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Home My WebLink About; Batiquitos Lagoon Restoration Plan; Batiquitos Lagoon Restoration Plan; 1985-07-17BATIQUITOS LAGOON RESTORATION PLAN July 17, 1985 I. PREVIOUS PLANS 1955 - Proposed agricultural use of lagoon after draining (Ayres) 1963 - Small marina proposed (Metcalf Properties) 1965-67 - Treated wastewater diverted to lagoon 1967 - County designates lagoon as a regional park 1975 - "Capt. Nemo's Secret Harbor" theme park proposed (Doulton) - World Cultural Center and Hilton Hotel proposed for north shore (Excel Foundation) " ^^^^5^i^os Lagoon Regional Park Master Plan completed by County lyai - Pacific Rim Development proposed for Rancho La Costa Properties (HPI Development Company) May 1983 - Pumped seawater proposal for east lagoon presented (HPI Development Company) June 1985 - Tidal Circulation Alternatives Study completed (Sarrmis Properties) July 1985 - Integrated Tidal Flushing Restoration Plan presented (Sanmis/HPI) August 1985 - Proposed field measurement of tidal circulation in laeoon (Sammis/HPl) ^ II. TIDAL PROCESSES AND CONSTRAINTS Table of Historical Lagoon Size and Siltation Since 1887 Year Tidal Volune Percentage of 1887 Year (Cubic Yards) Tidal Volume 1887 5,646,000 100.0 1888 4,849,000 85.9 1960 4,300,000 76.2 1965 3,620,000 64.1 1978 12,300 0.2 - Methods of maintaining tidal circulation are divided into two categories: equilibrium and non-equilibrium. Equilibrium methods require excavation of a sufficient volume of lagoon sediments to keep the lagoon entrance open via natural tidal scour. Non-equilibrium methods use artificial devices to -2- Batiquitos Lagoon Restoration Plan July 17, 1985 maintain a lagoon opening despite non-equilibrium conditions. An equilibrian configuration with an expected open duration of 20 - 30 years, would require excavation of about 4 million cubic yards. - Importance of upcoming tidal study to assess tidal range in lagoon vs. tidal range at coast. III. DREDGE REQUIREMENTS - 4,000,000 cubic yards from entire lagoon - Sill and bottom at -5' M.S.L. - Improved channel between flow constrictions - Cost $15 - 16 million BENEFITS: - Mimics natural lagoon dynamics of 100 years ago - Incorporates agency feedback - Provides flexibility for environmental/ecological enhancement IV. ENVIRONMENTAL CONSIDERATIONS - Benefits of ocean connection/tidal flushing - Wet/dry habitat - Consistent with expressed desires of affected agencies - Shallow/deep habitat - Respects wetland boundary (elev. 3.5' M.S.L.) - Provides for "30-year" closings - Removes high nutrient sediments -3- Batiquitos Lagoon Restoration Plan V. SUMMARY - Plan evolution and incorporation of agency input - Tidal flushing (similar to 100 years ago) - Equilibrium system with back-up - Variety of habitat types - $15 - 16 million 8731-84-00 07-10-85 ALTERNATIVES FOR MAINTAINING TICAL CIRCULATION IN THE BATIQUITOS LAGOON, CALIFORNIA SUMMARY AND CONCLUSIONS For the past 6000 years, deposition of upland sediments has continued to reduce the average depth and volume of Batiquitos Lagoon. The rate of deposition has increased significantly in the past 20 years, largely because of development in the tributary watershed. However, accelerated infilling of the lagoon started with construction of the first railroad bridge in 1881, and continued with construction of the coast highway bridges and associated fills in 1912, 1926, 1934 and 1952, and construction of the 1-5 bridge and approach fills in 1967. The decrease in tidal vol-jme due to natural and man-induced effects is summarized below for the period from 1887 to 1978. TIDAL VOLUME PERCEiNTAGE OF 1887 YEAR (CUBIC METERS) TIDAL VOLUME 1887 4,320,000 100.0 1888 3,710,000 85.9 1960 3,290,000 76.2 1965 2,770,000 64.1 1978 9,430 0.2 The above tidal volumes (tidal prisms) for the lagoon represent the vol'jme of water exchanged between the lagoon and the sea during one tidal cycle. The tidal prism volume, when compared with the cross-sectional area ot the channel that connects the lagoon to the ocean, provides useful mcor- mation on the ability of the lagoon to remain open (that is, connected by an inlet) to the ocean. Using the existing 144-foot opeair.g unaer Carlsbad Boulevard, and assuning typical values for wave heignc and direction, the table below shows the expected average time to closure for an open lagoon with the indicated tidal prism volune. TIDAL PRISM TIME TO CLOSURE- (CUBIC METERS) (YEARS) 3,120,000 30 3,050,000 20 2,720,000 10 1,890,000 5 824,000 1 32,600 0.2 * Long Tenn Average GEORGE S NQLTE AND ASSOCIATES ',•^1 f.. "i.>NMf t*4&'».U«S PL*NtJ(RS SM»VfvC)<»S -2- 8731-84-00 7-10-85 Inserting the existing tidal prism for the lagoon (9430 cubic meters) into the above table shows that the lagoon, ^vhen open to the ocean, can be expected to renain open for a period of much less than 0.2 years (2.4 months). This is substantiated by noting that the lagoon, when artificially opened in February 1985, stayed open for less than one month. The intent of this report is to reconinend methods and associated costs for creating and maintaining tidal circulation in the lagoon, in light of the foregoing conditions. Methods of maintaining tidal circulation are divided into two categories: equilibrium and non-equilibritm. Equilibrian methods require excavation ot a sufficient volume of lagoon sediments to keep the lagoon entrance open via natural tidal scour. Non-equilibrium methods use artifical devices to maintain a lagoon opening despite non-equilibrium conditions. Referring to the second table above, an equilibrian configuration with an expected open duration of 30 years, would require an excavated tidal prism of 3,120,000 cubic meters (4,078,000 cubic yards). The artificial devices used to maintain the opening of a non-equilibrian lagoon consist of various ways to move sand from the inlet as it accumulates there. Concepts presented include: bulldozer and pilot channel; fluidizer system with jetties; pier-mounted drag bucket; and dual siphon systan. The excavation requirements, initial costs, and annual operation and maintenance costs for each of the alternatives are sanmarized below. If a market is found for excavated sands, the initial cost of all alternatives can be reduced accordingly. ALTERMTIVE REQUIRED EXCAVATION (CUBIC YARDS) FIRST COST (3) ANNUAL COSTS (S) Equilibrium Method Bulldozer/Pilot Channel Method Fluidizer Method Pier-Drag Line Method Dual Siphon Method 4,078,000 1,065,000 1,065,000 30,000 30,000 14,358,700 3,270,000 3,624,300 665,187 3,120,000 -0- 2,000 1,000 8,000 10,000 GEORGE S NOLTE AND ASSOCIATES trv.i »'.0 eV/i«5»,Wt'J-Al. £Nr,.Ntl»S Pl.NMfBS SU"Vt»0»S