RESULTS AND DISCUSSION 



MAJOR GRAVEL REMOVAL HABITAT ALTERATIONS 



Habi tat Qual i ty 



Alterations of habitat quality observed at many of the sites consisted 

 primarily of substrate alteration and removal of both instream and bank 

 cover. Siltation, commonly associated with instream disturbances, was ob- 

 served at a few sites, but was not a major factor because most of the sites 

 were visited several years after mining had been completed. At three sites 

 where siltation was observed it was caused by eroding berms (Kavik River) 

 or melting aufeis fields (Washington Creek, Oregon Creek) (Figure 40). 



Two types of substrate alteration were observed: (I) a shift from a 

 moderately compacted gravel substrate to a very loose, unconsolidated sand- 

 gravel substrate, usually with considerable intergravel flow and (2) a 

 shift from a smooth, paved substrate which produced near laminar flow to a 

 more porous, irregular substrate producing turbulent flow. Most of the 

 substrate alterations recorded were Type I alterations with only two Type 2 

 alterations observed. Type I alterations occurred at four of the eight sites 

 where scraping was conducted in an active channel (Washington Creek, Oregon 

 Creek, Penny River, McManus Creek) and at four where flow subsequently 

 increased or diverted to inundate a scraped area (Sinuk River, Kuparuk 

 River, Sagavan irktok River, Ivishak River) (Table 13). The effects of this 

 type of alteration appear to be long-term, because this alteration was 

 noticeable at McManus Creek 16 years after mining. The effect on the sub- 

 strate was caused by removal of the armor layer, loosening of the gravels, 

 and subsequent washing out of fine materials. Formation of ice in the mined 

 areas appeared to prolong the recovery time of this type of alteration. 



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