SWAC OTEC Services Papers
1.4 m (55″) NELHA deep water intake pipeline during assembly.

Since 1979 Makai has designed a number of bottom mounted, down-the-slope, catenary, and pendant polyethylene pipelines for use in SWAC and outfalls.

These pipelines are suited for:

  • Seawater Air Conditioning (SWAC)
  • Ocean Thermal Energy Conversion (OTEC)
  • Marine Outfalls
  • Aquaculture and mariculture
  • Industrial Cooling and Power:
    • Waste heat power cycles
    • Power plant cooling
    • Liquefied Natural Gas (LNG) process cooling
    • Chemical process cooling
    • Other industrial processes with large cooling loads

Makai’s long experience with pipeline design and deployment has led to very cost-effective fabrication and deployment methods. One example is a typical SWAC polyethylene pipeline, which is fused into long sections onshore, filled with air, then towed into place and lowered to the seabed – often in a single day – minimizing expensive marine construction and weather-related risks.

Makai has also conducted extensive field research on practical and cost-effective methods of deploying large diameter pipelines – in both deep and shallow waters. In order to ensure the safety or our designs, Makai has developed special test equipment and procedures for testing polyethylene pipes under extreme loads and under negative (suction) pressure. Makai has been designing and working with deep water pipelines since 1979 and has designed a number of down-the-slope polyethylene intake pipelines and suspended pipelines.

Numerous firms place pipelines on the ocean floor – usually at great expense. Makai’s design services lead to reduced cost by assembling the pipe onshore where labor costs are lower. The assembled floating pipe is towed into place and mounted to the seabed – often in a single day – minimizing expensive marine construction and weather-related risks. 

Installing these unique deep pipes can place substantial loads on the pipe assembly during installation.  Makai conducts field research studying the installation and loading on large diameter pipelines – both deep and shallow.  Makai also develops and tests the procedures needed to accommodate these loads. Here, a 1:5 scale model of a 55" pipe and custom flange assembly is measured while it is pressurized, tensioned and severely bent. 

Installed Pipelines

Makai’s experience in pipeline design, analysis and deployment is summarized below:


Rehoboth Beach, Delaware – Treated Effluent Outfall 
Project Status: Ongoing, 2018

In Delaware, a $52.5 million project to eliminate the discharge of treated effluent from the Rehoboth Beach into the Lewes-Rehoboth Canal has been designed and installed. Part of this project involves installation of the force main pipe which is a 24-in., 11,400-ft.-long pipe leading from the wastewater treatment plant to the Atlantic Ocean. It travels approximately 6,000 ft. off the beach before diffusing treated wastewater into the ocean. The HDPE pipeline is horizontal direction drilled approximately 3,000 ft. followed by marine open-cut trench approximately 3,000 ft. Once the pipe is anchored in place with concrete collars, the open-cut trench is backfilled. The terminus of the outfall pipe consists of a 120-linear ft. diffuser comprised of eight risers, 1.5 ft. above the ocean floor, with four discharge ports per riser. Makai assisted Manson Construction by providing HDPE pipeline deployment analysis (pull forces, stresses, flooding rates required), ballast weighting schedule, design of precast concrete ballast weights, investigating anchoring methods, reviewing HDPE pipe pull head and towing assembly, and investigating pipe fabrication staging sites. Outfall pipeline installation is ongoing as of March 2018.


Burullus, Egypt – Twin 2.0m Diameter Intakes 
Project Status: Completed, 2018

In 2018 Makai completed the final design and construction support for the twin 2.0m diameter, 1.2km long HDPE intake pipelines and twin intake towers for the new Burullus power plant in Egypt. Makai worked directly for the marine contractor, Tideway (DEME), to provide final designs and installation guidance. This seawater supply system is designed to serve what will be one of the world’s largest natural gas-fired power plants. Design of the intake structures was driven by their shallow depth (5 meters) and the fact that breaking waves were present in the area. Makai was responsible for HDPE pipeline and installation specifications, intake system hydraulics including computational fluid dynamics analysis, intake tower and anchoring concrete structural designs and specifications, and contractor support during installation including design of lifting and staging assemblies.


Cayuga Power Plant – Cooling Water Intake System 
Project Status: Completed, 2017

Makai completed the final design of a cooling water intake system for a large power plant in Upstate New York. Final construction, installation and commissioning was completed in January 2017, and the system is now fully operational and supplying 170,000 gallons per minute (~10.7 cubic meters per second) of cooling water to a power plant. The Client is one of the nation’s first large utility plants to go through the EPA Clean Water Act, Section 316(b) process in its entirety. Screens were fine slotted mechanically cleaned cylindrical wedge-wire screens supplied by Intake Screens Incorporated (ISI). Makai used an integrated design approach, optimizing the structure through a continuous iteration of CFD (computational fluid dynamics), FEA (finite element analysis), and value engineering on the structural arrangement for constructability, fabrication, and shipping. Our team delivered a custom solution for the client that meets their strict hydraulic limitations, their budget, as well as the stringent EPA 316b guidelines that will help to preserve the marine ecosystem.

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Project Status: Ongoing

Makai has been contracted to carryout final design engineering services for Honolulu Seawater Air Conditioning LLC, a subsidiary of Ever-Green Energy of St. Paul, Minnesota. The overall goal of this ambitious project is to provide 22,500 tons of air conditioning to downtown Honolulu commercial and government buildings. As of 2010 Makai has completed the design of the large diameter deep water intake pipeline from 43′ (10.6m) depth to the intake depth at 1784′ (544m) stretching over a length of approximately 25,000 feet (7621m). Makai’s responsibilities have also included the design of a companion shallow water return water discharge pipe to a depth of at least 150′ (45.7m). It is anticipated that construction bidding on the offshore portion of this project will commence in 2011.


Credit: Kalyon Group
Credit: Kalyon Group
Credit: Kalyon Group

TRNC Drinking Water Supply – 1.6m Pipe, 2013
Project Status: Ongoing

In late 2013, Makai was contracted by a joint venture between Sigur Ros and Kalyon Group to perform deployment analysis for the on-bottom portion of a 63” (1.6m) diameter, 66 mile (107 km) long HDPE pipeline to transmit drinking water from the Turkish mainland to the island of Cyprus (Turkish Republic of Northern Cyprus). Makai performed pipe stress analysis, design of the holdfasts, pipe weights, and bridle system, and final deployment analysis and guidelines. Click here to watch a video of the “project of the century”.

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Project Status: On hold

In March of 2008, Makai completed the final design for the deep seawater intake pipeline, the return water pipeline and the pump station mechanical plant for a seawater air conditioning system to be built in the Piscadera region on the Caribbean Island of Curacao. This 3000 ton air conditioning system will supply cooling to 4 hotels and a power plant. A 915mm, 6 kilometer long intake pipeline extending to an intake depth of 850m has been designed, and construction is anticipated in late 2011.


Hawaii – 1m Pipe Repair
Project Status: Completed, 2013.

In 2011, Makai was contracted by the State of Hawaii to perform final design and construction oversight services for the repair of a deepwater 40” (1.0m) diameter HDPE pipe at the Natural Energy Laboratory of Hawaii (NELHA) located in Kona, HI. The pipe, originally built for ten year design life, has been in place for over 25 years. The pipe design involves a 915m long floating catenary section from 150m to 670m depth, and several of the chain bridles restraining the pipe had worn from corrosion and continuous motion over the years. Makai simulated the current pipe conditions using Orcaflex 3-dimensional finite element software, simulated repair solutions, and provided final design drawings and specifications. In July 2013, repairs were conducted and Makai provided on-site representation for our client, the State of Hawaii. The repairs were successful, and post-repair measurements showed excellent agreement with Makai’s model predictions and design specifications.

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Credit: Mark Gamba
Rendering by Earl Wilson, Brown and Caldwell
Credit: Mark Gamba

Lake Oswego, Oregon – Sewer Interceptor, 2011
Project Status: Completed, 2011.

The Lake Oswego Interceptor Sewer (LOIS) project, protects the water quality of Oregon’s Oswego Lake through seasonal changes in water temperature and in the event of an earthquake. The project replaced a 50-year-old corroded, undersized, and seismically vulnerable concrete cylinder sewer pipe under the lake with a larger, flexible, high-density polyethylene (HDPE) pipeline. LOIS is the first known buoyant gravity sewer in the world. LOIS’ submerged, buoyant stainless-steel access points provide entry points to the pipeline without affecting boat navigation, and the installation of removable access caissons allows cleaning and inspection equipment to be inserted into for infrequently required maintenance. Makai modeled and performed analysis for a 42-inch HDPE submerged, buoyant sewer interceptor. Makai used OrcaFlex to model the tension and stresses in hundreds of components (especially the tethers) to a very high degree of precision; the grade tolerance on the project was plus or minus ½ inch over several miles. Makai performed this work for Lake Oswego, Oregon and Brown and Caldwell Engineering. The project won two national awards. The Plastic Pipe Institute declared the Lake Oswego Sewer Interceptor Project as its Municipal Project of the Year, and the Association of General Contractors awarded their 2011 Grand Award to Advanced American Construction, Inc. for their work assembling the project.

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Bahrain – Cooling Project, 2005
Project Status: Completed, 2005.

In 2005, Makai designed intake and discharge pipelines to provide seawater to the Bahrain Diplomatic Area District Cooling Project’s air conditioning plant for condenser cooling. Seawater drawn from the Arabian Gulf is slightly warmed and then returned into near shore waters. The system, owned by Tabreed Bahrain, features a 63” (1.6 meter) diameter by 2240’ (683 meter) long intake pipeline, and a 55” (1.4 meter) diameter by 5104’ (1556 meter) long outfall pipeline with a 20 port diffuser, operating at a flow rate of 60,000 gallons per minute (3.79 m3/sec).


Credit: Enwave Energy
Credit: Enwave Energy

Toronto Pipelines
Project Status: Completed, 2003.

Makai performed significant design aspects for the three deep water intakes for ENWAVE’s Deep Lake Water Cooling Project in Lake Ontario. The deep (115 meter) intakes provide cold water for air-conditioning buildings in downtown Toronto and the municipal drinking water system with a maximum capacity of 58,000 tons. The system provides water of higher purity than is provided by the current intakes that obtain water from shallower depths. Each HDPE pipeline is five km long and 1.6m (63″) in diameter. The pipelines were installed during the summer of 2003.


Joint Kimberly-Clark and City of Everett WA 63″ Outfall Pipeline
Project Status: Completed, 2003.

Makai designed the deep water portion of a 63” (1600mm) diameter outfall pipeline for Kimberly-Clark Paper Company and the City of Everett, Washington. This pipeline delivered 70 MGD of treated municipal and industrial wastewater to a depth of 350 feet (107m) in Puget Sound. The total length of the deep water outfall was 2741’ (836m) and included a 1550’ (472m) diffuser section with 80 ports. The alignment included a 40 degree bend right at toe of a steep submarine slope. Makai devised a unique diffuser port plug design that allowed this outfall to be installed using standard controlled submergence techniques for deep water HDPE pipes, and then allowed the diffuser ports to be quickly opened using an inexpensive remotely operated vehicle. The pipeline was installed in late 2003 and has been in service since the spring of 2004.


55″ Diameter, 3000′ Deep Pipeline
Project Status: Completed, 2001.

Makai has engineered the main seawater supply source for the Hawaii Ocean Science Technology Park (HOST Park) at Keahole Point, Hawaii. This supply system consists of a cold-water pipeline (55″ diameter, 3000′ deep, and two miles long), a 55″ diameter warm water intake pipe, a tunneled shoreline crossing, and a shore-based pumping station. The system is the world’s largest and deepest cold-water pipeline and has the capacity to deliver 27,000 gpm of 4 deg. C. water and over 40,000 gpm of warm water to the technology park. Makai received a national award from the American Society of Civil Engineers for this project as one of the six most outstanding CE projects in 2003.

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Lake Source Cooling
Project Status: Completed, 1999.

Makai was selected by Gryphon International Engineering Services and Cornell University to design a 63″ diameter HDPE intake and a 48″ diameter outfall pipeline in Cayuga Lake, NY to provide 20,000 tons of centralized cooling for the university. The intake pipeline is two miles long with an intake at 250′ depth. The pipeline provides 32,000 gpm of cold water and has a 75-year lifetime. Construction was completed in 1999. The system has been operating since 2000 and has cut electricity needed for air conditioning by 87%.

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Indian OTEC Pipeline
Project Status: Completed, 1998.

Makai has provided conceptual designs and design guidance to the National Institute of Ocean Technology (NIOT) in Madras, India, for in OTEC intake pipeline and mooring system for a floating OTEC research barge in the Indian Ocean. This pipeline was designed to be 1 meter in diameter and to provide water from a 1000 meter depth.

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Four Outfalls in American Samoa 
Project Status: Completed, 1996.

Tafuna Outfall:  This polyethylene pipeline installed in 1996, is 24″ in diameter, 1500′ in length and extends from the shoreline to a depth of 95′. The pipeline is anchored along its entire length for protection against frequent hurricanes and the large waves and strong currents that accompany them. The anchoring systems used were a combination of rock bolts and Manta Ray sand embedment anchors.

Utulei Outfall:  This was a very challenging pipeline design and installation because of the extreme slope that existed along the course of the pipeline. The outfall pipeline is 24″ in diameter, 350′ in length, and it begins at the reef edge at a depth of 5′ and plunges to a depth of 165′. The pipeline has a free floating catenary section that spans the steep slope, and it is heavily anchored at the bottom in deep water.

Aunu’u Outfall:  This is a 6″ outfall, 400′ in length, designed to serve a small community of approximately 400 people. It is installed across a heavily exposed reef flat which is subject to high waves and currents. The pipeline is partially buried and is anchored to the reef with rock bolts.

Pago Pago:  In 1991, Makai designed and managed the construction of a long, medium depth outfall in Pago Pago Harbor, American Samoa. This 16" polyethylene pipeline is 8500′ long and discharges near the mouth of the harbor at 176′ depth. It carries waste water from the Starkist Samoa and the Samoa Packing Tuna Canneries. The pipeline was installed using the controlled submergence techniques and was accurately laid on a curved route along the edge of the harbor. Concrete covers were designed to protect the pipeline at isolated locations from ship anchors and harbor traffic. The lifetime of the pipeline was maximized by minimizing the use of exposed metallic parts in the underwater construction. The pipeline was designed and installed in a short period and was completed ahead of schedule and well under budget.


40″ Intake Pipeline Design and Installation
Project Status: Completed, 1987.

In a project with R.M. Towill Corporation, funded by the State of Hawaii and the U.S. Department of Energy, Makai designed a 40″ polyethylene cold water pipe to be used jointly by the Natural Energy Laboratory and the Hawaii Ocean Science and Technology (HOST) Park sites on the Big Island. At the time of construction, it was the largest deep-water intake pipeline in the world. This pipe is a larger and more rugged version of the previous MOE 12″ pipe design at NELHA and includes a 3000′ long buoyant section. Makai assisted in the deployment of this pipe to a depth of 2200′ in August 1987. It is currently a main source of water for the Natural Energy Laboratory.

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18″ Cold Water Pipeline
Project Status: Completed, 1987.

Makai designed and provided construction management for an 18″ down-­the­-slope cold water intake at the Natural Energy Laboratory of Hawaii. The goal was to install a reliable, minimal cost, deep-water intake system to 2000′. This polyethylene design differs from previous NELHA pipelines in that the deep water pipe is buoyed approximately 40′ off the bottom on a series of pendants, the deployment was accomplished without major offshore equipment. This pipeline was successfully deployed in October, 1987, and is still operational.

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OTEC Pipeline Research, Down-the-Slope Test 
Project Status: Completed, 1984.

Working under a subcontract to Hawaiian Dredging and Construction, on a NOAA/DOE program, Makai was responsible for the concept development, design and deployment planning for an 8′ diameter down-the-slope OTEC pipe test. Part of the test was the demonstration of diver-free installation techniques suitable for very deep, large diameter pipelines on the steep, 42 degree slope. The concept included a flexible pipe joint that conformed to the bathymetry. Pipe deployment was successfully accomplished as planned using heavy lift barges and closed-circuit underwater television. The design included instrumentation for the measurement of hydrodynamic loads on the pipe after installation. Makai subsequently analyzed the hydrodynamic data from this test project.

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Long Operating OTEC Cold Water Pipeline
Project Status: Completed, 1981.

Makai conceived, designed and managed the construction of an experimental, down-­the-­slope polyethylene OTEC pipeline, 12″ in diameter, for the State of Hawaii. This one-­mile long pipeline has an intake at 2000′ and utilizes a unique 3000′ long free-­floating catenary section to avoid contact with the steep, rocky bottom. The pipeline was installed in 1981 off Keahole Point, Hawaii. In spite of its “temporary” design life of 2 years, it has survived many major storms including a hurricane and was operational for over twelve years.

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Mini­ OTEC
Project Status: Completed, 1979.

Makai engineered several portions of the Mini-OTEC project under contract to Dillingham Corp. This project was a full demonstration of Ocean Thermal Energy Conversion (OTEC) and jointly funded by the State of Hawaii, Lockheed, Dillingham and Alfa Laval. Makai designed a 2′ diameter polyethylene pipe that served not only as an intake pipe from a 2000′ depth, but also as the “mooring line” for the 120′ x 35′ barge. The initial design for the barge layout, seawater intakes (cold and warm), effluent lines, and pumps was also done by Makai. Makai developed and planned the deployment scheme and participated in the at¬sea deployment. On August 2, 1979, Mini¬OTEC produced 50 kW of power and consumed 40 kW, for a net positive output of 10 kW. This was the first time that a positive output had been achieved from any OTEC facility. In 1980, the National Society of Professional Engineers awarded Mini-OTEC as being one of the ten outstanding engineering achievements in the United States that year.

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Makai has been involved in testing and evaluating pipeline materials relative to long term applications and deployment. Obtaining the maximum and safe performance from a pipeline is a key objective of any design and one that frequently requires research and testing to push pipeline materials beyond their familiar uses.

Makai has taken the pipeline deployment concepts that proved successful in actual installations and applied them to much larger pipelines. Pipelines in the range of 10′ to 12′ in diameter have been conceptually designed to be deployed quickly and economically.

The need to lower huge anchoring masses is a deployment obstacle with large pipelines. Makai has developed and tested "lightweight" anchors that simplify this deployment process.

Continuing work on warm water intakes lines has led toward the development of an easily installed pipeline hold-down system that firmly anchors the pipeline to the seafloor. Pipelines at Keahole Pt. are capable of withstanding a 50′ design wave. Such seafloor attachment systems are applicable to large and small pipelines in any service.


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