SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS 



SUMMARY 



Not al I of the major variables used to characterize the 25 material 

 sites were significant determinants of gravel removal effects. 



Among the Physical Site Characteristics, channel configuration was the 

 most important. Potential floodplain change is least for a braided river and 

 greatest for a straight river. Size of channel is a significant factor, with 

 the least change to be expected in a large system and the greatest in a 

 small system. This assumes equally sized material sites. Combining these two 

 variables, (channel configuration and size) gravel removal operations can be 

 expected to have the least effect on large braided rivers and the greatest 

 effect on small straight rivers. 



Influencing Physical Site Characteristics related to configuration and 

 size are the availability and size of unvegetated gravel bars, floodplain 

 width, and the distance that can be maintained between the mining site and 

 active channel. For example, in a small straight river system the floodplain 

 is narrow and gravel bars are neither plentiful nor large. Thus, to extract 

 gravel, either a significant length of active floodplain or the adjacent 

 inactive floodplain and terrace must be disturbed. In the latter case the 

 narrowness of the floodplain forces the operation to closely encroach upon 

 the active channel. In large river systems these problems can be less signif- 

 icant because gravel bars are larger and, if the inactive floodplain or 

 terrace are used, the wider floodplain al lows maintenance of a broader 

 undisturbed buffer zone between the material site and active floodplain. 



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