Creek, Middle Fork Koyukuk R i ver-Upstream and Jim River); and flooded pits 

 were created at seven sites (Penny River, Ugnuravik River, Dietrich R i ver- 

 Upstream, Prospect Creek, West Fork Tolovana River, Tanana River-Downstream, 

 and Tanana R i ver-Upstream) . 



The changes in habitat diversity were determined by the location of 

 mining and, to some extent, the type of mining. Braiding (decreasing habitat 

 diversity) occurred where the majority of flow went through a mined area, 

 such as where a meander was eliminated (two sites: Penny River, Middle Fork 

 Koyukuk River-Downstream), an inchannel island or gravel bar was removed 

 (five sites: Washington Creek, Kuparuk River, Sagavan irk tok River, Ivishak 

 River, Kavik River) or where excavation occurred in an active channel (five 

 sites: Washington Creek, Oregon Creek, Penny River, Nome River, Aufeis 

 Creek). Removal of gravel in active channels created braided areas in what 

 had previously been pool-riffle habitats, thus, in these cases there was 

 often a loss of instream and bank cover, substrate alteration, depth alter- 

 ation, spreading of flow combined with decreased velocity, and loss of pools 

 and riffles. Habitat diversity increased at two sites with incomplete 

 meander cutoffs forming backwater and ponded areas or side channels 

 (Skeetercake Creek, Middle Fork Koyukuk R i ver-Upstream) and with gravel 

 removal in a high-water channel to below the water table such that it con- 

 tained ponded water (Sinuk River) or annual flowing water (Jim River). 



Habitat diversity also increased at three sites where recent gravel 

 extraction or channel changes created low velocity backwater areas and 

 braided characteristics were not well established ( Sagavan irk tok River, 

 Dietrich River-Downstream, Middle Fork Koyukuk R i ver-Upstream) . Ponded areas 

 or low velocity backwaters were characterized by a sand to silt substrate. 

 The low velocity with associated clear water often allowed increased growth 

 of filamentous algae. Water temperatures were usually increased over those 

 in the active channel because of the dark substrate and poor circulation. 

 Similar effects, although not as great in magnitude, were observed where 

 side channels were formed at Jim River and Middle Fork Koyukuk River- 

 Upstream. Water velocities were reduced and increased silt deposition was 

 observed in the main channel. 



161 



