The increased braiding also increased the probability of aufeis forma- 

 tion in the mined areas. This effect was documented at Washington Creek and 

 Oregon Creek and was indicated at McManus Creek and Penny River. There may 

 have been additional ice formation at some of the North Slope sites, such as 

 Kuparuk River, Sagavan i rk tok River, and Ivishak River. The formation of 

 aufeis fields seemed to prolong the recovery of the site as the channels and 

 substrate remained unstable and siltation persisted during the melting 

 process. In addition, the water needed to create the aufeis field became 

 unavailable downstream, thus reducing water available for overwintering, 

 often the factor limiting fish populations in arctic rivers. 



Removal of Bank and Instream Cover 



Reduction of bank cover occurred whenever a portion of incised or 

 undercut bank was removed. At sites with this habitat alteration, the bank 

 was scraped to remove overburden in order to access underlying gravel de- 

 posits. The former bank with cover was changed to a gravel bar following 

 removal operations. Certain species, such as Arctic char and Arctic grayling 

 were strongly associated with bank cover and the loss of this cover led 

 to reduced population densities in the mined areas. Similarly, loss of 

 instream cover led to reduced densities in mined areas. 



Increased Habitat Diversity 



Habitat diversity increases were documented at three scraped sites, but 

 these were viewed as temporary increases at newly inundated sites. The 

 habitat diversity will decrease as braiding characteristics are established, 

 the channel cutoffs are completed, and the habitats become more uniform. 



Migration Blockages 



The combination of increased wetted perimeter and decreased depth 

 in mined areas created a situation that could lead to migration blockages 

 during periods of low flow. Such a situation occurred at the Aufeis Creek 

 site and possibly could occur at the Nome River site. The potential for 



210 



