The Siuslaw jetties ( sy-YOO-slaw) at Florence, Oregon, in the United States, are parallel rubble-mound structures at the entrance of the Siuslaw River, bounding the north and south banks and protecting the navigation channel. The jetties extend into the Pacific Ocean, with spur jetties designed to reduce breakers and shoaling across the sand bar. The U.S. Army Corps of Engineers (USACE) completed the jetties in 1917, and completed reconstruction and lengthening projects in 1962. USACE lengthened the jetties again in 1985, and spur jetties were added at that time to reduce the need for annual dredging.
Description The Siuslaw River enters the Pacific Ocean about 250 km (155 miles) south of the Columbia River. The jetties and spurs at the entrance are randomly-placed rubble-mound structures of armor stone weighing from 10,885-to 17,235-kg (12- to 19-tons). The jetties border the river channel on the north and south, and were built originally between 1910–1917, with the north jetty originally 2,957 m (9,700 ft) long, and the south jetty 1,980 m (6,500 ft) in length. A 1963 study described the jetty and channel system:
The principal harbor works at the mouth of the river consist of: (a) two quarrystone jetties 750 ft apart at their offshore extremities, the north jetty extending 3700 ft in a westerly direction along the edge of the north spit, and a south jetty extending 4300 ft in a westerly direction across the south spit; (b) an entrance channel 18 ft deep and 300 ft wide from deep water in the ocean to a point 1500 ft upstream from the seaward end of the existing north jetty; (c) a 5-mile-long channel 16 ft deep and 200 ft wide, with widening at the bends, extending from the entrance channel to Florence; (d) a turning basin 16 ft deep, 400 ft wide, and 600 ft long, opposite the Siuslaw docks at Florence; and (e) a channel 12 ft deep and 150 ft wide extending about 3 miles upstream from the turning basin... A reconstruction project is proposed for the south jetty which involves rebuilding the head and about 2250 ft of the trunk... By 1969, the north jetty had been rehabilitated and extended seaward 600 feet. A later U.S. Army Corps of Engineers (USACE) inspection report said, "In 1985, the jetties at the mouth of the Siuslaw River were again extended seaward. The north jetty extension was 580 m (1,900 ft) long, and the south jetty extension was 670 m (2,200 ft)." Spurs were also added to the end of each jetty during the 1985 construction.
The report described the 1985 construction of spurs:
...on the ocean sides of each jetty, 122-m-long (400-ft-long) spurs oriented 45 degrees to the main structure were constructed. The spurs originated 275 m (900 ft) shoreward of the jetty heads. The jetty heads were located in depths of about -7 m (-23 ft) mllw.
History
Prior to 1880, the Siuslaw River Valley was inhabited by the Siuslaw people, who used the river for transportation upstream by canoe for salmon runs or to reach hunting areas. The Coast Indian Reservation, including some Siuslaw lands, had been established in 1855, but from 1860 to 1875 the Siuslaw population declined from 129 to 45. Under the 1887 Dawes Act, land allotments were given in trust to the Siuslaws, but few were able to pay the property taxes. The decline in Siuslaw presence in the watershed brought the start of white settlement, and the expectation the river would be used by larger commercial craft to transport resources and goods.
1879 to 1910
The United States General Land Office Survey in 1879 (Florence area) rated the quality of the land along the coast as above average, and evaluated the resources available. Under the "Act to Improve Rivers and Harbors" of June 14, 1880, the USACE furnished reports on navigability of U.S. rivers. The 1880 report described Florence as "the name of the postoffice on the Siuslaw — a small settlement of five houses and about a dozen inhabitants". It said, "The river enters the ocean in a westerly direction, through an entrance 600 feet wide and 24 feet depth at low-water, between sandy shores. It has no headland on either side, and shifts from year to year north or south. Two years ago the mouth of the river was at least 1 mile north of its present position." It also reported one channel across the bar which was about a quarter mile from the entrance, with reported depth of "8 feet at low water". The report concluded, "The people living on the river... think that no improvement is required; all they ask is that an accurate survey be made and the depth on the bar be officially declared. When this is done and the entrance buoyed, it is thought small steamers and schooners can be induced to run into the river, and reasonable insurance can be obtained on their cargoes."
The second survey, in 1887, reported a Florence population of about 250, and said,
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