viously dry site during the second spring breakup following the activity. 

 This channel change caused flooding of approximately 90 percent of the 

 material site. This condition will remain as long as this side channel flows 

 through the site. 



Thus, at both the Jim River and Dietrich River-Downstream sites, mining 

 depth and site location characteristics also created permanently ponded 

 aquatic habitats which will lead to long-term loss of terrestrial habitats. 



Annual Hydraulic Stress. In addition to the creation of permanently 

 ponded sites, long-term loss and alteration of habitat occurred at sites 

 where the gravel removal operation resulted in significant changes in river 

 hydraulics. Examples of such changes include shifted channels, annually 

 flooded sites, and aufeis development within the material site. 



On the Seward Peninsula, the Penny River and Oregon and Washington 

 Creeks are small rivers with relatively narrow, densely vegetated flood- 

 plains. Penny River and Washington Creek flowed in a sinuous configuration, 

 while Oregon Creek flowed in a straight configuration. The portion of the 

 total disturbed area which was vegetated by dense, mature shrub thickets 

 prior to disturbance at each site was extensive (Oregon Creek 65 percent; 

 Penny River 80 percent; and Washington Creek 85 percent) (Table 28). At all 

 three sites, the working area (which was scraped to a level equal to or 

 slightly below normal water levels) extended across the entire floodplain 

 and at Washington and Oregon Creeks the disturbed area extended approxi- 

 mately 9 to 15 m beyond the floodplain banks and into the adjacent shrub- 

 tussock tundra. The resulting effect of these scraping operations created: 

 an unvegetated, flat floodplain which was 2 to 3 times wider than upstream 

 or downstream reaches; a floodplain that was equal to, or only slightly 

 higher in elevation (10 to 20 cm on the average) than normal summer flows; 

 and a wider channel with increased braiding, straighter configuration and 

 shallower flow (Figure 64). 



The effects of these induced hydraulic changes created direct impedi- 

 ments to vegetative recovery and thus they also resulted in long-term altera- 

 tion of the habitat structure of the disturbed reach in these floodplains. 



228 



