the water fans out and becomes shal lower and slower in velocity. Dissolved 

 oxygen and conductivity levels can also be altered. Benthic communities may 

 change from a community associated with the relatively stable channel of 

 a straight river to one that is better adapted to the less stable substrate 

 characteristic of braided areas. Removal or alteration of vegetated banks 

 and changes in pool:riffle ratios can alter the distribution of fish within 

 the immediate vicinity of the disturbance. Fish passage is obstructed if the 

 spreading of water sufficiently reduce its depth. 



The disturbances at the Oregon Creek site provided a situation con- 

 ducive to the formation of aufeis. Aufeis could have direct effects on fish 

 by eliminating or greatly reducing the flow downstream from the ice field, 

 thus threatening overwintering areas and spawning beds. Similarly, during 

 breakup, delayed thawing of the ice field could obstruct fish passage. 

 Benthic communities would be later in establishing at the disturbed site due 

 to the delayed melt of the ice field. 



The terrestrial environment will almost always be subject to distur- 

 bance for any site situated on a straight channel river. This vulnerability 

 is due to the rarity of large exposed gravel bars in the channel which 

 necessitates mining the adjacent vegetated f I oodp I a i n banks or terrace. At 

 the Oregon Creek site the vegetated overburden was removed and placed in a 

 row at the edge of the terrace. The gravel was removed from the exposed area 

 and from within the channel causing extensive spreading of the flow through 

 the exposed floodplain. Inundation of this area during high flow and the 

 build-up of an auf e is field greatly minimized the potential for stabili- 

 zation and revegetation of the disturbed area. This stabilization and revege- 

 tation had not occurred after 13 years, thus the likelihood of the site 

 revegetating in the near future is remote. 



The appearance of the floodplain was greatly affected at the Oregon 

 Creek site. This altered appearance will exist for a long time and will only 

 diminish when the channel begins to narrow and when adjacent areas revege- 

 tate. The potential for major changes in the appearance of a straight chan- 

 nel floodplain, that is mined, is great because of the limited availability 



347 



