The optimum current velocity recommended for the Ocean Farm is 10 cm/sec 

 (0.2 knot). An absolute minimum sustained velocity of 4 cm/sec (0.08 knot) is recommended. 

 These recommendations are for mean water speed past the kelp plants and are tentative until 

 more thorough experiments can be accomplished. The important parameter is relative water 

 speed which can be the combined result of current, swell, internal waves, and upwelling. If 

 factors other than primary current create an adequate water flow, the site could successfully 

 be located in an area where current velocity is reduced below the levels listed above as mini- 

 mum. Some degree of water movement is necessary, however, to ensure an interchange of 

 nutrient-depleted, high-waste-concentration water with fresh water. 



At the other extreme, sustained currents of relatively high velocity can be destructive 

 to the plants or cause them to trail horizontally, thus reducing their photosynthetic capacity 

 by reducing available light. Currents above 25 cm/sec (0.5 knot) tend to cause mature M. 

 pyrifera to trail towards the horizontal, approaching the depth of their substrate (W. North, 

 personal communication). For this reason, the maximum, mean sustained relative current 

 that can be tolerated within the marine farm is taken as 25 cm/sec. 



ENGINEERING LIMITATIONS/REQUIREMENTS 



The preliminary design criteria for a moored ocean farm grid system for Phase 1 and 

 2 farms have been delineated (Ref. 17). The wind is the principal driving force behind most 

 environmental parameters of importance to structural integrity. Although the wind itself 

 has a neghgible effect on submerged substrates and kelp plants and is not considered in the 

 engineering criteria, it is the driving force for both wave height and localized currents. Be- 

 cause wind is more frequently measured than other parameters it is discussed here and in 

 more detail in the meteorology section. For design purposes, the maximum significant wave 

 height (significant height defined as average height of the 1/3 highest waves) is set at 1 1 

 meters (35 feet) (the extreme wave height is set at 19 meters) and the significant period set 

 at 12.6 seconds. The design operational current is an omnidirectional 0.5 m/sec, with a 

 maximal total design current of 1 .5 m/sec. Above 1 .5 m/sec relative current the kelp plants 

 begin to come apart (W. North, personal communication). These engineering criteria were 

 defined after using a single cable dynamic load model with the worst case defined as the 

 substrate at a 15-meter depth experiencing 1 1 -meter waves with the peak load approximate- 

 ly 2.8 m/sec (effect of 0.5-m/sec current plus action of waves) (Ref. 17). In order to avoid 

 maximum wave heights and currents as delineated above and in Table 1, areas considered for 

 locating the marine farm should be as free as possible of gale-force winds (greater than 17 

 m/sec) and should be positioned to avoid (minimize probability of occurrence) storm-force 

 winds (25 m/sec or greater). 



At present, wave-powered pumps appear to be the most promising means of delivering 

 high-nutrient water to the farms (Ref. 18). First estimates indicated that a minimum mean 

 wave height of 1 meter is required to pump sufficient water to maintain desired nutrient 

 levels. A wave height of 2 to 2.5 meters is preferred to supply enough energy to upwell the 

 deep water needed to fertilize one acre (4000 square meters) of ocean farm with one pump 

 utilizing a 3-meter-diameter float (Ref. 18). 



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