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A trench which is below the foundation base line of a dam or other structure and is filled with an impervious material, such as clay or concrete, to form a watertight barrier.

Related Terms


  1. An undesirable action occurring during loose-drum spooling in which a layer of wire rope spreads apart and forms 2. A thin, watertight wall of clay or concrete built up from a cutoff trench cutoff wall cutting in cutting-off machine grooves in which the next layer travels.


(TE): This is obtained by adding to the draught moulded the distance between the moulded base line and a line touching the lowest point of the underside of the keel. This line is continued to the FP and AP, where it is used as the datum for the sets of draught marks.


(D): The vertical distance between the moulded base line and the top of the beams of the uppermost continuous deck measured at the side amidships.


Any apparatus designed for use in measuring with accuracy and precision the length of a base line in triangulation, or the length of a line in firstor second-order traverse.


A technique for making winds-aloft observations in which two theodolites located at either end of a base line follow the ascent of a pilot balloon; synchronous measurements of the elevation and azimuth angles of the balloon, taken at periodic intervals, permit computation of the wind vector as a function of height.


(T): The draught measured to any water-line, either forward or aft, using the moulded base line as a datum.


A system, in surveying, of quadrilaterals and triangles that include and are quite close to a base line in a triangulation system.


  1. The reference used to position limits of the territorial sea and the contiguous zone.
  2. One side of a series of connected survey triangles, the length of which is measured with prescribed accuracy and precision, and from which the lengths of the other triangle sides are obtained by computation. Important factors in the accuracy and precision of base measurements are the use of standardized invar tapes, controlled conditions of support and tension, and corrections for temperatures, inclination, and alignment. Base lines in triangulation are classified according to the character of the work they are intended to control, and the instruments and methods used in their measurement are such that prescribed probable errors for each class are not exceeded. These probable errors, expressed in terms of the lengths, are as follows: first order, 1 part in 1,000,000; second order, 1 part in 500,000; and third order, 1 part in 250,000.
  3. The line along the surface of the earth between two radio navigation stations operating in conjunction for the determination of a line of position.


For application to the provisions of the Marine Protection, Research, and Sanctuaries Act of 1972, those waters of the open sea lying seaward of the base line from which the territorial sea is measured.


An exceptionally dense cloud of great vertical development, occurring either as an isolated cloud or one of a line or wall of clouds with separated upper portions. These clouds appear as mountains or huge towers, at least a part of the upper portions of which are usually smooth, fibrous, striated, and almost flattened. This part often spreads out in the form of an anvil or plume. Under the base of cumulonimbus, which often is very dark, there frequently exists virga, precipitation, and low, ragged clouds, either merged with it or not. Its precipitation is often heavy and always of a showery nature. The usual occurrence of lightning and thunder within or from this cloud leads to its being popularly called THUNDERCLOUD and THUNDERHEAD. The latter term usually refers to only the upper portion of the cloud.

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