tracted during 1975 for conslruct i on of the Trans-Alaska Pipeline. Over- 

 burden within the working limits required disposition and stabilization 

 outside the active floodplain. Permit provisions required a 90-m undis- 

 turbed buffer between the working limits of the material site and active 

 channels of the Dietrich River. Braided channels that flowed east of the 

 material site were diverted west of the site by an upstream dike to pre- 

 vent active flow during excavation. Fine to coarse gravel with sand and a 

 trace of silt was excavated to a 0.9 m depth. Rehabilitation measures conduc- 

 ted after mining included sloping of all aliquots to the southwest. Various 

 aspects of this site are shown in Figures 47a and 73. 



Middle Fork Koyukuk River - Upstream and Downstream. The Middle Fork 

 Koyukuk River is a large, sinuous river which originates in the Brooks Range 

 at the confluence of the Dietrich and Settles Rivers and flows 116 km before 

 joining the North Fork Koyukuk to form the Koyukuk River. The Middle Fork 

 Koyukuk River flows in inconsistently spaced reaches of braided and single 

 channel patterns. 



The upstream study site is located about 92 km from the confluence of 

 the Middle Fork Koyukuk and North Fork Koyukuk Rivers at an elevation of 

 365 m. The downstream study site is 45 km from the confluence with the North 

 Fork Koyukuk River and 47 km downstream from the upstream study site at an 

 e I evat i on of 282 m. 



At the upstream study site gravel extraction was accomplished by shal- 

 low excavation of sparsely vegetated gravel bars associated with the active 

 channel and excavation to the same elevation in the contiguous, vegetated 

 al I uv i a I terrace. From August to November 1974, 135,000 m of gravel was 

 removed from about 20 ha. 



The material site is comprised of two parcels; the upper area encom- 

 passes a high-water channel while the lower area is situated on the inside 

 bend of the next meander downstream. The upper area was unvegetated prior 

 to gravel removal. Scattered stands of shrub thickets occurred within the 

 active floodplain portion of the lower area and the adjacent alluvial ter- 



'i'i 



