CHANNEL SLOPE AND STREAM ORIGIN 



Neither of these Physical Site Characteristics was found to greatly 

 influence the effects of gravel removal in f I oodp I a i n environments. Both 

 channel slope and stream origin are closely related to such factors as 

 drainage basin size and channel configuration, therefore, their influence on 

 the effects of gravel removal are dependent on these factors. The Physical 

 Site Characteristics are discussed separately because of specific impli- 

 cat i ons i nvo I ved. 



Channel Slope. Removal of gravel from a channel wi I I affect the channel 

 slope within the site and, perhaps, immediately upstream and downstream. 

 Usually this effect entails increasing the slope, which can have localized 

 effects on the floodplain. The main effect is to increase water velocity. 



Localized changes that can be expected due to the relationship of 

 increased velocity and increased slope are scour and alterations of aquatic 

 communities. Increased scour in a disturbed site can increase downstream 

 deposition of bed load materials where the water slows to the velocity 

 characteristic of the undisturbed channel. The greater scour potential in 

 the disturbed site decreases the stability of bed materials thus affecting 

 habitat for benthic organisms. 



Increased water velocity can directly affect benthic organisms by 

 displacing those not adapted to higher velocities and favoring those adapted 

 to these conditions. Similarly, fish may become redistributed locally be- 

 cause of water velocity changes. Those fish species or age groups preferring 

 lower velocities may displace to areas upstream or downstream. 



Altered velocity is not expected to change the terrestrial environment 

 or the scenic quality of an area. Indirectly, an effect might occur to water- 

 associated birds that are dependent on benthic organisms as a food source. 

 Any alterations to benthic communities could alter feeding sites for these 

 b irds. 



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