Volume I: Syllabus Ranch Palos Verdes, California
• Feasibility Report
Syllabus
This Draft Feasibility Report responds to Section 712 of the 1986 Water Resources
Development Act, Section 116 of the Water Resources Development Act of 1990, and the
1994 Energy and Water Development Appropriations Bill. These authorities requested the
Secretary of the Army to determine the Federal Interest in participating in shoreline erosion
mitigation measures for the purpose of providing additional stabilization for the Portuguese
Bend and adjacent landslide areas, and for the purpose of restoration of marine habitat.
A 1990 Reconnaissance Report concluded that the Corps of Engineers has no
authority to participate in improvements for the purposes of landslide stabilization. Accordingly,
the Feasibility Study and this Report focuses only on the Federal interest in participating in
marine habitat restoration measures along Portuguese Bend and adjacent areas in the City of
Rancho Palos Verdes.
Since 1956, the Palos Verdes Peninsula and adjacent Rancho Palos Verdes,
shorelines have experienced substantial erosion of shoreline material with deposition of
sediments and high turbidity in the nearshore and downcoast areas, resulting in significant
degradation of the marine rocky bottom and kelp habitat and ecosystem. The increase in
sedimentation is associated with the reactivation in 1956 of ancient landslides in the
Portuguese Bend and adjacent areas. Material associated with the landslide has contributed
an average of about 146,000 cubic yards of material a year into the Portuguese Bend coastal
area during the past 23 years, creating a coastal bluff highly vulnerable to erosion from
coastal waves. The Feasibility Study findings conclude that, on average, approximately 89,000
cubic yards of the eroded material deposits in the nearshore, burying many areas,of highly-
valued rocky bottom benthic areas and kelp habitats. The findings also conclude that the
remaining material has increased turbidity in the nearshore and downcoast areas, causing
losses and degradation of similar habitats.
In accordance with the authorizing legislation, an analysis of problems and needs and
• the desires of the Non-Federal Sponsor and other interests, the primary planning objective of
this Feasibility Study is the restoration of the marine environment along the Rancho Palos
Verdes shoreline. Study findings indicate that similar nearshore coastal areas located upcoast
of the Portuguese Bend landslide area currently have a higher valued rocky bottom habitat and
ecosystem. Historical documents show that the Portuguese Bend nearshore and downcoast
areas consisted of high value habitat at least equivalent to the upcoast areas. Prior to 1956,
the Portuguese Bend shoreline and nearshore area was composed of rocky benthic and
intertidal area which experienced minor erosion because of limited sediment material. These
conditions created tide pools, and benthic environment allowing for the development of giant
kelp habitats and ecosystems. Reports of commercial harvesting of giant kelp offshore of
Portuguese Bend further support the existence of a highly-valued environment.
The plan formulation process developed to meet the objective of restoring
environmental restoration, focused on alternative measures for reducing Portuguese Bend
bluff erosion, and the associated sediment deposition and increased turbidity. The study
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recognized that alternative plans to stabilize the Portuguese Bend landslide area could also
contribute to meeting the primary planning objective. The City of Rancho Palos Verdes and
other interests are continuing to analyze and develop and implement measures to stabilize the
landslide. The results to date appear to show that the rate of landslide movement has slowed
and may have stabilized in some areas. The Corps of Engineers review of available
information on the landslide concludes that there is a significant degree of uncertainty on the
long-term effectiveness of such plans. In view of the complexity of the landslide problem at
Portuguese Bend, and because participation in plans to stabilize the landslide is not within the
Corps of Engineers authority, landslide stabilization measures were not considered in this
Feasibility Study. However, the impacts of the landslide continuing and the associated impacts
on measures to reduce bluff erosion are considered in the formulation of alternative plans.
Measures considered to be effective in reducing the erosion of the Portuguese Bend
landslide bluff, were limited to the placement of offshore dikes or breakwaters which would
reduce wave energy reaching the bluff area and contain the material eroding from the bluff.
Measures such as revetment or construction of protective beach against the bluff are
considered to be potentially unstable due to continued landslide movement. Alternatives
considered were based on locating the dike at different offshore locations using information on
foundation stability. Alternatives developed and evaluated included plans locating the dike 200
feet offshore, Plan 1; 400 feet offshore, Plan 2, and 50 feet offshore, Plan 3. The estimated
first costs of implementing these plans are$20,117,000, $27,440,000 and $7,612,000,
respectively. The planning process also considered restoring the nearshore areas seaward of
the dikes by removing these sediments with natural wave energy over time, or by expediting
the restoration by removing the nearshore sediments through dredging— Plans 1a, Plan 2a
and Plan 3a. The estimated first costs of implementing these plans are $24,369,000,
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$31,533,000, and $11,949,000, respectively.
An incremental analysis considering the average annual cost of the dike alternatives
and the resulting ecological benefits was performed to determine which plan is the most
efficient with respect to minimizing costs per habitat units. Average annual cost based on a 50-
year economic life and a 6-5/8% interest rate, are estimated to be$2,384,000 and $2,697,000
for Plans 1 and 1a, respectively. These plans would need maintenance dredging in about 20
years to remove landslide material building up behind the dike which could impact the
structure. In addition, because of uncertainty of foundation stability at the 200 foot location, it is
estimated that about 25% of the structure may need to be repaired after 25 years. The
average annual costs for Plans 2 and 2a are estimated to be $2,137,800, and $2,439,100,
respectively. These plans are located on foundations which appear to be stable based on
review of geotechnical study findings. The location of the dike at this location would not need
any maintenance dredging behind the structure during the projects 50-year economic life.
However, it is expected that material may need to be removed after that time to avoid
encroachment of the landslide on the dike.
The alternative plans' benefits were based on the expected restoration of the
nearshore areas to similar areas located upcoast. The benefits were annualized based on the
rate of restoration as sediment deposits are removed by natural wave action or by dredging
and the value of the habitat created over time. The results of this analysis showed an increase
in net average annual habitat units restored ranging from 249.4 for Plans 1 and 3 to 276.9 for
Planala and 3a, and 241.3 for Plan 2 to 267.2 for Plan 2a. The average annual cost per
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average annual habitat unit ranges from a minimum of$8,900 for Plan 2 to a maximum of
40 $18,400 for Plan 3a.
The alternative selected at this time as the proposed Recommended Plan is Plan 2,
which locates the dike 400 feet offshore with natural removal of sediment deposits in the
restoration area by wave action. This plan is considered the National Ecological Restoration
Plan that minimizes the average annual cost per net average annual habitat unit restored. The
Recommended Plan is shown on Figure S-1, and the economic and environmental costs and
benefits are shown on Table S-1.
The study findings and proposed recommendations considered the potential impacts of
the Recommended Plan and the other alternatives. These impacts are documented in the
inclosed Draft Environmental Impact Statement/Environmental Impact Report prepared in
compliance to the National Environmental Policy Act, the California Environmental Protection
Act, and other Federal and State laws, policies, and guidelines. In general, all of the
alternatives are expected to have a favorable impact based on the restoration of nearshore
and downcoast benthic habitat to a higher valued rocky bottom marine ecology. The impacts of
concern related to further degradation of benthic habitat behind the dike areas, water quality
degradation behind the dike, the possibility of uncovering contaminated deposits in the
restored area, and the impacts of reduced sediment that contributes to beneficial uses in
downcoast and offshore areas. These impacts were carefully evaluated and the impacts were
found not to result in any significant adverse impacts to the environment.
• The implementation of the proposed Recommended Plan is expected to be
accomplished as a Federal and Non-Federal partnership in accordance with established
Federal laws, policies, and guidelines. The cost-sharing for the project is based on Section 210
of the 1996 Water Resources Development Act and Corps of Engineers' Engineer Regulation
(ER) 1165-2-501. The first cost of the project would be shared 65% Federal, presently
estimated to be$17,836,000, and 35% Non-Federal, presently estimated to be$9,604,000.
The Non-Federal Sponsor is responsible for 100% of the cost for operation, maintenance,
major rehabilitation, and replacements (OMMRR), estimated to be$117,700 on an average
annual basis, plus the cost for removal of material to avoid encroachment of the landslide on
the dike structure. Additional items of local cooperation required from the Non-Federal
Sponsor are presented in Chapter 9, District Engineer's Recommendation. The implementation
of the project will require Congressional authorization of the project for construction,
completion of final design and plans and specifications, and execution of a Project
Cooperation Agreement with the Non-Federal sponsor of the project. It is estimated that the
time required to complete these actions could range from two to four years, with construction
taking about one to one and a half years to complete.
The District Engineer proposes to recommend implementation of the Recommended
Plan, subject to reviewing the results of public coordination and review of the Draft Feasibility
Report, its findings, and proposed recommendations. Another requirement is a Non-Federal
Sponsor willing and able to provide the Non-Federal requirements for implementing the
Recommended Plan.
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PLAN! ALTERNATIVE 2 •• ' { m_
NOTES 100' 0 500' '•` j PI lT[gNTIK I.i .r FT'TON TO(
I. HYDRO CONTOURS RASED ON JULY 1995 USACE HYDRO SURVEY -20 �"•ammo*.ioor.eiwr
2. LAND CONTOURS BASED ON AUG 1995 AERIAL PHOTOGRAHETRY SCALE 1 ATl•
3. SOUNDINGS ARE GIVEN IN FEET NIIM _'' 7) �� }� "•-`•��'
111 • III
Table S-1. Economic Costs and Environmental Benefits
Recommended Plan
(October 2000 Price Levels)
First Cost
Construction Costs $23,537,000
Real Estate $35,000
Monitoring and Adaptation Plan $460,000
Planning, Engineering, and Design $1,883,000
Construction Management $1,525,000
Total First Cost $27,440,000
Cost-Sharing
Federal —65% $17,836,000
Non-Federal -- 35% $9,604,000
Average Annual Costs
Interest and Amortization (6-5/8% interest
rate/50 year economic life) $2,020,100
Operation, Maintenance, Major Replacements,
Repairs (OMMRR) - 100% Non-Federal $117,700
Total Average Annual Cost $2,137,800
• Environmental Restoration Benefits
Average Annual Habitat Units (AAHU) Increase 249.4
Incremental Cost Analysis $8,900/AAH
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