Siuslaw Jetties

The Siuslaw jetties ( ) 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:

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:

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.John B. Miller
Principles of public and private infrastructure delivery
p.146 ff, Springer, (2000) 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,

In 1891, the USACE began work on the Siuslaw north jetty. By 1892, ships were crossing the bar to carry freight in and out of the harbor at Florence, Oregon. A local newspaper reported that the steamer ''Chance'' was carrying a load of railroad iron down the Siuslaw, "probably for the U.S. government to be used in the Siuslaw jetty work." At that time, there were two channels crossing the bar at the mouth of the river, with the south channel the deeper at 12 feet.

The USACE began constructing a tramway in late 1892, spending approximately $70,000 in the first two years to transport rock that had been brought down river by barge from a quarry in Mapleton. In 1894, Daniel Kern of Portland was contracted to build 1000 feet of jetty for $11,250.50 According to ''The World'', "The fight to gain funds went on and although the jetties were unfinished and the bar crossing perilous, large boats still crossed the bar. During this period several boats were swamped on the bar or beached near the entrance." Rep. Binger Hermann secured funds in 1896 for "continuation of the work on the Siuslaw harbor".

By 1900, the jetties were still under construction, slowed by inadequate funding and the inherent difficulties of building underwater with active river and ocean currents. $20,000 had been spent in 1894, followed by $27,000 in 1896. The construction process involved setting pilings for the railway to support the tram, which was used to transport rock to the site of the jetty. A contractor commented to a reporter in 1900, while giving a tour of the building site via the tram, "...here is our trouble in a nutshell: we are dumping this rock into fifty feet of water; you can fancy how long it takes this filling to appear above the surface, and in the meantime the tide or rough water plays havoc with our piling. A few weeks ago we lost $1000 in timber and iron in a single night."

As of about 1903, pending acquisition of additional funding, jetty work was abandoned, with approximately 3,000 feet of the north jetty completed.

In 1909 I. B. Cushman of Cushman, Oregon, helped form the Port Commission and gained congressional approval of their bylaws. When the 1910 Rivers and Harbors Act required local interests to pay half the costs of federal construction projects, the Port Commission sold $324,000 in retirement bonds.

1912 to 1929

By the beginning of 1912, a total of $100,000 had been spent constructing the south jetty and approximately 3,000 feet of the jetty on the north bank. However, the part of north jetty already built had deteriorated and needed to be rehabilitated. Assistant U.S. Engineer W.G.Carroll was appointed to take charge of the reconstruction and building an additional 3,000 feet of the north jetty, and also to supervise work on the south jetty to be completed by contractors Johnson, Anderson & Co. The federal government and the Port Commission of Siuslaw shared costs.

When the jetty work withstood a large storm in 1915, the ''Oregon Daily Journal'' said, "The fact that they stood up under the terrific pounding that they have been given for the past two weeks show that the work is of the most stable kind."

The jetties were completed in 1917, and further inner harbor improvements in 1929, at a total cost for the project of more than $1,00,000.

1957 to 1969

By 1957, Sen. Richard L. Neuberger and Rep. Charles O. Porter of Eugene supported a Florence jetty reconstruction project. After Lane County built up the Coast Guard Road next to the north jetty, rehabilitation and additional dredging projects in 1958 and 1962 added 600 feet to the north jetty, deepened the entrance channel to 18 feet and the channel to Florence to 16 feet, and widened and deepened a 12-foot channel from Florence to Mapleton. The ''Eugene Guard'' reported, "extension of the jetty will be about 100 feet less than originally planned", due to the expense of additional quarried rock at the end of the jetties, in deeper water than had been anticipated. These projects were completed in 1969.

1982 to 1988

In December 1982, Congress approved $4 million to finance the first stage of a proposed $34-million extension of both jetties at the mouth of the Siuslaw River.

In 1983 the USACE contracted with Kiewit Pacific Company of Vancouver, Washington to lengthen the jetties "to keep sand from drifting into the estuary and clogging the port's boat channel". The $25 million project was to triple the length of the jetties, in an effort to eliminate 75 percent of the need for yearly dredging. Rock for the extensions was to be quarried near Mapleton.

Kiewit Pacific received a permit to use rock quarried on Siuslaw National Forest land near Mapleton, as well as use of the South Jetty Road in the Oregon Dunes National Recreation Area, as the access road for rock hauled to the south jetty. In use for a little more than a year, the quarry was closed in February 1985. In 1985, the project was completed, lengthening the jetties and adding the spurs.

Studies

Following the 1962 reconstruction and extension of the north jetty, the USACE developed a scale model to investigate design criteria for rehabilitation of the south jetty. According to the report, "Three designs for the trunk section and two for the head section were tested under various stillwater depths for both high and low tide, and for a range of wave heights and periods with the waves attacking the jetty sections at angles of 90 and 0 deg." The report made specific design recommendations on the number of layers, shapes of armor stones, and placement of the rock to repair and construct different areas of the jetty's trunk and head section.

The question of how the jetties affect sand drift and beach erosion was studied in 1975. J.R. Lizarraga Arciniega found "a seasonal reversal in the sand drift, but with a zero or near zero net drift over a several years time span".

Lizarraga Arciniega described the drift:

Between 1981 and 1991 the Coastal Engineering Research Center of the USACE conducted studies on "the impact of the jetty design on the entire area, including sediment shoaling in the channel and beach erosion or build-up". ''The World'' of Coos Bay described the study:

The USACE's 1995 study of the effectiveness of the spur jetties collected bathymetric data on currents around the jetties using "helicopter-borne near-shore survey system". The study concluded, "...the 1985 jetty improvements are a success... Navigability has been improved, construction cost of the spur system was estimated to be approximately $5 million less than the original design cost estimate for jetty extension... and annual maintenance dredging requirements have been reduced to approximately 100,000 cu yd".

See also

* Breakwater (structure)
* Causeway
* Coastal engineering
* Groyne
* Mole (architecture)

Notes

References

External links

Siuslaw River Bar Hazards

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Rivers of Oregon
Rivers of Lane County, Oregon
Breakwaters
Coastal engineering
Coastal construction
Oregon placenames of Native American origin
1917 establishments in Oregon