ANALYSIS OF POTENTIAL IMPACTS AND MITIGATING MEASURES 



In the following section, potential impacts of the proposed Kootenai 

 falls project on the wildlife resource are discussed, along with possible 

 means of mitigating these impacts and the overall potential effectiveness 

 of mitigation. 



Potential impacts are described in terms of their ultimate effect on 

 population size and/or the carrying capacity of the environment (that is, 

 the optimum number of animals which the environment can support over a long 

 period of time). In this sense, an adverse or negative impact may be de- 

 fined as an environmental change which (1) temporarily reduces population 

 size below carrying capacity, (2) increases population size above carrying 

 capacity, or (3) reduces an area's carrying capacity. Similarly, a bene- 

 ficial or positive impact is a change which (1) restores a depleted or 

 oversize population to carrying capacity, or (2) increases an area's carry- 

 ing capacity. For the purposes of this report, potential impacts were 

 grouped according to the four primary mechanisms by which populations or 

 carrying capacity may be affected: (1) habitat alteration, (2) displacement, 

 (3) changes in mortality or natality rates, and (4) physiological stress. 

 The relationships among these mechanisms of impact are complex, but this 

 categorization is nevertheless useful for purposes of impact analysis. 



The overall significance of an impact may be viewed from either a social 

 or a biological perspective (Sharma et al . 1975). Social significance is 

 dependent upon the degree to which a given impact affects the public's 

 sensibilities or system of values; thus, while destruction of a brood of 

 ducklings may not be biologically significant, it may outrage people and 

 assume a social significance that cannot be ignored. Biological significance 

 is best thought of in terms of measurable, long-term changes in carrying 

 capacity. Thus, if 100 tree squirrels should be destroyed, the impact to 

 the totsl population would be short-term (lasting a few years at most) and 

 hence not significant (s'nsu Sharma et al . 1975) -- the population would 

 recover relatively Cuickly, and carrying capacity would not be affected. 

 If ten osprey or fi\e bighorn sheep were destroyed, the impact would be 

 more long-lasting and hence more significant, since these species are rela- 

 tively scarce and have lower recovery rates, but carrying capacity would 

 still not be affected. If nesting habitat for five pair of osprey or winter- 

 spring habitat for five bighorn sheep were destroyed, however, the impact to 

 the population would be long-term (lasting mora than a few years) and carrying 

 capacity would be reduced -- a significant impact. 



Possible mitigating measures are discussed in this section; compensation 

 and enhancement manager^nt are dealt with in a later chapter. It should 

 be emphasized that the mitigating measures discussed below are not necess- 

 arily those which will ultimately be recommended by DNRC; selection of 

 appropriate mitigating measures in many cases requires tradeoffs with other 

 concerns as well as consideration of cost-effectiveness. For example, loss 

 of riparian habitat can be very effectively reduced by lowering forebay 

 elevation from 510 to 606 m (2000 to 1990 feet), but this would affect' many 

 other features of the project and such a recommendation is beyond the scope 



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