The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Document type:: Monograph

Structure type:: Chapter

Title:: Part IV. Engineering geology

Collection:: Economics Books

CHAPTER XX COAST DEFENCE, COASTAL WORKS, AND RECLAMATION Waves AND WavE Action—The remorseless attack of the sea has devoured wide tracts of coastland by marine abrasion, which is mainly the work of the waves. Their power de- pends on their size and speed. The length of a wave is the distance from crest to crest; the height is the difference in level between the crest and the bottom of the adjacent trough ; the amplitude is the height of the crest above the average level of the water. A wave appears to be an ad- vancing ridge, but that aspect is often as delusive as with the waves that sweep across a wheatfield as the stems sway before the wind. In waves of oscillation the particles of water revolve around a stationary point, and do not move forward; in waves of translation the particles ‘advance as well as revolve. Waves of oscillation occur in the open sea, where the depth of water is greater than the length of the wave. Where the depth is the less, the movement on the lower side is retarded by friction with the floor, and the particles move forward in the upper part of the circuit further than they go back in the lower part, and the water advances as a wave of translation. It has been objected, as by B. Cunningham (Harbour Engineering, 1918, p. 164), that in practice the distinction between waves of oscillation and of translation is artificial, as all sea waves cause some advance of the water. When the wave reaches shallow water the crest advances more rapidly than the base, and the front is fed with water more slowly than the back ; hence the wave curls over, and falls as a breaker. Waves on a beach are waves of translation; and the backward and forward move- ment gives the water its power of attack. The greatest oscillatory waves are in the Southern Ocean 238

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