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The data can be displayed in either feet or meters. Click the Submit button to apply the selected unit to the table of values for tidal datums. The heading of the table will reflect the units currently applied to the table. Link to other types of data for the same station using the links on the top. Links are highlighted only for data types that are available for the station.
Geodetic datum relationships to tidal datums are established at tide stations byconnecting tidal bench mark networks to the National Spatial ReferenceSystem (NSRS) maintained by NGS. There are two survey procedures usedto make this connection. The first is to connect the tidal bench markswith traditional differential levels to nearby geodetic bench markswith known geodetic elevations. The second is to occupy the tidalbench marks using a static GPS survey to determine the geodeticelevations of the bench marks directly. In all cases it is advised tomake the connections to more than one bench mark, preferably to threemarks, in order to confirm the connection and identify unstable benchmarks. The elevation relationship between geodetic datums andtidal datums should not be extrapolated away from a particular locationwithout correction or interpolation as the relationships vary withparameters such as variations in range of tide, bathymetry, topography,geoid variations, and vertical land movement. Any interpolation shouldbe done carefully, and where possible guided by the use of the National Ocean ServiceVDatum tool which can be obtained at:
Humanity may never get to witness that from Earth, but perhaps our relocated descendents will someday gaze up at the tidally locked Moon of another planet. So tonight, when you see the Man in the Moon gazing down at you fondly, remember the processes that keep him there, and think about the other planets in our solar system and beyond where different moon faces beam endlessly down on strange terrains.
The gravitational pull of the moon and sun along with the rotation of the earth create tides in the oceans. In some places, tides cause water levels near the shore to rise and fall up to 40 feet. People in Europe harnessed this movement of water to operate grain mills more than a 1,000 years ago. Today, there are tidal energy systems that generate electricity. Producing tidal energy economically requires a tidal range of at least 10 feet.
The United States does not have any commercially operating tidal energy power plants, although several demonstrations projects are in various stages of development. Two places in the United States with potential for tidal power are the Cook Inlet of Alaska, which has the second-highest tidal range in North America, and several places in Maine.
One type of tidal energy system uses a structure similar to a dam called a barrage. The barrage is installed across an inlet of an ocean bay or lagoon that forms a tidal basin. Sluice gates on the barrage control water levels and flow rates to allow the tidal basin to fill on the incoming high tides and to empty through an electricity turbine system on the outgoing ebb tide. A two-way tidal power system generates electricity from both the incoming and outgoing tides.
A potential disadvantage of tidal power is the effect a tidal station can have on plants and animals in estuaries of the tidal basin. Tidal barrages can change the tidal level in the basin and increase turbidity (the amount of matter in suspension in the water). They can also affect navigation and recreation.
Several tidal power barrages operate around the world. The Sihwa Lake Tidal Power Station in South Korea has the largest electricity generation capacity at 254 megawatts (MW). The oldest and second-largest operating tidal power plant is in La Rance, France, with 240 MW of electricity generation capacity. The next largest tidal power plant is in Annapolis Royal in Nova Scotia, Canada, with 20 MW of electricity generation capacity. China, Russia, and South Korea all have smaller tidal power plants.
Tidal turbines are similar to wind turbines in that they have blades that turn a rotor to power a generator. They can be placed on the sea floor where there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines have to be much sturdier and heavier than wind turbines. Tidal turbines are more expensive to build than wind turbines but can capture more energy with the same size blades.There are several demonstration tidal energy projects in various stages of development in the United states including:Roosevelt Island Tidal Energy (RITE) Project Pilot in the East River of New YorkWestern Passage Tidal Energy Project in MaineCobscook Bay Tidal Energy Project in Maine
A tidal fence is a type of tidal power system that has vertical axis turbines mounted in a fence or row placed on the sea bed, similar to tidal turbines. Water passing through the turbines generates electricity. As of the end of 2020, no tidal fence projects were operating in the United States.
A tidal stream crossing (tidal crossing) is a bridge or culvert that conveys tidal flow below a traveled way, such as a road, pedestrian path, or railroad. When properly designed and maintained, tidal crossings can balance the needs of people and the environment by providing a functional, reliable and safe transportation network that supports the continuous movement of people, goods, and services across coastal communities while allowing adequate tidal flow to maintain healthy tidal marshes.
In 2018, the NHDES Coastal Program and its partners assessed all known tidal crossings in New Hampshire's 17 coastal communities in accordance with the New Hampshire Tidal Crossing Assessment Protocol. Tidal crossing assessment data were used to rank and prioritize sites based on structure condition, flood risk and ecosystem health.
The Resilient Tidal Crossings NH Project was designed to better enable community officials and road managers to enact the strategic repair/replacement of tidal crossing infrastructure and to identify high priority restoration and conservation opportunities at tidal crossing sites.
Objectives: To evaluate the association between interleukin-6, interleukin-8, and interleukin-10 and clinical outcomes including mortality in patients with acute lung injury and to determine whether lower tidal volume ventilation was associated with a decrease in plasma cytokines in patients with acute lung injury.
Patients: The study included 861 patients enrolled in the National Heart, Lung and Blood Institute Acute Respiratory Distress Syndrome Clinical Network trial of lower tidal volumes compared with traditional tidal volumes for acute lung injury.
Conclusions: In patients with acute lung injury, plasma interleukin-6 and interleukin-8 levels are associated with morbidity and mortality. The severity of inflammation varies with clinical risk factor, suggesting that clinical risk factor should be considered when both developing and testing therapeutic interventions. Low tidal volume ventilation is associated with a more rapid attenuation of the inflammatory response.
BarrageAnother type of tidal energy generator uses a large dam called a barrage. With a barrage, water can spill over the top or through turbines in the dam because the dam is low. Barrages can be constructed across tidal rivers, bays, and estuaries.Turbines inside the barrage harness the power of tides the same way a river dam harnesses the power of a river. The barrage gates are open as the tide rises. At high tide, the barrage gates close, creating a pool, or tidal lagoon. The water is then released through the barrage's turbines, creating energy at a rate that can be controlled by engineers.The environmental impact of a barrage system can be quite significant. The land in the tidal range is completely disrupted. The change in water level in the tidal lagoon might harm plant and animal life. The salinity inside the tidal lagoon lowers, which changes the organisms that are able to live there. As with dams across rivers, fish are blocked into or out of the tidal lagoon. Turbines move quickly in barrages, and marine animals can be caught in the blades. With their food source limited, birds might find different places to migrate.A barrage is a much more expensive tidal energy generator than a single turbine. Although there are no fuel costs, barrages involve more construction and more machines. Unlike single turbines, barrages also require constant supervision to adjust power output.The tidal power plant at the Rance River estuary in Brittany, France, uses a barrage. It was built in 1966 and is still functioning. The plant uses two sources of energy: tidal energy from the English Channel and river current energy from the Rance River. The barrage has led to an increased level of silt in the habitat. Native aquatic plants suffocate in silt, and a flatfish called plaice is now extinct in the area. Other organisms, such as cuttlefish, a relative of squids, now thrive in the Rance estuary. Cuttlefish prefer cloudy, silty ecosystems.Tidal LagoonThe final type of tidal energy generator involves the construction of tidal lagoons. A tidal lagoon is a body of ocean water that is partly enclosed by a natural or manmade barrier. Tidal lagoons might also be estuaries and have freshwater emptying into them.A tidal energy generator using tidal lagoons would function much like a barrage. Unlike barrages, however, tidal lagoons can be constructed along the natural coastline. A tidal lagoon power plant could also generate continuous power. The turbines work as the lagoon is filling and emptying.The environmental impact of tidal lagoons is minimal. The lagoons can be constructed with natural materials like rock. They would appear as a low breakwater (sea wall) at low tide, and be submerged at high tide. Animals could swim around the structure, and smaller organisms could swim inside it. Large predators like sharks would not be able to penetrate the lagoon, so smaller fish would probably thrive. Birds would likely flock to the area.But the energy output from generators using tidal lagoons is likely to be low. There are no functioning examples yet. China is constructing a tidal lagoon power plant at the Yalu River, near its border with North Korea. A private company is also planning a small tidal lagoon power plant in Swansea Bay, Wales. 59ce067264