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INFORMATION
May 14, 1984
Santa Mon~ca, Ca1~fornla
TO: Mayor and Clty Councll
FROM: Clty Staff
SUBJEcr: Summary of Flnd1ngs ~nd Conc1us1ons of the Feaslb11lty
Analysis for the Reconstruct1on of the Santa Monica
P1er
Executive Snmmary
Backsround
On November 22, 1983, the Clty Council awarded a $283,640
contract to the englneering f~rm of Danlel Mann Johnson and
Mendenhall (DMJM) for a feaslbll~ty analysis of reconstructlng
the Santa Monlca Pier followlng the severe 1983 wlnter storm
damage.
Th1S staff report summar1zes the maJor find~ngs and
conclUSions of the consultant's draft report.
Sum~ary of Major FindinC]s and Conclusions
o Wave protection must be provided to protect the existing Pier
and to rebuild the destroyed portion.
J:he consultant
concludes that the Existing Pler would not wlthstand the force
of a slgnlflcant wave greater than 6 feet or a wave crest
higher than 21 feet.
Waves that submerge the Pler will cause
It to collapse. Therefore, some ~eans must be developed to
reduce the height of the waves when they reach the Pler.
o There are two viable alternatives for providing wave
protection. The consultant concludes that the two vlable
1
alternatIves are: Alternative A - rebuIld the offshore
breakwater to 15 feet; AlternatIve B - rebuild and stabilIze
the offshore breakwater at 6 feet and construct a 545 foot
long promenade, perpendicular to the end of the reconstructed
MunicIpal PIer, WhIch WIll act as a structural breakwater.
o Each of the alternatives is nearly equal in cost. The
apprOXImate cost of $14 mIllIon for each alternatIve makes
clear that the basis for the selection of the preferred
alternat~ve WIll be factors other than cost. The alternatIves
must be e'la1uated In terms of thelr aesthetIcs, thelr deslgn
strength and functl-onal characterIstIcs, and theIr impact on
the shoreline.
o Erosion of the shoreline will occur as long as the breakwater
remains in its damaged condition. The consultant concludes
that the Santa MonIca Beach IS now sufferlng erosion at the
rate of 5 feet per year and WIll continue to erode as a result
of the damaged conditlon of the breakwater.
o Many Scenarios for rebuilding the Pier were considered, but
most were found to be technically infeasible. The consultant
analyzed nlne different configuratIons and combinatlons for:
rebuIldlng the Pler, lncorporatlng breakwater protectlon and
determined that the two alternatives Indicated above are the
most vlable.
The others elther do not offer sufflcIent
protectIon to the pier or to the shorelIne, or they are too
maSSlve or too costly.
?
o The historical function of the lower deck to provide access to
the water and fishing can be provided in an alternative way.
One alternative way is provided by the deck area of the
promenade wh~ch would be 15 feet above the water, about the
same he~ght of the former lower deck, and would offer
extens~ve opportun~ties for fIshIng and stroll~ng.
RECOMMENDATION
Councll Members are requested to reVlew the attached document.
The Pler Restoratlon Corporatlon 1S expected to complete 1ts
reVlew and present Its recommendatIon to the Clty CouncIl.
<
Introduction
As lndlcated above, this report presents a summary of the
flndlngs and concluslons from the Feaslb1l1ty Analysis for the
Reconstruction of the Santa Monlca Pler, by the enginer ing flrm
of Daniel Mann Johnson and Mendenhall (DMJM). The attached
report 1S a draft; volume I Includes an executl~e summary and
detalled analysis of findings and conclus1ons, volume II conta1ns
all appendices.
The draft report concludes that there are two v1able alternat1ves
for reconstructing the Pier. Both of the alternatives are based
on the consultant's conclusion that to protect the eXIst1ng Pler
structure and to rebulld the destroyed portion, protection must
be provlded. There are two Jonds of protect1on and the two
alternatlves relate to the type of breakwater system involved:
Alternatlve A - rebulld offshore breakwater to an elevatlon of
+15 feet, Alternatlve B - stabil1ze the offshore breakwater to
+6 feet and construct a promenade at the end of the reconstructed
Municipal Pier WhlCh wlll serve as a structural breakwater. Under
both alternatlves, the Pler could be reconstructed all In tlmber
1f no lower deck were buil t, or If a lower deck were deSIred, the
piles and lower deck structure would be concrete and the upper
deck could be tlmber. It 1S posslble that the hIstorlcal
functlon of the lower deck, to provide access to fishlng and to
the water, could be provided In an alternative way.
4
Th~s draft report ~s be~ng made available to the C~ty Counc~l,
P~er Restoration Corporation and the general publ~c. City Staff
w~ll be work~ng with the pier Restorat~on Corporat~on and the
consultants over the next several months to ref~ne the report and
determ~ne the most viable alternative. ThlS recommendat~on wlll
then be brought to C~ty Council for reVlew and final approval.
The dlScussion wh~ch follows attempts to explain in slmple terms
the critical factors and the methodology used by the consultants
WhlCh brought them to the conclusions stated above.
Background
On November 22, 1983, the C~ty Council awarded a $283,640
contract to the englneerlng flrm of Dan~el Mann Johnson and
Mendenhall (DMJM) for a feaSlblllty analysis of reconstruct~ng
Santa Monica P~er following the severe 1983 storm damage. The
contract called for the completion of the following tasks during
thiS flrst phase:
I. ReView of EXisting Data including historical wave heights,
wave forces, sea level, and the shoreline.
II. On-slte Evaluatlon and Testing
DMJM's structural englneers lnspected the Pier deck,
structural framing and utillty systems to determlne the
extent of damage and required rehabllltation. J. Agi and
Assoclates (subconsultant) performed testing of plIes
uSlng a sonar technlque called "ultrasound" to assess
remaining structural capacity of each plle. Ocean
" .
Surveys, Inc. (subconsultant) provided the bathymetrlc
survey of the sea bottom and a s~de-scan survey to
determlne the location and magnltude of debrls at the
seabed. Converse Consultants (subconsultant) drllled
three SOlI borlngs to determine subso~l cond~tions.
III.
Evaluat10n of Reconstruction Deslgn Issues
Th~s task was the most complex and served to identIfy the
wave criteria and sediment budget analysis for the
shorellne. Tekmarlne, Inc., an aSSOCIate for DMJM for
Phase I, performed coastal eng~neering analysis. Dr.
SQnu of l'ekmar~ne 1S a worldWIde expert on thlS subJect.
Th1S work WIll be described In more detaIl in the next
sectIon.
IV. Development of Alternatlve Des1gns
Based on the 1nformation gaIned from the above surveys and
analysls, DMJM developed nIne pOSSIble scenarIOS for
rebuilding the Pier. These '",ere thoroughly analyzed and
narrowed down to fIve alternatIves which were further
analyzed and ranked. The result 15, in DMJM's oplnlon,
the two viable alternatIves:
(Al rebUIldIng the offshore breakwater to +15 feet, or
(3) stabilizIng the offshore breakwater at +6 feet and
constructIng a promenade at the end of the Pier.
The fInal task is the selection of the preferred alternatIve
which WIll be done by the Clty CouncIl in consultatIon WIth the
PRe.
6
Cr1t1cal Design Factors
To understand how DMJM arrlved at the two v1able alternatives, lt
is lmportant to conslder the englneering assumptions and the
maJor deslgn factors.
ThlS sectlon wlll brlefly address the
follow1ng:
o Reason for structural failure of Santa Monlca Pler durlng
1983 winter storms
o Design wave and design life for the Pler
o Protection afforded by breakwater to the Pler
o Shoreline stablllty
DMJM has determined that the waves during the wlnter storms were
of unusually high magnltude comblned with an extremely high sea
level. The lower deck was submerged and llfted up . The floatlng
of the lower deck resulted in the collapse of plles at the outer
end of the Munlclpal Pler. The debrls created by this collapse,
acted as battering rams ln a chain reaction WhlCh destroyed the
MunlClpal Pler and the south-easterly part of the Newcomb Pier.
From the above descr1ptlon lt lS clear that the critlcal factor
is the deslgn wave, that lS, the force of the wave that the Pler
must be able to wlthstand.
Generally accepted engineerlng
practlce lS to assume a 50-year llfe for a structure like the
Pler wlth a 10 percent probablllty that the design wave will be
encountered wlthln that 50 year span.
DMJM has determined
through extenSive analySiS that a 20 foot significant wave is the
deslgn wave. This means that a 20 foot h1gh offshore Significant
wave 1S the extreme condition for Wh1Ch the Pier and breakwater
7
must be designed. "Slgn1flcant wave" (8s) is a term used 1n
coastal engineering to descrlbe the height of a wave, however 1t
actually refers to the upper one-thlrd of the wave.
The consultant has also determlned that wlthin the expected life
of the structure, the level of the sea may r1se approxlmately
ten feet above mean low low water (MLLW).
In addlt10n to the slgnlflcant wave height and sea level, the
third crit1cal parameter is the crest of the slgnlficant wave at
the pOlnt when lt meets the Pler structure. The term used to
describe thlS point is "maXlmum wave crest elevation (crest
Hmax.)" The crest elevatlon has been shown to be crltical Slnce
a wave crest that is hlgher than the Pler structure wlll submerge
the deck and 11ft lt up causlng lt to fail. Attachment A
lllustrates the relatlonshlp between the slgnlflcant wave and the
maXlmum wave crest.
Thus, as DMJM determlned the probable wave crlterla, lt became
necessary to establisn upper wave llmlts for the eXlsting Newcomb
and Munlclpal Plers so that the odds are that they would not be
destroyed wlthln the 50 year llfe. The maX1mum slgniflcant wave
height the existlng tlmber plles could wlthstand is 6 feet.
Also, to avo1d submergence of the upper deck by the crest of a
wave, a maXlmum crest elevatlon of +21 feet from MLLW has been
set~ the upper deck lS now at +25 feet.
At t01S point it lS helpful to understand the effect of the
breakwater 10 reduclng wave helghts. The 20 foot slgnificant
8
wave, wh~ch ~s the extreme condit~on or~g~nates offshore ~n deep
water. As the wave travels toward the shore it is changed by
obstruct~ons, such as lslands, and by changes in water depth.
Based on DMJM's analys~s, the consultant determ~ned that the 20
foot wave height is reduced to 13 feet at the breakwater. A
breakwater also changes the character~stics of the waveS and
often r2duces the he~ght. Th1S effect 1S somewhat compllcated at
the Pier since the seabed between the breakwater and the pier
slopes upward Wh1Ch results in lncreased wave heights 1nshore of
the breakwater. Th~s effect on 'olaves ~s called shoaling.
The or1g1nal breakwater, bU11t ln 1934, was 10 feet above MLLW.
Over the years the breakwater was subJected to wave forces and
erOS10n and was, on the average, at +6 feet above MLLW pr10r to
the 1983 winter storms. The crest of the breakwater WdS severely
damaged dur1ng the storms and ~s now at an average he~ght of -6
feet below MLLI'J.
The establ~shment of a 6-foot sign~ficant wave and 21 foot
rnax~mum wave crest height as the tolerable wave llmits at the
Pler means that some type of breakwater pro~ect1on is necessary
to reduce the 13 foot slgn~f~cant wave he~ght at the breakwater
to a tolerable level for both the ex~st~ng and new port10ns of
the P~er.
The breakwater has an ~mpact on the shoreline as well. The
consultant has deterrn1ned that during the 20-year per~od after
the breakwater was bu~lt, the shorel~ne ln the area around the
Plet was subJected to sand accretlon and eros~on unt~l ~t reached
9
a state of equi11br1um wh1ch rema1ned unt11 the 1983 storm. The
result of the storm damage to the breakwater is that the beach 1n
the area of the pier 1S now suffer1ng erosion at the rate of
approxLmately 5 feet per year. The effects on the beaches south
of the P1er w1ll be stud1ed during the Env1ronmental Impact
Report phase of the PLer Reconstruction ProJect.
IdentLfLcation of Scenar10S
Once DMJM established the tolerable wave crLterLa, they studied
varLous conflguatLons and comblnatLons for rebu1lding che P1er
1ncorporat1ng breakwater protect1on.
They computed the wave
characteristics and analyzed the structural requLrements and
other 1mpacts, such as effects on the shorellne for each
scenario.
These scenarlOS include:
1) Do nothlng to the offshore breakwater
2) Allow offshore breakwater to deterlorate completely
3} StabLlize offshore breakwater to +6 feet
4} Restore offshore breakwater to origlnal 1934 deslgn
5) Ralse offshore breakwater to +15 feet (Alternat1ve A)
6) RebuLld composlte offshore breakwater with concrete
calsson
7) StabllLze offshore breakwater at +6 feet and construct a
545 foot promenade at end of P1er to elevatLon +18.5 feet
to serve as structural breakwater (Alternat1ve B)
8) Construct a 1,100 foot promenade to +21.5 feet and allow
offshore breakwater to deter10rate
9) Construct a 1,100 foot promenade to +18.5 feet and allow
offshore breakwater to aeterlorate
The consultant found that to do nothlng to the offshore
breakwater or only stablllze lt would requlre that both the
10
ex~st~ng deck and piles and the new port~on must be constructed
of concrete. In addltlon, do~ng nothing to ~he breakwater would
aggravate the rate of shore erOSlon. Therefore, DMJM ellminated
the f~rst four scenarios as techn~cally lnfeasIble and proceeded
to cons~der the flve remalnlng ones as vlable alternatives.
Analysls of Alternat~ves
To evaluate the viable alternatives, the consultant devised a
rank~ng system Incorporatlng the followi~g Important declslon
factors. These Include:
o Llfe Cycle Cost
o Structural Integrlty
o Shorellne Sedlment
o Environmental Conslderations
o Conformlty wlth Pler GUldelines
o Upper Deck Potential Expanslon
o Aestnetlcs
o Low Cost SubstItute to Lower Deck
o Sport Fishlng and Recreational Boat~ng Potentlal
A full d~Scusslon of the rank1ng and evaluatlon of the major
factors IS Included 1n the draft report. The consultant found
that Alternat1ve I, referred hereln as Alternat1ve A (rebulld
breakwater to +15 feet) and Alternatlve III, referred herein as
Alternatlve B (construct 545 foot promenade and stablllze
breakwater) ranked hlghest. EssentIally the ca1sson breakwater
and the 1,100 foot promenade alternatIves were too costly and too
11
massive.
The dlScussion below highlights the two viable
alternatives.
Attachments II and III graphically lllustrate
Alternatlves A and 8, respectlvely.
Alternatlve A: Ralse Outer Breakwater to +15 Feet
The rebulldlng of the rubble mound offshore breakwater to a
helght of +15 feet and a crest wIdth of 35 feet lS expected to
result ln a 6 foot slgnlficant wave heIght at the Pler, and a
maximum crest e1evatlon of 21 feet. The benefits or drawbacks
include:
o concrete lower deck lS feasible at +15 feet~ this means the
pLIes and upper deck supports must also be concrete
o if no lower deck IS bUllt, an all tlmber Pier IS feaslble
o eXIsting shorelIne equilibrium is expected to be sustained
o the bulk and heIght of breakwater would be clearly VISIble
from the shorelIne and PIer
o supply of fISh would increase and fIshIng from PIer would be
more successful due to smaller waves
AlternatIve B: Construct Promenade to ElevatIon +18.5 Feet In
CombInation WIth StabIlizing Offshore Breakwater to Ele-
vatIon +6
ThIS alternatIve aSsumes that the offshore breakwater WIll be
stabilIzed and rebuilt to 6 feet. A promenade of 545 feet In
length would be bUIlt perpendIcular to the end of the MunICIpal
PIer extendIng equal dIstances north and south. The promenade IS
deSIgned to absorb the force of the waves. It would consist of a
10" WIde concrete wall that IS 18.5 feet hIgh above the water.
Between thIS protective wall and the MunIcipal pier would be a
30-50 foot-WIde deck 15 feet above the water. The platform of
the deck must be concrete but the deckIng may be 'vood. ThIS deck
12
would be connected at varIOUS pOInts to the PIer and serve as
additional fIshIng and strollIng area.
The plIes supportIng the
promenade would be subJected to eKtreme forces and must be either
concrete or steel although they can be designed and treated to
look lIke wood.
The combined protectIon of the offshore
breakwater and the promenade would achieve ~he deSIred design
criteria.
BenefIts or drawbacks lnclude;
o All tImber PIer IS feaSIble
o Promenade may substltute for lower deck and prOVIde maXImum
fIshIng area; fiShIng activIty off promenade deck can take
place on eIther side of promenade
o Promenade must be closed to users during extreme storm
condltlons, approKlmately 5 days/year.
o CloudIness of the water onshore of the promenade lS expected
to be less than an all offshore breakwater
o EXIstIng shorelIne equilibrIum IS expected to be sustained
o PotentIal Increase In wave helght between the promenade and
the offshore breakwater during hIgh seas due to wave
reflectIon from vertIcal face of promenade
o Offshcre breakwater WIll be restored to +6 and WIll be
slIghtly more vlslble than origInal breakwater prlor to 1983
storms
o PotentIal creation of small fIshIng harbor adJacent to
Newcomb PIer by extending promenade
o Posslble InclUSIon of ferry landing or other boat launchIng
faclllty
o Creation of several dlfferent "protected" and "exposed"
habitats; substantIal Increase In number and dIverSIty of
fish
o Noticeable change to the phYSIcal confIguration of the Pler
Summary of Costs
This section provides a cost summary for each alternatIve. It
13
should be p01nted out that these are rough order magn1tude cost
estimates and are by no means f1nal, nor do they include further
eng1neering fees. The cost breakdown for the PIer constructIon
includes the cost of strengthen1ng and upgrad1ng the eXIscing
MunIcIpal and Newcomb P1ers, resto=lng the damaged PQrt10n of the
Newcomb P1er and reconstruct1ng the damaged portIon of the
MunIc1pal PIer. Also included 1S the cost of adding ut1l1t1es.
The cost noted here IS the inItIal capital cost, the 50-year lIfe
cycle cost IS prov1ded In the draft report.
14
Descr~pt~on
Alternat~ve A
Ral.se Breakwater
to 15 Feet
Alternatl.ve B
Promenade & Stabl1~ze
Breakwater
PIER RECONSTRUCTION
a) Structural
Strengthen Exist1ng MUnlCl.pa1
Pier
Strengthen Exist~ng Newcomb
P~er
Restore Damaged Newcomb PIer
Reconstruct Damaged Municipal
Pier
- Upper Deck
- Lower Deck
0) Ut1.11tles
Sewer and Water
c) E1ectrlca1
d) Upgrade Newcomb Pler
to 100 psf
e) 'Wearl.ng Surface for
New Deck
f) Replacement of EXIsting
Pavement
TOTAL PIER CONSTRUCTION
99,600
232,400
1,196,000
1,036,000
1,388,000
63,200
530,000
212,500
40,050
66,700
$4,864,000
15
99,600
232,400
1,196,000
1,036,000
N/A
63,200
530,000
212,500
40,050
66,700
$3,531,700
Descriptlon
Alternatlve A
Ralse Breakwater
to 15 Feet
Alternatlve B
Promenade & Stabillz~
Breakwater
Pler Reconstructlon
(total brought forward)
4,864,000
3,531,700
BREAKWATER CONSTRUCTION
a) Ralse outer break~ater
to +15 feet
9,526,000
N/A
b) Stablllze Outer Breakwater
at +6 feet
N/A
4,116,400
Promenade, 545 feet to
+18.5 feet
N/A
5,912,500
TOTAL BREAK~ATER
$9,526,000
$10,030,900
$13,562,600
GRAND TOTAL
$14,390,000
As lndlcated ln the descrlptlon of Alternatlve S, addltlonal options
are posslble includlng the extenslon of the promenade to create a
fishlng harbor and to provlde a ferry dock or boat launch. The costs
for these dlscretionary optlons are:
Add Flshlng Harbor-Dock
574,000
204,000
Add Ferry Dock
Add Boat Launch
200,000
978,000
, !:;
The Next Steps
As noted In the Introduction, the draft report is beIng made
available to the City CouncIl, PIer Restoration CorporatIon, and
the general publIC.
It wIll also be sent to the funding
agencies. The PRC is expected to reVIew and dISCUSS the draft
report over the next SIxty days and then make a report to City
Council with the PRC's recommendatIon on the preferred desIgn.
Following CouncIl's actIon and dIrectIon, a contract WIll be
negotiated wIth DMJM who will then b~gin work on Design
Development and the EnVIronmental Impact Report. They wIll also
perform hydraulic model-testIng on whichever breakwater system IS
selected and perform addItIonal geotechnIcal surveys.
The PRC IS expected to complete their reVIew and present a
recommendatIon to CIty CounCIl by AugGst, 1984. At that tIme the
Cl.ty CounCIl wIll be asked to make a deCISIon on the selection of
the preferred alternatIve.
Recommendation
CounCIl members are requested to review the attached document.
Attachments:
I Explanatory DIagram of Wave
II AlternatIve A: RebuIld Offshore Breakwater to 15 feet
III AlternatIve B: StabIlIze Offshore Breakwater at 6 feet
and Construct Promenade
Prepared by: JUdIth MeIster, Manager
PIer Development DIVISIon
Department of CommunIty and EconomIC Development
17
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