conditions. Visual effects of scraping operations depend greatly on the type 

 of river system, the location of the site, and the areal extent of the site 

 within the f I oodp lain. 



LOCATION OF GRAVEL REMOVAL 



Location of a gravel removal operation in relation to the channel of a 

 river was found to be the most important aspect influencing long-term change 

 to a floodplain environment. Whether a pit or scrape, in general, the loca- 

 tion of the site was a more important consideration than the type of site. 

 Site location in this section is discussed with minimal reference to the 

 type of site although the latter is a factor influencing the extent of 

 change. 



In-Channel Locations 



As used in this project, in-channel gravel removal includes areas in 

 the active channel, high-water channels, and abandoned channels. Fourteen of 

 the sites studied on this project were situated in high-water channels and 7 

 of the 8 sites located in the active channel also included areas in high- 

 water channels. From hydraulic and hydrological standpoints, material sites 

 in active and high-water channels caused the greatest long-term change to 

 the floodplain environment. 



Active Channel. Gravel removal operations in the bed of an active 

 channel cause a series of changes all basically related to changes in the 

 depth and location of the thalweg. The degree of change depends on the type 

 of channel configuration, principally whether it is a braided or a single 

 channel. In a braided system the channels generally shift throughout the 

 active floodplain on an annual basis. This is due to the lateral instability 

 of the individual channels. In these systems removal of gravel has the 

 effect of perhaps causing greater instability in the area of the distur- 

 bance. Changes occurring in a single channel river caused by removing bed 

 material are unknown because all seven sites with this mining location had 

 substantial alteration to adjacent deposits or banks. 



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