Chapter 6 



Impacts and Mitigation 



CHAPTER SUMMARY 



Wetlands are important to development activities 

 such as agriculture, forestry, port and harbor de- 

 velopment, oil and gas extraction, housing and ur- 

 ban growth, mining, and water-resource develop- 

 ment. Development activities that involve excava- 

 tion (or dredging), filling, clearing, draining, or 

 flooding of wedands generally have the most signifi- 

 cant and permanent impacts on wetlands. These 

 impacts vary from project to project, depending on 

 the scale and timing of the project, the type of 

 wedand affected, and many other variables. Direct 

 impacts associated with some development activities 

 often can be mitigated by redesigning the project 

 or modifying the construction timetable. 



The ability to restore significandy degraded wet- 

 lands to their original condition depends on the type 

 of wetland and on the degree to which it has been 



affected either by natural processes or by develop- 

 ment activities. For example, San Francisco Bay 

 wetlands that were once used for agriculture are 

 being restored by removing manmade dikes that 

 separated these wetlands from the bay. It is aJso 

 possible to create new wedands in areas that are 

 not subject to a high degree of wave action or swift 

 currents. Costs of creating new wedands in relative- 

 ly calm coastal environments range from as little 

 as $250/acre to over $6,000/acre. 



The ability to construct new wetlands should not 

 be used as sole justification for the unregulated con- 

 version of wedands to other uses: manmande wet- 

 lands do not necessarily provide the same values 

 as natural ones. In addition, it is probably not possi- 

 ble to create new wedands at the rate they have been 

 converted to other uses in the past. 



INTRODUCTION 



Generally, any wetland-development activity of 

 a significant magnitude has the potential to affect 

 wetlands adversely. This chapter identifies the ac- 

 tivities and operations that affect wetlands and 

 describes the nature of their impacts. The actual 

 impacts of an activity, however, are site and proj- 

 ect specific. In other words, an activity with major 

 impacts in one circumstance may have moderate 

 impacts in another. All major development activi- 

 ties responsible for wetland loss, including those 

 regulated under the 404 program, are included in 

 this discussion. 



The present ability to predict or monitor impacts 

 on wetlands also is evaluated in this chapter. Im- 

 pact assessment is a critical step in determining 

 what development activities to allow in wetlands 

 and how to mitigate potential impacts. The uncer- 



tainty associated with impact assessment influences 

 both the ability to safeguard wedands and the equity 

 of regulatory decisions. On the one hand, wetlands 

 require protection from project impacts that are not 

 always obvious; on the other, regulatory decisions 

 based on highly uncertain impact assessments may 

 impose unnecessary burdens on developers. 



Finally, opportunities for and limitations of 

 mitigating impacts are evaluated in this chapter. 

 Under the current regulatory program, mitigation 

 conditions are imposed on about one-third of all 

 permits processed annually; in comparison, less 

 than 3 percent of all applications are denied. This 

 suggests that the strategy of the 404 program is to 

 minimize or compensate for impacts rather than 

 prevent development. 



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