Patterns of beach erosion and accretion due to jetty construction
are examined for the coast of Oregon. All jetty systems are
included with the exception of those on the Columbia River, making a
total of nine systems.
All evidence indicates that these areas of the Oregon coast are
experiencing a seasonal reversal in the sand drift, but with a zero or
near zero net drift over a several years time span. Thus, shoreline
changes resulting from jetty construction are not the usual examples
of jetties blocking a net drift as found in southern California and
elsewhere.
In general, accretion of the shoreline took place adjacent to the
jetties following their construction, both to the north and south. This
accretion resulted mainly from the embayment formed between the
jetty and the pre-jetty shoreline, the embayment becoming filled until
the shoreline is straight and again in equilibrium with the waves such
that there is a zero net sand drift. In some cases, as at the entrance
to Yaquina Bay, the jetties are oblique to the trend of the shoreline
and so produced a protected zone from the waves where accretion
could occur.
Sand for the accretion adjacent to the jetties was derived from
beach erosion at greater distances from the jetties. The severity of
the erosion depended on the total amount of sand required for the
beach accretion to a new equilibrium, and the length of beach that was
undergoing erosion. When only a short stretch of beach occurs to
one side of the jetties, as at Bayocean Spit, then the resulting erosion
was particularly severe, in that case leading to the breaching of the
spit.
A computer model is developed to simulate the shoreline
changes that occurred following construction of the jetties on the
Siuslaw River mouth. The model demonstrates deposition next to the
jetty to fill the embayment created by the jetty, and erosion at
greater distances from the jetty. The shoreline advances of the
model agreed closely with the actual shoreline changes found in surveys
following jetty construction. / Graduation date: 1976
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28701 |
| Date | 30 June 1975 |
| Creators | Lizarraga Arciniega, Jose Roman |
| Contributors | Komar, Paul D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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