m3/yr with 413,000 m3/yr of sediment arriving from the north and 77,000 m3/yr
moving up from the south (Schwichtenberg, et al. 1997).
Ventura Harbor was constructed by local interests in 1963, and the original design
featured the arrowhead jetties, a middle groin, entrance channel, turning basin, and
three berthing basins. Because of funding limitations, the arrowhead jetties were not
constructed to full design length. This resulted in a wider entrance opening and jetties
terminating in shallower water, factors that contributed to excessive channel shoaling,
created dangerous wave conditions, and effectively closed the entrance an average of
66 days per year (Adams 1976).
In 1968 the US Army Corps of Engineers accepted responsibility for the entrance
channel and navigation structures. The Corps constructed a 457-m-long detached
breakwater with a large sand trap in the breakwater lee to the north of the north
jetty (see Figure 1). The breakwater was intended to decrease wave heights so long-
shore moving sand would settle in the sand trap and so navigation in the entrance
channel would be safer. The breakwater also provided shelter for dredging operations;
however, with an original crest elevation of 4.3 m MLLW the detached breakwater
is heavily overtopped during larger storms. The sand trap was excavated to depths
ranging between -8 m to -12 m MLLW to give a capacity of about 612,000 m3. It was
anticipated that dredging would eventually occur on a two-year cycle. Construction
of the detached breakwater and sand trap was completed in 1972.
The 1972 modifications were only partially effective. Rip currents and sand ac-
cumulation along the north jetty allowed sand to bypass a portion of the sand trap
and deposit in the entrance channel, and annual maintenance dredging was required
to maintain a -6 m MLLW entrance channel project depth. Between 1973 and 1989
dredging costs were US million. Problematic shoaling in the entrance channel
created dangerous navigation conditions; and between 1982 and 1990, there were 60
capsized or damaged vessels and 11 injuries at Ventura Harbor entrance. Hazardous
conditions prevented vessels from navigating the entrance during a substantial portion
of the year.
In 1989 the Corps of Engineers developed modifications to the Ventura Harbor struc-
tures and entrance channel to help alleviate channel shoaling and associated dangerous
wave conditions. The selected plan included four elements:
1. Construction of a 91-m-long spur groin (labeled "NJS" on Figure 1) off the tip
of the north jetty angled toward the sand trap. The purpose of this extension
was to deflect longshore currents to create a clockwise gyre, thus promoting
deposition for a more productive use of the sand trap.
2. Construction of a new South Beach rubble-mound groin 300 m south of the
south jetty. This structure extended about 200 m offshore to a depth of -1.8 m