MINE SCOUR 



Some effects of current-borne 

 sediments and bottom erosion on objects 

 on the sea floor have been determined 

 through the use of plaster- filled mine 

 cases. One case was placed on the 

 bottom 8 feet from the tower and oriented 

 in an east-west direction. Later, another 

 case was placed on the bottom and oriented 

 north- south. 



Continued observation by television 

 and scuba disclosed any movement or 

 burial of the mines. For the mine with 

 the north- south oriented position the on- 

 shore, off-shore surge was restricted 

 around the obstruction. An anaerobic 

 area developed on the sea floor, with 

 worm tubes projecting from the black 

 subsurface sediment. 



WHITE SEA URCHIN 

 Hytecbinus anamesus 



HEART URCHIN 

 Lovenia cordiformis 



neasure- 



Divers made repeated visual inspections and 

 ments of the environment around the mines. (A) During 

 winter, large sand ripples were observed moving 

 shoreward past the mine cases. Ripple crests tended 

 to orient parallel to the north-south mine case and to 

 incorporate the case within the ripple symmetry. 



(B) Initially, the white cases were coded with 

 stripes. Within 2 months the epoxy paint became 

 fouled with algae and small balinoid barnacles. 



(C) The small, white sea urchin, Hytecbinus ana- 

 mesus, migrated periodically through the area and 

 covered the cases for several days each time. Spiny 

 sand star, Astropecten armatus, attached to the 

 casings. The heart urchin, Lovenia cordiformis, was 

 found burrowing and feeding in adjacent sand ripples. 



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