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