HomeMy WebLinkAboutCDP 98-77; Ponto Beach Parking; Coastal Development Permit (CDP) (10)REYNOLDS
PLANNERS
m^m^^ Mrnrn
CIVIL
ENGINEERS
INC.
E N G 11 N E E R 1 N G
SURVEYORS
WAVE RUNUP IMPACT
FOR CARLSBAD PROJECT NO. 3618 / PONTO BEACH PARKING
Reference is made to the attached improvement plans for project location, and the existing and proposed
improvements for this project.
Background:
In 1996 the City of Carlsbad authorized and contracted for enhancements to Batiquitos Lagoon. Those
improvements, as it concerns this project, consisted of the construction of a new bridge for Southbound
Carlsbad Boulevard, opening the mouth of the lagoon, constructing stone jetties, placing dredged sand
along the beach, and overlaying the roadway asphalt pavement. Since as-built plans were not available,
investigations were undertaken with the project design firm of Moffit & Associates. According to the
Project Engineer, Mr. Mike Hemphill of Moffit & Associates, a under the sand armor stone rock
revetment was constructed West of Carlsbad Boulevard from the North logoon jetty to 100 feet North of
the jetty for wave erosion purposes.
In 1994 the U.S. Army Corps of Engineers prepared a Reconnaissance Report titled "PACIFIC COAST
SHORELINE, CARLSBAD, SAN DIEGO COUNTY, CALIFORNIA". This report is on file with the
City of Carlsbad, Engineering Department. Refer to the attached key map from the report identifying
Reach 5 wherein this project is located. Applicable excerpts from the report discussing Wave Runup and
Excessive Wave Runup issues are enclosed.
Conclusion:
This project will not have an adverse impact on existing Carlsbad Boulevard since it will provide
additional wave runup erosion protection for Southbound Carlsbad Boulevard and the existing bridge.
Sincerely,
RCE, Inc.
C. Tony Reynolds PE, President
477 LEXINGTON CIRCLE OCEANSIDE, CA 92O57 TEL: (76O) 966-1466 FAX: (76O) 966-1467
EMAIL: rce@nctimes.net
US Army Corps
of Engineers
Los Angeles District
RECONNAISSANCE REPORT
PACIFIC COAST SHORELINE, CARLSBAD
SAN DIEGO COUNTY, CALIFORNIA
MAIN REPORT
U.S. Army Corps of Engineers
Los Angeles District
300 North Los Angeles Street
Los Angeles, California 90053
January 1994
TABLE OF CONTENTS
™ 1.0 INTRODUCTION 1-1
1.1 Study Authority 1-1
• 1.2 Purpose and Scope 1-1
1.3 Study Conduct 1-1
1.4 Public Involvement 1-2
1.5 Prior Studies 1-2
1.5.1 Corps of Engineers Studies 1-2
— 1.5.2 Studies by Others 1-4
2.0 THE STUDY AREA 2-1
•
2.1 Location 2-1
2.2 Description 2-1
2.2.1 Reach 1 2-1
•
2.2.2 Reach 2 2-1
2.2.3 Reach 3 2-4
2.2.4 Reach 4 2-4
•
2.2.5 Reach 5 2-4
2.3 Physical Characteristics 2-5
2.3.1 Bathymetry 2-5
•
2.3.2 Local Geology/Sediment Characteristics 2-5
2.3.4 Tides and Sea Level 2-7
2.3.5 Water Levels 2-8
• 2.3.6 Currents 2-8
• 2.3.6.1 Offshore Currents 2-8
2.3.6.2 Longshore Currents 2-8
• 2.3.6.3 Cross-shore Currents 2-9
2.3.7 Waves and Storms 2-9
2.3.8 Littoral Processes 2-12
2.3.8.1 Sediment Sources and Sinks 2-13
2.3.8.2 Existing Structures, Beachfills, and Dredging
History . ; 2-14
2.3.8.3 Erosion and Accretion Rates 2-16
2.3.8.4 Historic Shorleine Changes 2-17
2.3.8.5 Historic Profiles 2-17
2.3.8.6 Longshore Transport 2-18
2.3.8.7 Sediment Budget 2-18
2.4 Social and Economic Factors 2-22
2.4.1 Location and Description 2-22
2.4.2 Demographics 2-22
2.4.2.1 Population 2-23
2.4.2.2 Tourism and Recreation as Major Industries . . . 2-23
I
I
I
I
I
I
4.2.11.2 Engineering Evaluation 4-59
4.2.11.3 Environmental Evaluation 4-59
4.2.12 Plan 12 - A Rubble-Mound Revetment in Reach 5 .... 4-62 V
4.2.12.1 Description 4-62
4.2.12.2 Engineering Evaluation 4-62
4.2.12.3 Environmental Evaluation 4-62
4.2.13 Plan 13 - A Groin System with Beachfill in Reach 1 ... 4-65
4.2.13.1 Description 4-65
4.2.13.2 Engineering Evaluation 4-65
4.2.13.3 Environmental Evaluation 4-67
4.2.14 Plan 14 - A T-Groin with Beachfill in Reach 3 4-70
4.2.14.1 Description 4-70
4.2.14.2 Engineering Evaluation 4-70
4.2.14.3 Environmental Evaluation 4-70
4.3 Identification of Justified Projects 4-77
5.0 FEDERAL INTEREST DETERMINATION 5-1
5.1 General 5-1
5.2 Purposes of Federal Participation 5-1
5.2.1 Hurricane and Storm Damage Reduction 5-1
5.2.2 Recreation 5-4
5.2.3 Mitigation of Shore Damage Due to Federal Navigation
Projects 5-4
5.3 Shore Ownership 5-4
5.3.1 Non-Federal Public Shores-Park and Conservation Areas . . 5-5
5.4 Beach Creation 5-5
5.5 Periodic Nourishment 5-5
5.6 Maintenance 5-6
5.7 Local Cooperation Requirements 5-6
5.8 Determination of Federal Interest in Shore Protection Plans at
Carlsbad, California 5-7
5.8.1 Requirement for Plans to be Justified Primarily on Storm
Damage Reduction Benefits 5-7
5.8.2 Requirement for Public Use, Access, and Parking 5-8
5.8.3 Mitigation of Impacts from Federal Navigation Projects . . . 5-8
5.8.4 Shore Protection For Reach 5 5-9 *S
5.8.5 Conclusion of Federal Interest Determination 5-9
5.9 Federal and Non-Federal Requirements For Implementation of
Shore Protection in Reach 3 5-9
5.9.1 Cost sharing of First Cost 5-9
5.9.2 Cost sharing of Periodic Nourishment and Maintenance . . 5-10
5.9.3 Other non-Federal requirements 5-10
6.0 IPMP/FEASIBILITY PHASE REQUIREMENTS 6-1
iv
c
Carlsbad
State
Beach
Reach 2
Agua
Hedionda
Lagoon
Pacific Ocean
12491004M
Figure 2.2 Five Reaches of Carlsbad Coastal Area
2.2.3 Reach 3
Reach 3 is the 4300 foot stretch between Tamarack Boulevard and the Terra
Mar housing development in front of Agua Hedionda Lagoon and Carlsbad
Boulevard. Carlsbad Boulevard reaches its lowest elevation in this reach ( +16.95
feet MSL). The three-
quarter mile length of this reach between the inlet and outlet jetties was the study
area for the May 1990, Section 103 Small Project Carlsbad Beach Erosion Control
Reconnaissance Study.
In the northern end of this reach, the Tamarack parking lot is protected by
approximately 400 feet of one to two-ton stone. Immediately south of the Agua
Hedionda intake jetty, Carlsbad Boulevard is protected by 350 feet of half-ton
stone. Due to annual dredging of Agua Hedionda Lagoon, the 2700 foot reach
between the intake and outlet is significantly wider during the summer than under
normal winter conditions. The geology is different in this reach, in that non-
erodible material is at -6.25 feet MLLW.
2.2.4 Reach 4
The fourth reach is made up of the Terra Mar housing development, which
stretches 2200 feet along the coast from south of Agua Hedionda to the northern
edge of South Carlsbad State Beach. This segment features twenty-nine
structures which are on top of the bluffs; the average first floor elevation is +38
feet MLLW. Sixteen of the structures are protected by riprap and thirteen by
gunite walls. The non-erodible material in this reach, a cemented sandstone, is
completely exposed during the winter and only a thin layer of sand exists at the
foot of the bluffs under normal summer conditions.
2.2.5 Reach 5
Reach 5, composed primarily of South Carlsbad State Beach, is
approximately 18,400 feet in length. It consists of a narrow beach backed by
unprotected, bluffs. Behind the beach, the cliffs rise between forty and sixty-five
feet, though at one point they are as low as fifteen feet. With the exception of
Carlsbad Boulevard, the camping area on top of the bluffs, and a few state park
stairways and lifeguard towers, there are no structures in this reach.
Currently, most of the beach is cobbled year-round. However, most
probable future conditions include the Batiquitos Lagoon Enhancement Project
2-4
which is being done in mitigation for the Port of Los Angeles expansion.
Approximately 1.5 million cubic yards of sand dredged from the lagoon will be
placed in this reach, specifically, at Encinas Creek, and jetties will be constructed
at the mouth of the lagoon. Port officials anticipate that the project will be
completed in March, 1997.
2.3 Physical Characteristics
2.3.1 Bathymetry
The deep water bathymetry offshore of Carlsbad is shown in Figure 2.3.
Carlsbad is located in the central portion of the Oceanside littoral cell bounded by
Dana Point in the north and Point La Jolla in the south. Figure 2.3 shows that the
bottom contours throughout much of this cell are gently curving and uniform. The
nearshore contours at Carlsbad are relatively straight and parallel, except where
Carlsbad submarine canyon approaches the shoreline. The head of this canyon is
located at approximately the 100-foot isobath. Nearshore slopes are steeper south
of the canyon.
2.3.2 Local Geology/Sediment Characteristics
Based on data gathered in connection with the Coast of California Study
from 1983 to 1986, the mean grain size in the littoral zone varied from 0.15 mm
to more than 0.4 mm depending on the season.
The City of Carlsbad made available to the Corps a number of geotechnical
reports that were done by private firms for both the city and private individuals in
preparation for the construction of seawalls. In Reaches 1, 2, and 4, the non-
erodible material at the foot of the bluffs was a cemented sandstone, at
approximately mean sea level { + 2.75 feet MLLW). Standard Penetration Test
(SPT) blow counts were in the range of 60 to 70 blows per foot. The bedrock was
generally under 5 to 8 feet of cobbles and sand. In Reach 3, bedrock was found to
at -6.25 feet MLLW, lying under silty sand. No reports were available for Reach 5
although it is reasonable to assume that the composition and location of the
bedrock is the same as in Reach 4.
2.3.3 Climate
The climate of coastal southern California is generally considered to be of a
semi-arid Mediterranean type, with mild winters characterized by about 10 to 20
inches per year of rainfall. According to USAED, Los Angeles (1986), the local
2-5
estimated that 200,000 square feet of the road pavement (2000 by 100 feet)
were severely damaged and the repair costs were estimated at $500,000. The
double perpendicular parking was replaced with a single row of angled parking.
During the storms of 1983, this angled parking was destroyed as approximately
100,000 square feet were lost.
Prior to the January 1988 storm, the city installed riprap along the shoulder
of the boulevard. Runup from that event did not cause serious erosional damage
to the roadway but did result in clean-up and repair costs of $158,256. Figure 3.1
shows the scour at the base of the sidewalk.
The Tamarack parking lot, north of the Agua Hedionda inlet, contains
approximately 200 parking spaces. Though fronted by revetment, the lot is
situated at +12.75 feet MLLW and is very close to the water line, and is thus
exposed to flooding and erosion. In 1983, this parking lot experienced
considerable damages which resulted in a reduction in width of approximately 30
ft. and loss of its curbing gutter. Emergency repairs were installed, but also lost in
the 1988 storms. Following this storm season, the state performed temporary
repairs on the parking lot.
3.1.4 Reach 4
While undercutting of the bluff from specific storm events is not a major
concern to homeowners within Reach 4, damages to protective structures have
been sustained over time from severe wave force. Following the 1978 and the
1983 events, a portion of the structures protected by riprap required stone
replacement resulting from wave damage. In addition, gunite structures protecting
the remainder of the seafront homes in this reach required substantial repairs.
After the 1983 event an estimated $65,000 was spent to repair gunite protective
structures on thirteen homes, while an estimated $150,000 was spent to rebuild
riprap revetments on sixteen homes.
3.1.5 Reach 5
Although Reach 5, the South Carlsbad State Beach, contains few
developments prone to damage, it has been damaged in recent years: the 1983
storm caused $96,602 in damage resulting from debris clean-up of destroyed
restrooms, stairways, and parking lot repairs. The most critical area in the reach is
at Encinas Creek where Carlsbad Boulevard is +18.25 feet MLLW and a box
culvert crosses over the creek at a particularly narrow part of the beach. The
exposed length is approximately 1000 feet long. The city reports that during the
storms of 1988 this structure was undermined and closed for several days. Repair
3-2
costs were between $5,000 and $10,000. Furthermore, the structure is old (circa
1923), in poor condition and appears exposed to erosion at the abutments. Figure
3.2 is a view from Carlsbad Boulevard towards Encinas Creek.
The bluffs fronting South Carlsbad State Beach campgrounds are an area of
particular concern for the local sponsor. The popular campgrounds bring in an
estimated $430,000 per year in revenues but are suffering from erosion. The
erosion is primarily due to runoff and other subaerial factors but waves and runup
have had some effect, albeit difficult to quantify. It is known that the beach
fronting the bluffs is denuded of sand virtually all year and therefore narrower and
thus has reduced protective capabilities. Figure 3.3 shows these bluffs.
3.2 Summary of the Analysis
The primary problem identified along the study area is the lack of protective
beach which leaves existing development exposed to storm waves and excessive
runup. Long-term erosion and storm recession further exacerbate the problem.
This section will summarize the analysis presented in the Coastal Engineering
Appendix for the potential for these problems to cause damage.
3-3
50 —
c
0
i-l
+>10>
<D
UJ
0 —
Carlsbad
Reach 5
State Pork Campground +63' MLLW
Earth Slope 1:1
Hard Pan +0.8'MLLW
Cobble Beach 1:4
Profiles:
— Maximum
-- Mean
— Minimum
100
Horizontal Distance (ft)
Figure 3.12 Schematic Profile of Carlsbad - Reach 5
Table 3.2. Storm Recession versus Return Period
Event
10
25
50
100
Shoreline Retreats (ft)
MHHW
43
47
50
52
MSL
89
96
100
104
MLLW
225
237
245
252
3.2.2 Runup
Runup has been calculated using the reaches and cross-sections presented in
Section 3.2.1. The beach conditions used are the profiles taken after the storm of
January 1988. Due to the bedrock conditions, only the profile in Reach 3 will
deepen over the 50 year period considered. As a result, only in Reach 3 will runup
increase. Due to the anticipated temporal nature of the beachfill in Reach 5, the
runups presented for this reach are done over the fully-scoured profile. Table 3.3
presents these runups.
3-15
/••s
, * , TABU 3,3 s
WAVE 8UNUP l£m {FEET MUW)
PRESENT CONDITION
RETURN
PERIOD
Reach 1
Section 1
Reach 1
Section 2
Reach 1
Section 3
Reach 1
Section 4
Reach 2
Reach 3
Reach 4
Section 1
Reach 4
Section 1
Reach 5
2
17.55
19.55
17.35
17.75
19.95
18.15
18.95
19.75
19.85
5
19.25
21.45
18.65
19.55
21.65
19.45
20.55
21.35
21.45
10
20.25
22.55
19.65
20.45
22.65
20.35
21.35
22.15
22.45
25
21.05
23.25
20.35
21.15
23.65
21.15
22.35
23.25
23.45
50
21.35
23.75
20.75
21.65
24.15
21.65
22.85
23.75
23.85
100
21.85
24.35
21.25
22.15
24.45
22.15
23.35
24.15
24.45
200
22.45
24.95
21.75
22.65
25.05
22.35
23.85
24.75
24.85
50-YEAR FUTURE CONDITION
Reach 3 21.35 22.65 23.45 24.25 24.75 25.35 25.75
3.3 Damages
The lack of adequate protective beaches leaves backshore structures
exposed to excessive runup and increased wave attacks. Factors such as
inundation, damage to protective structures, damage to structures, and erosion of
Carlsbad Boulevard, will be examined.
3.3.1 Inundation Damages
Excessive runup will cause significant content and structural damage to four
large structures in Reach 1. The remaining structures in Reaches 1 and 4 are all
above the elevation of the maximum runup. Inundation damage will occur when
3-16
3.3.4 Roadway Damages
Significant damages to Carlsbad Boulevard have occurred in Reach 3 and
less significant damages have occurred further to the south in Reach 5. A unique
feature of Reach 3 is that the bedrock is located at elevation -6.25 feet MLLW,
thus making the reach more susceptible to both storm-induced scour and long-term
erosion.
As previously discussed, it is assumed that over a fifty year period, Reach 3
will experience recession of 1 ft/yr and it is anticipated that the beach will erode to
the roadway and then continue to scour vertically. As a result, the depth at the
toe will continue to deepen, and the road could be exposed to greater wave
energy.
Damages to Carlsbad Boulevard in Reach 3 were based on the 1983 storm
event which produced an excess run-up of 4.1 feet over the top of the road. The
excess run-up was based on the portion of the boulevard exhibiting the lowest
elevation. The area of road eroded during each storm frequency was determined
and a replacement cost based for the required construction materials and labor was
applied. Tables 3.6 and 3.7 present the quantity of erosion which occurs to Reach
3 as the result of particular events. The economic loss as a result of this erosion is
included in Table 3.11.
The same excess runup-erosion relationship was used to analyzed the box
culvert in Reach 5. Table 3.8 presents the quantity of erosion which occurs as the
result of particular events. This area will initially have a substantially wider beach
as a result of the Batiquitos Enhancement Project. However, this beachfill is
anticipated to dissipate in approximately seven years. After that period, it is not
expected to provide measurable protection. Also after this period, no long-term
erosion will occur in this reach (due to the cobbles and a higher bedrock),
therefore, damages will not increase. The runup/damage analysis was performed
on this reach using the latter condition, but the economics analysis was done
assuming the damages would not begin until seven years after the beachfill had
been placed.
3-23
xTABLE 3,8 < , ,
CAflLSBAO BEACH* *'\ ' :
PRESENT WITHOUT PROJECT PHYSICAL DAMAGES
RETURN
PERIOD
2
5
10
25
50
100
200
WAVE
RUNUP
(FT)
19.85
21.45
22.45
23.45
23.85
24.45
24.85
EXCESSIVE
RUNUP (FT)
1.6
3.2
4.2
5.2
5.6
6.2
6.6
EROSION
(FT)
0
9
55
100
100
100
100
AREA
LOST (SO.
FT)
0
9,000
55,000
100,000
100,000
100,000
100,000
3.4 Economic Loss
Damages expected to result in each storm interval (2, 5, 10, 25, 50, 100
year exceedence frequency) were weighted by the probability of the storm
frequency by combining the depth-damage, stage-frequency, and stage-damage
curves. Equivalent annual damages were computed for an 8 percent discount rate,
the study year (1993), and the project base year (1997). Damages under existing
conditions for each storm interval are shown in Table 3.9. Total expected and
equivalent annual damages are shown in Table 3.10 and are separated by reach in
Table 3.11.
Damages to revetments are presented as calculated previously (see Section
3.3.2). Due to the difficulty in establishing maintenance costs for gunite walls, it
was assumed that these values were equal to those of revetments. Landscaping
fosses were estimated on the July 1993 site walk.
3-25
3.5 Recreation
As a result of the assumed 1 ft/yr erosion rate, for without project
conditions, beach area will decrease by approximately 466,400 square feet over
fifty years. The entire length of the Carlsbad coastline measures 33,000 feet with
an average width of 36 feet above the MHHW line. Total area of the beach under
current conditions, weighted by the actual beach width, is 1,200,770 square feet.
The percent loss of beach under these conditions is 39%. As a result, a decrease
in carrying capacity will result, and diminished beach area will be forced to supply
a growing number of beachgoers. The end result will be diminished recreational
experience to the beach user and, thus, a reduction in the willingness to pay for
this experience. Table 3.12 presents the present and future areas above the
MHHW line per reach.
Table 3.12 Present and 50 - Year Future Areas Above the MHHW Line per
Reach
Period
Present (ft2)
Present (acres)
Future (ft2)
Future (acres)
Reach 1
19,500
0.45
0
0
Reach 2
364,000
8.36
164,000
3.76
Reach 3
452,950
10.40
237,950
5.47
Reach 4
0
0
0
0
Reach 5
364,320
8.36
0
0
Beach attendance numbers were based upon the California Department of
Parks and Recreation's counts. Using a methodology developed in Section 6 of the
Economic Appendix, these numbers were broken down to determine the average
daily visitors per acre at any one time per month. The methodology then employed
a point system to calculate the recreational value of the experience. The value of
the experience does not begin to decrease until there are more than 100 persons
per acre.
Under without project conditions, parking conditions are assumed to be
sufficient to accommodate existing and anticipated parking requirements.
The increased beach width as a result of the Batiquitos Enhancement Project
was not considered into these without project conditions because the recreation
value of the Carlsbad beaches will not decrease until after the first seven years.
After that seven year period, the beachfill is assumed to have been dissipated, and
the Reach 5 beaches will be approximately in their without enhancement project condition.
3-29
locations in Carlsbad. The privately placed protective structures are composed of
large riprap (two ton) and gunite. "It is anticipated that $160,000 in damage to
protective structures will occur in the 50 year event. Homes are high enough and
set back far enough to warrant no need for further protection from inundation.
The revetment and gunite protecting the bluff appear to be preventing further bluff
erosion and therefore, the condition will not worsen with time.
Since there is essentially no beach above the MHHW line even during the
summer, the recreation value of this reach will not decrease with time.
3.6.5 Reach 5
As mentioned in Section 2.3.5, without project conditions include the
Batiquitos Lagoon Enhancement Project, which will initially provide a sufficient
level of protection to the box culvert. However, since the beachfill is to be
unconfined, it is expected that this protection will reduce to none within seven
years. Analysis indicates that the box culvert will then be exposed to storm
damages. After the removal of this protection, damages from the fifty year event
are anticipated to exceed $600,000.
The bluffs fronting South Carlsbad State Beach campgrounds are
experiencing erosion. While coastal processes have had some effect, the erosion is
primarily due to runoff and other subaerial factors. A review of aerial photos and
an inspection of the site, along with the absence of verifiable data to the contrary,
indicate that this threat is not substantial enough for this problem to merit further
investigation.
Historically, the beach in Reach 5 is virtually completely cobbled in both
winter and summer. The beachfill will initially provide significant recreation
benefits, but these will decrease as the fill is dissipated. After this has occurred,
the reach will return to its cobbled state and the recreational value of this reach
will decrease no further with time.
3.7 Conclusions
Four conclusions can be reached concerning the problems in the Carlsbad
Coastal Area:
1. Reach 3 suffers the most damage, primarily as a result of the exposure
of Carlsbad Boulevard between the inlet and outlets to Agua Hedionda
Lagoon to undermining during severe storms. The equivalent annual damage
3-32
Table 4.11c Plan 11: Economic Summary
Annual Benefits ($1000)
Annual Costs ($1000)
Benefit - Cost Ratio
881
1535
0.57
4.2.12 Plan 12 - A Rubble-Mound Revetment in Reach 5
4.2.12.1 Description
As shown in Figure 4.12, a 1,000-foot long rubble-mound revetment is built in Reach
5 to protect the portion of Carlsbad Boulevard at which the road elevation is 18.25 feet
MLLW. The typical cross-section of the revetment is similar to that shown in Figure 4.1 Ob.
The required 16,170 tons of rock are available from sources discussed in Section 4.2.2.1.
4.2.12.2 Engineering Evaluation
Construction of a rubble-mound revetment at Reach 5 is anticipated to have similar
effects as construction of the seawall described in Plan 9.
4.2.12.3 Environmental Evaluation
The environmental effects of this revetment will be similar to that of the revetment
discussed in Section 4.2.4.3, however, scour of the beach in front of the wall is expected
to increase because this site is more exposed to waves.
4.2.12.4 Economic Analysis
The costs associated with this alternative are summarized in Table 4.12a and the
benefits are presented in Table 4.12b. The Benefit - Cost Ratio is shown in Table 4.12c.
4-62
Pacific Ocean
0 400 800 1200
Scale in feet
11888114M
Figure 4.12 Plan 12 - Rubble-Mound Revetment, Reach 5