HomeMy WebLinkAbout1978-12-05; City Council; 5250-3; Consultants report: Agua Hedionda MaintenanceCITY OF CARLSBAD
AGENDA BILL NO.
DATE: December .5, 1978
DEPARTMENT: PUBLIC WORKS r. M -. c. Mgr. 7
Subject:
CONSULTANTS REPORT: AGUA HEDIONDA MAINTENANCE PROGRAM
Statement of the Matter
Council awarded a contract to David Smith & Associates on January 17, 1978 to
analyze the dredging requirements of the Agua Hedionda Lagoon in order to determine
the requirements for and feasibility of a long range maintenance program. Dr. Smith
has completed the work, and his report is forwarded as Exhibit B. The report indicates
that about 310,000 cubic yards of material would have to be removed to restore the
depth to -10 feet (mean sea level). A memo from the Director of Utilities & Maintenance
(Exhibit A) discusses these findings and recommends that the report be used to develop
City policies for the use and management of the lagoon. Dr. Smith's report should
be accepted and filed at this time in order to' close out his work.
EXHIBITS
A. Memo from Director of Utilities & Maintenance to City Manager of November 28,
1978.
B. "An Analysis of Dredging Requirements for Agua Hedionda Lagoon" by
David D. Smith and Associates. .
RECOMMENDATION-
Accept and file the report by minute motion. Direct staff to prepare recommendations
for Lagoon Maintenance policies and return a report within 30 days.
Council action:
12-5-78 Council accepted the report and directed that the contract with
Dr. Smith be closed out, and directed staff to pursue
preliminary actions toward the attainment of the necessary
data for purposes of coming up with- a decision on this matter
.during the course of the Local Coastal Program preparation.
November 28, 1978
MEMORANDUM
TO: City Manager
FROM: Director of Utilities & Maintenance
SUBJECT: Report on Agua Hedionda Maintenance Program
Council authorized a contract for consultant services with David Smith and
Associates on January 17, 1978 to analyze the dredging requirements of the
Agua Hedionda Lagoon in order to determine the requirements for and feasi-
bility of an orderly program to sustain the present recreational uses.
Interest in this matter was generated by the Agua Hedionda Specific Plan.
This plan, in general terms, recognizes the recreational potential for the
lagoon and suggests that the City should negotiate a long term lease for
the use of the water surface. The plan recognizes that maintenance dredging
is required and will continue to be required in the long term to maintain
the recreational aspects of the lagoon. It further recommends that various
funding sources be investigated to defray the cost of these maintenance efforts.
The purpose for the analysis by Dr. Smith was to quantify the generalizations
of the specific plan to determine:
1. How much siltation is there,
2. Where can it be disposed of,
3. How much will it cost now and in the future.
This information was considered necessary in order to develop basic policy
recommendations for the City Council and to provide a basis for future CIP
considerations.
Dr. Smith's analysis indicates that approximately 310,000 cubic yards of material
would have to be removed to return the middle and inner lagoon to the original
-10'MSL. dredged depth. Several options for this work were investigated and
range from $480,000 under contract to SDG&E to $790,000 for City purchase and
operated equipment. Additionally, cost figures were developed for dredging
efforts to less than the -10 MSL depth. Additionally, it appears that beach
disposal of the spoil is the only feasible alternative under current EPA criteria.
Dr. Smith's report, in my opinion, responds appropriately to our scope of work.
The report provides, at least in an order of magnitude sense, the costs of
maintaining the lagoon for it's present recreational uses, if it is to be City's
policy to remove the existing navigational barriers. Additionally, it provides
basic bottom profile information; so the affects of the operation of Encina 5
as relates to silt build-up, can be assessed.
Agua Hedionda (continued)-2-November 28, 1978
It is recommended that this report be used as a basic document for the
development of City policies for the management of the lagoon.
It is further recommended that the report be accepted and filed at this
time in order that I may close out the agreement with Dr. Smith.
ROGER/X. GREER
Director of Utilities & Maintenance
RWGrpag
AN ANALYSIS OF
DREDGING REQUIREMENTS
FOR
AGUA HEDIONDA LAGOON
Prepared For
City of Carlsbad
1200 Elm Avenue
Carlsbad, CA 92008
By
David D. Smith and Associates
Environmental Consultants
Box 1338
La Jolla, CA 92038
DDS&A 77-463
DAVID D. SMITH AND ASSOCIATES July 28, 1978
ENVIRONMENTAL CONSULTANTS
AN ANALYSIS OF
DREDGING REQUIREMENTS
FOR
AGUA HEDIONDA LAGOON
Prepared For
City of Carlsbad
1200 Elm Avenue
Carlsbad, CA 92008
By
David D. Smith and Associates
Environmental Consultants
Box 1338
La Jolla, CA 92038
DDS&A 77-463
July 28, 1978
DDS&A 77-463
July 28, 1978
CONTENTS
BACKGROUND
OBJECTIVES
WORK SCOPE
KEY QUESTIONS
BASIC FACTORS
VOLUME OF SEDIMENT
SEDIMENT ACCUMULATION RATE
DISPOSAL SITES
CRITERIA REGARDING USE OF DISPOSAL SITE
PERMIT REQUIREMENTS
TIME CONSTRAINTS
PUMPING DISTANCE
APPLICABLE DREDGING EQUIPMENT
ASSESSMENT OF DREDGE SIZE
PARTICULARS OF VARIOUS SIZES OF SUCTION DREDGES
NEAR TERM DREDGING PROGRAM
LONG TERM MAINTENANCE DREDGING PROGRAM
SDG&E AS CONTRACTOR
COST ESTIMATE
NEAR TERM DREDGING PROGRAM
RESTORATIVE APPROACH
INCREMENTAL APPROACH
LONG TERM DRE-DGING PROGRAM
OTHER CONSIDERATIONS
UNRESOLVED MATTERS
COST/BENEFIT ANALYSIS
EEL GRASS
EFFECTS OF ENCINA UNIT 5
SOURCES OF FUNDING
CONCLUSIONS
RECOMMENDATIONS
ACKNOWLEDGMENTS
REFERENCES CITED
DAVID D. SMITH AND ASSOCIATES
DDS&A 77-463July 28, 1978
BACKGROUND
Agua Hedionda Lagoon (Figure 1) is very actively used as a
recreation area by the residents of Carlsbad and adjoining
areas. At the present time, however, boating use of the
inner lagoon is restricted by sand bars and shoals.
By removing these barriers and undertaking an active
maintenance program, the usefulness of the lagoon for
boating and water skiing could be substantially increased.
In order to assess the questions of magnitude,
feasibility, and cost of a dredging program for near term
and long term maintenance of the lagoon, the City of
Carlsbad issued a Request for Proposals in November 1977.
In January 1978 the City contracted with David D. Smith and
Associates (DDS&A) to undertake the study, the results of
which are reported here.
OBJECTIVES
Briefly stated, the overall objective of the work
was to determine the feasibility and order-of-magnitude
cost of a maintenance dredging program for Agua Hedionda
Lagoon to facilitate recreational boating and related uses.
This feasibility and cost information would provide the
City of Carlsbad with a basis for deciding on the reasonableness
and desirability of undertaking such a maintenance dredging
program.
DAVID D. SMITH AND ASSOCIATES
Page 2 DDS&A 77-463
July 28, 1978
Air View of
Agua Hedionda Lagoon
Figure 1
Page 3 DDS&A 77-463July 28, 1978
Specific objectives of the work were to:
• Define the magnitude of the near term and long term
maintenance problem, with emphasis on:
(a) volume of sediment to be dredged
(b) availability of spoil disposal sites
t Provide recommendations on the scope of the
dredging program, addressing specifically:
(c) type of dredging equipment most suitable
(d) dredging by contractor versus City ownership
(e) support facilities and personnel to be
furnished by the City
(f) permits required, issuing agencies, and
time frame
t Prepare cost estimates for the near term and long
term dredging programs.
WORK SCOPE
For efficiency, the work scope set forth in the DDS&A
proposal and incorporated into the contract was divided into
a series of eight tasks: the first four tasks addressed
key technical and operational questions, and led to the
estimate of costs; the remaining tasks dealt with permit
requirements, possible sources of funding, and preparation
of the final report. The interested reader is referred
to the December 13th, 1977 DDS&A proposal for a detailed
DAVID D. SMITH AND ASSOCIATES
Page 4 DDS&A 77-463
July 28, 1978
description of the individual tasks and the work sequence.
For convenience of presentation in this report, the
results of the study are organized as follows:
I Key Questions
II Basic Factors
III Near Term Dredging Program
IV Long Term Maintenance Dredging Program
V Cost Estimate
VI Unresolved Matters
VII Conclusions and Recommendations
KEY QUESTIONS
Although the objectives and thrust of this study
are directed toward the magnitude, approach, and cost of
dredging the lagoons, it is important to recognize at the
outset that several key questions that are outside the
scope of this contract bear directly on the City's eventual
decision regarding this dredging.
These key questions are:
(1) Does the present and anticipated future level
of recreational boating use of the inner and middle lagoons
warrant a major expenditure on dredging?
(2) Will the U.S. Fish & Wildlife Service's (USF&WLS)
recent strong stand (a) favoring preservation of eel grass
habitat, and (b) opposing dredging in other lagoons and
estuaries constitute a significant obstacle to dredging
DAVID D. SMITH AND ASSOCIATES
Page 5 DDS&A 77-463
July 28, 1978
in Agua Hedionda Lagoon?
(3) Will the addition of SDG&E's Encina Unit 5
with its major increase in volume of intake water
increase or reduce the need for dredging in the middle
and inner lagoon and, if so, how much?
These unresolved questions should be borne in
mind while reading the balance of this report.
BASIC FACTORS
It is appropriate to review the results of our work
in terms of a series of basic factors that will determine
the feasibility, nature, scope, and cost of various
approaches to a dredging program for Agua Hedionda Lagoon.
These basic factors are:
(1) Volume of Sediment
(2) Disposal Sites
(3) Criteria Regarding Use of Disposal Site
(4) Permit Requirements
(5) Pumping Distance
(6) Time Constraints
(7) Dredging Equipment
VOLUME OF SEDIMENT
Determining the volume of sediment that has accumulated
since 1954 to form the obstructing shoals and bars in the
middle and inner lagoons was the key first step in the study,
Because this determination of sediment volume is fundamental
DAVID D. SMITH AND ASSOCIATES
Page 6 DDS&A 77-463
July 28, 1978
to selecting the type of dredging equipment and to
estimating the probable cost of the dredging program,
a reasonably accurate estimate of the sediment volume
was required. Therefore, with the approval of the City
of Carlsbad, DDS&A subcontracted with Rick Engineering
Company to carry out an engineering survey of the middle
and inner lagoons to determine the present water depths
and the dimensions of the various shoals and bars present.
Based on the results of this survey, two types of
volume estimates were then prepared: (a) an estimate
of the total volume of sediment that had accumulated to
form the obstructing bars and shoals, and (b) an estimate
of the various volumes of sediment that would have to be
removed if the bar and shoal areas were to be dredged to
various selected depths. In addition, the total volume
figure provided the basis for estimating average rate of
sediment build up since the lagoon was dredged initially
in 1954 by the San Diego Gas & Electric Company.
Using the results of the Rick Engineering depth
survey plotted on a 1 to 200 scale, DDS&A used a standard
planimetry technique to determine the approximate total
volume of accumulated sediment, as well as the approximate
volumes of sediment to be dredged in order to provide
water depths of six, eight, and ten feet in the middle and
DAVID D. SMITH AND ASSOCIATES
Page 7 DDS&A 77-463
July 28, 1978
inner lagoon— areas. The results of these calculations
are summarized in Table I; a copy of the detailed
calculations and the engineering surveys on which they
are based have been submitted to the City separately.
Briefly, the volume of sediment that has accumulated
in the recreational areas of the middle and inner lagoons
since dredging to -10 feet mean sea level (MSL) in 1954
totals about 310,000 cubic yards and that is the volume
which would have to be dredged to restore the depth to
-10 feet. To dredge to -8 feet, the volume would be approxi
mately 160,000 cubic yards, and to -6 feet, it would
be approximately 60,000 cubic yards. As evident from
Table I, about 85 percent of the volume to be dredged is
located in the inner lagoon. More specifically, the bulk
of the sediment in the inner lagoon is concentrated in a
series of bars and shoals comprising a fan-like mass
situated to the east of the mouth of the inner lagoon (at
the Interstate 5 bridge). This pattern is evident in
Figure 2 and is shown in some detail on the working
drawings supplied separately to the City by DDS&A.
Footnote ]_/
Note that all following references to the
volume of sediment in the lagoons refer to sediment in
(a) the middle lagoon, and (b) the western end of the
inner lagoon, and not to sediment in mudflat areas in
the extreme eastern end of the inner lagoon.
DAVID D. SMITH AND ASSOCIATES
Page 8 DDS&A 77-463
July 28, 1978
TABLE I
Approximate Volume of Sediment in Cubic Yards as a Function
of Depth - Agua Hedionda (middle and inner) Lagoon
Depth (Mean Middle & Inner Rounded
Sea Level) Middle Lagoon Inner Lagoon Lagoons Values
-5
-6
-7
-8
-9
-10
feet
feet
feet
feet
feet
feet
10
14
19
24
31
42
,270
,420
,020
,350
,200
,030
12
42
80
133
198
266
,260
,930
,310
,050
,140
,600
22
57
99
157
229
308
,530
,350
,330
,400
,340
,630
25
60
100
160
230
310
,000
,000
,000
,000
,000
,000
(13.6%)(86.4%)(100.0%)
Based on January-February 1978 depth surveys by Rick Engineering,
Planimetry and volume calculation by R. C. Odiorne, R.C.E.
DAVID D. SMITH AND ASSOCIATES
Rage 9 DDS&A 77-463
July 28, 1978
-1 <o *o ^ *a / /Ml/Iin » ' * * ^ • ** «.
^°l^ ' y/ffln;' ' ' • ^AJt
Page 10 DDS&A 77-463
July 28, 1978
It is emphasized that the volume estimates given
here are approximate only and that a more refined
estimate of quantities should be prepared before going
out to bid for the dredging work. A more refined
estimate would require an additional, more detailed
engineering survey.
Because the actual volume to be dredged will depend
on the horizontal dimensions as well as the depth of the
area to be maintained for recreational uses, it is
possible that judicious selection of the desired water
depths, and the shape and size of the area to be dredged
would reduce the sediment quantities to be dredged and
thus reduce dredging costs. Therefore, at the time of
preparing the bid specifications, it probably will be
desirable to consider several different depths and sizes
of recreational areas (and to calculate the dredging
volumes on a trial basis) before deciding on the preferred
depth, size, and shape. These refinements would be worth
considering after the results of the more detailed
engineering survey were available. Nevertheless, for
guidance in decision making by the City regarding the
order of magnitude cost of the work, the degree of pre-
cision of the volume figures given here is judged to be
quite adequate.
DAVID D. SMITH AND ASSOCIATES
Page 11 DDS&A 77-463
July 28, 1978
SEDIMENT ACCUMULATION RATE
Knowing the approximate total volume of sediment
that has accumulated in the recreational areas of the
inner and middle lagoons provides a basis for a crude
estimate of average sedimentation rates during the 24
year period since initial dredging, and thus a basis
for estimating roughly how much dredging is likely to
be required in the next 20 to 25 years. As shown in
Table I, for the middle and inner lagoons, roughly
310,000 cubic yards of sediment has accumulated. This
suggests an average rate of build up (in the 24 year
period since 1954) of about 13,000 cubic yards per year,
It should be emphasized, however, that this is the
crudest sort of average figure and, for the following
reasons, is of very limited usefulness in estimating
future accumulation rates.
1. The Agua Hedionda Lagoon system consists of the
subunits connected by narrow throats with the
outer lagoon connected to the ocean by a narrow
inlet. Because of this segmented character, the
lagoon constitutes a relatively complex hydraulic
system; this in turn makes accurate estimation of
sediment accumulation rates quite complicated.
2. More specifically, the accumulation rates in the
inner and middle lagoons would be expected to
differ considerably because the two have markedly
DAVID D. SMITH AND ASSOCIATES
Page 12 DDS&A 77-463
July 28, 1978
different sizes and shapes, and different hydraulic
geometries. Further, if sediment in the outer
lagoon is the principal sediment source (as various
lines of evidence suggest), then the middle lagoon
may serve as a crude sediment trap and the build up
of the middle lagoon bar might substantially delay
growth of the bar/shoal in the inner lagoon.
3. Calculation of the growth rate of the bar/shoal area
in the inner lagoon (and particularly the rate at
which it will reform following dredging) is a
moderately complex procedure. This is because bars
of this type do not build uniformly upward from the
lagoon floor but rather grow initially upward to the
surface in a ring-like form near the throat connecting
the two lagoons and then grow radially into the
lagoon to form a fan-like delta.
In short, the procedures for estimating sediment
accumulation rates for the middle and inner lagoons are
moderately complex and would require a variety of data not
presently available. Obtaining sufficient information to
serve as a basis for the necessary calculations may require
a considerable field measurement effort. Obtaining this
information and conducting the more refined calculations
of sedimentation rate are outside the scope of the present
contract. In addition, as discussed in a following section,
DAVID D. SMITH AND ASSOCIATES
Page 13 DDS&A 77-463
July 28, 1978
the impending addition of Encina Unit 5 with the
attendant increase in cooling water intake.volumes
may have significant (and as yet unknown) effects on
sedimentation rates in the inner and middle lagoons.
DISPOSAL SITES
An assessment of possible alternative disposal
sites for the sediment to be dredged showed that the
ocean beaches adjoining the seaward end of Agua Hedionda
Lagoon constitute the only reasonable disposal site.
Such alternatives as disposal of all or part of the
dredged material (a) on lagoon beaches, or (b) as land-
fill at terrestrial sites in the Carlsbad area were
considered and rejected. There is no evidence that the
lagoon beaches are suffering significant wave erosion
and thus need nourishment in any sizable quantity.
Based on the information available, there appear to be
no requirements for sizable volumes of landfill at
terrestrial sites in the Carlsbad area within reasonable
pumping or haul distances.
Disposal of the material by use as fill elsewhere
in the lagoon was not considered because (a) the Local
Specific Plan does not envision fills of this type,
(b) Coastal Commission policy opposes fills of this type,
and (c) conservation/resource agencies at state and
federal level are strongly opposed to such fills.
Disposal of the dredged material on the adjoining
DAVID D. SMITH AND ASSOCIATES
Page 14 DDS&A 77-463
July 28, 1978
ocean beaches is logical and appropriate for a number
of reasons. These reasons are:
1. In recent years these beaches have suffered
significant losses of sand as a result of wave erosion --
thus, the dredged sediment would help replenish these
losses.
2. The sediment dredged from the outer lagoon
by the San Diego Gas & Electric Company approximately
every two years is placed on these beaches as replenish-
ment material, as authorized by the pertinent Corps of
Engineers permit and the California Regional Water Quality
Control Board, San Diego Region Waste Discharge Require-
ments.
3. There is substantial evidence that the ocean
beaches are the source of much of the sediment comprising
the bars and shoals in question; this sediment apparently
moves into the outer lagoon via the entrance channel and
then is carried into the middle and inner lagoons.
4. The sediment that comprises the bars and shoals
in the inner and middle lagoons appears to comply with
the Corps of Engineers requirements for use of dredged
material as beach nourishment.
5. Virtually no alternative disposal sites are
available other than ocean disposal offshore. Pertinent
Corps and EPA regulations virtually preclude use of this
alternative; costs of such disposal offshore would be
prohibitive.
DAVID D. SMITH AND ASSOCIATES
Page 15 DDS&A 77-463
July 28, 1978
CRITERIA REGARDING USE OF DISPOSAL SITE
Use of the adjoining ocean beaches as a disposal
site would depend upon authorization by the Corps of
Engineers and other agencies (as discussed in the
following section), and would be conditioned on
satisfying the specific criteria requirements set forth in
the pertinent Environmental Protection Agency regulations
(1977, p. 2479). In this regard, however, see Footnote 1.
The EPA requirements for use of the beaches as a
disposal site concern the physical and chemical charac-
teristics of the sediment to be dredged. Briefly, the
material must be:
(a) predominantly sand size particles or larger,
(b) compatible with the material on the receiving
beaches,
(c) in addition, the material would probably
have to be virtually free of toxic chemicals.
Other factors which probably also will be considered by
the Corps in reviewing the City's request for use of
this disposal location include:
Footnote !_/
Contact with the Environmental Protection Agency
in Washington and San Francisco indicates that new regula-
tions bearing on dredged material disposal are being
developed by EPA and are likely to be issued in the next
6 to 18 months. The nature and scope of these new regula-
tions are still being formulated and, thus, analysis and
comment as to their effects on dredging at Agua Hedionda are
not possible at this time. Based on the limited information
presently available to us, however, it is likely that the
sediments to be dredged would meet the requirements of the
new regulations.
DAVID D. SMITH AND ASSOCIATES
Page 16 DDS&A 77-463
July 28, 1978
(a) the amount of turbidity that will result
from disposal on the beaches
(b) the need for sand as nourishment
(c) precedent for use of this site for dredged
material disposal
As to compliance with the three EPA criteria cited
above:
(a) The sediments to be dredged are predominantly
sand, as evidenced by the mechanical analysis data from
some 10 samples reported in Bradshaw and Estberg, 1973,
p. A-5). [Because of the 50 odd acres of lagoon floor
likely to be dredged, however, the Corps may require
mechanical; analysis of some additional bottom samples so
as to provide a better data base for their decision].
(b) Because the material is predominantly sand, it
therefore should be compatible with the sands present on
the ocean beaches in question. [The Corps may require
formal documentation of compatibility by means of
mechanical analysis of the beach sands. However, in view
of the use of the beach as a dredged material disposal
site by SDG&E, further documentation of compatibility
seems unnecessary].
(c) The chemical characteristics of the sediment
to be dredged would be expected to comply with any
reasonable EPA criteria for the following reasons:
(i) The area historically has been free of any
DAVID D. SMITH AND ASSOCIATES
Page 17 DDS&A 77-463
July 28, 1978
disposal of industrial waste or municipal
sewage.
(ii) According to the San Diego Regional Water
Quality Control Board (1967, p. 19), "...
the quality of Agua Hedionda Lagoon waters
is excellent."
(iii) According to SD6&E personnel, the State
Department of Public Health had issued a
certificate to San Diego Gas & Electric
Company to the effect that the waters of
Agua Hedionda outer lagoon were of suitable
quality for harvesting shellfish directly
for table use (Richmond, 1978, personal
communication).
(iv) Although agricultural chemicals, including
pesticides, probably have been used for a
number of years on crops in the fields to
the south of the lagoon, it is unlikely that
these chemicals are present in any significant
concentrations in the sands comprising the
bars and shoals to be dredged. This is
because pesticides are more typically associated
with clayey sediments than with sands.
In addition to the EPA criteria and Corps require-
ments cited, the California Water Quality Control Board,
San Diego Region (CWQCB-SDR) will set Waste Discharge
DAVID D. SMITH AND ASSOCIATES
Page 18 DDS&A 77-463
July 28, 1978
Requirements for a dredged material disposal project of
this magnitude. Obtaining these Waste Discharge Require-
ments would require submission of an application to the
CWQCB-SDR as discussed in the following section.
PERMIT REQUIREMENTS
Dredging and discharge of dredged material require
a permit issued by the Corps of Engineers. In order to
obtain this Corps dredging permit, an applicant such as
the City of Carlsbad would first have to obtain (a)
Waste Discharge Requirements and a Water Quality Certificate
from the -State Water Board, and (b) a Coastal Zone Permit
from the California Coastal Commission. Because some of
the beach area is a State Beach, use for disposal of
sediment would also require authorization from the California
Department of Parks and Recreation.
In order to obtain a Coastal Zone Permit, an applicant
must have a duly certified EIR. We understand that the
City of Carlsbad already has a certified EIR prepared in
connection with the Local Specific Plan. It is possible,
however, that a supplement to this EIR might be required
to deal with the proposed dredging in more specific detail.
The period of time required to obtain the Corps
permit and the subsidiary Water Board and Coastal Commission
DAVID D. SMITH AND ASSOCIATES
Page 19 DDS&A 77-463
July 28, 1978
permits varies considerably from project to project
depending on a number of factors (see Smith, 1975
and 1977) but a range of about 7 to 12 months is
generally realistic.
TIME CONSTRAINTS
It is probable that the period of time available
in which the dredging could be performed in any given
year would be limited to about seven months. To avoid
conflict with recreational use of the ocean beaches
at Carlsbad, the CSWRCB-SDR conditioned the SDG&E Corps
permit to restrict discharge on the beaches to the
seven month period October through April when recreational
use of the beach is generally low. It is logical to
assume that a similar restriction would be placed on the
City. This limitation on the time available for the work
tends to dictate the minimum production capacity (and
thus the minimum size) of the dredge.
PUMPING DISTANCE
Disposal of the dredged material on the ocean beaches
immediately seaward of Agua Hedionda Lagoon will involve
maximum pumping distances of roughly 4,000 to 5,000 feet,
depending on the location of the dredge, the alignment
of the pipeline, and the area of the beach being nourished,
However, if the beaches north of the Agua Hedionda Lagoon
outlet were to be used, then an additional 1,000 to 2,000
DAVID D. SMITH AND ASSOCIATES
Page 20 DDS&A 77-463
July 28, 1978
foot distance would be added. Pumping distance is an
important contributory factor in dredging costs. If the
required distance exceeds the pumping capability of the
dredge, then a booster unit must be added along the
pipeline with resulting additional costs, including extra
crew and fuel.
APPLICABLE DREDGING EQUIPMENT
With the approximate range in volumes of material
to be dredged and the disposal site known, selection of
the most suitable type of dredging equipment for the
work is the next logical step.
Based on (a) the 310,000 cubic yard maximum volume,
(b) the location and character of and the distance to the
disposal site, and (c) the shallow, partitioned, restricted
access character of the lagoon proper, it is clear that
only a portable hydraulic suction dredge could do the work
efficiently. Mechanical dredges and large, permanently
assembled hydraulic suction dredges were ruled out
because of problems with access, spoil transport, cost per
yard, and others.
ASSESSMENT OF DREDGE SIZE
The volume to be dredged, the time available (7 months)
to do the work, and, to a lesser extent, the distance to
the disposal site combine to dictate the size of dredge
required. Because of the very substantial costs involved
in mobilization and demobilization of a dredge, it is
DAVID D. SMITH AND ASSOCIATES
Page 21 DDS&A 77-463
July 28, 1978
assumed in this section that the work would be done
in a single time sequence without major interruption.
Thus, the time available would be the seven month
period during which beach disposal would be allowed
by the CSWRCB-SDR.
To accomplish a roughly 300,000 cubic yard
dredging project in seven months, a dredge with an
average production rate of at least 150 cubic yards
per hour would be required. This conclusion is arrived
at by the following calculation:
9eT°:edqed = Required Production Rate
Given:
(a) Volume = 300,000 cubic yards
(b) Time = 7 months = 3,600 dredging hours
(October through April = 30 weeks; 30 weeks
x 6 days/week x 20 hours/day = 3,600 hours)
Therefore:
300,000 divided by 3,600 = 83.3 yards/hour, or
rounded off, 85 yards/hour
If this calculation is refined to take into account
such adjustments as Christmas week shut down, a probable
volume larger than 300,000 yards, and other likely changes,
then the required production rate closely approaches
100 cubic yards per hour. Because of all the major
uncertainties involved in dredging work (breakdown, bad
weather, etc.), a substantial safety factor (say, 50
percent) should be incorporated; therefore, an average
production rate of about 150 cubic yards/hour appears
DAVID D. SMITH AND ASSOCIATES
Page 22 DDS&A 77-463
July 28, 1978
reasonable.
PARTICULARS OF VARIOUS SIZES OF SUCTION DREDGES
DDS&A contacted several major suppliers of portable
suction dredges for information on size, capacity,
pumping distance, purchase cost, leasing rates, and
shipping or transport costs. A synopsis of the results
of these queries is tabulated in Table II.
From examination of Table II, with respect to 150
cubic yards per hour for the required production rate,
it is clear that only the 12 inch and larger dredges
have throughputs in the appropriate range for doing
the restorative work in a seven month period.
This project's 4,000 to 5,000 foot pumping distance
would almost certainly require a booster pumping station
for dredges smaller than 12 or 14 inch; the costs
associated with adding this booster unit (crew, fuel,
additional mobilization costs, etc.) appear to make the
smaller dredges not cost effective.
Although not evident from Table II, it is likely
that if a dredge smaller than 14 inch were used on this
300,000 cubic yard job, there is a strong possibility
that the dredge would require a major overhaul before
the project were completed.
Regarding purchase cost,it is evident from the
Table that except for the Delta Dredge 12 inch, the
price for 12 inch and 14 inch dredges is in the $300,000
to $400,000 range; this figure is for the dredge only —
DAVID D. SMITH AND ASSOCIATES
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Page 24 DDS&A 77-463
July 28, 1978
all ancillary equipment such as pipe, pontoons, etc. is
extra.
Regarding lease rates, a new Ellicott Dragon 770
dredge can be leased at $25,000 a month; the lease rate
for ancillary equipment is 10 percent of purchase price
per month. Although not shown in the Table, some dredge
operating companies may lease dredges when the units are
idle. Because these dredges are used rather than new, per
month lease rates could be expected to be lower than the
lease rates for a new unit from Ellicott.
On the other hand, many companies appear reluctant to
lease equipment to anyone other than another experienced
dredging firm. This situation may serve to inflate lease
rates for used equipment.
DAVID D. SMITH AND ASSOCIATES
Page 25 DDS&A 77-463
July 28, 1978
NEAR TERM DREDGING PROGRAM
There are two major alternative approaches to the
dredging work under consideration for the near term
(i.e. next 2 to 5 years). These are: a restorative
approach and an incremental approach. In the Restorative
Approach, the areas of sand bars and shoals would be
dredged to virtually the original 1954 depth. This approach,
which probably would be the one favored by most dredging
consultants, would require moving a large volume of
sediment but should also provide the longest period before
future maintenance dredging of the lagoon would be required.
Specifically, as shown in Table I, dredging to -10 feet
(the 1954 depth) would involve removal of about 310,000
cubic yards, to -9 feet, about 230,000 cubic yards, and
to -8 feet, about 160,000 cubic yards.
The Incremental Approach, by contrast, would involve
removing only the upper portions of the shoal and bar
areas, i.e. dredging to a depth of, say, -5 to -6 feet.
This would require moving a substantially smaller volume
of sediment but would result in a much shorter interval
before further dredging were required. Specifically,
dredging to -5 feet would amount to about 25,000 cubic
yards, and to -6 feet, about 60,000 cubic yards.
Although the Incremental Approach at first blush
appears quite attractive because of the small volume of
sediment involved (and, therefore, the lower dredging
costs), it should be recognized that this approach has
DAVID D. SMITH AND ASSOCIATES
Page 26 DDS&A 77-463
July 28, 1978
some inherent disadvantages which tend to offset the
volume and cost advantages. These are:
1. Removal of the top of the bar-shoal areas does
not result in water depths satisfactory for water skiing
during all levels of the tide. Based on the DMJM report
(Barnes et al . , 1965, p. 37), at Mean Lower Low Water
the tide level is almost 3 feet below Mean Sea Level.
This tidal condition may occur on 2 or 3 days in
succession several times each month; inspection of
pertinent tide curves indicates that in some months as
many as one third of the low tides reach Mean Lower
Low Water.— Thus, dredging to -5 or -6 feet Mean Sea Level
would result in unsatisfactorily shallow water during
times of Mean Lower Low Water.
2. Because of the manner in which this type of bar
2 /forms and expands-', if the top of the bar/shoal area in
—Although extreme low tide levels theoretically
could reach elevations of -5 feet below Mean Sea Level,
according to tide gauge data from SD6&E tide levels in
Agua Hedionda Lagoon never drop below the Mean Lower Low
Water level, possibly because of the constricted nature of
the outlet (Dyson, 1978, personal communication).
—See description of bar buildup and growth in
preceding section on sediment accumulation rates.
DAVID D. SMITH AND ASSOCIATES
Page 27 DDS&A 77-463
July 28, 1978
the inner lagoon is trimmed to, say, -5 or -6 feet,
the bar/shoal's redevelopment and progressive extension
into the inner lagoon will take place at a much faster
rate than if the area were dredged to -9 or -10 feet.
An accurate estimate of how much faster would require
field measurements and calculations based thereon which
are beyond the scope of this study.
3. Because of the small size of the job, only a small
portable dredge would be economically suitable for the
work. Unfortunately, such dredges tend to have relatively
limited pumping distances and would require the use of
a booster pump unit to assist with pumping to the
disposal site. The cost of the booster tends to offset
the savings associated with use of the smaller dredge.
4. Even with small dredges, mobilization costs tend
to make up a sizable portion of the job cost. Therefore,
remobilization every 2 or 3 years to conduct the next
increment of dredging can amount to a substantial cumulative
cost.
DAVID D. SMITH AND ASSOCIATES
Page 28 DDS&A 77-463
July 28, 1978
LONG TERM MAINTENANCE DREDGING PROGRAM
Maintenance dredging over the long term (say, 20
to 25 years) can also be approached in two ways: i.e.
either a periodic incremental dredging effort every
few years to keep the bars and shoals in check, or a
repeat of one large restorative project when the shoals
and bars again become a significant problem, perhaps
10 to 15 years after the near term dredging work.
Generally speaking, the incremental approach for
long term maintenance dredging is the more typical in
the dredging projects with which DDS&A is directly
familiar, but this may not necessarily be the better
approach here because the recreational boating uses of
the middle and inner lagoons allow considerably more
leeway than do the rigorous depth requirements for most
navigation channels.
The choice of approach for the long term maintenance
program will depend to a large degree on two other
decisions, namely: (1) which approach is selected for the
near term dredging work, and (2) whether or not the City
decides to purchase a dredge. If the incremental approach
is chosen for the near term, this virtually commits to
the incremental approach for the long term. On the other
hand, if the restorative approach were selected for the
near term, then either of the two alternative approaches
could be selected for the long term program. Similarly,
if a dredge is purchased for the near term program (see
discussion of purchase versus other alternatives in
DAVID D. SMITH AND ASSOCIATES
Page 29 DDS&A 77-463
July 28, 1978
following section), then the availability of this
dredge would virtually dictate the incremental approach
for the long term program.
Several ancillary questions concerning the long
term maintenance program require consideration; these
are: (1) the length of the grace period before the
long term maintenance dredging program would have to
commence, (2) the probable frequency of maintenance
dredging, and (3) the relationship of the maintenance
program to possible effects from the addition of Encina
Unit 5. The length of the grace period and the frequency
of maintenance dredging would depend on a number of
factors, including: (a) the volume removed during the
/
preceding dredging work, which is a function of the
approach selected for that work, (b) sedimentation rate
and possible modifications therein, which depends to a
large degree on the effects of Encina Unit 5 (unknown
at this time), and (c) the ability of the water skiiers
to live with the bar, which is primarily a recreational
management decision. A discussion of possible effects
of Encina Unit 5 is presented in a following section.
As explained in an earlier section, developing an
accurate estimate of sediment accumulation rates in the
inner and middle lagoons is a moderately complex procedure
requiring data that is not presently available. Added
to this difficulty are the unknown effects that Encina
Unit 5 may produce. For these reasons, it is not possible
DAVID D. SMITH AND ASSOCIATES
Page 30 DDS&A 77-463
July 28, 1978
to offer more than the most generalized opinion
concerning the grace period and frequency of maintenance
dredging.
If we assume that: (a) the average accumulation
rate obtained from comparing the 1954 and 1978 depths,
namely, about 13,000 cubic yards per year, is a suitable
approximation, and (b) Encina Unit 5 will have no
significant effect on accumulation rates in the middle
and inner lagoons, then in the most simplistic terms,
if long term maintenance dredging is carried out at an
average rate of about 13,000 cubic yards per year (or
some multiple of that over a proportionately longer
period), we would expect not to be troubled with re-
buidling of the bar/shoal areas, provided other contributing
factors remain unchanged.
Further, given these same assumptions and recognizing
the way in which the bar in the inner lagoon forms, it
is reasonable to conclude that the grace period before
long term maintenance dredging is required would be sub-
stantially longer if restorative near term dredging had
excavated the inner lagoon to -9 or -10 feet than if it
were dredged only to -5 or -6 feet using the incremental
approach.
DAVID D. SMITH AND ASSOCIATES
Page 31 DDS&A 77-463
July 28, 1978
CONTRACT VERSUS PURCHASE
One of the objectives of this study was to examine
the question of whether it would be more desirable for
the City to contract for the dredging work or to purchase
and operate a dredge.
Addressing the near term dredging program first, the
principal alternative courses of action can be diagrammed
as follows:
PROGRAM APPROACH OBTAIN DREDGE BY
(OPEN MARKET
CONTRACT --- (
RESTORATIVE LEASE (SDG&E
PURCHASE
NEAR TERM (QPEN MARKET
CONTRACT --- (
INCREMENTAL LEASE (SDG&E
PURCHASE
As evident, for each of the two basic alternative approaches,
there are four alternative courses of action: purchase,
lease, and two types of contractor alternatives.
Obviously, each alternative course of action has pros
and cons; the more important and obvious of these are
listed in Table III. As evident from inspection of the
Table, pros outnumber the cons only for the SDG&E contract
alternative.
Although a rigorous quantitative assessment of costs
and benefits of each alternative is beyond the scope of
this study, some qualitative judgments can be reached. For
example, it seems clear that if the restorative approach is
DAVID D. SMITH AND ASSOCIATES
Page 32 DDS&A 77-463
July 28, 1978
TABLE III
PROS AND CONS OF CONTRACT, PURCHASE, AND LEASE ALTERNATIVES
CONTRACT - OPEN MARKET BID
Pros
• Might get "bargain" because of
right place/right time situation
CONTRACT - SD6&E
Pros
t Uses SDG&E dredging experience
• Piggy backs on SDG&E operation
• Cost would be lower because no
profi t
• Eliminates the "between dredging"
maintenance costs
CITY LEASE AND OPERATE
Pros
• Lease costs substantially lower
than purchase costs
• No long term maintenance costs
CITY PURCHASE AND OPERATE
Pros
• Freedom to dredge when needed —
not tied to anyone else's schedule
• Makes some sense with Incremental
Approach
Cons
• Possibly relatively few bidders,
therefore high costs
• Because of profit, cost would
be higher than SDG&E contract
Cons
• Tied to SDG&E schedule
• SDG&E probably would want to use the
Restorative Approach and not the
Incremental Approach
Cons
• Experienced personnel essential to
efficient operation
• Experienced personnel difficult to
obtain, particularly for relatively
short jobs
• Six months lease costs may equal 35 to
40 percent of dredge purchase price
• Some dredging firms very reluctant
to lease to municipalities
Cons
t Large capital outlay
0 Long term maintenance costs
• Experienced personnel essential to
efficient operation
• Experienced personnel difficult
to obtain
• Problem of personnel utilization
when not dredging
DAVID D. SMITH AND ASSOCIATES
Page 33 DDS&A 77-463
July 28, 1978
chosen, then the near term work should be contracted for
rather than carried out by the City using a leased or
purchased dredge. The reasoning behind this judgment is
that (a) purchase of a dredge large enough to do the
work comfortably in the allowed time would leave the
City with a machine on its hands that would be much larger
than necessary to do the periodic long term maintenance
dredging, and (b) lease of a suitable dredge engenders
the major problem of obtaining an experienced dredging
supervisor and crew.
On the other hand, if the incremental approach were
chosen, the lease or purchase courses of action become
somewhat more reasonable, if the experienced crew problem
can be ignored. With the incremental approach, the SDG&E
contract alternative becomes less viable because it is
likely that SDG&E would not want to participate in a
periodic small scale operation because of the nuisance
factor.
For the long term maintenance dredging work, a series
of alternative courses of action similar to those for the
near term may be considered except that (as described in
the preceding section on long term dredging), the decisions
made for the near term work may automatically determine
the courses of action for the long term work. Thus, if
the near term work is to be incremental, then the long
term will automatically be incremental as well (i.e. part
DAVID D. SMITH AND ASSOCIATES
Page 34 DDS&A 77-463
July 28, 1978
of the same program). Further, if the decision is to
purchase a dredge for the near term, then that dredge
would automatically be used for the long term programs.
SD6&E AS CONTRACTOR
SDG&E has indicated an interest in assisting the
City of Carlsbad with dredging of the inner and middle
lagoons primarily by serving as operational contractor
for the work on at at-cost basis. In order to do this
most efficiently and at the lowest cost, dredging of the
inner and middle lagoons probably would have to be
integrated with SDG&E's normal biennial dredging of the
outer lagoon. Because of the major cost savings.1ikely
to be associated with such an approach, other alternative
approaches whichmight otherwise be attractive to the
City are likely to be considerably less appealing financially,
DAVID D. SMITH AND ASSOCIATES
Page 35 DDS&A 77-463
July 28, 1978
COST ESTIMATE
One of the principal objectives of this study was to
prepare an order of magnitude estimate of the cost of
the near term and long term dredging work required in
Agua Hedionda Lagoon. Because of the two basic alternative
approaches to the dredging, and the four alternative
courses of action for conducting the work, we recognized
from the outset that there obviously would be a sub-
stantial range in estimated costs. For this reason, the
results of our cost analysis are presented here as a
series of cases which illustrate the range represented
by these alternatives.
It should be emphasized that because of the wide
variations in technical and economic factors to be
considered for a particular dredging project, and for a
number of other reasons, realistic cost estimates are
difficult and time consuming to prepare; this is particularly
true for lease and purchase options and for small volume
jobs. Therefore, the following cost information is most
dependable for the contractor bid and SDG&E contractor
alternatives for the restorative approach.
DAVID D. SMITH AND ASSOCIATES
Page 36 DDS&A 77-463
July 28, 1978
NEAR TERM DREDGING PROGRAM
RESTORATIVE APPROACH Volume: say, 300,000 cubic yards
Contract Via Open Market Bids
Based on current contract dredging costs for jobs of
this size, if the job were bid on the open market in mid-
1978, we could expect costs of about $2.15 to $2.50 per
cubic yard or possibly higher. Thus, cost would be on the
order of $645,000 to $750,000.
Contract With SDG&E
We recognize that SDG&E has considered the possibility
of deepening the middle and inner lagoons and has made a
preliminary assessment of the costs that might be involved
in such a project. Using the SDG&E cost data as a base,
it appears that if SDG&E, acting as contractor, carried
out the restorative dredging work for the City of Carlsbad
at cost, and if the work were carried out in mid-1978,
we could expect costs per cubic yard of about $1.60 to
$1.70. Thus, the cost for 300,000 cubic yards of dredging
would be about $480,000 to $510,000.
City Lease and Operate
Although many dredging companies are reluctant to
lease equipment to anyone other than another dredging
company, an order of magnitude estimate for the cost of
leasing a portable 14 inch suction dredge was obtained
via telephone from Western Pacific Dredging Co. in Portland,
DAVID D. SMITH AND ASSOCIATES
Page 37 DDS&A 77-463
July 28, 1978
Oregon. This estimate was as follows:
Monthly lease rate $ 20,000 to $ 25,000
x 7 months = $140,000 to $175,000
Mobilization & Demobilization $150,000
Therefore: $290,000 to $325,000
Plus substantial additional
lease costs for auxilliary say, $100,000
equipment (pipe, pontoons,
tugs, scows, etc.)
These figures do not include
substantial other costs to say, possibly
the City for crew, fuel,
maintenance, and insurance $100,000
Total $490,000 to $525,000
City Purchase and Operate
Purchase costs for dredges capable of doing the
Restorative Near Term dredging work in the 7 month time
period range in cost from about $300,000 to $400,000 (see
Table IV). For a dredge at the lower end of the price
range a booster unit would probably be necessary at an added
cost of, say, $80,000 to $100,000, which brings the cost
up to that of the larger, more powerful dredge at $400,000.
Pipe purchase costs would be $ 70,000 to $80,000
Thus, an average figure of $475,000
Plus transportation costs
The $475,000 figure probably represents somewhere between
60 to 75 percent of the City's total costs. If $475,000
represents about 60 percent of total cost for the Restorative
work using this approach, then total costs would be expected
to run about $790,000. If $475,000 represents about 75
DAVID D. SMITH AND ASSOCIATES
Page 38 DDS&A 77-463
July 28, 1978
TABLE IV
RANGE IN APPROXIMATE PURCHASE COSTS OF DREDGE SUITABLE FOR
RESTORATIVE PROGRAM
Manufacturer
Dixie Dredge
Corp.
Dredge Size (Discharge Diameter)
10 inch 12 inch
$304,000 $325,000
(Included here
for comparison
purposes even
though hourly
productive rate
is lower than the
150 cubic yards
considered a minimum
for this project.)
14 inch
Ellicott
Machine
Corp.
$350,000 to $400,000
(for either 12 or 14 inch)
(Average, say, $375,000)
Average Cost
(Rounded)
$300,000 $350,000 $375,000
Notes:
1. If booster pump unit were needed (probably with the
10 and possibly with the 12) add $80,000 to $100,000
for purchase.
2. Purchase of 5,000 feet of pipe would add $70,000 to
$80,000.
3. Transport/shipping costs for dredge, booster, and
pipe would add on the order of another $10,000.
DAVID D. SMITH AND ASSOCIATES
Page 39 DDS&A 77-463
July 28, 1978
percent of total cost, then total cost could be expected
to run about $635,000. These additional costs
would stem from auxilliary equipment costs, fuel
(about $50,000), crew, supervisory personnel, insurance,
and maintenance costs.
Summary
Of the four alternative courses of action for the
Restorative work, the SDG&E as contractor is least costly
($480,000 to $510,000), followed by City lease and operate
($490,000 to $525,000), followed by open market bid ($645,000
to $750,000), with City purchase and operate last at $635,000
to $790,000 .
It should be emphasized, however, that the City lease
and operate alternative contains a major hidden cost which
would drive the actual cost up substantially. Experience in
several California cities has shown that a leased dredge
crewed by municipal employees does not obtain the sustained
production rates necessary to yield the cost figures cited
above. For this reason, on an actual cost per yard basis,
both the City lease and the City purchase alternatives are
likely to be substantially higher than the open market bid
cost.
DAVID D. SMITH AND ASSOCIATES
paae 40 DDS&A 77-459y July 28, 1978
INCREMENTAL APPROACH Volume: say, 60,000 cubic yards
Contract Via Open Market Bid
Discussions with experienced dredging specialists
indicate that many dredging firms would be reluctant to
bid on a job this small because high mobilization and
demobilization costs would require a bid that would be
disproportionately high for the volume to be dredged.
However, one firm (She!Imaker, Inc., Newport Beach,
CA) offered the following order of magnitude estimate for
use of a 12 inch dredge (which they felt would be cheaper
than using a smaller dredge together with a booster unit):
Mobilization $ 75,000 to $100,000
Cost per yard:
$2.10 to $2.25 x 60,000 yards $126,000 to $135,000
Adjusted cost per yard Total: $201,000 to $235,000
(i.e. including mobilization) $3.35 to $3.92
Contract With SD6&E
At present, we have no basis for estimating the costs
for this Alternative. If this were the City's preferred
choice for other reasons, an estimate could be prepared
after rather extensive consultations with SDG&E. However,
it is unlikely that SDG&E would be interested in participating
in the periodic small scale dredging that characterizes the
Incremental Approach.
City Lease and Operate
Contacts with dredging specialists indicate that many
dredging firms are reluctant to lease equipment to anyone
DAVID D. SMITH AND ASSOCIATES
Page 41 DDS&A 77-463
July 28, 1978
other than another experienced dredging firm. Because of
this, lease rates would tend to be inflated. This situation,
together with the high, essentially fixed mobilization
costs of a suitable dredge —' appear to make the cost of
this Alternative excessively high for the volume to be dredged
With this in mind, a crude approximation of cost can be
developed as follows:
Because many dredging firms quote on a cost plus 10
percent overhead plus 10 percent profit basis, the Shell-
maker estimate cited earlier serves as a crude basis for
estimating what the City's costs might be. Thus, the $2.10
to $2.25/yard figures cited could be scaled down about 20
percent to give an indication of actual cost. This assumes,
however, that a crew comprised of municipal personnel can
operate the dredges as efficiently as a contractor crew.
The experience of several California municipalities (Santa
Barbara, Santa Cruz, and Ventura) has shown that such crews
are not able to obtain sustained high production rates.
Therefore, the contractor's estimate of cost, even with
overhead and profit included, is probably lower than the
City's costs actually would be. Thus, the City's costs with
—' In order to pump 4,000 to 5,000 feet, without the use of
a booster unit, a 12 inch or larger dredge is needed.
Mobilization costs for a 12 inch dredge (see preceding
summary of costs for contract via open market bid) would be
$75,000 to $100,000. If a smaller dredge were used, a booster
must be added to the system; this tends to offset any cost
reduction that would otherwise be gained.
DAVID D. SMITH AND ASSOCIATES
Page 42 DDS&A 77-463
July 28, 1978
this Alternative would at least equal and are likely to
exceed the $201,000 to $235,000 cost cited above for the
open market bid.
City Purchase and Operate
As indicated in Table II , purchase costs for a dredge
suitable for the Incremental program at a seasonal production
rate of (a) 25,000 yards every two years, or (b) 50,000 to
60,000 yards every four years (say, a 6 inch or 8 inch dredge)
would range from about $130,000 to $290,000 respectively.
Assuming a single booster would be adequate for the 8 inch,
and two units would be required for the 6 inch, and that each
booster costs about 30 percent of the dredge price, then we
have: 6 inch 8 inch
Dredge $130,000 $290,000
Booster $ 39,000 each $ 87,000
39,000
Pipe $ 50,000 $ 60,000
Total $258,000 $437,000
Say, $260,000 to $440,000, plus transportation costs.
Even the lower of the two figures constitutes a major capital
outlay. Added to this would be substantial additional costs
for auxilliary equipment, fuel, crew, supervisory personnel,
insurance, and maintenance. These costs might well run
$75,000 or more. Thus, total costs for the first incremental
dredging could be $335,000 which divided by 60,000 cubic
yards equals about $5.50/yard. Obviously, costs per yard
would decrease with each successive incremental phase of
DAVID D. SMITH AND ASSOCIATES
Page 43 DDS&A 77-463
July 28, 1978
dredging. Nevertheless, a preliminary calculation shows
that even after more than 10 years into the
incremental program, the cost per yard figures still
exceeds $3.00, and the total cost (including maintenance
and other costs between periods of dredging) would be
on the order of $750,000 to $800,000.
S umma ry
For the four alternative courses of action for the
incremental work, order of magnitude cost estimates for the
first increment are as follows:
Contract — Open Market
About $200,000 to $235,000
Contract - SDG&E
No estimate at this time
Lease & Operate
About $200,000 to $235,000
Purchase & Operate
About $335,000
Because of the imprecision of these cost estimates for the
incremental dredging work, it is inappropriate to rank
them.
The overall picture they give, however, is quite
clear: even ignoring the progressive increase in costs due
to inflation and the problems with achieving sustained
production rates with inexperienced crews, the costs per
yard for dredging sediment in 60,000 yard increments is
roughly half again to double that of removing all 300,000
DAVID D. SMITH AND ASSOCIATES
Page 44 DDS&A 77-463
July 28, 1978
yards in one operation. Thus, over a ten or fifteen year
period (the grace period we have assumed earlier as a
result of the Restorative Approach), dredging 60,000
yards every four years would almost certainly equal and
probably exceed the cost of the restorative dredging
work.
LONG TERM DREDGING PROGRAM
Costs for the long term dredging program are very
difficult to estimate at this time for a number of reasons,
including (1) the unknown impact of the addition of Encina
Unit 5 with respect to frequency of dredging, and the
duration of the interval before start up of the Long Term
Program; (2)'the duration of this interval also depends on
which approach is selected for the Near Term program, and
which approach is selected for the Long Term Program; in
addition, (3) the degree of cost escalation due to inflation
and other factors depends on how long before the start up
year.
For these reasons, it is impractical to attempt to
estimate costs of the Long Term Program at this time.
OTHER CONSIDERATIONS
By not dredging the middle lagoon, it might be
possible to reduce costs (the middle lagoon requires a
separate set up of the dredge for a relatively small volume
of yardage to be removed). On the other hand, if the middle
lagoon were not dredged, some of the sand in the middle
DAVID D. SMITH AND ASSOCIATES
Page 45 DDS&A 77-463
July 28, 1978
lagoon would be shifted to the inner lagoon, thus accelerat-
ing sediment buildup there.
DAVID D. SMITH AND ASSOCIATES
Page 46 DDS&A 77-463
July 28, 1978
UNRESOLVED MATTERS
As pointed out at the outset of this report, there
are several as yet unresolved questions which have a key
bearing on the City's eventual decision whether to under-
take the dredging work and how it should be carried out.
A brief discussion of these key questions follows.
COST/BENEFIT ANALYSIS
Because of the very substantial costs that would be
involved in dredging the middle and inner lagoons, it
would be appropriate to carry out a rudimentary cost/benefit
analysis to determine if the present (and anticipated future)
recreational use of the two lagoons warrants an expenditure
of the magnitude that would be required for the dredging
work.
Such an analysis would probably require some type of
survey to define use rates, the characteristics of the user
population, and the extent to which the present bars and
shoals are an encumbrance to recreational use.
EEL GRASS
According to Bradshaw et al . (1976, p. 43),
there are about 70 acres of eel grass habitat in
Agua Hedionda Lagoon. Based on Bradshaw's map of
habitat types (1976, Plate 11), probably more than three-
fourths of this acreage is located in the inner and middle
DAVID D. SMITH AND ASSOCIATES
47 DDS&A 77.453
July 28, 1978
lagoons. Dredging removal of the bars and shoals in
these two lagoons would probably disturb extensive
portions of this eel grass habitat, particularly in
the inner lagoon.
In the past year, the U.S. Fish & Wi1dlife Service has
taken a very strong and effective stand in opposition
to several dredging projects and in particular those
which would disturb eel grass or other types of valuable
aquatic or wetlands habitat. For this reason, it will
be essential to determine what the U.S. F&WLS
position is likely to be with regard to the dredging
work being considered for Agua Hedionda Lagoon.
EFFECTS OF ENCINA UNIT 5
Construction of the SDG&E Encina Plant's Unit
5 is virtually complete and the Unit will come on
line in the fall of 1978. The addition of this Unit
will increase the Plant's cooling water intake by
about 60 percent. It is likely that this substantial
increase will have marked effects on circulation patterns
and sediment accumulation rates in the outer lagoon and
possibly to some extent in the middle and inner lagoons.
For example, SDG&E anticipates on an intuitive basis
that sediment accumulation will accelerate and that
DAVID D. SMITH AND ASSOCIATES
Page 48 DDS&A 77-4639 July 28, 1978
dredging of the outer lagoon may have to be carried out
annually from then on rather than every other year as at
present.
As far as DDS&A can determine, no technical studies
have been carried out as yet to assess or predict these
effects. Given these conditions, it is virtually
impossible to predict the nature and degree of effects
likely to be experienced in the middle and inner lagoons.
Inasmuch as these effects could have a critical bearing
on the need for dredging in the middle and inner lagoons,
it is clear that the City should defer a decision regarding
dredging until the character and extent of these effects
becomes clear.
It is possible, for example,that sediment accumulation
rates in the middle and inner lagoons will increase,
remain essentially the same, decrease, or possibly even
shift to a negative value (i.e. sediment being removed
from the 1agoons).
In the meantime, in order to determine what the
effects are, it would be necessary to carry out periodic
engineering surveys of the bottom topography in parts of
the two lagoons. Such a survey program should cover a
period of 1 to 2 years; suggestions as to the type and
frequency of surveys required will be submitted to the
City separately.
DAVID D. SMITH AND ASSOCIATES
Page 49 DDS&A 77-463
July 28, 1978
SOURCES OF FUNDING
In the course of this study, queries regarding
possible funding assistance for this dredging work were
made by DDS&A to several Federal and state agencies
including the U.S. Army Corps of Engineers, NOAA's Office
of Coastal Zone Management, and the State of California's
Department of Navigation and Ocean Development, among
others. While the answers DDS&A received have not been
encouraging, it may still be worthwhile for the City to
pursue the following courses at least one more step:
(a) Because the dredged sediment will be used to
nourish an eroding beach, it is conceivable that the
Corps might view the dredging work as appropriate for
some level of financial support.
(b) As we understand it, the Office of Coastal Zone
Management (OCZM) has loan and grant money for certain
recreational projects that meet specific guidelines;
generally, however, the money is not to be used for con-
struction activities.
(c) OCZM also has funds for certain types of projects
that have been impacted by energy related activities or
facilities. The Agency guidelines applicable to this
funding apparently are inordinately complex.
DAVID D. SMITH AND ASSOCIATES
Page 50 DDS&A 77-463
July 28, 1978
CONCLUSIONS
(1) It is feasible to dredge Agua Hedionda middle and
inner lagoons with a portable hydraulic suction dredge.
(2) The only presently feasible location for disposal
of the dredged material is the ocean beaches adjoining the
outer lagoon. The sediments to be dredged appear to meet
the EPA criteria for disposal as beach nourishment. Use
of this disposal location will involve pumping distances
of 4,000 to 5,000 feet and possibly farther.
(3) For restoration of the middle and inner lagoons to
their 1954 depth (i.e. -10 feet Mean Sea Level) about 310,000
cubic yards of sediment would have to be removed. By
contrast, to cut the tops off the bars/shoals to a depth
of -5 or -6 feet would require removal of about 25,000 and
60,000 yards, respectively.
(4) An accurate estimate of the rate of sediment accumulation
in the two lagoons is not possible with the information
presently available. However, comparison of the 1978 survey
with information for 1954 indicates that an average
accumulation rate for this 24 year period is roughly 13,000
cubic yards per year total for the two lagoons.
(5) The Water Board is almost certain to limit the dredging
work to a 7 month period in any given year in order to
avoid conflict with recreational use of the beach. This
time constraint tends to dictate the minimum size of dredge
suitable for the work.
DAVID D. SMITH AND ASSOCIATES
Page 51 DDS&A 77-463
July 28, 1978
(6) Analysis of the required near term (2 to 5 years)
work indicates that two basic alternative approaches are
possible: i.e. a restorative approach and an incremental
approach. The restorative approach would involve removal of about
300,000 cubic yards and restore lagoon depths to -10 feet.
This approach would require a major initial expenditure
but would result in a substantial grace period before
recurrent maintenance dredging became necessary, say, on
the order of 10 to 15 years.
The incremental approach would involve removal of the
tops of bars and shoals down to a depth of -5 to -6 feet
and would involve excavating some 25,000 to 60,000 cubic
yards respectively. Although costs would be lower, the
grace period. before maintenance dredging would be much
shorter, possibly 2 to 3 years.
(7) If the restorative approach were bid on the open
market it would probably cost on the order of $650,000 to
$750,000. If, on the other hand, SDG&E served as contractor
on an at-cost basis, the price would probably be on the.
order of $480,000 to $500,000. If the City of Carlsbad
purchased a dredge suitable for this work, initial capital
costs alone would amount to on the order of $475,000;
operating and maintenance would add another $150,000 or more.
Dredges suitable for this work may be available for ^ease
depending on the level of activity in the dredging industry;
leasing costs for equipment for this work could range up
to $390,000 to $425,000, plus roughly another $100,000 to
$150,000 for fuel, crew, maintenance, and insurance costs.
DAVID D. SMITH AND ASSOCIATES
Page 52 DDS&A 77-463
July 28, 1978
(8) If the Incremental Approach (say, 60,000 cubic
yards) were bid on the open market, the first increment
would cost on the order of $200,000 to $235,000 because
fixed mobilization costs comprise a disproportionately
high percentage of the cost of a small job. Because of
the considerable nuisance factor associated with a
periodically recurring small dredging job, it is unlikely
that SDG&E would be interested in acting as a contractor
for the incremental approach. Lease of a dredge for the
incremental work would probably cost the City about as
much as having the job done by a contractor — say, $200,000
or more. If the City of Carlsbad purchased a suitable small
dredge (say, 6 inch), initial capital costs would be on the
order of $260,000 at the lowest. Operating costs could run
$75,000 or more for each dredging increment, and between-
job maintenance and insurance costs would be expected to be
high.
(9) A key and possibly critical problem with the City
purchase and lease alternatives for the Incremental Approach
is the major difficulty in finding, hiring, and holding
experienced dredging personnel for jobs that are incremental
in nature.
(10) On balance, although the Incremental Approach involves
a lesser expenditure of funds at a given time, over a 10 to 15
year period costs for the Incremental program are likely
to exceed the cost of the Restorative Approach, even before
considering the effects of inflation.
DAVID D. SMITH AND ASSOCIATES
Page 53 DDS&A 77-463
July 28, 1978
(11) Because the addition of Encina Unit 5 may have
significant effects on sediment accumulation rates in
the middle and inner lagoons and because these effects
cannot be predicted at this time, it is important that
a decision as to dredging in the lagoons be deferred
until the nature and degree of these effects are known.
This determination probably will require periodic moni-
toring surveys over a one to two year period.
(12) In order to determine if the present and anticipated
future level of recreational use of the lagoons warrants
a major financial expenditure for dredging, a rudimentary
cost/benefit analysis should be carried out.
(13) Selection of a Restorative versus Incremental Approach
to be used for long term (20 to 25 years) maintenance dredg-
ing depends in part on the decisions made for the near term
dredging work. This uncertainty together with the unknown
effects of Encina Unit 5 make it impractical to estimate
costs for the long term maintenance work at this time.
(14) When the results of the monitoring program have defined
the effects of Encina Unit 5, the questions of: (a) need
for dredging, and (b) alternative courses of action should
be examined in that context.
(15) If the need for dredging remains unchanged and the
rate of sediment accumulation does not increase or decrease
significantly, then the results of this present assessment
are expected to remain valid.
DAVID D. SMITH AND ASSOCIATES
Page 54 DDS&A 77-463
July 28, 1978
(16) Based on a careful review of the various alternatives
available to the City, it appears that, given present
conditions in the lagoon, and if the work were to be
undertaken now, the most prudent and cost effective
alternative would be to contract with SDG&E at cost to
carry out the Restorative dredging work (i.e. about 300,000
cubic yards) on behalf of the City. This would take advantage
of SDG&E's considerable knowledge, skill, and experience
in dredging work, would spare the City the major problems
associated with obtaining dredging supervisory personnel and
crew, and would eliminate the maintenance and insurance
problems associated with a major capital equipment unit.
DAVID D. SMITH AND ASSOCIATES
Page 55
DDS&A 77-463
July 28, 1978
RECOMMENDATIONS
(1) Defer a decision on dredging the lagoons until the
effects of the addition of Encina Unit 5 are known.
(2) After Unit 5 comes on line, monitor the effects on
the middle and inner lagoon for a one to two year period.
This monitoring program would require precise engineering
surveys of the bar and shoal areas in the two lagoons;
these probably should be carried out quarterly.
(3) Concurrently with the monitoring program:
(a) Conduct a rudimentary cost/benefit analysis
to determine whether or not a major expenditure is
warranted in order to facilitate recreational use
of the lagoons.
(b) Determine the likely position of the USF&WLS
concerning disturbance of the eel grass habitat
areas that the dredging would entail.
If the cost/benefit analysis results are favorable and if
the contacts with USF&WLS indicate that the envisioned
dredging work is acceptable to that agency, then the follow-
ing recommendations apply:
(4) If it becomes evident from the monitoring program
results that the bars/shoals are static or continuing to
grow, then proceed with arrangements for the near term
dredging program.
(5) On the other hand, if the monitoring results show
that the bars/shoals are diminishing in size, then reassess
DAVID D. SMITH AND ASSOCIATES
56 DDS&A 77-463
July 28, 1978
whether or not the level of recreational use versus possible
dredging costs warrants:
(a) Waiting to see how far and how fast the new
hydraulic regimen will reduce the size of the bars/
shoals, or
(b) Undertaking the near term dredging work
regardless of the assistance the new regimen may
provide.
(6) Based on the reasoning set forth in this report and
summarized in Conclusion 16 above, the City should open
preliminary discussions with SDG&E regarding the latter
serving as operational contractor for the dredging work.
(7) In addition, the City should contact two or possibly
three dredging firms and request them to inspect the site
and prepare a preliminary estimate of what contract dredging
would cost in, say, 1980. These preliminary estimates are
likely to be considerably more accurate than the order of
magnitude costs given in this report.
DAVID D. SMITH AND ASSOCIATES
Page 57 DDS&A 77-463
July 28, 1978
ACKNOWLEDGMENTS
We wish to express appreciation to the following
individuals for their cooperation and assistance in
carrying out this project: Messrs. Paul D. Bussey,
Roger W. Greer, James C. Hagaman of the City of Carlsbad;
Marion G. Horna, H. E. "Ted" Richmond and William G.
Dyson of the San Diego Gas & Electric Company; Professor
John S. Bradshaw of the University of San Diego; Dr. Gordon
A. Robilliard of Woodward-Clyde Consultants; and Charles
Holt and his colleagues with the Los Angeles District of
the Corps of Engineers.
DAVID D. SMITH AND ASSOCIATES
Page 58 DDS&A 77-463
July 28, 1978
REFERENCES CITED
Barnes, B., P. Neal , L. Williams and J. Brown, 1965,
Carlsbad Small Craft Harbor, Carlsbad, California.
Daniel, Mann, Johnson, and Mendenhall, 105 p.
Bradshaw, J. S. and G. N. Estberg, 1973, An ecological
study of the subtidal marine life of Agua Hedionda
Lagoon. Environmental Studies Lab., Univ. of San
Diego, 123 p. + appendix.
Bradshaw, J. S., B. Browning, K. Smith and J. Speth,
1976, The natural resources of Agua Hedionda Lagoon.
Calif. Dept. Fish and Game, U.S. Fish and Wildlife
Service, Coastal Wetland Series #16, 110 p. + appendices.
Dyson, W. G., 1978, Personal communication regarding levels
of extreme tides in Agua Hedionda Lagoon.
Environmental Protection Agency, 1977, Ocean dumping, final
revision of regulations and criteria. Tu., Jan. 11,
part VI, Fed. Reg. v. 42, n. 7, p. 2462-2490.
Richmond,-H. E., 1978, Personal communication regarding
quality of water in outer Agua Hedionda Lagoon.
San Diego Regional Water Quality Control Board, 1967,
Water quality control policy for Mission Bay including
tidal prism of San Diego River and Agua Hedionda Lagoon.
State of Calif., The Resources Agency, 30 p. + appendices
Smith, D. D., 1975, Disposal of dredged material - a key
environmental consideration in the construction of major
nearshore and coastal marine facilities. Amer. Soc.
Mech. Engr., New York, 75-WA/Pet-7, 7p.
Smith D. D., 1977, Dredged material, ocean disposal, and
the regulatory maze. In Palmer, H. D. and M. G. Gross,
eds., Geologic aspects of ocean waste disposal. Proc.
Soc. Econ. Paleon. and Mineral. Ann. Mtg., June 1977,
Dowden, Hutchison & Ross, Stroudsburg, PA, in press.
DAVID D. SMITH AND ASSOCIATES
SAN DIEGO GAS & ELECTRIC COMPANY
P.O.BOX1831 SAN DIEGO, CALIFORNIA 92112
(714) 232-4252
November 27, 1978
Mr. Paul D. Bussey
City Manager
City of Carlsbad
1200 Elm Avenue
Carlsbad, CA 92008
Dear Mr. Bussey:
Once again, it is time for San Diego Gas & Electric to
perform regular maintenance dredging of the outer portion of
Agua Hedionda Lagoon, Carlsbad, California. Dredging will be
in accordance with U. S. Army Corps of Engineers' Permit No.
75-33, and San Diego Coast Regional Commission's Blanket
Development Permit No. F-1835. The work has again become
necessary due to a build-up of sand inside the power plant's
intake channel and lagoon.
Dredging operations are scheduled to commence in
February, 1979,andwill be completed in May, 1979. Mobiliza-
tion of equipment for dredging operations will begin in
January, 1979. Approximately 75 days of actual dredge opera-
tions are anticipated. This is based on moving 6,000 cubic
feet, per day, and estimating that we will move 450,000 cubic
feet of dredge material from the lagoon. Dredging will pro-
ceed on a 24-hour basis, 6 days per week, with the seventh
day for repairs.
As in the past, and in conformance with our State
Lands Commission Industrial Lease No. P.R.C. 932,1, dredge
spoil from Agua Hedionda Lagoon will be deposited on the
ocean beach frontage, westerly of Carlsbad Boulevard.
Should you have any questions regarding this project,
please contact me at 232-4252, Extension 1718.
Sincerely,
W. D. Ciesielski
Right-of-Way Agent
WDC:mel Governmental Right-of-Way
AN INVESTOR OWNED CORPORATION