thus forming a protective slope. This left between 3 m to 6 m of original berm
undisturbed.
Plan 2. One worrisome aspect of Plan 1, and the 1996 design, was the need to
excavate to a depth below the toe of the 1992-repaired armor slope (located at -3.7
m MLLW) to place the new toe berm. During excavation there would be a risk of
initiating a slope failure, resulting in costly repairs and project delay. Plan 2 was
designed with a 1-m-thick layer of B-2 stone ranging between 0.630.95 m in stone
diameter, over a 1-m-thick layer of C-stone quarryrun. This plan featured a 3-m-wide
horizontal bench at -1.0 m elevation and a sloping berm having a 14.3-m horizontal
extent. At the end of the test, a scour trench had formed and a portion of the sloping
berm was undermined, but Plan 2 provided plenty of reserve protection, and the design
should protect the structure for currents well above the flow condition tested.
The Los Angeles District of the Corps of Engineers planned to construct the pro-
tective toe berm as part of a maintenance dredging contract that was being put out
to bid at about the same time as the Plan 2 test was completed. Based on physical
model results, the Plan 2 design replaced the 1996 design in the bidding documents.
However, after bids were requested, it was realized that the berm elevation of Plan 2
was significantly higher than the -4.5 m elevation of the rock sill (also a problem with
the 1996 design). This would prevent larger dredges from accessing the sand trap
to the north of the north jetty, and it represented a serious navigation hazard for
smaller dredges and other vessels. Potential costs associated with dredge and vessel
grounding, and possibly the need to remove the berm at some later date, made Plan 2
much less desirable than originally thought. (Additional details and cross-sections for
the Plan 1 and Plan 2 toe protection designs are given in Hughes and Schwichtenberg
(1998).
Plan 3. The potential problems of Plan 2 were corrected by the Plan 3 design shown
in the upper portion of Figure 6. This berm was composed of only C-stone quarryrun
and featured an 11.6-m-wide by 3-m-thick horizontal bench at an elevation of -4 m
MLLW. Risk to the existing breakwater toe was lessened by excavating on a slope as
illustrated in Figure 6.
The model was run for 9 hours under the same water depth and flow conditions
as the previous two alternative plan tests. Plan 3 proved to be fully adequate as
indicated by the lower sketch of Figure 6. Consequently, the Los Angeles District
issued an amendment to the plans and specifications utilizing the toe berm design
shown in the Plan 3 cross-section.
Summary and Conclusions
Since its original construction in 1963, the entrance to Ventura Harbor has undergone
a series of engineering modifications in an effort to decrease deposition of littoral
sediments in the navigation channel. In 1994 a spur groin was added to the tip
of the north Ventura Harbor jetty, narrowing the gap between the north jetty and
detached breakwater. This modification appeared to promote increased trapping of
sediment during normal weather conditions; but during strong storms, southward
12
Hughes/Schwichtenberg
Previous Page
