With respect to the stability of the structure, water currents are the 

 most important physical oceanographic measurement. It is necessary to 

 monitor currents because of the possible effects of the forces associated with 

 currents on scour (erosion) and fill of sediments and on the contributing effect 

 of currents on overturning moments, which directly influence the stress distri- 

 bution pattern on the foundation supporting medium. In general, scour and 

 fill will not be much of a problem in the deep-ocean areas because of the 

 relatively small current magnitudes that will be encountered there. For 

 example, the average current of 0.1 knot (=»5 cm/sec) reported for one of 

 NCEL's STU sites would have a negligible effect on scour, as is shown in 

 Figure 14 (after Hjulstrom 26 ). The effect of this current on the overturning 

 moments of the structure, however, could be very significant, depending on 

 structure characteristics. Thus, the magnitude and direction of the predomi- 

 nant currents will have to be evaluated using instruments listed in the next 

 section. 



The biological oceanographic parameters that should be assessed in 

 the detail survey phase are those responsible for visibility, fouling and bio- 

 deterioration of engineering materials. Since the procedures to evaluate these 

 quantities are not well established, it is difficult to generalize on the technique 

 for site survey for all water depth locations. Presently, the techniques used to 

 assess these effects include water sampling, trawling, and exposure of material 

 specimens to the biological environment. It is believed that more rapid tech- 

 niques could be developed that could be applied to site surveys. Research 9 ' 15 

 in this area, however, is being conducted to determine those biological elements 

 which are responsible for fouling and biodeterioration. The results of this 

 research could lead to the techniques that could be used to evaluate the biolog- 

 ical characteristics of each site in detail surveys. 



Biological effects resulting from animal behavior are beyond the scope 

 of this report. These effects, however, may be very significant to seaf loor 

 structures and their servicing vehicles. One example of unpredictable animal 

 behavior is the well-publicized encounter between a 200-pound swordfish 

 and the submersible Alvin at a depth of 1 ,809 feet. 27 Fortunately, in this 

 encounter none of the submersible occupants were injured and the submersible 

 was not damaged. Another incident involving a swordfish is described in 

 Reference 28. In this instance a 300 pounder attacked a polypropylene rope 

 at a depth of 1 ,000 feet and became trapped with its bill wedged between the 

 strands of this rope. If this rope had been an umbilical power supply line to 

 a manned bottom structure, as an example, the effects could have been 

 disastrous. Other marine animals such as whales, sharks, and squid may have 

 caused damages to lines and cables. 28 



26 



