Chapter 3: Problems, Needs and Opportunities • Rancho Palos Verdes,California
Draft Feasibility Report
Chapter 3. Problems, Needs and Opportunities
This Chapter presents analyses of problems, needs, and opportunities for
environmental restoration along the Rancho Palos Verdes coastline. The analysis examines
the Study Area conditions based on present and expected future conditions under conditions
without any plans being implemented by Federal or Non-Federal interest to improve or alter
these conditions. In general, the problem in the Study Area can be analyzed in four major
areas: 1)the landslide movement seaward; 2) the erosion of landslide material and sediment
production; 3)sediment deposition and increased turbidity; and 4)the resulting degradation of
the environment along Portuguese Bend and adjacent areas.
Landslide Movement
As indicated in Chapter 2, the landslide problems in the Rancho Palos Verdes Study
Area are of the block-glide type whose failures occur along a planar surface, and rotational
failures appear to occur at the seaward toe of the landslides. In the Study Area the landslides
• occurred along bentonite and bentonitic layers within the Altamira Member of the Monterey
Formation. Bentonites are rich in the clay mineral montmorillonite, and become very weak
when saturated by water. Consequently, movement of the landslide is related to high
groundwater levels and drainage of high amount of precipitation which impact on the bentonite
layers, as well as causing the saturated soils to become heavier and less stable, particularly
along steep bluff areas. In addition, many geologists believe that the continued erosion of the
shoreline bluff prevents adequate material to counteract the driving force at the toe of the
landslide. Further information on the landslide and landslide movement is presented in the
Geotechnical Appendix.
Landslide Stabilization Measures Effects
In 1984, the City of Rancho Palos Verdes began the Portuguese Bend Stabilization
Project. This project consists of dewatering wells, drainage improvements, and grading of
portions of the landslide. The plan also included grading to redistribute mass within the active
landslide. As a result of these efforts, the landslide movement reduced significantly, and
appeared to be stable until January 1995. Heavy rains, no maintenance of soil cracks in the
surface of the subslide, secondary slides and alluvial deposition appearto cause the subslides
to begin moving. At the present time, the east-central subslide of the Portuguese Bend
landslide aooears to be moving at an average rate of 0.25 inches per day, or 7.6 feet per year.
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Future Landslide Movement
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Future movement rates are difficult to predict. A comparison of historic trends indicate
rates have varied from near zero (1990-1995)to 1.5 inches per day in 1983 and 1986. Short-
term rates of movement has been as high as three inches per day in 1956, following
reactivation. Assuming no change in overall current conditions, it is assumed for this report that
the current slide movement rate, 7.6 feet per year, will continue in the future.
Bluff Erosion and Sediment Production
Prior to the current landslide activities, shoreline erosion was not a significant problem.
The benthic area consisted primarily of bedrock and rocky bottom material and the shorefront
consisted of rocky tide pools and some areas of sandy beach. Since the activation of the
Portuguese Bend landslide in 1956, a sediment plume has been visible in the nearshore
waters of Portuguese Bend, Figure 3-1.This plume has been created by the continual erosion
of the landslide shoreline by wave action. Suspended sediments from the active landslide toe
can be seen up to 1.5 nautical miles offshore. Along Abalone Cove, little or no erosion of the
landslide-generated material has occurred for several years because of the present upslope
stability.
Figure 3=2 shows the 200-foot shoreline change at Portuguese Bend from 1959, three
years after the slide started, to 1982.
At Portuguese Bend, the landslide material that is carried to the shoreline has covered
the previously existing beach, and created a large 80-foot high bluff. The bluff, which has
extended the shoreline out into the cove about 200 feet, as illustrated in the photographs on
Figure 3-3, is continually being eroded by waves and tide.
Almost 6,000,000 cubic yards of landslide material has been eroded from the shoreline
since 1956, as shown on Figure 3-4. This material has been deposited in the nearshore and
offshore areas, and transported downcoast. It provided excess sediment and silt to a wide
area off the coast of Portuguese Bend.
Figure 3-5 shows average yearly loss of material calculated for several intervals of time
since the reactivation of the landslide. These yearly rates ranged from a low of about 86,000
cubic cards a year from 1955 to 1976, to a high of about 292,000 cubic yards a year from 1984
to 1987. Additional information on bluff erosion and historic erosion volumes is presented in
the Geotechnical Appendix.
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Figure 3-2. Shoreline Evolution—Portuguese Bend ' •
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Figure 3-3. Portuguese Bend
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Figure 3-4. Cumulative Landslide Material Loss
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• Figure 3-5. Average Yearly Loss of Material
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3-7
Figure 3-6 delineates the primary impact area, and other areas of significant sediment
dispersion within the Study Area.
Sediment Deposition and Turbidity
The seaward movement of large amounts of landslide material has resulted in the
deposition of material in the nearshore area and transport of sediment offshore and
downcoast. The fine sediment material has been redeposited over a wide area of the coastal
zone, and the local marine environment has been significantly altered by both the sediment
and turbidity.
A sediment survey was conducted in the Portuguese Bend area to identify the current
sedimentary conditions in Study Area. The Study Area measured approximately 4,000 feet
along the coastline to the 60 foot isobath Figure 3-7. Additional samples, shown in Figure 3-8,
were taken inside and outside the Study Area from nearby locations in Abalone Cove and at
Lunada Bay for comparison. The survey shows that the vast majority of the area inside the 25-
foot isobath along Portuguese Cove is covered with about one meter of sediment. The
sediment thickens seaward in the central part of the Study Area. The range of unconsolidated
sediment thickness seaward of the 25-foot isobath ranged from 1.7 to 3.7 meters, with the
thickest located in the central portion. These data show some differences from the Dill and
Norall (1995) data which show sediment thickness in this area to be five-to-ten feet. These
difference could be explained by variations due toseasonal storms, swell characteristics.
An analysis of erosion rates and sediment deposition amounts was accomplished by
the Corps of Engineers to support present deposition amounts located in Portuguese Bend 1111..
Cove and downcoast areas under present and future conditions.As indicated in Chapter 2, the
net average annual estimated transport rate for sediment material along the Rancho Palos
Verdes area is estimated to be about 107,000 cubic yards a year in the southeasterly direction.
Prior to the landslide reactivation,sediment material available to this area was limited to stream
and some bluff contributions which were wellbelow this transport amount. Consequently, all
the material entering this reach was transported out by wave energy.
The sediment budget analysis of the control volume that exists along the Rancho Palos
Verdes area indicates a deposition or accumulation rate of about 89,000 cubic yards a year
and about 79,000 cubic yards that is transported out of the control volume area. Under
without-project conditions, it is assumed that these volumes will continue in the future further
increasing sediment deposition depths and contributing to continuous turbidity to adjacent and
downcoast area.
Evaluation of Without-project Habitat Values
The landslide movement at Portuguese Bend, which has moved material 200 feet into
Portuguese Bend Cove and deposited an average of 89,000 cubic yards a year into
Portuguese Bend and adjacent areas over the last 40 years, has had severe impacts on
marine habitats. These marine habitats have been covered over by landslide debris and
1110
34
• Figure 3-6. Landslide Sediment Dispersion
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5 SEDIMENT THICKNESS IN FEET On
AREA 4
F.
o
AREA 3 s.4, .1 ,.;,‘ ,Ls_.
-- .
al
o
"*"... ..%,,,,. . ....� a '�"k 7,,. " p
" >;`_ AREA 5 <
to
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ti 0SFrPN., � •r o
\:"'"..... ..., ,
wiN......
•
41)
et
r �t /�
■M aW MR \V
OM I
NOTES.
i Qom -
! Q7'
4 0
1. HOLOCENE SEDIMENT THICKNESS OVER BEDROCK MI..�saw-
CCONTOUR INTERVAL 5 FT1 . SOURCE. R.F. DILL ET AL. 1995
I.mac nvFNmr
► [sa. suer
N
LOSNUI mum.oamaItu O
2. USACE JULY 1995 HYDRO SURVEY CONTOURS AT 10 FT INTERVALS. PLATE M
3. LAND CONTOURS FROM 00-95 AERIAL SURVEY AT 1a FT INTERVALS. �. SEDIMENT THICKNESS
SUPPLIED BY THE CITY RPV. memw RECDVERYIIMPACT AREAS—
sediment eroded from the shoreline by waves and tide, and nearshore and offshore areas
have been impacted by siltation and turbidity. The study focus is on controlling the111.
sedimentation and turbidity in the nearshore and offshore zones that result from erosion at the
shoreline, which impacts the marine biological community of the area, displayed on Figure 3-6.
Historical Conditions
. Prior to the 1950s, rocky reef areas and many intertidal pools were present along the
shore and in the nearshore area from Abalone Cove, around Portuguese Point and Inspiration
Point, and through Portuguese Bend to Bunker Point. Information presented in the Draft
EIS/EIR shows a history of kelp forests around the Palos Verdes Peninsula, Figure 3-9.The
changes of forests over time reflect decreases in size due to urbanization in the 1940s that
continued into the 1960s. It also reflects a decrease in all kelp forests in Southern California
during the"warm water"years of 1957-1959, but most began to increase again in the 1960s,
especially in San Diego Region. However kelp forests along the Palos Verdes peninsula
continued to decrease. Restoration efforts, initiated in 1967 and 1971 met with little success
until 1973-74, when offspring of kelp were found at a restoration site in Abalone Cove.
Additional efforts taken during the 1970s resulted in about 84 acres of kelp along the Palos
Verdes Peninsula by July 1977. However, it was also found that failure of kelp forests to grow
to depths of about 50 feet along several reaches of the Peninsula appear due to burial of the
rocky substrata. Diving reconnaissance surveys in Abalone Cove and Portuguese Bend
revealed expanses of sand in depths greater than about 30 feet where large kelp beds were
depicted in early kelp bed surveys.
Present Conditions411
Today, many rocky areas located in the Portugese Bend Cove area are now silted and
smothered to a lesser or greater degree by landslide-generated sediment. Portuguese Bend
supported a rich and diverse marine flora and fauna typical of Southern California intertidal
and subtidal communities. Unaffected rocky reefs adjacent to Portuguese Bend (e.g., Palos
Verdes Point) support an extremely productive kelp forest; they serve as a graphic reminder of
the diverse biological community that is lost to the extensive sedimentation and turbidity
caused by the eroding landslide bluff.
In addition to the impacts from deposition of sediments, the near-constant turbidity
plume and its associated water column impacts on marine biological resources are presumed
to extend at least to the 30-foot isobath from Portuguese Bend to Whites Point. This area of
impact, shown in Figure 3-8, that were focused on during the study include about 71 acres of
bottom habitat in the Portuguese Bend Area (Areas 1,2,6,and 3), 173 acres of existing reef
area at Bunker Point(Area 4), and 230 acres along the nearshore from Bunkers Point to
Whites Point(Area 5). and the nearshore area from Bunker Point to Whites Point. As
discussed in the Draft EIS/EIR, excessive turbidity(i.e., decreased light penetration) is known
to reduce the growth rates and fertility of marine plants and reduce the survivability of marine
plant's gametophytes. From marine biological surveys performed in these areas, it is known
that the quality of existing kelp forest habitat downcoast of the landslide are degraded by the
near-constant turbidity plume.
•
3-12
'. Figure 3-9. Changes in Distribution of Kelp Beds— 1928-1980
Malaga Cove ) •
:.Malaga Cove
Flat Rock Point /` •' Fiat Rock Point
Bluff Cove / Bluff Cove fi Palos Verdes Point r/ r.
( �rr/Pxlos Verdes Point
kLunada Bay ii unada Bay
Christmas Tree Cove 1 ' `i. Christmas Tree Cove
4ll I •
,ti.
••td`Pt.Vicente Abalone Cove 1f7;,Pt.Vicente Abalone Cove
t� 'ortu ese Point Portugese Point inspiration Point
• 9 Inspiration Point .m,,`,‘• ••-c:
`� D
-4".Portugese Bend • '''Portugese Bend
------_, ,tw Bunker Point ._ �1> Bunker Point
•\V4NIly,�i�� White Pointe • •�\_White Point
Rl„i44 Pt Fermin - `Pi.Fermin
a 1928 ���\ b 1947
,/ Malaga Cove ;Malaga Cove
r ...Flat Rock Point ,/Flat Rock Point
Bluff Cove
/Bluff Cove
Palos Verdes Point ;Palos Verdes Point
rLunada Bay 41)Lunada Bay
~.Christmas Tree CoveChristmas Tree Cove
• •N Pt.Vicente Abalone Cove •
\N• . Portugese Point •11•Pt.Vicente Abalone Cove
nspiration Point G I Portugese Point Inspiration Point
•••--_______'•-.-----:--- f- -ortugese Bend -'.' ortugese Bend
Bunker Point
\ �' \••.•` Bunker Point
White Point —1
��\� v '.� ••WhitePoint .
�,••.\2`9 .Pt:Fermin '` Pt.Fermin
c 1964 d 1974
Malaga Cove !Malaga Cove
Flat Rock Point %Flat Rock Point
•p .Bluff Cove `V t8luff Cove
',/
/ T' •-s
,'Palos Verdes Point ,i,/'Palos Verdes Point
Lunada Bay :tb�Lunada Bay
'''''i Christmas Tree Cove t
3...Christmas Tree Cove
- ti
•1`•
Pt.Vicente Abalone Cove ;1:Pt.Vicente Abalone Cove
��,���Portugese Point inspiration Point Portugese Point;nSpiratior.Pc nt
SG���` .Portugese Bend ;. ,
•�crtugese Bend
• Bunker Point
' � \� __J '+L.�Bunker Paint
White Point `White Point
N '�. ' Pt.Fermin `y,..
•
�.• t.�` Pt.Frm-
•
e 1977 i 1980 _
3-13
Habitat Evaluation Method Used
Through coordination with natural resources agencies (CDF&G, NMFS, USF&WS), the
consensus was that a reasonable assessment of the potential benefits of with-project verses
without-project conditions might be achieved by comparing the marine habitat of several sites in
the Study Area. (It is noted that representatives from U.S. Fish and Wildlife Service expressed
major concerns with the method which is discussed in Chapter 7). Based on previous surveys
of the Study Area, five areas of impact Palos Verdes Point, Abalone Cove, Bunker Point,
Bunkers Point to Whites Point, and Point Fermin. Palos Verdes Point was used as a control
Point for the evaluation method since it represents a healthy rocky reef area on the Palos
Verdes Peninsula because it is outside the areas impacted by turbidity and it is relatively dose
to the impact areas.
Characteristics of locations Within the Study Area
Recent benthic and other ecological surveys have been conducted in the Study Area in
1989, 1990, 1996, and 1997. Based on these surveys, the without-project conditions
characteristic of locations in the Study Area are as follows.
Portuguese Bend
The Portuguese Bend area is adjacent to the most severe erosion and sedimentation.
Sedimentation has covered up the natural reefs resulting in transformation from historic kelp to
a soft bottom community continuously impacted by additional sediment deposition and turbidity.
The environment consists of fine sediments that are uncharacteristic of the Palos Verdes •
Peninsula. The homogeneous soft bottom habitat is broken by sporadic boulders which
protruding through the mud, revealing the past rocky habitat conditions. Turbidity in this area is
extremely high.
Bunkers Point
Immediately downcoast of Portuguese Bend, the soft bottom is replaced by rocky reefs,
both low and high relief, which support a kelp bed to ad depth of at least 60 feet. The turbidity
plume is normally present here, except when the longshore current runs upcoast. The area is
reminiscent of other points on the peninsula with a noticeable reduction in benthic macroalgae
and invertebrates.
Bunkers Point-Whites Point
This area experiences high turbidity from the landslide. In this area, the benthic
community of invertebrates and algae was absent from the 30-foot isobath to the low intertidal
zone. In the quiet waters between these points on the peninsula, kelp may or may not be
present, but in its absents an urchin barren community, consisting primarily of purple urchins,
dominates the substrate.As such, this area is atypical for the Palos Verdes Peninsula. In
deeper water from 45 to 60 feet, there is a relatively healthy kelp bed.
10
3-14
r'0 Point Fermin
This area has not been surveyed as part of this Feasibility Study and therefore is not
included in the estimate of plan benefits. However, the area is still impacted to some degree by
turbidity from the landslide.
Abalone Cove
Abalone Cove is impacted to some degree from the turbidity plume when the longshore
current runs upcoast. Sediment deposits exist on a low-lying reef that appears to be smothering
the reef. Abalone Cove and the accompanying area of Pirates Cove have sheer reefs
proximate to the palisades which support many rocky reef species on the points. At the base of
these reefs along the 30-foot isobath, the rock is replaced by a sand bottom. The fine
sedimentation associated with the slide can be seen on these reefs.
Palos Verdes Point
The upcoast area of Palos Verdes Point, which appears not be affected by landslide-
generated sediment and turbidity, has a hard rock/kelp assemblage of fishes, invertebrates,
and algae.
Habitat Values
After a consensus was reached among the Corps of Engineers and the resource
111agencies (U.S. Fish and Wildlife representatives still expressed concerns, which are covered in
the Draft Coordination Act Report ,and discussed in Chapter 7), the Corps contracted the
Vantuna Research Group (VRG)to use the Habitat Valuation Determination Method (hereafter,
called the VRG Method) previously developed by VRG to quantitatively assess the relative,
9
habitat values of Portuguese Bend,Abalone Cove and Palos Verdes Point. As stated, it is',
expected that these areas would serve as examples of with-project and without-project
conditions expected in the Feasibility Study Area.
The VRG Method uses marine fish guilds in its valuation determination. The density
(abundance/area), fidelity (frequency of occurrence), and biomass (mean weight or length)from
data collected in the Study Area are the parameters used in the calculations. The product of
these parameters for each guild are calculated for sites. The sum of the products for a site,
allows for a quantitative comparison of the three sites.
The results of the habitat valuation using the VRG method are discussed in detail in
Appendix Cl of the Draft EIS/EIR. The following modified Habitat Evaluation Procedure
(modified HEP) for the without-project condition analysis uses the values generated by the VRG
Method.
Habitat Evaluation Procedures (HEP) is a habitat-based evaluation procedure; it is used
to give a quantitative, numerical value to biological resources of concern. HEP, developed by
the USFWS, is a formal process whereby tested habitat suitability models for certain species
are used which directs the measurement of certain habitat variables for the selected species
410 (e.g., percent of canopy cover, number of snag trees, stream temperature, percent ground
3-15
cover, etc.)to obtain a Habitat Suitability Index(HSI). This is then used to obtain a numerical
rating of habitat units for the selected species. The modified HEP tailors the HEP process to a
particular application and/or to a certain level of effort desired by the user.
Table 3-1 shows the Habitat Values developed for each location.
Table 3-1. Calculation of Habitat Values by Location
Bunker Pt
Palos Abalone Portuguese Bunker to Pt
Method Verdes Pt Cove Bend Point Kelp White's Pt Fermin
Diver Transects 2,171 1,124 37 963 1,156 1,156
Canopy/Beach 2,342 674 798 798 798 798
Seines
Cryptic Fish 1,206 253 0 253 253 253
Totals 5,718 2,051 834 2,013 2,206 2,206
Note: The square-root standardized habitat values(hectares)were calculated for the five impacted areas
and control(Palos Verdes Pont) by each sampling method based upon the methods of Bond et a/. In review
j and incorporated values from Stephens et a/. 1996.
Without-Project Habitat Evaluation �V
The habitat value calculated for Palos Verdes Point by the VRG Method was considered
the value of high quality kelp habitat and, therefore, equivalent to a "1.0" value in HEP. The
habitat value of the other key locations (Portuguese Bend, Bunker Point, and Bunker Pt.-
Whites Pt.)were considered relative to the Palos Verdes Point-habitat value and a ratio of the
two was used to generate a maximum habitat value in the"0.1 - 1.0" range normally used in a
HEP analysis. (For example, the maximum habitat value of Portuguese Bend was calculated as
834/5719= 0.15; Bunker Point was 2013/5719= 0.35; etc.; see values in Table 1 of Appendix
Cl of the Draft EIS/EIR). The product of these habitat values and the area of key locations
gives habitat units, as traditionally done in HEP.
Tables 3-2, 3-3 and 3-4 show the calculations of Average Annual Habitat Units under
without Project conditions for the three major impact areas at Portuguese Bend, Bunker Point,
and Bunker Point to Whites Point. It is noted that the calculations are based on the assumption
that there would be no change in the value of the habitat or area impacted over the 50-year
economic life considered for this Feasibility Study. However, as noted in the sediment budget,
continuation of the slide and deposition of sediments is expected in the future which could
further increase the without project habitat values. The increase was not estimated due to the
uncertainty on the location of depth of sediment deposition and accordingly the without project
values are somewhat conservative. In addition the impacts at Abalone Cove and Point Fermin
have not been included because of some uncertainty on the stability of the landslide at Abalone
Cove and the effects of turbidity at Point Fermin. Further details of the analysis are presented in
3-16
• the Draft EIS/EIR. Table 3-5 summarizes the Average Annual Habitat Units for the Study Area
under the without-project condition.
Table 3-2. Without-Project Average Annual
Habitat Units
Portuguese Bend Area —Areas 1, 2 and 3
Target Habitat Area Habitat HUs between
Year Value (Acres) Units Target Years
0 .15 71 10.65 --
5 .15 71 10.65 53.25
5 .15 71 10.65 17.75
5 .15 71 10.65 53.25
50 .15 71 10.65 479.25
Total HUs between Target Years 532.50
Average Annual HUs—50 years 10.65
Table 3-3. Without-Project Average Annual
Habitat Units
Bunker Point Area —Area 4
Target Habitat Area Habitat HUs between
Year Value (Acres) Units Target Years
0 .35 173 60.55 --
1 .35 173 60.55 60.55
15 .35 173 60.55 847.70
50 .35 173 60.55 2,119.25
Total HUs between Target Years 3,027.50
Average Annual HUs—50 years 60.55
•
3-17
•
Table 3-4. Without-Project Average Annual
Habitat Units
Bunker Point-Whites Point Area —Area 5
Target Habitat Area Habitat HUs between
Year Value (Acres) Units Target Years
0 .39 230 89.7 --
1 .39 230 89.7 89.70
15 .39 230 89.7 1,255.80
50 .39 230 89.7 3,139.50
Total HUs between Target Years 4,485.00
Average Annual HUs—50 years 89.70
Table 3-5. Study Area Without-Project Habitat Values
(Average Annual Habitat Units -AAHUs)
Location AAHUs •
Portuguese Bend 10.7
Bunker Point 60.6
Bunker Pt.- Whites Pt. 89.7
Total 161.0
•
3-18