Table of Contents & Project ReportPROJECT STUDY REPORT
SAN RAMON CANYON DRAINAGE SYSTEM
PREPARED FOR:
CITY OF RANCHO PALOS VERDES
PUBLIC WORKS DEPARTMENT
PREPARED BY:
Harris &Associates.
34 EXECUTIVE PARK,SUITE 150
IRVINE,CA 92614-4705
(949)655 -3900
January 11,2011
Prepared By:
Randall Berry,PE
RCE #44642
RGB stamp here
Reviewed By:
Alan Braadvedt
Senior Project Manager
Approved By:
Ron Dra900,PE
Senior Engineer of Public Works
TABLE OF CONTENTS
I.EXECUTIVE SUMMARY 1
II.INTRODUCTION 4
III.BACKGROUND 7
IV.AGENCY INVOLVEMENT 11
V.COMMUNITY INVOLVEMENT 11
VI.EXISTING CITY OF LOS ANGELES (CLA)STORM DRAIN AT 25TH STREET 12
VII.PROPOSED STORM DRAIN STANDARDS AND DESIGN CRITERIA 14
VIII.ENVIRONMENTAL REQUIREMENTS.
IX.GEOTECHNICAL REQUIREMENTS .....
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X.STORM DRAIN DESIGN ALIGNMENT ALTERNATiVES 21
XI.RECOMMENDED ALTERNATIVE 29
XII.PALOS VERDES DRIVE EAST (PVDE)SWITCHBACK STABILITY 29
XIII.CANYON SLOPE MONITORING 33
APPENDIX
Appendix A -KDMM Aerial
Appendix B -GMU Geotechnical Report
Appendix C -SFC Environmental Expanded Initial Study
Appendix 0 -San Ramon Hydrology
Appendix E -Existing City of Los Angeles Storm Drain (Asbuilts,Hydrology and
Hydraulics)
Appendix F -Design Alternatives Detailed Discussion
Appendix G -Proposed Alternatives (Plans,Hydrology and Hydraulics)
Appendix H -Cost Estimates
Appendix 1-Letter to Gordon Teuber ("25 th Street Interim Basin Grading~Solution)
Appendix J -Table 1 Design Criteria
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City of R~ncho P~los Vo::rdc~San Ramon Stoml Drainage Sytitelll -Projccl Study Rcporl
I.EXECUTIVE SUMMARY
I.EXECUTIVE SUMMARY
Introduction:
Harris &Associates was retained by the City of Rancho Palos Verdes (RPV)to define the
drainage problems in the San Ramon Canyon.identify alternative solutions to the problems and
present the findings in a Project Study Report (PSR).The PSR is intended to evaluate and
present information regarding at least three alternative solutions and to aid in identifying specific
environmental,geotechnical,right-of-way and other construction related elements.Information
presented in the PSR represents planning level construction estimates and includes soft costs
which help in programming the required budget for the selected design alternative.
Furthermore,information presented in the PSR will assist those involved in determining how to
proceed with programming and engineering design decisions to manage the runoff that flows
through the canyon and minimize erosion and the resulting flooding and debris on 2S th Street.
Background:
San Ramon Canyon conveys storm water runoff generated within the canyon and the upstream
tributary watershed approximately 3,300 feet downstream.The runoff is then received by a
storm drain inlet system at 2S TH Street.The existing inlet cannot accommodate the water and
debris that are delivered to it.The first 1,ODD-feet of the canyon,beginning at the upstream end
of the canyon's existing storm drain outlet,are relatively stable.The next 1,SOO-feet pass
through the dormant South Shores Landslide with unstable,3D-foot high,vertical canyon walls.
These vertical walls extend for several hundred feet as they pass through the Tarapaca
Landslide.This landslide is moving westward and is forcing the streambed in that direction,
thereby undermining the Palos Verdes Drive East (PVDE)switchbacks and a sewer line located
adjacent to the roadway.The last 800-feet of the drainage course navigate what used to be a
2S-foot deep canyon with a pipe placed in the invert of the canyon,where the 2S TH Street
embankment was constructed across the canyon.This section of the canyon is now completely
filled with debris generated from the canyon.The erosive forces of the runoff continue to
generate large amounts of debris,which are deposited on 2S th Street during most storms,
typically blocking access along the road.
Roadway flooding and debris deposits on 2S th Street have been a problem for area residents
and commuters for many years.Downstream development within the natural drainage path
included the installation of a drainage system that did not anticipate or accommodate the
amount of debris that is currently generated within the canyon.The inlet system that was
originally installed at the base of the roadway fill was extended vertically in the 1990's to
accommodate canyon sediment as it rose to a level that now matches the adjacent roadway.
The localized Tarapaca Landslide began to move shortly after the millennium which significantly
increased the amount of debris generated within the canyon.The low strength of the surface
soil in the canyon near the switchbacks coupled with the westerly migration of the streambed is
a concern specific to the stability of the PVDE switchbacks and adjacent sewer line.A shelf
ready,early action construction project is being designed to facilitate efforts to stabilize the
slopes adjacent to the lower PVDE switchback roadway,if the encroachment of erosion should
continue.
This ongoing cycle of flooding and deposition of rock and mud on 2S th Street threatens the
safety of downstream residents in the Palos Verdes Shores Mobile Home Park.Road closures
and the cleanup of the mud and rock debris is an ongoing maintenance problem that restricts
through traffic and emergency access to the Palos Verdes Peninsula.All vehicles,including
safety personnel,are prevented from using the roadway until the mud/debris has been cleared .
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City or Rancho POlI(»l Verdes San ROlmoll Stom.Drai"Olge System -Protect Study Report
I.EXECUTIVE SUMMARY
A solution to this continuing flooding is long overdue.The question this PSR is seeking to
answer is which solution will best serve residents,commuters,the City of Rancho Palos Verdes
(RPV),the City of los Angeles (ClA)and los Angeles County (LAC).
Alternatives:
The terms of the Project Study Report (PSR)assignment required Harris to investigate at least
3-alternative designs and assess each on a number of criteria including effectiveness of the
design concept,constructability,geological feasibility,coordinating with other agencies,
environmental impacts and required mitigation,schedule,cost and others.Six alternatives were
investigated,including a do-nothing option,leaving the canyon in an "as-is"condition,and
another "cheap-fix"upgrade solution for the existing system.The PSR and appendices detail
each of these alternatives.The conclusion reached was that Alternative lA is the preferred
design.Although estimated to be 7%more costly than the lowest cost feasible solution,the
design is infinitely superior and has far fewer administrative,environmental and uncertain issues
associated with it.
Recommended Alternative 1A -Mid~canyon inlet with "tunnel alignment"Storm Drain
outletting to bluff:
Alternative 1A consists of the construction of a mid-canyon inlet structure,located slightly up-
stream of the upper switchback.The inlet structure is connected to the ocean with a 3,900-foot
long,54-inch pipe in a "tunnel alignment"that outlets below the oceanfront bluffs.The entire
length of this storm drain (SO)alignment falls within the City of Rancho Palos Verdes (RPV)
allowing RPV sole jurisdiction and is almost entirety within City owned land,requiring only
construction easements.The inlet structure will be located in the "middle"of San Ramon
Canyon,which will intercept flood waters north of the Tarapaca Landslide.
The storm drain conveys flows from the inlet structure southwesterly through a tunnel
approximately 1,900-feet in length to a point just south of Palos Verdes Drive South (PVDS).
From there,the next 1,700-feet of the pipeline will be constructed,using the standard open
trench (cut and cover)type of construction running parallel to the City boundary adjacent to
Palos Verdes Shores Mobile home Park in the City of Los Angeles.The pipe will be installed
within an existing dedicated 100-foot wide utility easement within Palos Verdes Shoreline Park
that was specifically set aside for utilities such as this proposed storm drain.The 1DO-foot wide
easement has less strict environmental impact requirements,serves as a firebreak for the
adjacent mobile home park and includes an informal hiking trail to the ocean.The final 300-feet
of pipe from the bluff top to the beach will run in a 38%sloped "slant drain"tunnel to an outlet
structure located at the base of the bluff.
The portion of the canyon downstream of the mid-canyon inlet structure,which runs through the
Tarapaca landslide,will be filled with up to 3D-feet of dirt.This is proposed to eventually stabilize
the canyon slopes and create an elevated creek bed with flatter side slopes.This portion of the
canyon would convey nothing more than side slope run-off.An access road from PVDE along
the westerly side of the canyon would be constructed to provide access for maintenance of the
upstream inlet structure.
The complete cost (construction plus soft costs)of this Preferred Alternative is estimated to be
$19.2 million.
Conclusion I Recommendations:
The recommended Alternative for the San Ramon Canyon Drainage Systems is Alternative 1A.
The advantages of this mid-canyon inlet with "tunnel alignment"storm drain outletting to the foot
RHarris &Assodates
City of Rancho Palos Verdes San Ramon Storm Drainage System – Project Study Report
I. EXECUTIVE SUMMARY
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of the bluff, combined with the disadvantages associated with other alternatives, make this the
recommended project solution. This recommended alternative has a competitive construction
cost and potential fast track implementation schedule, is the most environmentally compatible,
requires the least amount of right-of-way or drainage easements and falls entirely within the City
of Rancho Palos Verdes’ jurisdiction.
This recommendation is also supported for the following reasons:
1. It diminishes the erosion and undercutting in the canyon to nearly negligible, thereby
protecting PVDE switchbacks and adjacent sewer.
2. It substantially reduces the amount of flow being delivered to the existing CLA storm
drain at 25th Street.
3. It diminishes erosion and minimizes debris transport to allow “clear water” flows to reach
the existing CLA storm drain at 25th Street.
4. It provides a design that will accommodate flow from the side slopes within the canyon.
5. It provides a design that will restore and protect the existing streambed.
6. It provides the highest level of flood protection (except for a slightly higher level provided
by Alternative 1B, which costs more and has more significant environmental impacts)
Alternative 1A also rated number 1 in the objective “Risk Chart” (see page 28 of this PSR)
while the “No Project” alternative rated last. Although the “No Project” alternative would cost
nothing today, it could potentially be most expensive long-term solution. Further, doing nothing
to improve conditions could compromise the lower PVDE switchback in the next 5 to 7 years,
based on the present rate of erosion estimated at five feet per year. Additionally, doing nothing
could compromise the existing sewer line in the next 2 to 3 years.
As part of this PSR, Harris & Associates has identified a conceptual plan for a “shelf ready”
Early Action PVD Switchback Stabilization Project that will stabilize the lower PVDE switchback
and protect the existing sewer line in case delays occur in the implementation of the
recommended San Ramon Canyon Storm Drain construction due to funding, easement
acquisitions and/or lengthy outside agency approvals. Final design of the Early Action project
should be completed by Spring 2011
City of Rancho PalOli Verdcs San Ramon Stonn Drainage SySIClll -Project SlUdy Reflort
II.INTRODUCTION
II.INTRODUCTION
Harris &Associates (H&A)was retained by the City of Rancho Palos Verdes (RPV)to provide
a comprehensive Project Study Report (PSR),including preliminary concept design alternatives
for the San Ramon Canyon Drainage System.The PSR effort also includes a separate "shelf~
ready~construction project which would serve as an interim stabilization measure for Palos
Verdes Drive East (PVDE)should it prove to be necessary,before funding the ultimate final
design and construction can be completed.The PSR also included an investigation of the
project site for existing conditions including geology,biological assets,topography,etc.H&A
sub~contracted the following services to the following companies to capitalize upon their
expertise:
KDM Meridian -Aerial Mapping I Survey I Right-of~Way I Base Sheets for Plans (Appendix A)
GMU Geotechnical Inc.-Geotechnical Study Report (Appendix B)
SFC Consulting -Environmental Assessment I Expanded Initial Study (Appendix C)
EXISTING LOCATION MAP
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Cily or Rancho Palos Verdes 511n Rlllllon 510nll Dl"llillage 5yslem -Projccl Study RCI'0rt
II.INTRODUCfION
A.Project Limits
The subject San Ramon Canyon Drainage System falls within of the jurisdictions of the City of
Rancho Palos Verdes (RPV),and City of Los Angeles (CLA)San Pedro community and is
generally bounded by:
Boundary Edge:Defining Feature (Applicable City Jurisdiction)
•Northwest:Palos Verdes Drive-East (PVDE)Uswitchbacks"(RPV)
•Southwest:Palos Verdes Shoreline Park I Open Space (RPV)
•South:Pacific Ocean
•Southeast:Palos Verdes Shores Mobile Home Park &Golf Course (CLA)
•Northeast:Friendship County Park (LA County owned /RPV)&Tarapaca Road (RPV)
•North:Calle Aventura,PVDE and San Ramon Drive (RPV)
B.Purpose &Need
The primary goals of this PSR and associated preliminary concept design alternatives are to
protect Palos Verdes Drive-East (PVDE)switchbacks and to provide aU-weather access on 25th
StreeVPalos Verdes Drive-South (PVDS).The PSR is intended to review,evaluate and present
solutions to mitigate drainage and erosion problems experienced within the San Ramon
Canyon,which is located within the RPV and CLA.These problems affect the stability of the
lower PVDE switchback and access on 25th Street I PVDS.In addition,secondary goals are to
improve stormwater quality and the stabilization of adjacent roadways,slopes and properties.
The periodic flooding associated with almost every storm event is exacerbated by movement at
the Tarapaca Landslide that provides a continuous source for new sediment to the creek bed,
which in turn is transported downstream to 25 th Street.A cycle of erosion of the toe of the
Tarapaca Landslide and subsequent land movement refills the creek bed with newly loosened
sediment and makes the implementation of a project solution all the more urgent.Further,the
Tarapaca Landslide is redirecting powerful storm flows towards the toe of the opposite
(westerly)slope,below the lower PDVE switchback.This results in a loss of buffer between the
roadway and edge of the vertical canyon erosion of approximately five feet per year (estimated).
There are a number of interim solutions that the CLA may consider taking to protect 25 th Street
and the residents below the 25 th Street roadway embankment.These would largely involve the
relief of hydraulic pressure against the embankment and could include boring pressure relief
conduits through the embankment;the installation of vertical sub-soil drainage stacks that drain
into the existing storm drain under the road,etc.These potential projects would be outside the
City of RPV's jurisdiction and are therefore beyond the scope of this PSR,however they have
been raised here for consideration by the CLA.
Concern and support for a solution in the local community is growing rapidly as expressed at
several community meetings specifically held to discuss the issue.The public is well aware that
the present condition threatens to disrupt an all-weather public access,a continuous evacuation
corridor for the Palos Verdes Peninsula and emergency responder access along the 25 th Street
I PVDS and PVDE transportation corridors.It is also important to note that the existing condition
poses a significant threat to life and property from flooding and debris flows at 25 th Street and
the Palos Verdes Shores Mobile Home Park immediately downstream.
Additional issues that will also be remedied as part of all alternatives are as follows:
Page 5 of 34 RHarris &Associates
City of Rancho Pal06 Ve,dc6 San Ramon Slorm Drainage Syslcm -Projccl SlUdy Repon
II.INTRODucnON
Surface Drainage Erosion at PVDE Switchbacks:The existing drainage from the PVDE
switchbacks is intercepted by several small culverts that outlet at various locations on the
westerly San Ramon Canyon slopes.As part of the the San Ramon Canyon Improvements
project,these existing drainage improvements will be closely analyzed and recommendations
will be made to reduce erosion and improve the conveyance of these flows.Initial
improvements being considered include:
1.Installation of energy dissipators,such as rip rap downstream of the culvert outlets
2.Improved inlet grating to prevent obstructions
3.Surficial backfill!grading downstream of the existing outlets where erosion has occurred
Tarapaca Road Cul-De-Sac Down-Drain Stabilization:The Tarapaca Road cul-de-sac
currently drains to an inlet with a "down-drain~corrugated metal pipe (CMP)outlet along the
easterly canyon slope that has several concrete and steel anchors holding the pipe in place
along its alignment.During a January 2010 storm event the outlet pad at the canyon bottom was
considerably undermined.As part of any alternative solution pursued,this area should be
shored up and protected to prevent any further erosion and undermining of the existing drain
outlet.The catch basin inlet along Tarapaca Road should also be closely analyzed during the
PS&E phase to determine its adequacy of intercepting a 50-year storm event.Additional inlets
maybe needed to make sure that surface flows do not bypass catch basins or overtop street
curbs.
Water Quality Issues:Although a significant amount of the project flows are from natural
canyon runoff there are also residential roadways and PDVE runoff that are tributary along the
top of the ridge.Presently the "first flush"flows from the streets above are absorbed into the
pervious natural canyon invert,which essentially eliminates the need for related water quality
treatment systems to protect the runoff to the ocean.Further,as part of any design alternative
pursued,a low flow diversion system will be incorporated into the mid-canyon inlet structure to
allow "first flush"flows and other low flows to be conveyed to the natural canyon downstream so
that the canyon creek bed does not become completely dry.Methods of interception of
sediment and debris will also be reviewed as part of the design of the upstream inlet structure,
with more stringent requirements for collection applying to any alternative outletting the CLA
storm drain in 25 1h Street.However,natural sediment that is generated by the canyon is not a
pollutant,which is why any alternative outletting directly to the beach will allow "bulked"flows to
pass.For the new beach outlet alternatives the conveyance of natural canyon sediment will
reduce the amount of maintenance and debris removal required at the mid-canyon inlet
structure.
C,Objectives
This PSR details the existing conditions and known history of the existing geology,drainage and
erosion problems.It defines the hydrologic conditions and hydraulics of the existing CLA Storm
Drain downstream of 25 th Street as well as for the proposed alternative alignments.It includes
the analysis and evaluation of impacts and the feasibility of several alternative alignments
(including establishing a list of associated pros and cons,required outside agency approvals,
land acquisition!easement needs and costs,geotechnical constraints,environmental impacts
and mitigation costs,and realistic implementation schedules associated with each alternative).
The alternatives considered will also be well detailed via preliminary concept design plans.
Further,for reference purposes,various exhibits within the report depict the following:
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Cil)'of Rancho Palos Verdcs Sail Ramon SlOnn Drainagc S)'slcm -Projccl SlUd)'Report
III.SE'ITING
Existing Facilities Exhibit -this map shows existing City of Los Angeles owned and
maintained storm drain facilities beginning at 25 th Street (see Appendix D)
Hydrology map showing the drainage area tributary to the existing City of Los Angeles
owned and maintained storm drain south of 25 th Street,which outlets to the Pacific
Ocean (see Appendix D)
Hydrology and Hydraulic calculations for the 50-year storm event peak discharge (Q5~
for the existing City of Los Angeles owned and maintained storm drain south of 25
Street,which outlets to the Pacific Ocean (see Appendix D)
Detailed write up and analyses of the various design alternatives (see Appendix E)
Hydrology map and calculations for the 50-year and 100-year storm event peak
discharge &050 and 0100)for the drainage area tributary to the San Ramon Canyon
north of 25 t Street (see Appendix F)
Preliminary Conceptual Storm Drain Plan and Profile Sheets for each alternative
alignment solution,including supporting hydraulic calculations (see Appendix G)
Detailed cost estimates for each alternate alignment solution (see Appendix H)
III.SETTING
PVDS I 25 th Street is the main East-West access route for the south side of the Palos Verdes
Peninsula.Within the City of Los Angeles (CLA),it crosses the natural San Ramon Canyon
drainage system.The road was built upon 25-feet of imported fill embankment placed in the
canyon.A culvert was placed at the bottom of the embankment to allow canyon drainage to
pass downstream.Over the years the canyon upstream of the road has been filled flush to the
roadway surface with sediment (see Photo 1:San Ramon Canyon looking south toward
25th Street).Photo 1
San Ramon Canyon consists of moderate to steep
sloping terrain that yields fast flowing runoff.This
runoff collects within the natural canyon channel.The
total watershed area upstream of 25 th Street is 187
acres,of which 160 acres is in RPV,including 3 acres
of Los Angeles County (LAC)owned land at
Friendship Park.The remaining 27 acres are within
the CLA.The steep watershed concentrates run-off in
high flow rates (Q100 =262 cfs and Q50 =217 cfs).
The high velocity flows occur over relatively short
durations and are capable of conveying a
considerable amount of debris.
Photo 2
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Cily or Rancho Palos Verdes San Ramon SlOnn D~il1age Syslcm -Projccl SlUdy Rcport
III.SETfING
The periodic flooding associated with almost every storm event is significantly exacerbated by
the Tarapaca Landslide (see Photo 2:Tarapaca Landslide looking east from pvoe
sWitchbacks).The landslide provides a continuous source for new sediment to the creek bed,
which in turn is transported downstream to 25th Street.A cycle of undercutting of the toe of the
Tarapaca Landslide and subsequent land movement refills the creek bed with newly loosened
sediment.Then rainstorms of even modest intensity transport material downstream and begin
to undercut the toe again.Further,changes to the streambed alignment,caused by this
repeating cycle,have redirected powerful storm flows towards the opposite wall of the canyon.
The wall of this canyon supports the two PDVE switchbacks (see Photo 3:Aerial view of
existing erosion at the lower PVOE switchback)resulting in an erosion rate estimated to be
about five feet per year.Geologists estimate that PVDE could be destabilized if the canyon
walls are eroded an additional 35-feet towards the roadway.
The situation is further impacted by the constraints of the existing inlet structure at 25th Street.
The culvert under 25th Street was originally constructed as a 42-inch CMP crossing.A roadway
embankment over the culvert was constructed using 25-feet of imported fill.Debris laden flow
which is constricted through the culvert has led to the silting up of the canyon and inlet,which
eventually filled the 25-foot deep canyon to the level of the 25th Street roadway (see Phot01 on
previous page and Section A-A on next page).Over the past 40 to 50 years,as sediment
built up,the original inlet pipe was extended vertically upward multiple times to the new/raised
sediment surface to allow at least some of the surface flow to make it to the culvert crossing.
Per CLA staff,inlet maintenance and sediment excavation was originally prevented due to lack
of an access/maintenance easement onto the private property upstream of 25th Street.More
recently,growing environmental constraints contributed to CLA's limited maintenance efforts for
fear of disturbing nesting birds,etc.and/or incurring fines for lack of proper environmental
studies and clearances to do the required maintenance work.
The presently configured inlet upstream of 2S\l1 Street consists of a raised galvanized steel cage
(see Photo 4:Existing Inlet at 2S1h Street)over an inlet opening that consists of only two 12-
inch CMP (see Photo S)oriented to flow northerly.These are intuitively deficient to convey the
peak flows generated from San Ramon Canyon,which are flowing south.Moderate rainfall can
quickly overwhelm the two pipes resulting in saturation of the accumulated sediment upstream
of the road and at times ponding above the roadway grade.Ponding depths have reached as
high as two-feet above the road surface (see Photos 6 &7:2S1h Street flooding and regularly
occurring debris accumulation,respectively).The contrasting views of Photos 4 and 7
create ~before~and ~after"views of the sediment accumulation that regularly occurs at 2S\l1
Street.Even with the two additional existing catch basin inlets on the south side of 25 th Street
there is insufficient capacity to convey flow to the existing 25\l1 Street Storm Drain.This flooding
cycle occurs regularly during the rainy season between October 15 and April 15 each year.
Photo 4
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Photo 5..
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Cily or Rallcho Palos Vcrdu San Ramon Slonn O .....inagc S)'Slcm -Projccl SllIdy Repo"
III.SETTING
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SAN RAMON CANYON
CREEK PROFILE
SECDON A A
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Q'lY OF RAHCtO I'I\L08 'tIEI'DEIl
SAN RAMON CANYON
SECTION A~A
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City of Rancho Palos Verdes San Ran.on SlOn"Drainage Syslem-Projecl Sludy Rcporl
III.SElTlNG
Photo 6 Photo 7
When flooding is severe enough to over top the concrete barrier K~rails,a buildup of water
against the perimeter wall on the south side of 25th Street occurs.This wall was built along the
northerly edge the Palos Verdes Shores Mobile Home Park (See Photos 6 &8).The existing
block wall is permanently leaning from the strain of past debris-laden ponding in the roadway
(see Photo 8:Perimeter wall is "bowed"(see black arrow)from flooding pressures).The
distress on this perimeter wall is significant because it is essentially performing as the ~Iast line
of defense~to hold back the 25th Street floodwaters.If toppled over,the result will be a flash
flood down the 25-foot high 2:1 road embankment,and through the mobile home park
potentially risking both life and property.A flash flood could potentially also erode the
downstream embankment of the roadway where it is breached,releasing stored sediment
currently held in place by the road (see Photo 9:Aerial view of 2S lh 5t at mobile home park).
Photo 8 Photo 9
The City of RPV has had an informal agreement with the City of Los Angeles to share in the
effort to prepare for storm events and to clean up the area after flooding occurs.This
agreement is in the process of being formalized.The 25 th Street right-of-way extends only 15'
north of the edge of the paving,which severely limits the ability of the Agencies to clean out the
area around the inlet to the drain at the toe of the embankment.The area beyond the right-of-
way-is privately owned and completely within the City of Los Angeles.RPV had repeatedly
urged CLA to contact the owner to obtain an easement,however are not aware of any progress
in that regard.
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City of Rancho Palos Verdcs San Ramoll SlOnn Drainagc Syslcm -Projcct Siudy Rcport
IV.AGENCY INVOLVEMENT
NOTE:Photo 9 actually captures the regular debris removal operation is in progress,with the k-
rail removed and an excavator filling a dump truck with accumulated sediment.The flooding of
25th Street requires action to periodically close all or portions of the road until flooding subsides
and the debris is removed,as was the case during the January 19,2010 storm event (see
Photo 6).Debris removal was accomplished with only minor street road closures during the
December 2010 multi day storm events.After each storm even,maintenance is performed to
remove the debris from the street and to reduce the elevation of the debris fill behind the K-rails
(see Photos 7 &9).
IV.AGENCY INVOLVEMENT
The importance of keeping 251h Street open at all times is of utmost concern to the City of
Rancho Palos Verdes (RPV),City of Los Angeles (CLA)and Los Angeles County (LAC).For
several years RPV has been closely monitoring the situation.They have been looking for
solutions and funding and have met regularly with key staff members from CLA and LAC to
identify the issues relating to the drainage system and investigate solutions to stop the flooding
cycle.
Most recently,as part of this PSR process,RPV held a meeting on June 17,2010 with CLA and
LAC staff with renewed energy and urgency.RPV discussed the project issues,the role of each
agency,and the possibility of coming to an agreement I game plan to move a project solution
forward.A summary of the key items discussed during this meeting are as follows:
•LAC indicated that while Los Angeles County Flood Control District (LACFCD)has flood-
control interest in this community,they do not have a jurisdictional interest.
•There is a maintenance agreement currently being developed between RPV and CLA for
pre-storm preparedness and post-storm clean up at 25th Street and San Ramon Canyon.
•CLA has applied for a grant with the Federal Emergency Management Agency (FEMA)
to improve the existing inlet at the north side of the 25th Street.The funding request was
denied.
•RPV requested that CLA immediately approach the owner of the property upstream of
25 th Street to determine if they would be receptive to granting a temporary easement for
emergency maintenance and grading of a debris basin before the winter storms of 2010
&2011.RPV requested that H&A prepare an exhibit illustrating an "251h Street Interim
Basin Grading~solution to temporarily provide debris storage capacity for the pending
storm season (see Appendix 1).RPV sent this exhibit to CLA,to be used for contacting
the property owner.RPV has not heard back whether this request was successful at
time of this writing.
•CLA confirmed that they support RPV's efforts to pursue a comprehensive solution,
however they clarified that they are severely short on drainage improvement funds.
V.COMMUNITY INVOLVEMENT
Public support for the project is growing along with their concerns about the dangerous
conditions at 25th Street during storm events.Public comments have confirmed that now that
this PSR process is underway,they are more confident that their issues are being addressed.
Community support and involvement will be a key element in procuring future funding for the
project.
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VI.EXISTING CITV OF LOS ANGELES (CLA)STORM DRAIN AT 25TH STREET
In order to keep the general public informed and to improve communication,RPV has
proactively taken the following steps:
•Established a link on the City's website for easy access and updated project information
•City Council regularly discusses the project status and welcomes input from the
community
•Periodically notices are issued to people signed up on their "ListServ"program so that
updates on the project can be e-mailed to their home computers
•RPV held an "information gathering"meeting on Wednesday,May 12,2010,at Miraleste
Intermediate School to introduce the PSR team,discuss the study elements,allow the
public to voice their concerns,and to distribute a public opinion survey that the public
filled out and returned to the City with their written suggestions,questions and concerns.
•RPV held a "progress meeting"on Wednesday,July 21,2010,again at Miraleste
Intermediate School,to update the general public on the status of the engineering,
geotechnical and environmental investigations. Preliminary concept designs were
presented to present the alternatives considered,show the direction the City is heading,
and solicit additional community feedback.
VI.EXISTING CITY OF LOS ANGELES (CLA)STORM DRAIN AT 25'"STREET
POOto10
As part of this PSR,a detailed hydrology and
hydraulics (H&H)analysis was performed on the
existing CLA storm drain that begins at 25th
Street and runs to the ocean discharge point on
the bluff.This study included a detailed
confirmation of the tributary area boundaries in
the field.The existing storm drain that accepts
the San Ramon Canyon runoff has its headworks
just upstream of 25th Street (see Photos 4,5 &
7),is owned and maintained by the CLA,and
has a mainline pipe size that ranges from a 42-....-
inch CMP,to 48-inch reinforced concrete pipe ~...J
(RCP),to 72-inch RCP to eventually to an 84-inch RCP that outlets from mid-bluff face into
the Pacific Ocean (see Photo 10).
Since CLA was not able to provide the requested H&H analysis and/or supporting data,H&A
was directed by RPV to perform a detailed H&H analysis of the existing storm drain system.
This analysis is important for any design alternative that would use the CLA storm drain as
an outlet system.Based on a detailed confirmation of the drainage boundary,the use of the
LACFCD approved software WMS 8.0 for hydrology,and WSPG software for hydraulics,it
was determined that the existing storm drain south of 25 th Street,is "technically"adequate
(see "QUALIFICATION"discussion that follows)to handle the flows produced by a 50-
year storm re-occurrence.By the time it daylights out of the coastal bluff face,the existing
storm drain conveys a total 050 =490 cfs,which is generated by a total tributary area of 375
acres (see Appendix D for the Hydrology Map &calculations for the existing system).
Page '12 or 34
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City of Rancho Palos Verdes Sail RamOIl Stonn Drainage Syslem-Project SlUdy Repon
VI.EXiSTING CITY OF LOS ANGELES (CLA)STORM DRAIN AT 25TH STREET
QUALIFICATION:Although the existing CLA storm drain south of 2Sth Street was
"technically"determined to be hydraulically adequate,there are several significant issues
associated with this system that make a "qualification ft statement necessary.These issues
undermine the confidence of the system's long-term ability to perform.In addition to the
previously identified upstream inlet /debris basin deficiencies,the following should be
addressed if a solution is selected that allows improved canyon flow into this system:
Photo 11
•
•
In order to convey the SO-year storm event peak flow rate,velocities as high as 48
feet per second (33 mph)are calculated (see Appendix D).These resulting
velocities are well beyond the recommended maximum of 20 fps +/-for the
reinforced concrete pipe material utilized within the existing system.Based on the
as-bums available through the City's website (NavigateLA.lacity.org),the existing
storm drain was not constructed to have an extra-thick PCC cover over the interior
steel reinforcement or a steel plate lining to be able to handle high velocities as is
recommended when velocities exceed 20 fps.This means that one of two things will
happen if the existing CLA storm drain is to be utilized as the outlet system for RPV's
proposed storm drain at San Ramon Canyon.Either the interior concrete lining over
the steel reinforcement in the RCP will be pre-maturely worn and scoured,requiring
an accelerated future replacement or the flows simply will not be able to pass as
quickly as required.The second result means that something less than a SO-year
storm event peak discharge would be conveyed by the storm drain and would likely
cause flows to continue to back up on 2Sth Street.This may result in continued
flooding at 2Sth Street even with an improved storm drain system in place.This would
also be the case if/when a storm larger than SO-year storm event peak discharge is
experienced.
CLA provided closed circuit television (CCTV)inspection videos of portions of their
existing storm drain south of 2S th Street (performed on March 8,2001 and August 9,
2007).The videos covered approximately 760 lineal feet of 48-inch RCP (from as-
built station 19+1S.S9 to the existing inlet at the north side of 2Sth Street,see
Appendix 0 for CLA Storm Drain As~builts).The length of pipe that was video
inspected is approximately one third of the total existing storm drain length.The
video showed that there were several serious physical defects in the existing system
including:several separated pipe joints (see Photo 11 where an offset pipe joint
has been backfilled with rocks
and mortar)and other condition
issues that prevented the CCTV
inspection from proceeding any
farther.Due to the importance of
knowing the condition of the entire
existing storm drain system it is
recommended that CLA perform a
detailed CCTV video inspection of
the entire length of the storm drain
to fully assess its condition.This is
especially important if the 2S th Street
Storm Drain is going to be utilized as
the downstream outlet system for
the proposed San Ramon Canyon
drainage system.
Page 13 of34 BHarriS &Associates
City of Rancho Palos Verdcs San Ramon Ston"Drainagc System -Proiect Study Report
VII.PROPOSED STORM DRAIN STANDARDS AND DESIGN CRITERIA
• A detailed review of the as-buill plans for the existing CLA storm drain south of 25 th
Street (see Appendix D)revealed that the system was constructed in multiple
phases over many years.The storm drain includes multiple sharp horizontal angle
points and multiple sharp vertical grade breaks all along its alignment.Such angle
points and grade breaks are not conducive to good long-term hydraulic performance
and are also typically an increased source for localized wear,scouring,pulled joints,
etc.This is especially concerning given the high velocity requirements and poor
physical condition of the existing drainage system as previously mentioned.
•Since the existing CLA storm drain system is presently only being supplied with the
minimal flows intercepted by a few catch basin inlets at 25 th Street,the existing storm
drain has yet to experience the predicted high velocities under the present developed
tributary conditions upstream.The existing storm drain may have experienced a
large magnitude storm in the past that was able to flow directly into the upstream
inlet with impediment from accumulated debris.However,that would have been
before the subsequent 40-years of upstream development,which changed the runoff
characteristics,and increased the amount of runoff the system must now convey.
Again,this is a source of significant concern given the high velocity requirements and
poor existing physical condition of the existing drainage system.
• A portion of the existing storm drain system passes under residential dwellings within
the Palos Verdes Shores Mobile Home Park (see previous "Existing Location
Map"),which is not a standard practice and the associated risk should be revisited if
additional flows are to be introduced into the existing drainage system.
•The existing mid-bluff outlet (see Photo 10)also presents a serious CLA storm drain
system deficiency that needs to be remedied before any additional flow can be
conveyed by this existing system.This concern is twofold because,in addition to the
lacking hydraulic capacity,the long-term stability of the bluff (and adjacent houses)is
at stake and subject to undermining due to unchecked erosion.Even now,with
lesser flows,the adjacent residents complain about the windswept uback-spray"that
inundates their properties,which would only worsen with increased flows.
VII.PROPOSED STORM DRAIN STANDARDS AND DESIGN CRITERIA
A.Storm Drain Design Standards and Pending MTD Process
Although the proposed storm drain improvements will likely be constructed by RPV,one of
the alternatives proposes to construct a portion of the storm drain within the CLA's
boundary.This proposed alternative would connect to the CLA drainage system thus it
would have to be reviewed and approved by CLA.RPV is also considering the alternative of
transferring the maintenance of this storm drain alternative within the RPV boundary over to
LAC through the Miscellaneous Transfer Drain (MTD)process.If the MTD process is
pursued it will require the review and approval by the Los Angeles County Public Works
Land Development Department (LAC)
However,it should be noted that the MTD process will likely not be allowed for any tunnel
option that outlets onto the beach.As was the case with RPV's McCarrell Canyon Storm
Drain Project,two factors will make any coastal bluff tunnel alternative non-transferable:
Page 14 of34
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Cit)'of Rancho PalQij Vcrdc~Siln Rallwn Stoml Drllinilge Systcm -Project Study Reporl
VII.PROPOSED STORM DRAIN STANDARDS AND DESIGN CRITERIA
1.As was the case with the RPV's McCarrell Canyon Storm Drain Project,the geotechnical
determination that the bluff stability has a factor of safety (FS)less than 1.5.(Note a FS
=1.0 means the bluff slope is in imminent danger of failing.)
2.The lack of a drivable maintenance access road to the outlet structure on the beach
would most likely make any coastal bluff tunnel alternative non-transferable.
Further,any alternative that connects to a CLA storm drain would be complicated by the fact
that LAC has a standing agreement with CLA not to accept the transfer of any CLA storm
drains because CLA is required to maintain its own drainage systems.Conversations to
date with LAC staff have not ruled out entirely as to whether they would accept the San
Ramon Canyon Drainage System through the MTD process.However LAC made it clear
they would require a drivable access road along the entire drainage system alignment.
Presently,grading an access road in San Ramon Canyon is not envisioned to be practical,
given the narrowness of the canyon,the anticipated non-drivable rip rap energy dissipator
~drop structures~and the desire to keep the environmentally sensitive creek as natural as
possible after construction.See Appendix F for the discussion section comparing each
alternative and for additional information regarding the feasibility of pursuing the MTD
process.
Regardless of whether the MTD process will be pursued,as an appropriate precaution,the
most conservative storm drain design criteria will be utilized throughout the preliminary
design analysis of this PSR.The design criteria utilized is consistent with the Los Angeles
County Public Works Hydrology Manual,dated January 2006,the Los Angeles County
Flood Control District Hydraulic Design Manual,dated March 1982,and Los Angeles County
Public Works Standard Plans,2000 Editions.
B.Storm Drain Design Criteria
See Appendix J for Table 1 which illustrates the primary criteria followed for the storm drain
design analyses.
C.Storm Drain Hydrology and Sediment Production
As part of this PSR a detailed confirmation of the tributary drainage boundaries was
performed for both the San Ramon Canyon and the entire existing CLA Storm Drain system
from 25 th Street down to the beach outlet,including all tributary lateral systems.The
Modified Rational Method hydrology criteria used for this study are outlined in the latest Los
Angeles County Public Works Hydrology Manual,dated January 2006.The program
Watershed Modeling System (WMS)software package 1 was utilized to perform the detailed
hydrology analysis.The site is located within Los Angeles County Debris Potential Area
(DPA)Zone 6 and soil type numbers 2 and 17.These parameters establish that the natural
San Ramon Canyon is capable of generating 5,434 cubic yards of debris.This debris
volume would have to be addressed in any CLA inlet structure I debris basin design due to
their design requirement to accept only ~c1ear f1ows~into their drainage systems.
1.MODRAT Interface by the Environmental Modeling Research laboratory at Brigham Young University.Version 8.0,build
date February 23,2007,copyright 2006,serial 101693.
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Cily or Rancho P..los Verdes San Ramon Stonn Drainage Systcm -Project Study Report
VII.PROPOSED STORM DRAIN STANDARDS AND DESIGN CRITERIA
Peak flow rates were calculated for two different levels of storm reoccurrence.namely,a SO-
year storm (Q50 =217 cfs)and a 100~year storm (Q100 =262 cfs)and the results are listed
in the alternative storm drain discussion section.CLA and LAC only require that the
proposed San Ramon Canyon Drainage System be designed to convey a Capital Flood (SO-
year storm event peak discharge,050).Design flow for alternatives using the existing CLA
system utilized a 50-year storm event peak discharge.This is because a SO-year storm
event peak discharge is all the existing CLA storm drain system is capable of accepting.
However,for alternatives not using the CLA storm drain as an outlet a 100-year storm event
peak discharge design flow is recommended,since only a minor pipe upsizing is required
(from a 48-inch to S4~inch diameter)to provide this level of protection.Utilizing this larger
pipe size also may actually reduce the bottom line construction cost due to the smaller
annular backfill required in the proposed aO-inch tunnel cross section.
Preliminary level (30%+1-complete)storm drain "plan and profile"sheets and typical cross
sections have been prepared for the various alternative storm drain alignments (see
Appendix G).
D.Storm Drain Hydraulics
All mainline storm drain hydraulic modeling was performed utilizing Water Surface Pressure
Gradient (WSPG)Computer Hydraulic Analysis Program 2 .The WSPG program computes
and plots uniform and non-uniform steady flow water surface profiles and pressure gradients
in open channel or closed conduits with regular or irregular cross sections.The
computational procedure is based on solving Bernoulli's equation for the total energy at
each section and Manning's formula for friction loss between the sections in a stretch of
pipe.
The Manning's equation is the most commonly used flow resistance formula for the analysis
of open channel and gravity flow pipe systems.The equation modified to English Units is
show below:
Q=1.486AR 2J3 S"Where:A =Area of pipe (sf)
n Q =Sewer flow (cfs)
'n'=Manning's roughness coefficient
S =Slope of Energy Grade Line (ftlft)
R =Hydraulic Radius (tt)
Since the recommended storm drain pipe material is high density polyethylene (HOPE)(due
to the proposed steep installation profile slopes)the 'n'value of 0.012 applies to the
evaluation of both the tunnel and canyon alternatives above 2S th Street.Downstream of 2S lh
Street a Manning's n =0.013 was utilized for the existing Rep system.
Using the WSPG program,each of the alternative alignment scenarios were studied to
produce the resulting storm drain hydraulic grade line (HGL)and are as shown on the
conceptual storm drain plan and profiles sheets (see Appendix G).
2.LACFCD F0515P,software package by Woodcrest Engineering,15790 Rancho Viejo,Riverside.CA 92506,Copyright
1996).
Page 16 of 34 HHarriS &Associates
Cil)'or Rancho PlilOli Verdu San RllmOll Siorm Orain;lge Syslem -PrujeCI Slud)'Report
VUI.ENVIRONMENTAL REQUIREMENTS
VIII.ENVIRONMENTAL REQUIREMENTS
A.Environmental Clearance Jurisdictional Agencies
Per SFC Consultant's Expanded Initial Study (see Appendix C)there are no riparian plant
species,hydric soils or conducive hydrology to support a wetlands habitat within the affected
project area.However,San Ramon Canyon is still a jurisdictional drainage course that is
under the jurisdiction of the Army Corp of Engineers (ACOE)as part of the River and
Harbors Act.It is also under the jurisdiction of the California Department of Fish and Game
(CDFG)and the Los Angeles Regional Water Quality Control Board (LARWQC8).If a
drainage alternative is chosen that would put an outlet structure on the beach it will come
under the jurisdiction of the ACOE (again as part of the River and Harbors Act)and the
LARWQC8.Permits from these agencies will likely be required for impacts to jurisdictional
waters.Impacts to biological species and habitat will be mitigated through the Natural
Community Conservation Plan (NCCP)as discussed below.To avoid reproducing all of the
environmental findings and recommendations the referenced report is considered an
integral part of this PSR.
B.Natural Community Conservation Plan (NCCP)
Fortunately RPV anticipated the need to repair or improve drainage systems in several
canyon areas throughout the City and realized that these drainage projects would
necessitate work in potentially sensitive habitat areas.Thus they established a citywide
Natural Community Conservation Plan (NCCP).This plan identified biological resource
areas and established habitat preserves,such as the Palos Verdes Shoreline Park I Open
Space site (south of 25th Street I PVDS and west of San Pedro I CLA).It was estimated that
these future City drainage improvement projects would result in a cumulative combined loss
of 10-acres of Coastal Sage Scrub (CSS)habitat and 24-acres of non-native grassland.
This anticipated loss has already been mitigated through dedication of City property,
resulting in 3D-acres of offsite CSS mitigation and 12-acres of offsite non-native grassland
mitigation.See the mitigation measure discussion item that follows.
C.Environmental Clearance Obstacles
Alternatives 1A (with tunnel alignment that outlet directly to the beach)is estimated to
impact approximately 0.04 acres of jurisdictional waters in San Ramon Canyon.The impact
area on the bluff face is estimated to be 0.02 acres and extends onto the beach area below.
Alternative 18 (same as Alternative 1A but extending storm drain to connect to the upper
canyon outlet structure)is estimated to impact approximately 0.06 acres of jurisdictional
waters in San Ramon Canyon.The impact area on the bluff face is estimated to be 0.02
acres and extends onto the beach area below.
Alternatives 2A (with canyon alignment that outlet to the 25th Street storm drain)is estimated
to impact approximately 0.79 acres of jurisdictional waters in San Ramon Canyon,with
limited or no impact to the beach bluff (except if required to improve the existing mid-bluff
outlet).Alternative 28 (same as Alternative 2A but extending storm drain to connect to the
upper canyon outlet structure)is estimated to impact approximately 0.81 acres of
jurisdictional waters in San Ramon Canyon,with limited or no impact to the beach bluff
(except if required to improve the existing mid-bluff outlet).
Page 17 oC34
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City of Rancho Palos Verdc8 San Ramon Stoml Drainage Syslem -Projccl SllJd)'RqlOrI
VIII.ENVIRONMENTAL REQUIREMENTS
The following are the jurisdictional agencies,along with the permits and requirements of
each,for the San Ramon Canyon Storm Drain Project
1.Army Corp of Engineers (ACOE):Section 9 and Section 10 of the Rivers and Harbors
Act,especially due to the grading within San Ramon Canyon the project,will likely
require a Section 10 permit.
2.California Department of Fish and Game (CDFG):A CDFG 1602 permit will be
required to address impacts to the maintained drainage channel.CDGG will request the
regional board to review their recommendation and hence issue a 401 permit.
3.Los Angeles Regional Water Quality Control Board (LARWQCB):Permanent Best
Management Practices (BMP's)will be required for long-term maintenance and water
quality purposes.Also a National Pollutant Discharge Elimination System (NPDES)
construction document will be required either as part of the LARWQCB requirements or
as part of the LAC Municipal Separate Storm Sewer System (MS4)Permit.
4.Coastal Resource Management (CRM)District:The study area lies within the Coastal
Resources Management (CRM)District with a terrestrial designation CRM-10.The area
contains some terrestrial wildlife value and the offshore waters are protected in this
CRM.All marine resources (Le.kelp beds,abalone habitat,rock reef habitat,etc.)are to
be protected against impacts should the new ocean outlet alterative (1A,1B)be
selected.
5.City Natural Community Conservation Plan (NCCP):See previous discussion item
and mitigation measures that follow.
D.Mitigation Measures Required:
1.Canyon Invert Fill:Re-vegetation of the streambed and affected canyon slopes with
native vegetation will be required.Re-vegetation activity will include a plant palette,
consistent with the Resource Agency and Native Plant Society criteria,that lists exact
species of plants to be restored and the native plants be used derived from local genetic
sources.NOTE:the !J..rmm-Canyon Connection Alternatives 1Band 2B will have more
significant impacts regarding the invert filling operations than the Mid~Canyon Inlet
Alternatives 1A and 2A simply because more pristine canyon will be disturbed by fill and
grading.Further,it has been noted that the upper canyon is more stable,suffers less
from erosion,has more bedrock outcroppings and has a rockier invert in general.This is
largely what is driving the Mid-Canyon Inlet Alternatives 1A and 2A to stop where they
do.Upstream of that point,the canyon is more natural and stable therefore,there is less
need to improve I disturb it.Many hilllop homes look down to this natural upper canyon
thus their pristine canyon views would also be impacted by Alternatives 1Band 2B.
2.No significant loss to raptors and migratory birds or their habitats are expected,and
therefore no mitigation is required.As a Best Management Practice (BMP),we
recommend that if grading or construction occurs between March 1 and August 31,the
area should be monitored on a regular basis for 30 days prior to any disturbance.This is
done to ensure that no nesting is occurring.Monitoring would require a short period of
observation (approximately one hour)to ensure that no birds were coming and leaving
Page 18 of34
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City of R'UICho Palos Verdes San Ran.on Stom.Drainage System -ProjeCt Stlldy Report
lX.GEOTECHNICAL REQUIREMENTS
their nests on a regular basis.If birds are using a nest in the area,then it would be
recommended that either construction be rescheduled to after the breeding season or
that a qualified biological monitor be present during construction to ensure that nesting
birds do not abandon the nest until the young are fully fledged.
3.BMP's:Best Management Practices (BMP's)shall be implemented for the project and
are included in the Mitigation Monitoring Program for water quality.The PS&E
construction document preparation phase for the alternative ultimately chosen would
also fully detail the construction BMP requirements.
4.Cultural Resources:No cultural resources were found to exist within or adjacent to the
project area.However,mitigation has been provided in order to off-set the potential for
unknown buried prehistoric or historic archaeological remains.
5.Native American Consultation:A record search of the sacred land file has failed to
indicate the presence of Native American cultural resources in the immediate area.The
GabrielinofTongva Tribal Council recommended monitoring during grading of the inlet
structure area.
IX.GEOTECHNICAL REQUIREMENTS
Per GMU Geotechnical's Geotechnical Study Report (see Appendix B)all of the proposed
design alternatives are considered feasible as long as the recommendations in the report
are followed.Based on the results of GMU Geotechnical's investigation and analyses,the
following ten (10)conclusions were presented:
1.Design Alternatives 1A,18,2A, 2B,3 and 4 are considered to be feasible,provided the
design considerations and recommendations for additional work presented in this report
are followed.
2.The site is predominately underlain by the South Shores landslide,an ancient,dormant
landslide complex.
3.The site includes the Tarapaca Landslide.
4.None of the design alternatives will adversely impact the repaired San Ramon Canyon
failure area,located offsite to the north.
5.Groundwater should not be a significant impact to any of the design alternatives for the
project.
6.The site will be subject to seismic hazards in the future;however,none of the design
alternatives will increase the likelihood or magnitude of these impacts.
7.It is feasible to stabilize the Tarapaca Landslide and reduce erosion at the toe through
the construction of a gravity-type buttress (fill).
8.The switchbacks of PVDE are currently considered to have safety factors 3 at or greater
than 1.3.Approximately 35 to 40 feet of additional lateral erosion/failure would have to
occur before the factor of safety is reduced to 1.0 (imminent failure)at the lower
switchback.
9.The existing 8-inch sewer line east of the PVDE switchbacks should be protected as
soon as possible in order to avoid damage to the line from canyon wall erosion,since
this sewer line is actually closer to the San Ramon Canyon erosion than the PVDE road.
3.Safely faclor :::lhe ralK>of the maximum stress thai a structural part or other piece 01 material can withstand 10 the maximum
stress estimated for it in the use for which it is designed.and in Ihis applicable case of slope stability FS :::1.5 Is considered "safe"
and FS:::1.0 is considered to be in imminent danger of failure.
Page 19 of34 BHarriS &Associates
City of Rancho Palos Verdes San Ran.on Stonn Drainage System -Projecl Study RCPUM
IX.GEOTECHNICAL REQUIREMENTS
10.The initially proposed conceptual easterly canyon access road would have required
significant corrective grading and/or stabilization of the cuts;therefore,the road has
been located to a more favorable site on the westerly canyon slope.
The last geotechnical item #10 above,regarding the lack of suitability of the placing an access
road to the mid-canyon inlet structure on the easterly canyon slope,came after H&A had
already developed a conceptual easterly access road layout (see Appendix G).Instead an
access road to the mid-canyon inlet structure on the westerly canyon slope will be
recommended and only terrace drains &down drains will be constructed on the easterly canyon
slope to keep surface water from flowing into the top of the Tarapaca Landslide ~head~scarp"
(which is the open gap at the top of the slide area which is visible in Photo 2).A conceptual
illustration of the new westerly canyon slope access road and easterly canyon slope terrace /
down drains is shown on the below.
t
"-•I
po---, ,••-
-!J-,/----
I'I '-'4 I,y-
I'IlOl'OS[D ll£T....tefI(l ~PI'lOI'05dl mIIUoCI:IlflMll ;"
"\.'.1 I
~,"':'~,'\,
"
,...
II ",
""~\':.>~
Page 20 of 34
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_Harris &Associates
Cily or Rancho Palos Vcrdcs San Ranloll SlOtm Drainagc Systcm -Projcct Smdy Rcpon
X.STORM DRAIN DESIGN ALIGNMENT ALTERNATIVES
X.STORM DRAIN DESIGN ALIGNMENT ALTERNATIVES
The aerial topographic survey specifically obtained for this study was used to layout out and
analyze several alternate storm drain design alignments.The alternative alignments were
narrowed down to two (2)primary storm drain alignments,each with a "sub-option"extension
to the Upper San Ramon Canyon,as well as a low-cost possible alternative,and a "No
Project"or do nothing alternative.This resulted in a total of six (6)alternatives (1A,1B,
2A, 2B,3 &4)being considered for the San Ramon Canyon Drainage Study (see Appendix
F &G).Following is a brief summary of each alternative alignment,including pros and cons
that will help determine the preferred solution for the San Ramon Canyon Drainage System
(see Appendix F for a more complete explanation of each alternative).
A.Alternative 1A -Mid-canyon inlet with "tunnel alignment"that outlets to the bluffs
Alternative 1A consists of a mid-canyon inlet with 54-inch HOPE pipe in a "tunnel
alignmene that outlets to the bluffs.The entire length of this storm drain alignment falls
within the City of Rancho Palos Verdes (RPV)allowing RPV sale jurisdiction.The
upstream terminus is a proposed inlet structure in the "middle"of San Ramon Canyon at
a location that was strategically chosen to intercept flood waters above the Tarapaca
Landslide.At this location bedrock "daylights"in the existing canyon bottom and side
walls (see Photos 12 &13:Bedrock at "mid-canyon"invert and downstream
adjacent wall).
Photo 12
The 54-inch storm drain pipe would then
convey flows to the southwest in an 80-
inch diameter tunnel approximately
1,gOO-feet in length with no horizontal or
vertical grade breaks (to facilitate
construction) to a launching pit location
just south of 25 th Street I PVDS (see
Photo 14).(The tunnel construction will
actually proceed uphill from the
launching pit until it daylights in the
canyon invert just downstream of the
proposed inlet structure location.)The
method of installation going downstream
from the launching pit then changes to
open trench.Open trench construction
involves surface excavation of a trench,
placing pipe and backfilling.At the
Page 21 of34
Photo 13
Photo 14..
"Harris &Assodates
Cily or Rancho Palos Verdcs San Ramon Slonn Drainagc SYlIlcm -I'rojcci Slud)'RCI'0n
X.STORM DRAIN DESIGN AUGNMENT ALTERNATIVES
upstream end of the open trench reach there is a horizontal angle point and vertical
grade break in order to bring the alignment parallel with the RPV and CLA boundary line.
The alignment will remain within an existing 100-foot wide utility easement dedicated
within the RPV-owned Palos Verdes Shoreline Park and Open Space that was
specifically set aside for utilities such as this proposed storm drain.The 100-foot wide
easement has lesser environmental impact requirements and also serves as a firebreak
for the adjacent mobile home park and a hiking trail path passes through it to the ocean
(see Photo 14).
The open trench reach proceeds downstream approximately 1,700-feet to a point 200-
feet from the ocean bluff top where a second launching pit is proposed (see Photo 15).
From the launching pit,which will require tunneling to proceed downstream due to the
intent to minimize access impacts on the beach,a 3B%sloped slant drain would be
tunneled for approximately 300-feet.The tunnel will "daytighf at the bottom of the bluff
face (see Photo 16),which would be similar to the recent McCarrell Canyon Storm
Drain slant drain tunnel outlet &structure (see Photo 17).The slant drain will be
comprised of an BO-inch diameter tunnel with a 54-in HOPE pipe placed inside.The
outlet structure would be constructed at the bottom of the bluff,with the pipeline above
the high tide mark.
Photo 17
.._Harris &Associates
PliJlo 16
-
PIiilo 15
Alternative 1A Facts:
•Tributary area =123.7 acres
•050 =144 cfs (FYI only)
•0100 =170 cfs (Actual system accommodates
0100)
• Mid-canyon inlet structure
•aO-inch diameter x 1,900 foot tunnel
•aO-inch diameter x 295 foot slant drain tunnel
•4B-inch HOPE mainline (req'd for 0100)
•54-inch HOPE mainline x 4,095 foot
(recommended to minimize the PCC annular
backfill in the tunnel &allow a future liner,if needed)
•Bluff bottom outlet structure
•Total Cost:$19.2 million
Page 22 of 34
Photo 18
City of Rancho Palos Verdes San Ramon Stuml Drainage System -Project Study RCllOrt
X.STORM DRAIN DESIGN AUGNMENT ALTERNATIVES
To end the cycle of the canyon's historical erosion problems generated and fed by the Tarapaca
Landslide,a ~gravity buttress~fill of approximately 20 to 3D-feet in depth would be placed just
downstream of the new mid-canyon inlet structure along the entire length of the existing
Tarapaca Landslide (see Section E-E on Alternative 1A,Sheets 5 of 6 and 6 of 6 in
Appendix G)which would raise the existing canyon's invert and flatten the side slopes of the
canyon.
The Ygravity buttress~fill within the canyon would also support Palos Verdes Drive East
switchbacks.The fill combined with the proposed storm flow diversion,decreases to negligible
the threat of a potential failure of the switchbacks that is deemed possible if the present rate of
erosion toward the switchbacks is not addressed.The interception of the canyon flows at mid-
canyon and the raising of the invert by filling the canyon would prevent significant erosion of the
canyon invert and,as a collateral benefit,would eventually stabilize the Tarapaca Landslide
(see previous Photo 2).Ungrouted rip rap rock energy dissipators are proposed at regular
intervals to flatten the canyon invert grade and concentrate the energy dissipation to these rock-
lined areas.The interception of the flow at mid-canyon would also significantly decrease the
amount of flows that is currently reaching the existing CLA storm drain s~stem at 25 th Street.
This should result in elimination of the flooding and debris deposition at 25 t Street (see Photos
6 &7 of PSR).
B.Alternative 1B -Upper-canyon inlet with "tunnel alignment"that outlets to the bluffs
Alternative 1B consists essentially of the same
design approach and alignment as Alternative 1A
with some exceptions.Instead of constructing a
large mid-canyon inlet within San Ramon Canyon,
a smaller mid-canyon inlet would be constructed
and the proposed storm drain alignment would be
extended upstream.The upper canyon reach
would consist of a 48-inch HDPE pipe installed
within "prepared canyon bottom backfill"that would
be imported and placed along the natural canyon
invert (see Alternative 18 conceptual plans and
Typical Section 0-0 in Appendix G).The
proposed pipe installation would extend an
additional 1,300-feet upstream of the Mid-Canyon inlet structure location,and would be
connected with a junction structure to the existing upper San Ramon Canyon storm drain
outlet pipe (see Photo 18).The existing outlet structure was constructed as part of the slope
repair and terrace drain construction performed in 2002 and would be removed to allow for
the pipe-to-pipe junction structure connection.The 48-inch HOPE pipe in this upper-canyon
alignment would be placed above a perforated 12-inch diameter pipe in a sub-drain rock
galley (see Typical Section 0-0 in Appendix G).No excavation below the existing canyon
floor would be done.The placement of the storm drain would be on top of "bedding"which
would be placed above the canyon floor.
The remaining alignment downstream would be the same as Alternative 1A with the only
difference that a small mid-canyon inlet structure would be required to pick up flows that are
tributary to the natural canyon slopes before they can continue down towards the Tarapaca
Landslide.This smaller Alternative 1B mid-canyon inlet would be located where the larger
Alternative 1A mid-canyon inlet would be.This would be the last chance to intercept any
additional surface flows that are tributary to the natural canyon slopes (and from the down..
Page 23 of 34 "Harris &Associates
Photo 19
City of Rancho Palos Verdes San Ran,oll SlOnn Dnillage System -Project Sl1ldy Repon
X.STORM DRAIN DESIGN AUGNMENT ALTERNATIVES
drain for the Tarapaca Road cul-de-sac and Tarapaca Slide "brow ditch ft above the head-
scarp).
The thought process driving this "sub-alternative"is that since the main line storm drain
flows have already been collected from the housing tract above San Ramon Canyon and
confined to a pipe it may be advantageous to keep these flows in
a pipe rather than allowing these concentrated flows to again
flow free in the natural channel bottom (see Photo 19).
Alternative 18 Facts:
•Tributary area =98 acres (top connection point)
•Tributary area =123.7 acres (as alignment leaves Cyn into
tunnel)
•Q50 of 122 cfs (FYI only,top connection point)
•050 =144 cfs (FYI only,as alignment leaves Cyn into tunnel)
•Q100 of 143 cfs (Actual system accommodates 0100,top
connection point)
•0100 =170 cfs (Actual system accommodates Q1oo,as
alignment leaves Canyon into tunnel)
•Upper-canyon connection junction structure
•48-inch HOPE mainline (req'd for a Q1oo)use in upper canyon to tunnel diversion
•Small mid-canyon inlet structure
•80~inch diameter x 1,900 foot tunnel
•80-inch diameter x 295 foot slant drain tunnel
•54-inch HOPE mainline (use from tunnel to beach,recommended to minimize the PCC
annular backfill in the tunnel &allow a future liner,if needed)
•Bluff bottom outlet structure
•Total Cost:$23.2 million
C.Alternative 2A -Mid~canyon inlet with "canyon alignment"outletting to 25 th St SD
Alternative 2A consists of a mid-canyon inlet,at the same location as Alternative 1A,with a
48~inch HOPE pipe in a "canyon alignment"down San Ramon Canyon past the Tarapaca
Landslide.This alternative would outlet into the existing CLA Storm Drain at 25 th Street (see
previous Photos 4 - 9 and Section A-A on page 9 showing the existing San Ramon
Canyon intersection with 25 th Street).The majority of the length of this storm drain
alignment falls within the RPV,however the most downstream portion will pass through
private property within CLA and as such RPV will not have sote jurisdiction over this
alternative.Similar to the other mid~canyon inlet Alternative 1A,the proposed upstream inlet
structure location was strategically chosen to intercept flood waters above the Tarapaca
Landslide where bedrock "daylightsft in the existing canyon bottom and side walls (see
previous Photos 12 &13).
The storm drain then conveys flows southerly in a "canyon alignment"along San Ramon
Canyon (see previous Photo 1)past the Tarapaca Landslide (see previous Photo 2)
approximately 1,900·feet in length where it will connect to the existing CLA storm Drain at
25 th Street (see Appendix D for CLA storm drain as-built plans).A small portion of 42-
inch CMP was left in place under 25 th Street when CLA constructed the 48-inch RCP storm
Page 24 of 34 RHarriS &Associates
City or Rancho Palos Verdcs San Ramon Stonn Drainagc Systcm -Projcct Sludy RCJlOrt
X.STORM DRAIN DESIGN ALIGNMENT ALTERNATIVES
drain downstream.Since the 42-inch CMP was left in place,half the width of 251h Street will
now need to be open cut to an approximate 30~foot depth to remove this 42~inch bottleneck.
Because "clear water"will have to be delivered to the CLA storm drain system per their
requirements,a very large debris basin structure would be require at the mid~canyon inlet.It
is envisioned that the debris basin and inlet structure for Alternative 2A and 2B will be
significantly larger than the inlet structure required for Alternative 1A and 1B)because
"bulked"flows will be allowed in Alternatives 1A and 1B.
The proposed storm drain construction will follow along the canyon's horizontal alignment
above the existing canyon floor with a minimum cover of 5~feet to the proposed new and
raised canyon invert such that no trenching will be required within the canyon floor (see
Section C-C on Alternative 2A and two plan &profile sheets 1 of 2 and 2 of 2 in
Appendix G).The proposed pipe slope will range from 21.5%maximum to 6.0%minimum.
The proposed canyon installation wilt require a fill along the canyon of up to 30~feet at some
locations.The elevated creek bed and steep side canyon slopes would be graded to have
less severe slopes similar to all of the other alternatives.The filling of the canyon would
again act as a buttress for both the Tarapaca Landslide and the PVDE switchbacks to
drastically reduce the potential for future slope failures.
Unfortunately the CLA storm drain,beginning at 25th Street and downstream to the existing
mid~bluff outlet,has some known deficiencies that were identified in a CCTV inspection
provided by CLA (separated pipe joints).It was also noted on the CLA SO record plans,
there is insufficient concrete cover over the interior reinforcement steel to withstand the
anticipated high velocity flows and abrupt horizontal angle points and vertical grade breaks.
In addition,the substandard bluff outlet is eroding the bluff face (see previous discussion
section VI."Existing CLA Storm Drain At 25th Street"for more detailed information).
Note that the correction of the previously identified 25lh Street Storm Drain system
deficiencies would need to be constructed in addition to the construction described here.
Alternative 2A Facts:
•Tributary area =184 acres
•Qso=219 cfs (Actual downstream existing system accommodates Qso)
•Q1ClO =263 cfs (FYI only)
•Mid~canyon inlet structure
•48·inch HOPE mainline
•CLA 25th Street storm drain outlet I connection
•Total Identified Cost In City of Rancho Palos Verdes $12.4 million
In City of Los Angeles $5.5 million
O.Alternative 28 -!:!.e.e!r-canyon inlet with "canyon alignment"outletting to 25 th St SO
Alternative 2B consists essentially of the exact same design approach and alignment as
Alternative 2A with some exceptions.Instead of constructing a large mid·canyon inlet within
San Ramon Canyon,a smaller mid~canyon inlet would be constructed and the proposed
storm drain alignment would be extended upstream.The upper canyon reach would consist
of a 48·inch HOPE pipe installed within "prepared canyon bottom backfill"that would be
imported and placed along the natural canyon invert exactly the same way as Alternative 1B
would be extended above Alternative 1A (see Alternative 28 conceptual plans and
Typical Section 0·0 in Appendix G).The proposed pipe would extend an additional 1,300·
feet upstream of the Mid·Canyon inlet structure location and would connect with an existing
Page 2S or 34
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"Harris &Associates
City or Rancho Palos Verde~San Ramon Stonn Drainage Sy~tem -Project SlUdy Report
X.STORM DRAIN DESIGN ALIGNMENT ALTERNATIVES
upper San Ramon Canyon storm drain outlet pipe with a junction structure (see previous
Photo 18).The 48-inch HOPE pipe in this upper-canyon alignment would be placed above a
perforated 12~inch diameter pipe (see Typical Section D-D in Appendix F).No excavation
below the existing canyon floor would be done.The placement of the storm drain would be
on top of "bedding"which would be placed above the canyon floor and covered.
The remaining alignment downstream would be the same as Alternative 2A with the only
difference that smaller mid-canyon inlet structure would be required.This mid-canyon inlet
would intercept any additional surface flows that are tributary to the natural canyon slopes.
It would also intercept flows from the down drain for the Tarapaca Road cul·de-sac and the
ditch just above the distinct step along the upslope edge (head-scarp)of the Tarapaca Slide.
Alternative 28 Facts:
•Tributary area =98 acres (top connection point)
•Tributary area =184 acres (northerly side of 25 th Street)
•050 of 122 cfs (top connection point)
•050 =219 cfs (northerly side of 25 1h Street)
•0100 =143 cfs (FYI only,top connection point)
•0100 =263 cfs (FYI only,top connection point)
•Upper·canyon connection junction structure
•48-inch HOPE mainline in upper &lower canyons
•Small mid-canyon inlet structure
•CLA 25th Street storm drain outlet I connection
•Total Identified Cost:In City of Rancho Palos Verdes $15.9 million
In City of Los Angeles $5.5 million
E.Alternative 3 (Low Cost):Upsize 25 th Street inlet and line existing canyon invert
Alternative 3 is a low cost approach that proposes to line the existing stream bed with
ungrouted rip rap materials that would reduce erosion in the streambed and would also
include constructing a very large debris basin just upstream of 25 th Street to capture
sediment and pass only clear water flows to the CLA storm drain at 25 th Street.The
maintenance cost for the large debris basin would be more substantial and ongoing because
accumulated debris would have to be cleared for the proper functioning of the inlet.
ThiS alternative would not address the Tarapaca Landslide,so there would continuously be
debris flowing to the existing CLA storm drain system,and continued pressure on the PVDE
roadway.
Alternative 3 Facts:
•Tributary area =187 acres
•050 =144 cfs
•0100 =217 cfs
•Ungrouted rip rap lined creek bed
•Upper 25 th Street inlet structure with large debris basin
•CLA 25th Street storm drain outlet I connection
•Total Cost:$3.7 million
Page 26 of 34 BHarris &Associates
CilY uf Rancho Palos Verde~Sail Ramon Sloml Drainage s,'stcm -Project Study Rcpufl
X.STORM DRAIN DESIGN ALIGNMENT ALTERNATIVES
F.Alternative 4 -"No Project"Alternative /Leave Existing Conditions "As Is"
Alternative 4 proposes to leave conditions as they presently exist.As a result of proceeding
with this alternative,the City should expect continued flooding and sediment deposition at
25 th Street during moderate rain events every winter (see previous Photos 6 &7).
Continued flooding at 25 th Street could even ultimately result in significant losses to property
and is potentially life threatening if the ponding should breach the mobile home perimeter
wall and continue unchecked downstream of 25 th Street.The City could also expect the
eventual failure of the lower PVDE switchback after a 5 to 7 year period if erosion is allowed
to continue in conjunction with the Tarapaca Landslide debris deposition cycle (see
previous Photo 2).Essentially the "No Project Alternative"would allow all of the previously
detailed potentially dangerous conditions to remain and carries considerable risk from both a
maintenance and access standpoint and a future liability/claim standpoint.This "no project"
alternative is NOT to be confused with a "no cost"alternative.It could likely end up costing
much more than any of the other alternatives in the longwterm if a serious "claim"should ever
arise.Such a serious claim would likely require that one of the other alternatives be
constructed in addition to the cost of setlling the claim.
Alternative 4 Facts:
•Tributary area =187 acres
•Qso=144cfs
•QHlO=217 cfs
•Tarapaca Landslide to continue cycle of uncheck debris flow
•Existing deficient inlets at 25 th Street
•Existing deficient mid-bluff outlet structure
•Total Present Cost Annual Maintenance
•Total Future Cost Unlimited maintenance costs,loss of emergency access to the Palos
Verdes Peninsula and unlimited future claim liability (property damage 1 loss of life)
Page 27 of 34
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City or Rancho Palos Verdes San Ramon Stoml Drainage System -Project Study Report
XI.RECOMMENDED ALTERNATIVE
XI.RECOMMENDED ALTERNATIVE
The recommended alignment is Alternative 1A.Its advantages,combined with the
disadvantages associated with other Alternatives 1B,2A, 2B,3 &4,make this the
recommended project solution for the following reasons:
•Rated number 1 in the Risk Chart on the previous page
•It is the arguably the least expensive alternative (only 7%more costly than
Alternative 2A's identified costs),while providing the greatest flood protection
(greater than Q100)of any alternative (except for the more expensive and
environmentally undesirable upper-canyon extension Alternative 1B).Thus it
could be argued that it potentially provides the most value (benefit per cost).
NOTE:If Alternative 2A solution were to be pursued its lengthy time schedule
would likely trigger the need for an interim project to stabilize the PVDE
switchbacks (see discussion item that follows),which would result in
additional total project costs.
•It meets all project goal requirements for stabilizing Tarapaca Landslide and
delivering significantly less storm flows to 25 th Street,which are also likely to be
classified as acceptable "clear flows"to LAC's storm drain.Most of the non-
diverted flow will be potentially ~absorbed"into the permeable rocky river bed
upstream of 25th Street before ever reaching the system.
•It requires the shortest design time and construction schedule,thus providing
potential relief per an expedient schedule possible of any alternative.This would
likely prevent the need for an interim project to stabilize the PVDE switchbacks.
•It is the least environmentally impacting,since it would disturb the least amount
of sensitive natural canyon via the tunnel alignment.It also requires the least
amount of environmental mitigation,and conserves the maximum amount of
long-term maintenance resources with less truck trips to haul away fine
sediment.
•The tunnel alignment does not require trenching across 25th Street I PVDS (or
PVDE)and thus minimizes public inconvenience and traffic impacts during
construction.
•The entire project alignment falls within the City of Rancho Palos Verdes'
jurisdiction,which will reduce the costs and length of time needed for design
preparation and processing for outside agency approvals.
•Alternative 1A would require the least amount of right-of-way and easements
needed for its construction.
XII.MAINTAINING PALOS VERDES DRIVE EAST
(PVDE)SWITCHBACK STABILITY
The upper PVDE switchback was found to be more stable
than the lower switchback because it has a larger offset
from the San Ramon Canyon creek bed.It also has not
experienced as much erosion primarily because it is
Page 29 of 34
City or Rancho P",I()ll Vcrdes 5"'11 Ramon Stonn Drainagc Systcm -Projco;;t Sludy Rcport
XII.MAINTAINING PALOS VERDES DRIVE EAST (PVDE)SWITCHBACK STABII.JTY
upstream of the Tarapaca Landslide and thus does not have falling debris pushing flows
westerly toward the switchback.The stability of the lower PVDE switchback was analyzed to
have an existing safety factor of 1.4 (FS =1.0 means failure could be imminent).An analysis
was performed to see how much more of the existing canyon wall would have to be eroded in
order to bring the factor of safety (FS)of the lower switchback to a value of 1.0.The existing
slope face would have to be eroded back approximately 35~feet from where it presently stands
before the roadway would be in a state of imminent failure.The upper PVDE switchback was
analyzed to have an existing safety factor of 1.3 and in order to bring it down to a safety factor
of 1.0 the canyon wall would have to be eroded back 40-feet before the roadway would be in a
state of imminent failure.Based on recent data,it is estimated that the present rate of erosion
of the canyon,westward in the vicinity of the lower switchback,is approximately 5-feet per year.
If the erosion were to continue unchecked at this rate,the lower PVDE switchback could be
destabilized within 5 to 7~years.It is important that an accurate monitoring system be installed to
provide more scientific data on the rate of erosion.Immediate installation of a monitoring
system is highly recommended to establish a true rate of erosion.
An additional concern is the safety of the existing 8~inch sewer line,which is located between
the San Ramon Canyon and the PVDE switchbacks.Even less erosion is required to
compromise the existing sewer since it is closer to the canyon edge.If a permanent solution is
implemented rapidly and both PVDE and the Tarapaca Landslide are stabilized then a separate
sewer relocation project may not be warranted.However,if a viable solution is not implemented,
continued erosion in this area may result in the failure of the existing sewer line.If delays are
encountered then RPV should consider relocating or otherwise protecting the existing sewer
line,especially in the area of the lower switchback,where the line appears to be closest to the
top of the eroded canyon wall.
It is recommended that PVDE and the sewer be protected if permanent improvements to
address the erosion within the canyon are not constructed before the estimated 5 to 7~years
during which time it is feared that unchecked erosion could destabilize the lower PVDE
switchback.RPV may wish to pursue a separate interim construction project that would
improve the stabilization of the PVDE switchbacks and sewer in the interim if a lengthy delay is
experienced to fund,design and construct the recommend San Ramon Canyon Drainage
Improvement project.
Recommended Separate Interim Project to Stabilize PDVE Switchbacks and Sewer:
In conformance with recommendations in GMU Geotechnical's Report (see Appendix B),the
following are alternative projects,which could be pursued by RPV to address the stability of the
PVDE switchbacks and sewer as a separate interim project (the cost of each was rated as $
expensive,$$more expensive and $$$most expensive):
A.Cast-in-drilled-hole (CIDH)Piles:Installation of CIDH piles into the existing slope
outside of the PVDE switchbacks,especially the lower switchback,would be one
possible solution to enhance the stability of the switchbacks as a separate interim
project.This solution has the advantage of relatively easy access from the lower
PVDE switchback where the CIDH pile caissons would be placed at an 8~foot
spacing (on center),to a depth of approximately 50~feet,and would require
approximately eighty (80)caissons total.
Page 30 of 34 IIHarriS &Associates
CilY of Rancho PalO\i Verdc8 San Ramon Sionn Drainage S)'slcm -Projcci Smdy Rcpon
XII.MAINTAINING PALOS VERDES DRIVE EAST (PVDE)SWITCHBACK STABIUTY
CIDH piles solution construction cost estimate =$$(detail analyses pending)
A list of "pros"&"cons"associated with this interim solution are as follows:
PROS:
•This solution has the advantage of relatively good access from the lower
switchback where the CIDH pile caissons would be placed.
•This solution is technically feasible and will have less extensive negative
grading impacts than are associated with any other solution requiring access
I work within the San Ramon Canyon creek bed and slopes.
•This solution would be considered the most permanent of all the "interim"
switchback stabilization solution alternatives.
•Will provide protection to existing sewer line.
CONS:
•This might be considered a costly "interim"switchback stabilization solution,
as it would become redundant once permanent solution is installed.
•The contractor may encounter difficult.but not insurmountable,drilling
conditions.
•In addition to the difficulty of the drilling installation,this solution would have
potentially significant traffic impacts on PVDE.
B.Canyon Bottom Rip Rap Installation:Installation of ungrouted rip rap or similar
type of revetment in the canyon bottom could be placed as another possible interim
project solution to enhance the stability of the switchbacks.The intent would be to
control and reduce the amount of erosion encroachment towards the PVOE
switchbacks.
Rip Rap solution construction cost estimate =$(see Appendix H)
A list of "pros"&"cons"associated with this interim solution are as follows:
PROS:
•This is the least costly "interim"switchback stabilization "build"solution.
•This solution is "technically"feasible to provide "temporary"relief from erosion
as long as the rip rap rock can be placed in a way to form a trapezoidal creek
bottom and a suitable installation method can be devised without triggering
land movement in the adjacent steep canyon slopes.
CONS:
•This solution has the disadvantage of requiring very difficult and impactful
access,most likely directly from 25 th Street.with a temporary access road
likely graded up the canyon from the bottom.
•This solution is less desirable from an environmental perspective due to the
associated negative grading impacts to allow access and work within the San
Ramon Canyon creek bed and slopes
•This solution is considered to provide only "temporary"relief because it would
not place a significant enough "buttress"fill to hold back the Tarapaca
Landslide,thus any future movement would simply bury the rip rap rock,with
a potential net affect as if it were never placed.
Page 31 of 34 IIIHarriS &Associates
CilY of Rancho Palos Verdes San Ramon SlOnn Drainage Syslelll -Projecl Study Report
XII.MAINTAINING PALOS VERDES DRIVE EAST (PVDE)SWITCHBACK STABIUTY
•Installation would be difficult.The reason this is dissimilar to the proposed
~buttress fill"grading operations called for in the primary alternative solutions
detailed elsewhere is that this interim solution will not have the benefit of:1)
as thoroughly studied designs that the future alternatives will have;2)two
access roads;or 3)the luxury of utilizing an intended "controlled"knock down
of adjacent slopes as part of a buttress fill placement,thus prolonging the
dangerous vertical slope conditions with workers potentially in harm's way.
C.Gravity Buttress Fill at the Tarapaca Landslide:A third and final build option as
an interim stabilization measure for the PVDE switchbacks would be the installation
of a 20'~30'high "gravity buttress"fin for about 750'along the toe of the Tarapaca
Landslide.This would require a fabric wrapped rock sub-drain with 12-inch
perforated PVC pipe and a 48-inch HOPE flexible pipe system buried along the invert
of the canyon bottom.This solution would also require an inlet structure and access
to this for maintenance.
Gravity Buttress solution construction cost estimate =$$$(see Appendix H)
A list of "pros"&"cons~associated with this interim solution are as follows:
PROS:
•Although very costly,the gravity buttress fill solution is actually one portion of
option 2 long-term permanent solution.It really is much more than an
~interim"switchback stabilization solution,this is more permanent which could
be established as part of the permanent solution.However the inlet structure
would become redundant.
•This solution is feasible (see detailed discussion in Alternative 1A and other
alternative write-ups).
CONS:
•This solution will require a major access road from the PVOE switchbacks,
although it will not have as extensive of a mid-canyon inlet structure in place.
This would add to the risk of clogging and/or an emergency overflow down
the canyon.This will likely snowball into the implementation of the full
"canyon alignment"solution to the City boundary,with only a missing link in
the downstream connect to the storm drain at 251h Street and larger /fully
accessible upstream inlet structure.This seems ambitious as an "interim"
solution,potentially redundant if the tunnel alternative is pursued,and may
not even be allowed by CLA even as a temporary interim solution.
•This solution has the disadvantage of requiring very difficult and
environmentally impactful access,most likely directly from 251h Street,with a
temporary access road likely graded up the canyon from the bottom.
•This solution is not desirable from an environmental perspective due to the
associated negative grading impacts to allow access and work within the San
Ramon Canyon creek bed and slopes.It is assumed this solution would be
performed on an emergency fast-track basis and as such would not have the
benefit of the full environmental mitigation and feedback process.
•This solution is considered to provide only "temporary~relief because it would
not place the ultimate mid-canyon inlet structure,full access road and direct
connection to the 251h Street storm drain.
Page 32 of34 HHarris &Associates
Cily of Rancho Palos Verdcs San Ramon Slonn Drainagc Sylllcm -Projccl Swdy Repon
XIII.CANYON SLOPE MONITORING
•The deficient inlets at 25 1h Street would still be overwhelmed,if not more so,
and would continue to experience flooding at 25th Street.
D."No Interim Project"Alternative:The City of Rancho Palos Verdes may choose to
proceed with no interim action to protect the switchbacks at this time.It is only
recommended that RPV consider this uNo Interim Projecf Alternative if the
previously detailed recommended San Ramon Canyon Drainage solution is
implemented quickly,within 5-years maximum.If a long-term solution for San Ramon
canyon cannot be implemented within 5~years then one of the Uinterim ft project
solutions should be considered.This is important because waiting longer than 5-
years has the potential to change this "no cosf UNo Interim Project"solution into a
very costly condition if the PVDE switchbacks were to fail.Costs include potential
loss of life,loss of emergency access along PVDE,and the cost of emergency
repairs and related liability claims.
Note:RPV staff has instructed Harris &Associates to prepare a set of ushelf-readyft
plans and specifications for the CIDH Pile interim solution for the City's potential use
in bringing a construction contractor on board,should the previously recommended
San Ramon Canyon Drainage solution not be implemented quickly.
Note:None of the proposed interim solutions will reduce the flooding and danger at
25 1h Street.
XIII.CANYON SLOPE MONITORING
There is an additional short-term and long-term benefit from the knowledge of any land
movements that might be taking place before and after construction,with the specific intent of
measuring any that happen during or because of our construction.To this end several slope
monitoring monuments will be installed to periodically monitor the land movement within the San
Ramon Canyon.They will be installed as deep as 10-feet in some locations to make sure they
reach bedrock or the solid equivalent.A tripod auger rig will drill a 12-inch diameter hole to a
depth of up to 10-feet and a 6-inch PVC sleeve will be installed with a fixed survey rod
cemented in the center.This would have an access cover that can be removed to enable
periodic GPS survey readings.The proposed ten (10)locations for the survey monuments are
shown on the map on the next page.
These monuments will be surveyed periodically using GPS methods that are tied into the
existing City GIS system and control networks.The first survey will be done to establish the
baseline position of each monument from which all future measurements will be referenced.
The frequency of subsequent surveys will be as often as every 6 months,depending on the
movement noted and could be isolated to chosen specific locations where movement is noted
on a more frequent basis.
Page 33 of 34 RHarriS &Associates
c;'y ur Rancho Palos Verdcs San Ramoll Stoml Drainage Systcm -ProjCCl Study Rcporl
XIII.CANYON SLOPE MONITORING
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Page 34 of 34
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