race had to be cleared of mature white spruce and balsam poplar prior to 

 gravel removal. Overburden was not present on the active floodplain area, 

 however, 15 cm of organic silt were stripped from the alluvial terrace and 

 disposed of southeast of the lower area. 



An undisturbed 30-m buffer was maintained between the active chan- 

 nel and the working limits of the lower area; natural depressions and minor 

 channels through the buffer were augmented by construction of perimeter 

 dikes not exceeding 0.3 m above the natural buffer elevation. Caterpillar 

 tractors with rippers and self-loading bottom dump scrapers were used to 

 excavate to depths of 0.9 m in the active floodplain and 3.0 m in the adja- 

 cent al I uv i a I terrace area. The upper area was scraped to a depth of 0.9 m. 



Material extracted from the active floodplain was seasonal ly frozen, 

 sandy, fine to coarse rounded gravel. The al I uv i a I terrace provided frozen, 

 interlayered silty and sandy gravel to the water table. Screening and stock- 

 piling of select material was conducted on the floodplain. Permit provisions 

 required that unused material of silt size and finer be disposed of outside 

 the active floodplain; unused coarse material from the screening process 

 could be evenly spread in the gravel removal area. 



During site rehabilitation the disturbed area was graded to an even 

 bottom with cut faces no steeper than 2:1, stockpiles were removed, and 

 outlet channels were constructed at the downstream end to allow high-water 

 drainage. Revegetation within the active floodplain was not attempted due 

 to the likelihood of periodic flooding. Various aspects of this site are 

 shown in Figures 15, 47b, 49, 52, and 88. 



The Middle Fork Koyukuk River-Downstream site was developed by shal- 

 low scraping of a sparsely vegetated lateral gravel bar within the active 

 floodplain. The gravel removal operation was conducted during the winters of 

 1975 and 1976 with 215,000 m of material removed from 28 ha. Permit pro- 

 visions required overburden encountered within the working limits to be 

 disposed of and stabilized outside the active floodplain. 



56 



