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SUBMARINE CANYONS 
Description of Submarine Canyons 
Submarine canyons are sea-floor valleys that begin as notches in the conti- 
nental shelf from which they cut as troughs into the continental slope and 
terminate in fans of sediment on the lower slope or continental rise. They 
are viewed by some marine scientists as being ideal locations for disposal 
of polluted dredged materials, that is to say, those appropriate for spe- 
cial care measures. It is emphasized, however, that not all canyons are 
equally appropriate; hence decisions as to their use should be made on a 
canyon by canyon basis. 
Suitability of Submarine Canyons as Polluted Material Dumpsites 
There are several factors favoring use of submarine canyons for disposal of 
dredged material. Foremost among these is the fact that they are usually 
dynamic features that normally act as conduits for the transport of sedi- 
ment from the continental shelf to deep parts of the slope or abyssal 
plain. Menard (1955) realized this after he demonstrated that the quanti- 
ties of sediment in subsea fans and aprons at canyon mouths far exceeded 
the volume of rock removed during erosion of the canyons. Anothere favor- 
able factor is that the amount of life on the floor of some active canyons 
is quite sparse (Shepard and Dill, 1966). 
Certain canyons, however, may be favored migration routes for fish and some 
shellfish such as lobsters may live at and around the canyon mouths. Can- 
yons serving these purposes probably should not be used for disposal. 
Some concern has also been expressed that upcanyon currents might trans- 
port material back up onto the continental shelf. Currents in most cases 
probably do alternate upcanyon and downcanyon with periods ranging from 
less than one hour to near semidiurnal tidal periods (Shepard and Marshall, 
