Hab i tat D i vers! ty 



The result of decreasing habitat diversity, that is, creating uniform 

 habitats by gravel removal operations, was to favor certain species or life 

 history stages over others. One of the main indicators of reduced habitat 

 diversity was increased braiding in the mined area caused where gravel 

 deposits were scraped to below the water line or where flow subsequently 

 increased to inundate the mined area. This type of habitat alteration oc- 

 curred at 10 study sites (Washington Creek, Oregon Creek, Penny River, Nome 

 River, Aufeis Creek, Kuparuk River, Sagavan irktok River, Ivishak River, 

 Kavik River, and Middle Fork Koyukuk River-Downstream) (Figures 43 and 45, 

 Table 13). The channels in a braided area usually have a uniform depth, 

 velocity, and substrate with minimal bank cover. The areas were general ly 

 characterized by increased wetted perimeter, reduction in channel depth, and 

 reduced mean velocities (Figure 46). At Washington Creek (Figure 46a), for 

 example, the cross section in the upper mined area (Cross Section 3) had the 

 greatest wetted perimeter at al I flow levels, but most of this was in shal- 

 low open channels with little cover. Similarly, at Oregon Creek (Figure 

 46b) the wetted perimeter at cross sections in the mined area (Cross Section 

 2 and 3) was considerably greater than that in the upstream area and ap- 

 proached or exceeded that of the Cripple River cross sections, a river 

 with greater than three times the estimated mean annual flow of Oregon 

 Creek. Again, the Oregon Creek mined area channels were wide and shallow, 

 providing low quality and low diversity habitat. The final example, 

 Sagavan i rktok River (Figure 46c), showed a similar pattern with the mined 

 area cross sections having a greater wetted perimeter, but a shallower depth 

 profile than cross sections in undisturbed areas. 



Habitat diversity was increased in some other mined areas by the crea- 

 tion of new habitats. Three types of new habitats were usually found: (I) 

 low velocity backwater areas, (2) a side channel off the main river, and (3) 

 a flooded pit forming a pond habitat (Figures 47 and 48). Low velocity back- 

 water areas were found at five sites (Sinuk River, Skeetercake Creek, 

 Sagavan irktok River, Dietrich River-Downstream, and Middle Fork Koyukuk 

 Ri ver-Upstream) ; side channel formation occurred at three sites (Skeetercake 



156 



