Currents 



Phase 1 and 2 farms will probably be moored and therefore the surface currents 

 could be a major contributor to the water movement around the plants. Current speeds 

 greater than the minimum (4 cm/sec) requirements are observed almost continually through- 

 out the eastern Pacific survey area. Current speeds less than the optimal (10 cm/sec) can 

 occur in the north Pacific gyral area, 25° to 45°N and 130° to 160°W. and in the southern 

 extreme of the CaUfornia Current, 20° to 25°N. Because of the tendency of the plants to 

 deflect toward the horizontal in currents of greater than 25 cm/sec, sustained currents of 

 greater than this speed may have to be avoided, at least for the relatively smaU Phase 1 and 2 

 moored systems.* Areas where currents greater than 25 cm/sec are observed for significant 

 periods of time, include the northern Davidson Current during the winter and the Alaska 

 Current to the north. Also, the North Equatorial Current, the Equatorial Countercurrent, 

 and the South Equatorial Currents exhibit speeds greater than 25 cm/sec much of the time 

 between 5°S and 15°N from the coast to the western edge of the survey area. 



Areas which meet the optimal current ranges (10 to 25 cm/sec) include the westward- 

 moving North Pacific and Subarctic Currents, 35° to 42°N; most of the Cahfornia Current 

 region south of 40°N; the northern portion of the North Equatorial Current region from the 

 coast westward between 15° and 20°N; and the South and Central American coastal areas 

 from the equator to central Mexico (20°N). 



With the advent of floating OFEF's, current velocities above 25 cm/sec may become 

 less restrictive because the farms can float with the currents, thus reducing the relative water 

 motion. In floating farms, the importance of wind mixing, internal waves, and upwelling 

 velocity is increased while the importance of surface current velocity is decreased in relation 

 to nutrient uptake rates. However, the energy requirements and engineering limitations for 

 station-keeping must be considered as well. 



ENGINEERING CRITERIA 



Currents 



Although current engineering limitations are not yet well defined, design require- 

 ments which meet certain minimal environmental forces will have to be met. A 50-cm/sec 

 operational current is assumed for developmental design of the substrate structure (Ref. 17). 

 A 1 .5-m/sec sustained current is the initial engineering design limitation value. Both the 

 operational and design currents are above the biological sustained current limitation of 25 

 cm/sec. In terms of engineering current limitations, the only areas which have sustained cur- 

 rents above 50 cm/sec are the South Equatorial Current and the northeastern portion of the 

 survey area near Vancouver Island (Fig. 7). Currents of 100 cm/sec are observed in the 

 California and Davidson Currents under extreme conditions (Figs. 5 and 6, these measure- 

 ments are from ship drift and may be somewhat elevated). Storm-generated currents may, 

 however, become highly important in terms of plant and structural survival (see Appendix E). 



*Ambient currents will probably not penetrate far into large OFEF's, see Ref. 16. 



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