average of 1.5-m in depth at the Penny River to over 7 m deep at the 

 Dietrich Ri ver-Upstream, West Forl< Tolovana River, and Tanana River- 

 Downstream sites. The pits were either connected or unconnected to adjacent 

 active river channels, however, in all cases they were permanently filled 

 with ponded water (Figure 63). Surface areas ranged from 7.5 ha at Tanana 

 Ri ver-Upstream to 0.1 ha at Ugnuravik River. Six of the eight sites were 

 separated from the active floodplain and were completely vegetated with 

 mature white spruce-paper birch and/or willow and alder shrub thickets prior 

 to excavation. At these sites the depth and subsequent flooding created 

 aquatic habitats that led to long-term loss of terrestrial habitats. At the 

 two other pit sites, the excavations occurred in unvegetated point bars 

 (Ugnuravik River) and unvegetated lateral bars (Kavik River). Thus, no 

 vegetated habitat disturbance occurred. 



Excavation of deep pits, however, was not the only gravel removal 

 method that led to development of permanently ponded water and consequently 

 the long-term loss of terrestrial habitats. The combined gravel removal and 

 site location characteristics at the Jim River and Dietrich River-Downstream 

 sites also led to permanent ponding. 



At the Jim River, gravel was scraped from within and immediately adja- 

 cent to a high-water channel. The resulting profile at the completion of the 

 scraping operation resulted in an almost circular depression in the middle 

 of the worked area. The high-water channel traversed this depression. Since 

 this channel carries summer flow, it consequently had formed an annually 

 ponded area of approximately 4.5 ha over this centrally depressed portion of 

 the II ha site. Before clearing and gravel removal, with the exception of 

 the approximately lO-m wide high-water channel, this site contained a di- 

 verse complex of mature and intermediate-aged white spruce-paper birch 

 stands with scattered willow and alder thickets. 



The Dietrich River-Downstream site was scraped to an average depth of 

 I to 1.5 m in a rectangular shaped 7.5 ha. The area was separated from the 

 active floodplain by approximately 150 m prior to the activity. However, the 

 depth of excavation was the probable cause of a permanent channel change by 

 a major side channel of the Dietrich River. This channel entered the pre- 



227 



