Falkland Current—A South Atlantic Ocean current setting northeastward along the east coast of Argentina. first reduction—A method of determining high and low water heights, time intervals, and ranges from an arithmetic mean without adjustment to a long-term series through comparison of simultaneous observations.

float we l l—A stilling well in which the float of a float-actuated water level gauge operates. See stilling well.

flood axis—The average set of the tidal current at strength of flood.

flood current (flood)—The movement of a tidal current toward the shore or up a tidal river or estuary. In the mixed type of reversing current, the terms greater flood and lesser flood are applied respectively to the two flood currents of greater and lesser speed of each day. The expression maximum flood is applicable to any flood current at the time of greatest speed. See flood strength.

flood interval—The interval between the transit of the Moon over the meridian of a place and the time of the following flood strength.

flood strength (strength of flood)—Phase of the flood tidal current at the time of maximum speed. Also, the speed at this time. See strength of current.

Florida Current—A North Atlantic Ocean current setting northward along the south-east coast of the United States. A segment of the Gulf Stream System, the Florida Current extends from the Straits of Florida to the region off Cape Hatteras.

flow—The British equivalent of the United States total current. Flow is the combination of tidal stream and current.

flushing time—The time required to remove or reduce (to a permissible concentration) any dissolved or suspended contaminant in an estuary or harbor.

forced wave—A wave generated and maintained by a continuous force.

fortnight—The time elasped between the new and full moons. Half a synodical month or 14.765,294 days. See synodical month.

Fourier series—A series proposed by the French mathematician Fourier about the year 1807. The series involves the sines and cosines of whole multiples of a varying angle and is usually written in the following form:

y =AB + A1 sin x + A2 sin 2x + A3 sin 3x + ... B1 cos x + B2

cos 2x + B3 cos 3x + ...

By taking a sufficient number of terms the series may be assumed to represent any periodic function of x.

free wave—A wave that continues to exist after the generating force has ceased to act. See gravity wave.