Table 1. Waves heights produced by three vessels 

 (after Sorensen, 1967).^ 





Displacement 

 (kn) (ton) 



Speed 

 (m/s) 



Distance from 

 30 m 



sailing line 

 150 m 



Vessel type 



Max . wave 



height 



(m) 



Max. wave 



height 



(m) 



Cabin cruiser 



27 



3 



3.1 



0.2 



0.1 







5.1 



0.4 



0.2 



Reconverted 

 air-sea 

 rescue vessel 



310 



35 



3.1 

 5.1 



0.1 

 0.4 



0.2 



Fireboat 



(reconverted 



tug) 



3050 



343 



3.1 

 5.1 



0.1 

 0.5 



0.1 

 0.3 



^ Water depth was approximately 12 meters. 



g. Tidal Currents . Planting failures for otherwise favorable sites often 

 result from the action of tidal currents. Marsh plantings as well as estab- 

 lished marshes are particularly vulnerable to undermining by strong tidal 

 currents. The location and potential migration of tidal channels in the 

 vicinity of prospective plantings should be considered. 



h. Discussion. Planting will be successful along some shorelines with 

 unfavorable characteristics just as plantings along some shorelines with 

 favorable characteristics will fail. Consequently, it is advisable to examine 

 prospective sites carefully for unusual features that may affect planting fea- 

 sibility. For example, some sites are subjected to elevated water levels 

 (wind setup) during most periods of strong onshore winds. It has been possi- 

 ble to establish bands of marsh within the inter tidal zone, which is below the 

 most violent wave action, on some of these shores. Here erosion may continue 

 for some time above and behind the planted marsh but the eroding sediments are 

 trapped by the marsh, thereby widening and strengthening it. As this contin- 

 ues wave attenuation will increase and the eroding zone will eventually become 

 either stabilized naturally or ready for planting. The ipvesenoe of patahee of 

 healthy maveh on ov near the site is an indieatian that the site is ptantable. 



Achieving successful erosion control with vegetation often requires both 

 perseverance and patience. First, severe storms during establishment may 

 cause temporary setbacks, even on highly promising sites, but these setbacks 

 should not discourage the planter. More formidable and expensive coastal 

 engineering structures are often damaged by the untimely occurrence of severe 

 storms. In most cases storm damage in plantings can be repaired by replanting 

 the damaged areas. Second, a planting will require 1 to 3 years to achieve 

 stability. A rapid establishment on difficult sites should not be expected. 



1. Summary . No single parameter or list of parameters can accurately 

 predict the success or failure of a planting. It is, rather, a question of 

 odds and probabilities. Under the best conditions the success of a planting 



37 



