Type 2 substrate alterations were documented at two locations, both on 

 medium size North Slope rivers (Table 15). In one case, Ugnuravik River, 

 the upstream area showed near laminar flow that was changed to turbulent 

 flow while in the other case, Shaviovik River, the reverse occurred - the 

 upstream flow was turbulent whereas the flow through the mined area was 

 laminar. Such changes would be expected naturally where localized substrate 

 or slope differences alter flow characteristics. 



Bank cover is provided by structures on or features of the stream 

 bank that provide shelter from surface predation and reduce visibility. Ex- 

 amples of bank cover include overhanging vegetation and incised or undercut 

 banks, thus bank cover was eliminated when mining removed these features 

 (Figures 41 and 42). These types of bank cover were typically present in 

 straight, sinuous, meandering or split channel rivers, but were less common 

 in braided rivers. Significant bank cover loss was observed at 6 of the 21 

 scraped sites, Sinuk River, Washington Creek, Oregon Creek, and Penny River 

 sites on the Seward Peninsula, at the Skeetercake Creek site on the North 

 Slope, and at the Middle Fork Koyukuk R i ver-Upstream in the Northern In- 

 terior (Table 13). 



Instream cover is created by obstructions, such as boulders or logs, 

 that provide slack water where fish can hold position with minimal energy 

 expenditure and reduce predation from above by being less visible. Water 

 depth can also function as cover, because deep pools and runs offer more 

 overhead protection and often lower velocities than shal low riffles. Certain 

 species, such as Arctic char and Arctic grayling, are often associated with 

 instream cover. Instream cover was reduced at five sites, Washington Creek, 

 Oregon Creek, Penny River, Kavik River, and Sagavan ir k tok River, as a result 

 of directly removing boulders and large cobbles or altering flow such that 

 new channels did not possess this habitat (Figures 43 and 44). At six sites. 

 Gold Run Creek, Washington Creek, Oregon Creek, Aufeis Creek, Skeetercake 

 Creek, and Sagavan i rk tok River, the channel configuration was altered so 

 that the channel was wider and shallower in the mined areas, thus the in- 

 stream cover provided by depth was reduced by lowering the ratio of pools to 

 r i f f I es. 



151 



