to a height less than that sufficient to prevent overtopping. Such partial 

 barriers need not even extend above low water. Since construction and 

 maintenance requirements for a submerged breakwater are economically less 

 than those for a high breakwater, such structures should be seriously 

 considered when a partial barrier is adequate. Provisions should be 

 made to indicate the location of the submerged structure so that it is 

 not a hazard to navigation. 



SaO ENVIRONMENTAL CONSIDERATIONS 



Shore protection measures by their very nature are planned to 

 result in some modification of the physical environment. However, 

 thorough planning and design require that the full impact of that modifi- 

 cation on the ecological and aesthetic aspects of the environment be 

 fully considered and understood. If there is potential for significant 

 adverse effect to any environmental feature, design analysis of a shore 

 improvement project should include alternatives for avoiding or mitigat- 

 ing that adverse effect. Therefore, design analysis should include a 

 multidiscipline appraisal of the total impact of the project, to include 

 environmental quality as well as economic benefits. The necessity for 

 this appraisal at the planning and design stage is apparent and required 

 by law. If there is a probability for conflict between planned construc- 

 tion and environmental quality, a final decision by appropriate authority 

 based upon social, technical, and economic analysis will be required. 



In recent years the question of total environmental quality reached 

 top levels of public concern. Published technical information on this 

 question is scattered through many disciplines, and the lack of quantifi- 

 able base-line data precludes reliable quantitative forecasting of most 

 environmental and ecological changes resulting from manmade structures. 

 Two recent works addressed specifically to this question are Rounsefell 



(1972) on the ecological effects of offshore construction and Thompson 



(1973) on ecological effects of offshore dredging and beach nourishment. 

 Both papers include state-of-the-art evaluations from the ecologist's 

 perspective, and extensive bibliographies, with some entries annotated. 

 Both describe and discuss direct and indirect effects of several cate- 

 gories of coastal protective works, and discuss procedures for evaluat- 

 ing those effects. Both agree that it is of utmost importance to obtain 

 necessary data on probable environmental impact of proposed construction 

 at an early stage of the project planning. Accurate assessment of pre- 

 project environment is essential, not only for initial planning and design, 

 but also for later design modification or alternatives that could bear on 

 either mitigation of environmental change or enhancement of other aspects 

 of the environment. The works of Rounsefell and Thompson suggest that the 

 methods of shore protection discussed in this manual would generally not 

 result in long-term undesirable ecological changes for individual projects. 

 However, this opinion is qualified to the extent that cumulative effects 



of numerous works of certain types could conceivably result in some deteri- 

 mental long-term changes. A further requirement is recognized for addi- 

 tional base-line data and knowledge of the quantitative ecological -physical 

 relationships. This information can be developed by monitoring before-, 

 during-, and after-construction effects on coastal projects. 



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