Chapter 8: Conclusions •
y Palos Verdes, California
• Rancho
Draft Feasibility Report
Chapter 8. Conclusions
The major conclusions of the Rancho Palos Verdes Environmental Restoration
Feasibility Study to date are:
a. Historically, the Palos Verdes Peninsula including the Portuguese Bend Cove and
downcoast marine benthos area consisted of rocky bottom substrate that provided for
establishment of kelp forest ecosystem with associated diversity of species with high
ecological, commercial and recreation value. The existence of the kelp forests have been
impacted by water temperatures, and other environmental conditions over time. Kelp forest
recovery efforts since the early-1970s have been successful along most of the Palos Verdes
Peninsula except for the Portuguese Bend Cove area, and downcoast kelp forests are
somewhat degraded as compared to upcoast areas.
b. The Portuguese Bend landslide and adjacent landslides became active in the1956
time frame. Since 1956, it is estimated that over 6,000,000 cubic yards of material has been
eroded from the landslide bluff by wave action. This sediment budget indicates on an average
annual basis that about 89,000 cubic yards is deposited in the Portuguese Bend marine area,
40 and 79,000 cubic yards is moved downcoast and offshore. The deposition of landslide material
has impacted about 71 acres of rocky habitat in the Portuguese Bend area, and has increased
turbidity causing impacts to existing reefs and kelp along about 173 acres at Bunkers Point
and 230 acres from Bunkers Point to Whites Point.
c. Surveys conducted during the Feasibility Study and methods used to estimate the
habitat values indicate that the Portuguese Bend Cove and downcoast areas are significantly
degraded as compared to areas along Palos Verdes Peninsula that are not impacted by the
landslide. The reduction in values as compared to a the high quality control area off of Palos
Verdes Point are estimated to be 65%to 85% at Portuguese Bend and the downcoast areas.
d. There is great interest by the City of Rancho Palos Verdes and others to restore the
natural kelp forest ecosystem along Portuguese Bend and adjacent downcoast areas, which is
the primary planning objective of the Feasibility Study.
e. Any solution to restoring the ecosystem in the Portuguese Bend area must consider
impacts of the landslide on foundation conditions and structures along the coast. Although the
City and other interests have made great efforts to stabilize the slide, landslide,movement
continues along the Portuguese Bend coast. Based on geotechnical studies conducted, it
appears that stable foundation exists about 400 feet off coast in about(-18 foot, MLLW depth).
The slide plane and toe of the slide appears to be in the vicinity of the coastal shoreline,
although test results indicate movement along several reaches.
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f. The only alternatives considered viable involve constructing a containment
dike/breakwater to reduce wave action that impacts and erodes the landslide bluff and
contains the eroded material from depositing and increasing turbidity downcoast. The
alternative locations of the dike examined are about 400 feet offshore, 200 feet offshore, and
about 50 feet offshore. Two options were included for each alternative to allow for sediment
deposit removal by natural wave action (since sources of sediment will be contained, wave
energy is expected to scour the nearshore areas out to about-30 feet MLLVV) or mechanical
dredging.
g, The analysis of costs and benefits of the alternative plans indicate that the
alternative plan locating the containment dike 400 feet offshore with natural scouring of
offshore sediments is the alternative that has the least average annual cost per average
annual habitat unit, and is considered the National Environmental Restoration (NER) Plan.
h. The NER plan will result in a total increase of 241.3 average annual habitat units at a
total average annual cost of about$2,137,800 or an average annual cost of about$8,900 per
average annual habitat unit. The cost of restoring the Portuguese Bend rocky substrate and
associated kelp ecosystem is found to be an efficient restoration plan as compared to
construction costs for rocky reef type habitats experienced by California State Fish and Game,
which are close to$13,000 per average annual habitat unit.
I. The total first cost of implementing the plan is$27,440,000, to be cost-shared 65%
Federal and 35% Non-Federal. Maintenance of the project will require repair of the dike
structure caused by wave action on the structure estimated to cost on an average annual basis111,
about$117,100. In addition, removal of landslide material that accumulates behind the
containment dike will be required before it impacts on the structure. Based on historic rates of
movement, material removal will not be required for the 50-year economic life of the project.
About 7 million cubic yards of material will need to be removed by Non-Federal interests after
year 50 to extend the life of the project for another 50 years.
j. The Draft Environmental Impact Statement/Environmental Impact Report indicates
that there would be further loss of degraded quality habitat within the dike, which is offset by
the restored habitat outside the dike. Other impacts of concern are water quality within the
containment area, air quality during construction, and traffic and haul road impacts during
construction and maintenance operations. Further design studies will focus on designing the
dike to minimize adverse water quality impacts,and location of haul roads and associated
traffic will be designed to avoid or minimize adverse impacts. The recommended plan is also
not expected to cause any adverse or beneficial impact on landslide activity. Accordingly, no
significant adverse impacts are expected from the Recommended Plan.
k. Coordination of the plan development and associated costs and benefits has
resulted in a number of concerns raised by the US Fish and Wildlife Service. These concerns
including the potential for uncovering contaminated material, reducing material available for
covering offshore contaminated areas, impacts on terrestrial habitat and species have been
considered and do not appear to result in any significant impacts. The USFWS also has a
number of concerns with the methods used to estimate habitat values, which have been
considered. The method used was developed in coordination with several Federal and State
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fish and wildlife resource agencies and experts and is considered reasonable.
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I. The City of Rancho Palos Verdes has been a full partner in the conduct of the
feasibility study, which included providing 50% of the cost of the study with cash and inkind
services. The City in general supports the findings of the study. The City is continuing to
monitor the landslide movement along the shore and is interested in locating the containment
dike nearer to the shore, if information can show the foundation conditions are stable. A final
decision on the City's interest in proceeding with the Recommended Plan will be made after
completion of public review of the Draft Feasibility Report.
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