develop an armor layer comparable to that in ttie undisturbed area. Ttie 

 development of an armor layer in the gravel removal area is also greatly 

 dependent on the location of the area relative to the active channel and the 

 resulting flow characteristics through the site. The location and extent 

 of gravel removal may be such that an armor layer may not develop until 

 the area fills in sufficiently to have appropriate hydraulic character- 

 istics for armor layer development. 



Channel Erosion. Channel erosion in the form of local scour was not 

 observed at any of the study sites. The potential exists for local scour to 

 develop as a result of flow obstructions in the form of material stockpiles, 

 overburden piles, and diversion dikes. This potential was discussed in the 

 previous section discussing hydraulics. 



Channel degradation was observed at four sites and may have been devel- 

 oping at three other sites. At Washington and McManus Creeks, obvious degra- 

 dation had occurred upstream from the site in the main channel. At the two 

 Dietrich River sites, degradation was occurring in high-water channels; at 

 the downstream site, one of the high-water channels developed into an active 

 side channel after work completion. Channel degradation resulting from 

 gravel removal activity has been documented elsewhere (Woodward-Clyde 

 Consultants 1976b, Li and Simons 1979). Li and Simons (1979) suggest that 

 the installation of check dams can restrict upstream degradation. Sheridan 

 (1976) discusses in-channel gravel removal, noting that the pits filled in 

 with sediment; a similar situation occurred on Sinuk River with no apparent 

 degr adat i on . 



Sediment Transport. Changes in sediment transport due to gravel removal 

 were difficult to evaluate. The ratings given in Table 8 are thus highly 

 subjective. A few possible changes which were suggested by the sedimentary 

 features in and around the material sites are discussed below. It is likely 

 that most scraped sites exhibited an increase in suspended load during the 

 first flood event and possibly during one or two subsequent events as the 

 material in the gravel removal area was washed clean of the fine grain 

 sizes. This increase was thus likely a temporary increase common at most 



121 



