HomeMy WebLinkAbout3307; CARLSBAD BLVD SHORE PROTECTION; GEOTECHNICAL INVESTIGATION;Woodward-Clyde Consultants
APPENDIX A
GEOTECHNICAL INVESTIGATION
FOR
CARLSBAD BOULEVARD SHORE PROTECTION
CARLSBAD BEACH STATE PARK - AREA 3
Field Investigation
The surface conditions at Carlsbad State Beach - Area 3 were documented during several visual reconnaissances of the area between July 11 and July 22, 1988. On July 11, 1988,
four test borings were drilled at the approximate locations shown on Figure No. 2. The
borings were advanced to depths ranging from approximately 3 feet to 42 feet. The drilling
was performed by an 8-inch diameter hollow stem auger mounted on a B-61 drill rig and
under the direction of an engineering geologist from Woodward-Clyde Consultants. The
geologist logged the borings as they were advanced. Samples of the subsurface materials
were obtained from the auger cuttings and using a modified California drive sampler (2-
inch inside diameter and 2-1/2-inch outside diameter) with thin brass liners. The sampler
was generally driven 18 inches into the material at the bottom of the hole by a 140-pound
hammer falling 30 inches. The sampler was driven less than 18 inches where gravel or
cobbles prevented penetration or caused excessive damage to the sampler. The disturbed
cuttings from the auger were placed in plastic bags and the thin metal liner tubes containing
the relatively undisturbed samples were removed from the sampler, sealed to preserve the
natural moisture content of the sample,and returned to the laboratory for examination and
testing. A Key to Logs is presented as Figure A-i. Final Logs of the Test Borings are
presented on Figures A-2 through A-6. The descriptions on the logs are based on the field
logs, sample inspection, and laboratory test results. The ground surface elevation at the
boring location was estimated from the topography on the Plans for the Improvement of
Carlsbad Boulevard," City of Carlsbad, Project No. 3205.
Laboratory Tests
The materials observed from the auger cuttings and in the samples obtained from the test
borings were visually classified and evaluated with respect to strength, dry density, and
moisture content. The classifications were substantiated in the laboratory by performing
grain size analyses of representative samples of the soils. Moisture content and dry density
determinations were made on relatively undisturbed samples. The results of the moisture
content and dry density tests are presented on the Logs of Test Borings at the
corresponding sample location. The results of the grain size analyses are shown on
Figures A-7 and A-8.
General Geologic Setting and Subsurface Soil Conditions
-
The study area is located along the low-lying coastal margin of Agua Hedionda Lagoon.
Agua Hedionda Lagoon represents the backfilled channel or "drowned river mouth" of
Agua Hedionda Creek. Like other river, courses in coastal San Diego County, Agua
Hedionda Creek incised (or eroded down into) its channel during the last major late
a/1j12 A-i
Woodward-Clyde Consultants
Pleistocene glacial low stand of sea level (approximately 15,000 to 20,000 years ago).
During the past 10,000 years (Holocene epoch), post-glacial sea level rise to its present
level resulted in a reduced capacity of the creek to transport sediment. Consequently,
predominantly fine-grained sediment was deposited within the channels. Similar to other
coastal lagoons, longshore drift has produced a barrier beach along the mouth of the
lagoon. The migration of the lagoon's outlet channel at the mouth of the lagoon has, in the
recent geologic past, eroded away older Pleistocene and Eocene sediments and deposited
the sand and gravel materials encountered in our subsurface explorations. Elevations along
the existing Carlsbad Boulevard, which extends along the top of the beach, vary from
roughly 13 to 16 feet above Mean Sea Level.
Our subsurface investigation encountered beach and channel sands and gravels to depths of
up to 41-1/2 feet from the ground surface. The upper 9 to 11 feót of each boring was
composed of 1 to 3 feet of recently dredged sand underlain by rounded gravel and cobbles
approximately 1 to 6 inches in diameter. These recent gravel and cobble deposits represent
back-beach berm deposition by high energy winter storm events. The gravel and cobbles
are also exposed on the beach foreshore. Underlying the cobble berm are interbedded sand
and gravel deposits of probable beach and channel origins. The sampler penetration values
in these materials generally ranged from approximately 20 to over 70 blows per foot. Most
of the higher values were influenced bygrave1s. The moisture contents and dry densities in
these materials generally ranged from approximately 15 to 25 percent and 90 to 100 pounds
per cubic foot, respectively.
The current groundwater level along the proposed shore protection alignment generally
follows the tide level. It should be anticipated, however, that there may be some lag of the
water level behind any shoreline protection structure.
a/1j12 IA-2
Project: Carlsbad Boulevard Shore ProtectiOn KEY TO LOGS
Date Drilled: Water Depth: Measured:
Type of Boring: Type of Drill Rig: - Hammer:
-C- L IE 0
.
Material Description
C
0 Ma E 0,a ca Z CD
Ow
Surface Elevation: Elevation:
0 ........ - DISTURBED SAMPLE LOCATION
Obtained by collecting the auger cuttings in a plastic bag.
- - MODIFIED CALIFORNIA SAMPLER
Sample with recorded blows per foot was obtained with a
Modified California drive sampler (2" inside diameter, 2.5"
5 - - outside diameter) lined with sample tubes. The sampler
- was driven into the soil at the bottom of the hole with
a 140 pound hammer falling 30 inches.
Fill 10-
-
Sand
-
Sand/Gravel
15-. - - Gravel
-
GS - Grain Size Distribution -
20-
25—
30
IV
Project: Carlsbad Boulevard Shore Protection Log of. Boring No: 1
Date Drilled: 7-11-88 Water Depth: 14.5' Measured: At time of drilling
Type of Boring: 8" HSA . Type of Drill Rig: B-Si Hammer: 140 # at 30" drop
see Key to Logs. Fig. A-I
(l w.. -
Material Description . a
Cl) 0
Surface Elevation: Approximately 14' MSL
0 - I 1 2.5" Asphalt concrete; 7.5" gravel base over moist, light I - gray brown, silty sand - LI FILL
1I Loose to medium dense, moist, gray, sandy gravel and gravelly - - sand with 2" to 4" cobbles (GP-SP)
51
-
I -
J U
I Medium dense wet gray with light reddish brown (mottled locally) 10— poorly graded fine sand (SP) I 1-2 17 18 96
GS
GS
15 - 1-3 Dense wet gray, gravelly sand (SP) with sandy gravel (GP)
- layers
- 14 12/
- 6"' "On gravel
20-
15 31/
- 6"" 'On gravel
Very dense wet, gray, poorly graded fine to medium sand
- (SP SM) with silt and pebbes and shells locally
25-
- 1-6 76' 'On gravel 18 111 GS
Project: Carlsbad Boulevard Shore Protection Log of Boring No: 1 (Cont'd)
Material Description a
Cn -o
30 1-7 (Continued) very dense wet gray, poorly graded fine to74 medium sand (SP SM) with silt and pebbles and shells -
locally -
35- -
18 60 -
17 112 GS
40- -
19 95 -
- Bottom of Boring at 41.5 feet :
45- - -,
50- -
55- - -
60- -
65
Project: Carlsbad Boulevard Shore Protection Log of Boring No: 2
Date Drilled: 7-11-88 Water Depth: 13' Measured: At time of drilling
Type of Boring: 8" HSA - Type of Drill Rig: B61 Hammer: 140# at 30" drop
see Key to Logs, Fig. A-I
Material Description
- Surface Elevation: Approximately 13' MSL
- o 2-1 3" Asphalt concrete; 6" gravel base over moist, gray, silty sand
- 2-2 FILL
• - : Loose to medium dense, moist, gray, sandy gravel (GP).
• : with rounded cobbles (2"-4") -
5- • -
• •
: .
-
-- --- Grades to-------------------
10 - . Dense, wet, gray, gravelly sand to sandy gravel (SP-GP)
-
-
2-3 51
-
Medium dense wet gray, poorly graded fine sand (SP) with
- layers of shells and pebbles locally
- 15 UR -
-
24 10/ O n gravel 24 90 GS 6""
20 - Sandy gravel layer (GP) with shells - 25 45/
- 6"" "On gravel -
Bottom of Boring at 21.5 feet
-
25-
30 11,
• • __ __ __
Project No: 8851268E-S1,01 Woodward-Clyde Consultants Qh Figure: A-4
Project: Carlsbad Boulevard Shore Protection • Log of Boring No: 3
Date Drilled: 7-11-88 Water Depth: None encountered Measured: At time of drilling
Type of Boring: 8" HSA Type of Drill Rig: B61 Hammer: 140# at 30" drop
see Key to Logs, Fig. A-i
Material Description
CO
Surface Elevation: Approximately 13' MSL
0 Dry to moist, brown, silty sand with gravel
- FILL
-
My
- Loose to' medium dense, moist, gray, sandy gravel (GP) with.
rounded cobbles (3"-4"). -
Refusal at 2.5' on cobbles -
-
5-
10-
-
15-
-
I
20-
25-
30
Project No88S1268E.SIOI I Woodward-Clyde Consultants Figure: A-5
Project: Carlsbad Boulevard Shore Protection Log of Boring No: 4
Date Drilled: 7-11-88 Water Depth: 14' Measured: At time of drilling
Type of Boring: 8" HSA Type of Drill Rig: B61 Hammer: 140# at 30" drop.
see to_Logs, Fig. A-i _Key
LJ J Material Description CD CO)
Surface Elevation: Approximately 15.5' MSL
0 6" Asphalt concrete over moist, olive brown, sandy gravel
•
4-1
• FILL
- ________ Moist, olive brown, gravelly sand • . .
- FILL
4-2 Loose to medium dense, moist, gray, sandy gravel (GP)
•
•
Medium dense moist light gray, poorly graded fine sand (SP) 10 -4-3 with interbeds of silty sand shells and fine gravel layer
- 6 16 94 GS
15—
-
- 44 10/
0~4 On 24 98 GS gravel
Dense, wet, gray, gravelly fine sand (SP-GP) 20 - -
- 4-5 61" "On gravel •
%Dense, wet, dark gray, poorly graded fine sand with gravel (SM)j
Bottom of Boring at 22.5 feet -
25—
• -
30
•
Project No: 8851268E-Sl01 I Woodward-Clyde Consultants Figure: A-6
)O 0
I
100
LI
I
UNIFIED SOIL CLASSIFICATION
COBBLES
I
GRAVEL 0".
SAND .1 I M
•
SILT OR ClAY
U.S.ffl!I m nscu . SDVE no. I HYDROMM
GRAIN SIZE IN MILL1Mgl'ER
SYMBOL BORING DH
mx
t DESCRIPTION
1-1 POORLY GRADED SAND WITH GRAVEL (SP)
1-2-4 POORLY GRADED FINE SAND (SP)
A 1-6-4 POORLY GRADED FINE TO MEDIUM SAND WITH SILT
O 1-8-4 POORLY GRADED FINE TO MEDIUM SAND (Sp-sM)
(Sp)
Remark:
885126819 SI01 CARLSBAD BLVD. SHORE PROJECT
Woodward Clyde
Coneultanta GRAIN SIZE DISTRIBUTION Figure No. A-7 San Diego, CA
100
0
I
UNIFIED SOIL CLA3IFICATI0N
COBBLES
I
GRAVE!, I SAND
-
— i ICDIJSEI . i FINE SILT OR CLAY
MA. mm u I us.arapAlm SWE No. 1 HYDROMCM
3 3/43/8 4 10 20 400 140200
II___liii -I
II___11111 ---1 II___11111__1 1111:_III1I I II__lilil- I oilI P SIIIIIIILp - - a
lIIIIIII..II,I.
p p lisa - as pp
Em — 5
20
40
60 lxi C-)
lxi 04
80
100
ra
GRAIN SIZE IN MilLIMETER
SYMBOL BORING DH 1i & DESCRIPTION
o 2-4-4 POORLY GRADED FINE SAND (SP)
E3 4-3-4 POORLY GRADED FINE SAND (Si')
4-4-4 POORLY GRADED FINE SAND (SP)
Remark:
Woodward Clyde Consultants
COASTAL CONSIDERATIONS
FOR
CARLSBAD BOULEVARD SHORE PROTECTION
CARLSBAD BEACH STATE PARK - AREA 3
General
The subject area is located along a barrier beach at the mouth of the Agua Hedionda lagoon
between the inlet and outlet jetties for the outer portion of the lagoon. The elevations along
Carlsbad Boulevard in this area, which extends along the berm at the back of the beach,
generally range from approximately +13 to +16 feet (MSLD). Carlsbad Boulevard is
partially protected by the beach which is typically 150 to 200 feet wide and is partially composed of gravel and cobbles. The sand levels vary seasonally and are mostly removed
during high tides and storms during the winter. The subject area is generally situated near
the middle of the Oceanside littoral cell. A recent report by Tekmarine, Inc. indicated that
the Oceanside littoral cell is basically "sand-starved." However, despite the deficiency of
sand, the coastline of Carlsbad manages to maintain a finite beach width; this appears to be.
due to the abundance of gravel and cobbles in the area. The subject area also receives sand
nourishment every 2 to 3 years from dredging of the lagoon. Erosion of the beach and
damage to the roadway due to high tides and storm waves occurs on a periodic basis.
Maximum Tide and Still Water Level
Based on records from 1925-1953 and 1956-1970, the Army Corps of Engineers' Shore
Protection Manual (SPM) gives a maximum observed water level at San Diego of +7.6 feet
above MLLW. Tidal predictions for this area are based on daily predictions for San Diego.
The corrections to the high water predictions are 0.90 for La Jolla, south of Carlsbad, and
0.91 for San Clemente, north of Carlsbad, implying that conditions along this portion of
the coast, including those at Carlsbad, are fairly uniform.
Flick and Cayan (1984) have examined extreme high water levels at San Diego, including
the 1982-83 winter, which included high astronomical tides, meteorological effects
associated with the many storms, and the extreme effects of El Niño. The highest recorded
level at San Diego is +8.5 feet in late January, 1983. This was nearly a foot above the
predicted level. Applying the correction for La Jolla
- San Clemente gives a value of 0.91 x 8.5 = +7.74 feet for the Carlsbad site. Adding an allowance for 0.35 feet sea level rise in
50 years, and 0.5 feet for local wave set-ups, gives the following Design Still Water Level:
Maximum Observed Tide 7.74 feet MLLW (Mean Low Low Water) Sea Level Rise .35 Local Wave Set-Up .50 - Design Still Water Level 8.59 or approximately 8.6 feet MLLW (or 5.7 MSLD)
a/1j12 IB-i
Woodward- Clyde Consultants
NOTE: In the calculations, Mean Lower Low Water (MLLW), the datum for both nautical
charts and tide tables, is taken as the vertical datum. The Mean Sea Level Datum of 1929,
which is generally used for onshore topographic maps, is approximately 2.9 feet above
MLLW.
Beach Profiles
Beach profiles have been made in the area by Walton, Flick, and Murray in 1982 and 1983;
by the Army Corps of Engineers in 1983 and 1984; and Tekmarine, Inc. in 1987 and 1988.
As a part of our study, Woodward-Clyde Consultants also made four beach profiles on
July 19, 1988 at the approximate locations shown on Figure No. 2. These latter profiles.
are attached as Figure B-i.
An evaluation of the various beach profiles indicates that the sand on the backshore beach
area generally varies about 4 to 5 feet in thickness and is typically completely removed after major storms. The beach width (to MLLW line) near the middle of the site varied from a
maximum of approximately 300 feet after nourishment to a minimum of approximately 150 feet after major storms during the period between 1982 and 1988. A small sand berm
generally develops in the profile during the winter at about 250 to 350 feet offshore. This
berm also appears to be removed during a major storm. The inclination of the foreshore
(where cobbles are generally exposed) generally ranges from about 6:1 to 10:1 (horizontal
to vertical). The bottom flattens below the MLLW line to inclinations on the order of about
30:1 to 50:1. Beyond a distance of about 500 feet offshore the bottom inclination is
generally about 60:1 to 70:1 extending to at least 2,000 to 3,000 feet offshore. For
purposes of design it is assumed that the beach slope in front of the shore protection
structure will be approximately 30:1 to 50:1.
Design Scour Depth
The current beach profiles and test borings indicate that the top of the cobble berm at the
site generally ranges between approximate elevations of +8 to +12 feet (MSLD), is about 8
to 10 feet thick and extends about 50 to 100 feet out (west) from the proposed shore
protection alignment. The available beach profiles indicate that since 1982, the top of this
berm near the middle of the site has not eroded below approximate elevation +8 feet
(MSLD) and that the face of the berm near the middle of the site has not been eroded any
closer than about 30 feet from the proposed alignment. The erosion at the north end of the
site appears to be somewhat more severe and the erosion at the south end somewhat less
severe than at the middle of the site. For purposes of preliminary design, it is assumed that
the maximum depth of scour in front of the shore protection structure along the west side of
Carlsbad Boulevard will be elevation zero (MSLD).
a/1j12 B-2
Woodward- Clyde Consultants
Design Wave Height
The breaking wave height in front of the shore protection will depend upon the beach
inclination in front of the structure, the design scour depth in front of the structure and the
maximum still water level. Based on the above information, it is estimated that maximum
design water depth at the toe of the structure will be approximately 5.7 feet and the
maximum breaking wave height will be about 6 feet. It is further estimated that the
maximum runup on a 1-1/2:1 inclined rock revetment and a vertical seawall would be
approximate elevations + 15 feet and +18 feet, respectively. Typical calculations for design
are attached.
.
a/1j12 -
-
. B-3
L R/W
+18 I I 9
+16- 1 I 9Riprap
+14
+12 )çRirrari 'k
I 0 O°OO-. +10
i o Q- P-3 (South End)
+8 \ '1 P-1 CL
+6 I P-2f'\
'A 0% 'Os. a +4
U P-4 0
(North End)_-"055 z +2 050 0. 01
-2 - . See Figure 2 for prfile locations
Profiles on 7- 19-88
Centerline elevation from Plan for
4 Improvements of Carlsbad Boulevard
City of Carlsbad Project No. 3205
-6 - Centerline of Carlsbad Boulevard
R/W - Westerly edge of Carlsbad Boulevard
-8 Improvements right of way.
0 100 • 200 • 300
DISTANCE FROM CENTERLINE OF CARLSBAD BOULEVARD (Feet)
- .
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APPENDIX C
USER BENEFIT CALCULATIONS
FOR
CARLSBAD BOULEVARD SHORE PROTECTION
CARLSBAD BEACH STATE PARK - AREA 3
General
It is generally anticipated that loss of user benefits will be due to damage from high tides
and storms. For this analysis, it is assumed that the Carlsbad Boulevard Improvements,
are contructed and that damage will occur on a periodic basis. The value of the benefits lost
is estimated from the value of lost time, lost use of the area, and cost of repairs and
maintenance. The following assumptions are made for the evaluation:
A 50 year useful life for the project;
Major damage due to storms once in five years;
Minor damage due to storm twice in five years;
General maintenance required in years of no significant damage;
A minimum average beach use of 3,000 persons per day;
An average future daily traffic for Carlsbad Boulevard of 27,000 per day;
An average daily bicycle traffic of 200 per day; and
Gas, water, electric and storm drain utilities present in Carlsbad Boulevard.
Loss of Beach Users Benefits
It is generally considered that the beach season in Carlsbad is year around. Maximum use
will be in the summer (May through September) weekends and holidays. Minimum use
will be weekdays during the winter. The California Department of Parks and Recreation
consider Area 3 as the most highly used beach in this area. Based on California
Department of Parks and Recreation information, this approximately 2,600 feet of beach
had an estimated total of 1,825,000 visitors in the 1980-81 fiscal year. Based on this
information, it is estimated that park use will average about 5,000 persons per day and have a minimum use of about 3,000 persons per day.
It is anticipated that most damage will occur in December, January and February and most
loss of use due to restricted access and parking during repair and maintenance time will be
in January, February, March and April. For this estimate, it is assumed that beach use will
be reduced by 50 percent for four months (120 days) after a major storm and 25 percent for
two months (60 days) after a minor storm. Thus, for a five year period it is estimated that
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90 days of beach use would be lost or approximately 18 days per year. It is further
assumed that this loss will be during minimum use time; thus, the average total user day
lost per year is 54,000.
If the value of each recreation day benefit is assumed to be $1.50, the annual beach user benefit loss will be:
Annual Beach user Benefit Loss = 1.5 x 54,000 = $812000
Loss of Bicycle Lane Use
Carlsbad Boulevard has a dedicated bicycle lane along its full length in the proposed project
area. This is considered a main recreational bicycle travel lane in the area and is
conservatively estimated to have an average daily traffic of 200 and an annual traffic of
73,000. Each trip is considered equivalent to a recreation-day benefit at a value of $1.50 per trip.
It is estimated that the bicycle lane would be closed during maintenance and repair for 120
days one year and 60 days for two years, for a total of 240 days during a 5 year period.
* This is an average of 48 days per year, or 9,600 trips per year.
Thus, the annual bicycle user benefit loss will be:
Annual Bicycle user Benefit Loss - 1.5 x 9,600 = $14,400
Loss of Time due to Traffic Reduction
Carlsbad Boulevard is a main north-south travel way which has an estimated future average
daily traffic volume (ADT) of 27,000 vehicles. This traffic level is anticipated to be
reached and exceeded within the next approximate 20 to 25 years. It is estimated that traffic
would be detoured for a period of 60 days after a major storm and 20 days after a minor
storm, or a total of 100 days during a five year period. This is an average of 20 days per
year which is equal to 540,000 vehicle trips.
Loss of Carlsbad Boulevard would require this traffic to go east on Tamarack Avenue
approximately 0.6 miles to Interstate Highway 5, south on Interstate 5 to Cannon Road and then east on Cannon road approximately 0.4 miles to the coast. Using a vehicle operating
cost of $0.30 per mile would produce a total annual vehicle operating cost for using the
detour of:
Annual Vehicle Operating Cost = 0.30'x (0.6 + 0.4) x 540,000 = $162,000
This detour would also result in lost time for the occupants of the vehicles. Assuming the
average occupancy rate is 1.5 persons per vehicle, the average speed is 35 miles per hour,
and the value of a person's time is $5.00 per hour, it will give an annual lost time cost for
use of the detour of:
Annual Lost Time Cost = 5.00 x (0.6 + 0.4) x 1.5 x 540,000/35 = $115,715
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Woodward-Clyde Consultants
Facility Replacement Costs
It is assumed that each existing utility would have to be replaced over a length of 2,500 feet
once during the design life of 50 years. The estimated cost for the replacement of each
facility is as follows:
High pressure gas main 140,000 Water main 120,000 Electrical lines 20,000 Telephone lines 20.000
Total Cost $300,000
For a design life of 50 years and an interest rate of 12 percent, the annualized cost is
determined by multiplying the total cost by 0. 12042.
Annualized facility replacement cost = $300,000 x 0.12042 = $36,126
Imorovement Rer,lacement/Maintenance Cost
It is anticipated that after each major storm (once every five years) the sidewalk, street
lights, a portion of the pavement, the bike lane and storm drain inlets will have to be
replaced. It is estimated that the cost for this work will be approximately $180,000 or an
annual cost of $36,000.
It is anticipated that some repair and maintenance will also be required after minor storms
(twice every five years). It is estimated that this work will be approximately 25 percent of
the major damage, or an annual cost of $9,000.
During years where there is no storm damage, it is estimated that normal maintenance will
be about $5,000 per year or a total of $10,000 for two years. This is an annual cost of
$2,000.
Total Annual Improvement Replacement/Maintenance Costs = $47,000
Other Losses
It is also anticipated that temporary reduction to,beach access in and travel through this area
will reduce the tourist use of the area. This will in turn result in lost revenue to businesses
in Carlsbad and corresponding losses of sale tax revenue. For purposes of this study, it is
estimated that such losses might be on the order of $50,000 per year.
Woodward-Clyde Consultants
APPENDIX D
SHORE PROTECTION STRUCTURES
FOR
CARLSBAD BOULEVARD FOR SHORE PROTECTION
CARLSBAD BEACH STATE PARK - AREA 3
General
The primary purpose of the shore protection structure in the subject area is to protect
Carlsbad Boulevard and the associated improvements, including walkways, bicycle lane,
parking and utilities. With this primary purpose in mind, various alternative structures may
be considered taking into consideration several other objectives. The intent is to select a
low cost alternative that has a low level of maintenance and is aesthetically pleasing. Other
objectives include minimizing encroachment onto the beach, reduce construction-related
impacts and provide both lateral and vertical beach access.
The proposed structure will generally be located along the westerly edge of the Carlsbad
Boulevard Improvements right-Of-way. A walkway will be constructed behind and for the
entire length of the structure within the right-of-way. The walkway would have an
elevation ranging from approximately +13 to +15 feet with a 3.5-foot high railing along the
ocean side. It is anticipated that most vertical structures would be extended up to form the
railing at an approximate top elevation +16.5 to +18.5. It is anticipated that stairways,
ramps and lifeguard facilities will encroach onto the beach from 5 to 10 feet beyond the right-of-way in certain areas. Additional encroachment onto the beach would be required
depending on the selected design. A general discussion of various alternative structures is
presented in the following paragraphs.
Rock Revetment-
The existing roadway is currently protected by dumped rock and rubble at the north and
south ends of the project. These existing revetments do not appear to be designed and
generally require annual maintenance and repair, particularly at the north end. Both
revetments tie into the existing rock jetties for the inlet and outlet to Agua Hedionda
Lagoon. It is anticipated that these revetments would be replaced for a distance of
approximately 250 feet and 175 feet at the north and south ends, respectively. The
revetment could also continue along the road between these two areas. It is anticipated that
the top of the revetment would be of approximate elevation +16 feet (MSLD) for most of
the alignment and raise up to approximately +20 feet at the north end. It would slope down
at an approximate inclination of 1-1/2:1 (horizontal to vertical) to a toe elevation of about -2
feet. A typical section is shown on Figure No. D- 1.
Advantages of this shore protection method are that it provides good wave energy
absorption, has a reasonable cost, can be rapidly constructed, has low maintenance
requirements and will easily tie-into the existing rock revetments and rock jetties at both
ends. Disadvantages include a relative wide encroachment onto the beach (approximately
30 to 40 feet), difficult access across and through the revetment, and collection of debris.
Woodward-Clyde Consultants
Reinforced Concrete-Vertical Wall
This structure would be a conventional reinforced concrete L-shaped wall. The top of the
wall would be at approximate elevation +17.5 feet and the bottom of elevation +3 feet with
a cut-off wall extending to approximate elevation -1 feet. The stem of the wall would be
about 18 inches thick and the L-portion could extend back into the right-of-way. This wall
would have to be supported on piles.
Advantagesof this seawall are that it has a low encroachment onto the beach (less than 2
feet), the anticipated maintenance is low and the stairways and ramps could be easily
incorporated into the wall. Disadvantages include a high cost and difficult construction.
Reinforced Earth Wall
This type of wall is a patented structure that is composed of precast reinforced concrete face
panels tied-back into a zone of compacted select fill by steel reinforcing strips. The face of
the wall could be located along the edge of the right-of-way and the approximately 12 feet
long reinforcing strips could extend back into and under the proposed walkway and other
improvement. The toe of this wall would be at approximate elevation -1 feet and would be
protected by rock extending about 10 feet Out onto the beach below an elevation of +6 feet.
A typical section is shown on Figure No. D-2.
Advantages of this wall are that it is easy to construct, has a low cost and could be built
with a moderate encroachment onto the beach. Access stairs and ramps can also be easily
incorporated into the design. Construction would require additional excavation and
compaction of soil and a larger encroachment into the right-of-way or out onto the beach.
Corrosion of thle reinforcing strips needs to be considered in the design.
S tresswall
Stresswall is another patented structure that is generally composed of precast reinforced
concrete tie-backs and precast reinforced concrete panels backfilled with compacted select
soils. The dimensions and construction area would be similar to the Reinforced Earth
Wall. It would also require toe stone and a shallow cut-off wall. A typical section is
shown on Figure No. D-3.
The advantages and disadvantages of this wall are similar to the Reinforced Earth Wall;
however, corrosion of steel strips is not of concern.
Vertical Sheet Pile Walls
Vertical sheet pile walls could be constructed of either steel or concrete and could either be
cantilevered with toe stone or anchored with deeper penetration. The anchored wall would
have minimum encroachment on the beach, but would require additional excavation and an
underground anchor within the right-of-way. The steel sheeting is easier to drive than the
concrete sheeting (which would probably require excavation of the cobble layer and
jetting).
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Woodward- Clyde Consultants
Corrosion of the steel needs to be considered in the final design. Typical sections are
shown on Figures Nos. D-4 and D-5.
Other Shore Protection Structures
Other types of shore protection that could be considered include cribwalls, Fabriform (a
patented product consisting of nylon bags filled with concrete) and steel H-piles with wood
or concrete lagging.
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Street and Walk
Handrail
• Crest Elevation Varies +16' to +20'(MSLD)
J 11 Approximate 2
1 Lap Filter
• A-Stone (two ton)
Beach Level
Cloth 5'
• B-Stone (400 ibs) Filter Cloth ••
•.••.
'V 6" Quarry Waste
-
• Base at -2' (MSLD) -
"kLap Filter Cloth 5'
W000WARD-CLYDE CONSULTANTS
—+17.5'
Reinforced Concrete Cap
—+14.0'
Reinforced Earth Wall
Typical Beach. Level
- ;; @" •, ff/c'/ - - •••
—+6.0' •
Toe Stone
Filter Cloth
9'
--1.0'
Reinforced Concrete Footing
Walkway
Filter Cloth
Reinforcing Strips
12'
Reinforced Concrete Cap
+17.5'
+14.0'
Reinforced Concrete Stresswall
Typical Beach Level
+6.0'
Toe Stone +5 0, lue Stone
01
61 91 Filter Cloth
Walkway
Filter Cloth
Concrete Cut-Off
REINFORCED CONCRETE "STRESSWALL" WITH TOE STONE
rAflT.SPAT' 1:flT1T1PVAPfl ST-WRP PPnTrCPT(Th1
-lr7 r-I
+17.5
/ -
-20