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Development of Wave Protection for Port of Long Beach Pier F

Authors:
  • City of Long Beach, California

Abstract and Figures

Coastal engineering studies were performed to define site and design conditions for the development of new docking facilities and a wave protection structure at Pier F in the Port of Long Beach, California. The new facilities will provide docking to a fireboat, pilot and port security boats with lengths ranging from 30 to 110 feet (9.1 to 33.5 m). The study showed that yearly wave conditions exceed accepted wave height criteria for small craft harbors and that wave protection would be needed. While most wave protection structures would be adequate to provide the necessary wave protection, site conditions and project requirements proved to be very challenging conditions that limited the applicability of typical structures. A floating breakwater was analyzed along with fixed structure alternatives such as rubble mound, caissons, concrete sheet and cylindrical pile breakwaters, and the preferred steel sheet/king pile breakwater.
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Development of Wave Protection for Port of Long Beach Pier F
Claudio. Fassardi
1
; Yang Zhang
2
, Ph.D. and George E. Gordon IV
3
, P.E.
1
CH2M Hill, 6700 E. Pacific Highway, Suite 180, Long Beach, CA 90803; PH (562)
493-8300; FAX (562) 493-8308; email: claudio.fassardi@ch2m.com
2
CH2M Hill, 1101 Channelside Drive, Suite 200 S, Tampa, FL 33602; PH (813) 386-
1990; FAX (813) 386-1991; email: yang.zhang@ch2m.com
3
Port of Long Beach, 925 Harbor Plaza, Long Beach, CA 90801; PH (562) 283-7364;
FAX (562) 283-7351; email: gordon@polb.com
ABSTRACT
Coastal engineering studies were performed to define site and design
conditions for the development of new docking facilities and a wave protection
structure at Pier F, in the Port of Long Beach, California. The new facilities will
provide docking to a fireboat, pilot and port security boats with lengths ranging from
30 to 110 feet (9.1 to 33.5 m). The study showed that yearly wave conditions exceed
accepted wave height criteria for small craft harbors and that wave protection would
be needed. While most wave protection structures would be adequate to provide the
necessary wave protection, site conditions and project requirements proved to be very
challenging conditions that limited the applicability of typical structures. A floating
breakwater was analyzed along with fixed structure alternatives such as rubble
mound, caissons, concrete sheet and cylindrical pile breakwaters, and the preferred
steel sheet/king pile breakwater.
INTRODUCTION
The Port of Long Beach (POLB) plans to build a new Fireboat Station No. 15
and docking facilities at Pier F that will replace outdated existing ones, where boats
and docks are experiencing the adverse effects of wave agitation. These will include a
boat bay for the Long Beach Fire Department (LBFD) new fireboat; docks for boats
operated by the Jacobsen Pilot Service (JPS), the Long Beach Police Department
(LBPD) and the POLB Security Division; a fuel station; and a hoist and platform to
launch small boats and handle containers and equipment. The new facilities will
improve the functionalities of the existing ones, and will provide docking to a wide
range of boats with a variety of missions. The 17-boat fleet, to be docked along an
approximately 800-foot (244 m) waterfront, includes a fireboat, pilot and port
security boats with lengths ranging from 30 to 110 feet (9.1 to 33.5 m).
Pier F is located adjacent and on the east side of the POLB main entrance
channel. The 75-80-foot (22.9-24 m) deep channel passes through a narrow 900-foot
(274 m) gap formed by the southern end of Pier F to the east and the Navy Mole to
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the west. Figure 1 shows the location of Fireboat Station No. 15 at Pier F and the
Middle Breakwater sided by the San Pedro Breakwater to the west and the Long
Beach Breakwater to the east.
Figure 1. Location of Fire Station 15 at the POLB.
Wave conditions at Pier F are, in general, relatively benign. Waves generated
within the Los Angeles-Long Beach (LA-LB) harbor by the average year-round 10-
knot (5.2 m/s) southwest wind are not problematic for the boats and docks currently
at Pier F. However, the typical 30+ knot (15.5 m/s) southerly (prefrontal) winds in the
winter, associated to the passage of cold fronts, generate 1 to 2-foot (0.3 to 0.6 m), 2-
second period waves within the harbor that are problematic for the docks and boats,
in particular due to their relative broadside angle of incidence. In addition, the
offshore 4 to 10-second waves generated by the prefrontal winds in the winter and the
12 to 16-second swell generated by tropical hurricanes along the Pacific Coast of
Mexico during the summer penetrate through the LA-LB harbor breakwaters causing
an undesirable “surging” that also affects boats and docks.
In order to determine the need and type of wave protection that could
potentially be necessary for the new docking facilities at Pier F, coastal engineering
studies and investigations were performed. These included numerical modeling of
wind waves within the LA-LB harbor, the penetration of offshore swell and long
waves (infragravity), and ship and tsunami induced currents.
WAVE PROTECTION ASSESSMENT
The need for wave protection in small craft harbors is generally assessed using
guidelines such those developed by the ASCE (1994) and the Permanent International
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Association of Navigation Congresses (PIANC, 1995) which define allowable levels
of wave conditions in harbors. Table 1 shows the wave criteria per ASCE (1994)
where the allowable yearly maximum wave event is 1 foot (0.30 m) for 2-second
waves and 0.5 foot (0.15 m) for waves of periods greater than 2 seconds. This criteria
is the same as PIANC (1995) and consistent with others found in general design
guidelines for small craft harbors.
Table 1. ASCE (1994) wave criteria for small craft harbors.
In order to determine if wave protection would be necessary according to the
ASCE (1994) criteria, wave conditions and frequency of occurrence at Pier F needed
to be determined. Unfortunately, long-term wave measurements or hindcasts at the
site were not available to perform this analysis. However, hourly wind measurements
at Pier J and Pier F from April 2005 to date from the National Ocean Service’s
PORTS program, and a long-term wave hindcast outside the LA-LB harbor in the
vicinity of Angel’s Gate were available. In combination with numerical wave
modeling these data were used to determine wave conditions at Pier F generated by
winds within the harbor and those resulting from waves that penetrate through the
LA-LB harbor breakwaters. Two numerical wave models were used: a) MIKE 21 FM
SW, a spectral wind-wave model, was used to simulate the generation and
transformation of waves due to wind within the LA-LB harbor and b) MIKE 21 BW,
a Boussinesq wave model, to simulate the transformation of deep water waves to
shallow water, the generation of long waves, and the penetration of these waves to the
Pier F area.
The PORTS’ wind records at Pier J and F allowed for the simulation of time
varying wind waves within the harbor, and corresponding conditions at Pier F, that
would be more realistic than those resulting from constant wind speed/direction
derived from frequency tables. Pier F is exposed to the west to the POLB West Basin,
which has a relatively short 2,000 m fetch; and to the LA-LB harbor to the south
which has a longer, approximately 3,000 to 4,000 m fetch. Wave conditions at Pier F
generated by the passage of cold fronts in the winter are of particular interest for the
assessment of wave protection at Pier F. As cold fronts approach, the prefrontal wind
is usually southerly, typically increasing in speed and becoming gusty. As the cold
front passes the wind direction changes clockwise to settle usually in a northwesterly
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direction after the front has passed. The passage of the cold front typically takes 24
hours. Table 2 shows the wind wave conditions at Pier F due to the passage of
selected cold fronts in the period from April 2005 to November 2011. Waves
generated within the harbor by southerly prefrontal winds exceed the 1-foot (0.3 m)
wave height in all cases, and at a rate of more than once per year. After the front has
passed, the westerly winds generate 1-foot (0.3 m) wave heights at a rate of
approximately once per year.
Table 2. Wave conditions at Pier F due to the passage of cold fronts.
Because boat users at Pier F also reported that swell is also problematic, the
magnitude of the swell that reaches Pier F was also estimated by means of numerical
modeling. Figure 2 shows the deep water wave windows and sources that affect the
LA-LB harbor. Short period local seas and northern hemisphere extratropical storm
swells approach the harbor from a westerly direction, while prefrontal seas, tropical
storm swells and southern hemisphere extratropical swells approach from the south.
The westerly local seas and the southern hemisphere extratropical swells are in
general of small magnitude and were not considered for analysis.
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Figure 2. Wave windows and sources.
Table 3 shows a summary of wave conditions at Pier F due to 1-year
extratropical and tropical storms and prefrontal winds, derived from a long-term deep
water wave hindcast in the vicinity of Angel’s Gate. Resulting wave conditions are
dominated by a swell of approximately 0.5 foot (0.15 m) or less, with long waves in
the 1 to 4 inches range (0.03 to 0.10 m) and with periods of about 3 minutes.
The results of the wave analysis indicated that waves within the harbor
generated by passage of cold fronts exceed the recommended wave height criteria
(i.e. ASCE, 1994 and PIANC, 1995), in particular when combined with the seas/swell
generated offshore by storms and which penetrates into the harbor through the
breakwaters. Therefore, wave protection for the planned new docking facilities was
considered necessary. Yearly swell conditions, however, are within the wave criteria.
Table 3. Wave conditions at Pier F due 1-year deep water waves.
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SITE CONDITIONS
Pier F is protected by a rip-rap revetment with a crest elevation of
approximately +15 feet (4.6 m) MLLW and a 1v:1.5h slope down to a depth of
approximately -20 to -25 feet (6.1 to 7.6 m) MLLW. Beyond the 25-foot (7.6 m)
MLLW depth contour the bathymetry features a steep slope ranging from
approximately 0.25 between the 20 and 40-foot (6.1 and 12.2 m) MLLW contours, to
0.75 between the 40 and 65-foot (12.2 and 19.8 m) MLLW contours. Beyond the 65-
foot (19.8 m) MLLW contour the bathymetry is relatively flat down to the 70-foot
(21.3 m) MMLW contour where the bank of the ship channel commences. The
waterfront runs approximately in a north-south direction and three docks are currently
in operation: a Public dock on the south, the LBFD fireboat dock on the north and the
JPS dock in between. Figure 3 shows the bathymetry in feet MLLW and the existing
docks.
Figure 3. Bathymetry (feet, MLLW) at Pier F and existing docks.
Wind, waves, passing vessels and tides all contribute to the generation of
currents that could affect the planned new docking facilities at Pier F. Because of the
funneling effect that the 900-foot (274 m) narrow gap between Pier F and the Navy
Mole could induce, currents were considered in the assessment of the design. Wind,
wave and the maximum tidal induced currents at Pier F of less than 0.5 knot (0.26
m/s) are negligible when compared to the reported 6-knot (3.1 m/s) currents induced
by the tsunami in Japan on March 2011, or the return currents induced by large
tankers during their passage through the gap. Therefore, only the ship induced return
currents and tsunami currents were analyzed and considered for design.
Pier F users reported that large oil tankers and containerships could generate
currents of approximately 3 knots (1.6 m/s) , parallel to the shore and in the direction
opposite to the ship travel as they enter the port through the gap. These ships, which
enter in a laden condition at about 3 to 4 knots (1.6 to 2.1 m/s) , are in the 1,000-foot
(304.8 m) length range, with beams in the order of 150 to 250 feet (45.7 to 76.2 m)
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and drafts of approximately 60 to 65 feet (18.3 to 19.8 m). Currents induced by ships
traveling in the outbound direction and in ballast were reported as negligible.
The Alaskan Class tanker ship was selected as a representative ship and
numerical hydrodynamic simulations were performed using MIKE 21 FM HD, using
a time and space varying pressure field to simulate the moving ship. The numerical
model was used for two purposes. First, to verify the predicted ship induced currents
against currents estimated from observations and currents measured during a one
month program at two locations: one at a potential location for a breakwater, the other
at the potential location of the new fireboat boat bay. Secondly, to explore the effects
of fixed breakwater alternatives on the current field, and to assess the hydrodynamic
loads on the breakwaters (fixed and floating), docks and boats. Figure 4 shows a
comparison of measured and predicted current speeds at the planned fireboat boat bay
location (bbcm) due to the passage of the “Alaskan Frontier” oil tanker at
approximately 3.1 knots (1.6 m/s) with a draft of 50.1 feet (15.3 m). Measured and
predicted current speeds are in very good agreement, in particular when considering
that the track of the ship has an effect on the magnitude of the induced currents and
that an assumed track, instead of the actual track, was used in the model. The
comparison of model predictions against measurements and visual observations of
drifters led to conclude that maximum current speeds induced by large tankers
passing at 3 knots (1.6 m/s) with 50 to 65 foot (15.3 to 19.8 m) draft would be less
than 2 knots (1 m/s) along Pier F.
Figure 4. Current speed due to the passage of the ‘‘Alaskan Frontier’’.
Current fields due to tsunamis were studied using the MIKE 21 HD model,
and a scenario from the Tsunami Hazard Assessment performed by Moffatt & Nichol
(2007) for the Port of Los Angeles and POLB. From the 6 tsunami scenarios
examined in that assessment, the Catalina Fault tsunami was chosen, as this scenario
is expected to generate the strongest currents, in the order of 8 knots (4.1 m/s),
through the Navy Mole-Pier F gap. Figure 5 shows, for this scenario, the current
speeds and directions in the vicinity of the gap for the peak ebbing flow. Currents in
excess of 10 knots (> 5m/s) are noted at the southern tip of Pier F and currents in the
order of 2.5 to 3.5 m/s (5 to 7 knots) along Pier F’s waterfront. Similarly to the ship
induced current model, the tsunami model was used to study the effects of fixed
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breakwater alternatives on the current field, and to assess the hydrodynamic loads on
the breakwaters (fixed and floating), docks and boats. Modeling results showed that
the inclusion of an approximately 200-foot (61 m) long, shore-perpendicular, fixed
breakwater near the south end of Pier F, as expected, would slow down the current
along Pier F to approximately 1.5 m/s (3 knots). However, at of the tip of the
breakwater, strong 3+ m/s (6+ knots) currents would result from narrowing the Pier
F-Navy Mole gap, requiring special considerations in the design of that section of the
breakwater.
Figure 5. Catalina Fault tsunami peak ebbing current field at Pier F.
WAVE PROTECTION ALTERNATIVES
Feasible alternatives for wave protection were difficult to define. While most
would be adequate to provide the necessary wave protection, the need to
accommodate a relatively large fleet, no interference with navigation, and site
conditions such as deep water depths and steep bottom slopes, seismicity, and
potentially strong tsunami induced currents proved to be very challenging conditions
that limited the feasibility of most structures. A floating breakwater was analyzed
along with fixed alternatives such as rubble mound, caissons, concrete sheet pile,
cylindrical pile and steel sheet/king pile breakwaters.
Because a breakwater layout that would protect the new docks and boats
against southerly and northwesterly waves would be impractical from operations and
navigation perspectives, preference was given to protect the new docks and boats
from southerly waves with a breakwater, and mitigate their exposure to the broadside
northwesterly post cold front wind waves by arranging most berths in a shore-parallel
orientation, combined with individual slips and four-point moorings for each boat.
The analysis of the wave climate indicated that a floating breakwater would be
adequate to protect the planned new facilities from wind waves. With transmission
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coefficients in the order of 40%, a shore-perpendicular 160-foot (48.8 m) long, 15-
foot (4.6 m) wide and 5-foot (1.5 m) draft floating breakwater would mitigate the 2-
second southerly waves generated in the LA-LB harbor due to the passage of cold
fronts and provide a wave climate for the planned new facilities that would satisfy
criteria such as ASCE (1994) and PIANC (1995). However, it would offer no
protection against swells, also reported as problematic at Pier F, given the low
breakwater beam to wave length ratio. The proposed arrangement of the berths in a
shore-parallel direction would only mitigate the effects of southerly incoming swells.
Mooring the floating breakwater by means of lines (taut or catenary) and piles
was analyzed. A catenary system in the deep water depths at Pier F would allow for
large lateral excursions that would take needed space from the limited space available
for docks and boats. A taut (pre-tensioned) mooring line system, on the other hand,
while featuring reduced lateral excursions, would impose obstructions to the small
vessel off-channel traffic (i.e. tugs, barges, etc.), in addition to requiring more
maintenance, and higher redundancy in the event of mooring line failure. Compared
to a pile system, a mooring line system is significantly more compliant and therefore
the loads induced by waves will be smaller than on a pile system. The deep water
conditions at the site will require significantly long piles, and the potentially high
hydrodynamic loads on the breakwater and piles by tsunami currents would required
specialized structural design of the piles and breakwater-pile interface.
A rubble mound breakwater was discarded early on because its excessive
footprint would obstruct small vessel navigation, in addition to encroaching
significantly in the limited area available for the new docks and boats. Relative to a
rubble mound breakwater, a breakwater consisting of concrete prismatic 20 x 30 feet
(6.1 x 9.1 m) base, 43-foot (13.1 m) high gravel-filled caissons would have a reduced
footprint, but the massive weight needed to provide stability would create large forces
in the event of an earthquake, and overturning moments would create very high
pressures at the toe where a well compacted gravel base could provide the necessary
foundation strength, but not the liquefiable underlying soils present at the site. The
very steep bottom slopes of liquefiable bottom soil between the shore and the main
channel would also impose difficulties to the design and construction of the gravel
mat for the caissons’ foundation.
Both concrete sheet and cylindrical pile breakwaters would offer the
minimum footprint required to minimize encroachment into small vessel navigation
areas and maximize the space for the new docks and boats. Similarly to the rubble
mound and caisson breakwaters, maintenance would be minimal. The sheet pile
breakwater would include batter piles, and the cylindrical pile version would feature
48-inch prestressed hollow piles driven closely together to form the breakwater. Since
a space is required between each cylindrical pile for driving, additional 24-inch
square filler piles would be needed to fill that space to effectively block waves and
currents. Structural analysis of these breakwaters showed, however, that their bending
and shear capacity would not be sufficient to withstand 100-year wave conditions or
extreme tsunami currents.
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A sheet/king pile breakwater appeared to offer the best solution for the site
conditions and project requirements. It offered the advantage of small footprint and
structural capacity, in addition of not featuring the batter piles of the concrete sheet
pile breakwater. This type of breakwater consists of a series of cantilevered piles
embedded in the bottom, with strength provided by a combination of HZ king piles
and AZ sheets between them. This would be a relatively light structure, and therefore
seismic loads would also be relatively low compared to the concrete cylindrical pile
breakwater. Mitigation against corrosion would be provided by means of marine
epoxy coating and a cathodic protection system. From an environmental perspective,
however, this breakwater and all other fixed breakwater types analyzed, would be
consider fill and would trigger an Environmental Impact Report (EIR), which from a
schedule perspective could be considered a disadvantage.
CONCLUSION
The development of a wave protection structure for the planned new docking
facilities at Pier F in the POLB constitutes a good example of how site conditions,
operation and project requirements could be more relevant for the selection and
design of a wave protection structure than the wave conditions themselves. Detailed
coastal engineering analysis helped to expose the relevance of these requirements and
conditions, and allowed for the identification of the optimum structure.
REFERENCES
American Society of Civil Engineers (1994). Planning and Design Guidelines for
Small Craft Harbors, Manuals of Practice (MOP) 50.
Madsen, O.S., Shusang, P. and Hanson S.A. (1978). “Wave Transmission Through
Trapezoidal Breakwaters.” Proceedings of the 16th International Conference
on Coastal Engineering, Hamburg, Germany, 2140-2152.
Moffatt & Nichol (2007). Tsunami Hazard Assessment for the Ports of Long Beach
and Los Angeles. Final Report.
Permanent International Association of Navigation Congresses (PIANC) (1995).
Criteria for Movements of Moored Vessels in Harbours – A Practical Guide.
Report of Working Group No. 24, Supplement to Bulletin No. 88.
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ResearchGate has not been able to resolve any citations for this publication.
Article
In a previous paper Madsen and White (1977) developed an approximate method for the determination of reflection and transmission characteristics of multi-layered, porous rubble-mound breakwaters of trapezoidal cross-section. This approximate method was based on the assumption that the energy dissipation associated with the wave-structure interaction could be considered as two separate mechanisms: (1) an external, frictional dissipation on the seaward slope; (2) an internal dissipation within the porous structure. The external dissipation on the seaward slope was evaluated from the semi-theoretical analysis of energy dissipation on rough, impermeable slopes developed by Madsen and White (1975). The remaining wave energy was represented by an equivalent wave incident on a hydraulically equivalent porous breakwater of rectangular cross-section. The partitioning of the remaining wave energy among reflected, transmitted and internally dissipated energy was evaluated as described by Madsen (1974), leading to a determination of the reflection and transmission coefficients of the structure. The advantage of this previous approximate method was its ease of use. Input data requirements were limited to quantities which would either be known (water depth, wave characteristics, breakwater geometry, and stone sizes) or could be estimated (porosity) by the design engineer. This feature was achieved by the employment of empirical relationships for the parameterization of the external and internal energy dissipation mechanisms. General solutions were presented in graphical form so that calculations could proceed using no more sophisticated equipment than a hand calculator (or a slide rule). This simple method gave estimates of transmission coefficients in excellent agreement with laboratory measurements whereas its ability to predict reflection coefficients left a lot to be desired.
Tsunami Hazard Assessment for the Ports of Long Beach and Los Angeles
  • Moffatt
Moffatt & Nichol (2007). Tsunami Hazard Assessment for the Ports of Long Beach and Los Angeles. Final Report.
Criteria for Movements of Moored Vessels in Harbours – A Practical Guide
Permanent International Association of Navigation Congresses (PIANC) (1995). Criteria for Movements of Moored Vessels in Harbours – A Practical Guide. Report of Working Group No. 24, Supplement to Bulletin No. 88.