16 kilometers seem to be overly optimistic. Plugs failed at the Point 

 Pinole site despite the fact that it was totally sheltered from pre- 

 vailing winds; it faced a fetch of up to 14 kilometers. 



5. Cordgrass-Mussel Bioconstructs . 



Plugs harvested from mats of cordgrass in association with ribbed 

 mussels have not been previously tested as a bank stabilization technique. 

 However, studies by Newcombe (1941-1946) at Wachapreague , Virginia, found 

 that smooth cordgrass marshes could be established on bare mud areas by 

 heeling in plugs dug from a climax, mat formation cordgrass mussel 

 community (Fig. 11). Pestrong (1972), in his geological studies of San 

 Francisco Bay, observed that these cordgrass-mussel communities had 

 effectively riprapped many channel banks in the South Bay. 



Cordgrass-mussel bioconstructs were planted in June 1977 at Alameda 

 Creek (areas 2-6) . Data on the growth and survival of cordgrass-mussel 

 transplants are summarized in Table 5 (Newcombe, 1978). 



a. Alameda Creek (Area 2) Plantings . Alameda Creek is the high 

 erosion site, as discussed previously. The area 2 plantings were de- 

 stroyed by bank erosion by June 1978. Instead of "washing out," as the 

 plugs did in the wave breaker plots, they were undermined by erosion of 

 the surrounding substrate until they were sufficiently exposed for waves 

 to dislodge them. Before the plantings were destroyed, their growth was 

 relatively vigorous. The plugs exhibited extensive rhizomal growth by 

 December 1977 (Table 6). Many rhizomes, some of considerable length, 

 grew from the transplants but they were exposed and destroyed by sub- 

 strate erosion before developing more than a few shoots. By February 

 1978 all surviving plugs in this plot were damaged too severely for 

 further rhizomal shoot development. 



b. Alameda Creek (Areas 3 and 4) Plantings . Alameda Creek (areas 

 3 and 4) had the greatest exposure to wind waves of the study areas. 

 Winds blow onshore at these areas about 65 percent of the time with an 

 average speed of 16.4 kilometers per hour over a fetch ranging from 6 



to 27 kilometers. At area 3, a well-developed cordgrass-mussel community 

 already existed. Plugs planted in area 3 exhibited 100 percent survival 

 after 1 year. The number of stems decreased, as expected, from December 

 1977 to February 1978, and then increased again by June 1978. This fluc- 

 tuation was due to waves associated with winter storms. The changes of 

 shoot height and numbers for the cordgrass-mussel bioconstructs matched 

 those of the surrounding cordgrass so closely that it was difficult to 

 discern the bioconstruct transplants at the site after December 1977. 

 The surrounding cordgrass also made it impossible to determine rhizomal 

 shoot characteristics. The success of transplanting in this plot demon- 

 strated that any initial biological stress incurred by the transplanted 

 cordgrass had no lasting detrimental effect on plant survival and growth. 



At area 4, no vegetation existed before planting. Cordgrass-mussel 

 bioconstructs planted in this area had good survival after 1 year, but 



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