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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. 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LO CM v^ O O ^j-. 1 O CO in 3 i— Q. - Ooo •cd" Oo LO 1o LO o CM LO —•3- r— S_ O CMi^ c oen (O OS— r*^o r*^ ^j -t-> CU 0 C 0 T- • •r- JC D- .— 0 S- i— fO Ouj s: o . to cu >»> s- •r- to -l-> r— fO r— C O CU Cto tocu t- CUo.-o CU 3 S- i— CJ t_ C">— k— cu JC 4J •M Ocs- o o TOto « 1 S- 3 >, 0 Cto oII 3 CUc c •to ••- o o cu>> to jQ E •>to ^C CU 4^* oO JC tO tO 4-> O Q •— Q S- M- O O M- •• 4-> CU CU OL T3 J- -r- CU <O Q. i — to •• CL4-> S- CL to CU 3 O -(->to o to Oc co o O C JQ •I— •!— -M tO tOto to toE cuS- r— JC O 0 <+- -0 3 c c to •r- IO 4-> c cu c O to (U to E •O JC CL CU C_> '*— to S- 3to 3 cr QQ Q- CU *-s^. r— | 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