The site is exposed to Atlantic Ocean storms, with predominant swell from
300 deg north in the winter months. The sponsor-predicted 50-year return period
wave height ranged from 6.7 to 7.5 m. A secondary summer storm swell is inci-
dent from approximately 230 deg north.
The existing main breakwater is shown in Figures 3 and 4, with the layout
view in Figure 4 dividing the breakwater into seven profiles. The porous break-
water consists of a traditional rubble mound fronting a recurved seawall. The
crest elevation of the seawall is +8.15 m CD (CD refers to the lowest theoretical
chart datum) while the crest elevation of the 6.25-tonne-tetrapod armor layer is
approximately +7 m CD. The head of the breakwater was virtually destroyed by
storms over 25 years and its remnants are completely submerged. The remaining
tetrapod-armored trunk section extends south for approximately 180 m from
Profile 1 (Figure 4). The existing tetrapod section extends down to
approximately 0 m CD.
The depth along the toe varies from near 2 m along the trunk to 9 m on the
head, so the significant wave in the design spectrum is depth limited. The water
level can vary up to 2 m due to a combination of both tide and storm surge. The
seaward bottom slope is relatively steep, averaging between 1V on 12H to
1V on 15H. The foundation at the site consists of layers of sand over bedrock or
old breakwater remnants with sporadic rock outcroppings. Net littoral drift is to
the south.
Much of the trunk section shows considerable damage to the existing tetrapod
armoring. The main armor of tetrapods was under-designed for the 50-year
return period, 7-m significant wave height at the head. Tetrapods along the trunk
section north of Profile 4 have remained relatively stable.
Purpose
A breakwater rehabilitation has been proposed for Vale de Cavaleiros. The
rehabilitation would include extending the breakwater length, placing all sal-
vageable tetrapods in Profiles 1 through 4, and placing Core-Loc armor units on
the remainder of the structure. At the request of Joint Venture Rhein Ruhr
Ingenieur-Gesellschaft mbH and BCEOM Socit Franaise d'Ingnierie (JV
RRI-BCEOM), a breakwater stability model investigation was initiated by the
U.S. Army Engineer Waterways Experiment Station's Coastal Engineering
Research Center. The study goal was to evaluate the stability of the Core-Loc
armor layer for the proposed rehabilitation of the breakwater.
This report describes the design and facilities used (Chapter 2), and results of
the three-dimensional stability study (Chapter 3). The study is summarized in
Chapter 4. Appendix A contains photographs of the three-dimensional model
and Appendix B includes symbol notation used in the report.
3
Chapter 1 Introduction
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