QUANTIFICATION OF CHANGES 



At each of 1"he 25 study sites an attempt was made to quantitatively 

 rate the degree of change of selected river characteristics due to the 

 gravel removal operations. When quantifying changes, the selected charac- 

 teristic should be compared before and after the gravel removal operation 

 under similar flow conditions. Whenever possible, this was done using aerial 

 photographs. Aerial photographs often did not provide the necessary detail, 

 or the lack of information concerning flow conditions in the photographs 

 made such comparisons less meaningful. Thus, the upstream sample area was 

 assumed to represent the undisturbed condition for many of the comparisons. 

 After comparisons were made, a rating scale was applied to establish the 

 relative degree of change occurring in physical characteristics at the 

 various sites. 



A scale was selected ranging in value from to 10, with being a 

 very large decrease in the quantity of a characteristic, 5 indicating no 

 change, and 10 being a very large increase in the quantity of a character- 

 istic. Intermediate values reflect various degrees of change between the 

 extreme values. More specific meanings of the degree of change for each 

 characteristic are given in the following RESULTS AND DISCUSSION section. 



All sites were rated using the rating scales. Sites with more than 

 one physical response to the gravel removal activity were given more than 

 one rating. These sites included Sinuk River, Washington Creek, Oregon 

 Creek, Aufeis Creek, and Middle Fork Koyukuk R i ver-Upstream. At all other 

 sites, the physical changes resulting from the gravel removal operation were 

 similar throughout the site. The gravel removal areas for all sites are dis- 

 cussed in general in the previous section (DESCRIPTION OF STUDY RIVERS). The 

 separation of the gravel removal areas for the hydrologic and hydraulic 

 analyses at selected sites is described in the following paragraphs. 



At Sinuk River, different responses to gravel removal were observed for 

 two gravel removal locations. These locations are shown in Figure I I . An 

 island that split the channel upstream of the highway bridge was completely 



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