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The first of its kind, the tidal pump system will utilize almost two miles of underground piping, two ocean outfalls located 30 feet below sea level, and an innovative diffuser system configured to dissipate velocity during the exchange.

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Engineers explored alignments, configurations, materials and construction methods to further define the tidal pump concept, its potential cost and implementation schedule. The team proposed a fully-closed system, similar to a low pressure water distribution system. To improve flow integrity and reduce head loss, pipes will remain full at all times, while the tidal head provides the pressure to move ocean and canal water through the system.

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Project Description

Now known as the best little beach in Delaware, more than 50 years ago the tiny oceanfront town of South Bethany, Delaware, faced a major crisis-its plans for growth were stymied by the limited number of waterfront home sites available to attract more residents and tourists. Construction began on a five- mile system of dead-end canals to create residential waterfront property west of Route 1.

Like many canal systems worldwide, South Bethany's canals are now plagued with severe water quality problems. Poor circulation, sediment accumulation, low oxygen levels, excessive nutrients, and pollution have led to declining shellfish communities, pungent and harmful algae blooms, and fish kills.

South Bethany's canal system outlets to the Atlantic through inlets that are more than 10 miles away. This great distance is the root cause of the poor circulation in the canals, but it may also be the cure. The distance causes the tides in the canals to be opposite that of the ocean.

Based on a concept developed by Lloyd Hughes, a former councilman and retired engineer, the town of South Bethany commissioned Oceaneering International Inc. and KCI Technologies Inc. to evaluate the feasibility and develop preliminary designs for a tidal pump to circulate the water in the canals using only tidal differential to power the system.

Engineers explored alignments, configurations, materials and construction methods to further define the tidal pump concept, its potential cost and implementation schedule. Effective hydraulic analysis posed a crucial design challenge because of the low head differential and resulting low operating velocities. The tidal differential between the canals and the Atlantic averages only two feet. To deliver the required circulation through the system, each omponent had to be optimized for flow performance by reducing friction wherever possible.

The team proposed a fully-closed system, similar to a low pressure water distribution system. To improve flow integrity and reduce head loss, pipes will remain full at all times, while the tidal head provides the pressure to move ocean and canal water through the system. The concept of a fully-closed tidal pump, and its resemblance to a water distribution system, allowed application of water distribution design and modeling techniques.

Engineers performed hydraulic analyses using WaterCAD, the industry- wide definitive model for complex pressurized pipe networks, to identify the most advantageous alignment and component arrangement and determine flows at the canal and ocean inlet/outfalls in combination with pipe roughness, pipe age and marine growth.

Another critical design challenge was estimating the effect that the harsh marine environment might have during construction and operation. Environmental factors that may affect the tidal pump include ocean currents and waves, sedimentation of sand and other debris, corrosivity of seawater, depth of the piping, and fouling from marine organisms.

Data on wave force, scour, ocean depth, and storm and wave frequency were compiled and evaluated for comparison with potential system alternatives. Engineers identified the surf-zone as the most extreme environmental component of the project, and designed pipes buried below the level of potential beach erosion to prevent possible exposure.

The team also researched and evaluated expected marine growth in the system. Accurate estimates of marine growth and their effect on velocity were keys to system viability because barnacles and vegetative cover could reduce flow in the pipes and cause operational problems. Marine growth attaches more effectively in low flowing conditions and since the pipe is inundated, the entire pipe surface area is exposed to growth. The team conducted a hydraulic analysis to evaluate possible capacity reductions in system capacity resulting from marine fouling and prepared operational cost estimates and schedules for cleaning and maintenance.

Tidal power represents a largely untapped, completely renewable energy source. Careful consideration was given to establish how much power the tide would deliver to the system. Engineers determined how much energy in the form of hydraulic head would be available during an average day and compared this to the energy required by a conventionally powered pumping system to provide the same system flow. The results of this evaluation established how much conventionally generated energy would be conserved by using the tides, how much potential carbon dioxide emissions would be removed from the atmosphere by using the system, and whether the town could obtain renewable resource grant-based funding for construction. Detailed calculations established that using tidal power instead of a conventional pump would save approximately 7,900 Kilowatt-hours per year, almost the same power usage as a typical American household, and remove nearly 7,200 pounds of carbon dioxide emissions over the same time.

Although the conventionally generated power savings of the system is modest, it represents a move towards sustainable, fully renewable sources of energy wherever the opportunity exists. Changes at incremental levels, like the South Bethany tidal pump project, can add up and provide renewable power for the future, reduce the need for non-sustainable generated power and reduce greenhouse gas emissions.

The first of its kind, the tidal pump system will utilize almost two miles of underground piping, two ocean outfalls located 30 feet below sea level, and an innovative diffuser system configured to dissipate velocity during the exchange. The tidal pump will completely circulate the water in the canals in less than 30 days, providing immediate improvements in water quality, which had become so degraded that residents frequently complained of odors and algae blooms, and swimming had been restricted for health reasons. The system will also help keep these water bodies productive in terms of recreational opportunities and fish production.

Pleased with the results of the preliminary design, South Bethany is currently in the process of identifying grant funding sources and preparing a contract to move forward with the next phase of project development.

Once constructed, the tidal pump will serve as a model for other communities facing similar water quality problems and for municipalities considering innovative sustainable projects. This ground-breaking concept represents a major step toward incorporating sustainability into public works projects and will stand as an example to other communities and municipalities facing similar challenges that solutions can be both effective and sustainable.