English

Nonfloating structures used for concealing waterfowl hunters. They usually consist of a wooden framework covered with brush. They are essentially unreported to any charting authority when built. They are unlighted and often constructed in navigable water without regard to the possible hazard they pose, especially to the small craft operator. Many are substantial structures built on piles. Even after they are eventually reduced to ruins the pilings may persist for years.

A LAYER in the OCEAN or ATMOSPHERE where REFRACTION and, probably, REFLECTION result in the trapping and propagation within the LAYER of SOUND WAVES or ELECTROMAGNETIC WAVES.

Notification of a given action for general information through appropriate authorities within a reasonable amount of time in a suitable manner. Used in the context of the United Nations' Law of the Sea Convention.

A sea area where dredged material or other potentially more harmful material e.g. explosives, chemical waste, is deliberately deposited. See also SPOIL GROUND.

Duration of flood is the interval of time in which a tidal current is flooding, and the duration of ebb is the interval in which it is ebbing; these intervals being reckoned from the middle of the intervening slack waters or minimum currents. Together they cover, on an average, a period of 12.42 hours for a semidiurnal tidal current or a period of 24.84 hours for a diurnal current. In a normal semidiurnal tidal current, the duration of flood and duration of ebb will each be approximately equal to 6.21 hours, but the times may be modified greatly by the presence of a non-tidal flow. In a river the duration of ebb is usually longer than the duration of flood because of the fresh water discharge, especially during the spring months when snow and ice melt are the predominant influences.

Duration of rise is the interval from low water to high water, and duration of fall is the interval from high water to low water. Together they cover, on an average, a period of 12.42 hours for a semidiurnal tide or a period of 24.84 hours for a diurnal tide. In a normal semidiurnal tide, the duration of rise and duration of fall will each be approximately equal to 6.21 hours, but in shallow waters and in rivers there is a tendency for a decrease in the duration of rise and a corresponding increase in the duration of fall.

Any substance com­minuted or pulverized, especially EARTH or other solid matter in a minute and fine state of subdivision, so that the particles are small and light enough to be easily raised and carried in a CLOUD by the WIND.

Ensemble of particles of DUST or SAND energetically lifted to great HEIGHTS by a strong and turbulent WIND. Also called sandstorm. Also written as two words.

Manoeuvring of a vessel to keep a position relative to a seabed feature; normally underwater acoustic position fixing systems are used for this purpose.