tern, the magnitude of effect depending completely on the degree to which the 

 bar was disturbed. Any significant changes to the hydraulic geometry of the 

 reach causing subsequent disturbance to adjacent vegetated areas will lo- 

 cally alter the appearance of the floodplain. 



Banks. Probably the most consistent long-term changes to a floodplain 

 occurred when banks were destroyed or greatly modified during a gravel 

 removal operation. In these cases significant changes to the hydraulic 

 geometry of the river occurred. Banks typical ly are stable and function to 

 restrict the flow of the river to the channel except during high flows. When 

 these are removed or disturbed the river is no longer contained and it 

 begins to wander and erode the adjacent floodplain. This wandering results 

 from the hydraulic forces of the river impinging on newly exposed bank ma- 

 terial. Where banks are made of stable materials the degree of erosion 

 should not be greater on the newly exposed bank than what occurred natural ly 

 before the site disturbance. Where the newly exposed bank materials are not 

 stable erosion will occur at a rate faster than occurred previously. Also, 

 if the newly exposed bank is situated at an angle to the flow different than 

 what occurred natural ly in that reach of the river, erosion could be aggra- 

 vated because of the increased hydraulic force on the bank. 



Generally, channel width increases with bank destruction. Previous 

 discussion identified that increased channel width can result in reduced 

 water velocity, reduced water depth, changes in water temperature, and 

 dissolved oxygen, and increased sedimentation. Aquatic biota would reflect 

 these altered habitat conditions by changes in benthic communities to those 

 that are adapted to riffle areas with unstable substrate and changes in 

 distribution of fish in the reach affected by the disturbance. Undercut and 

 vegetated banks are heavily utilized by fish as cover and removal of this 

 habitat can greatly reduce the local abundance of certain species. 



The effects on the terrestrial environment include destruction of 

 riparian habitat during site clearing with resultant effects on faunal 

 distribution. The decreased lateral stability of the channel can cause more 

 destruction after site closure if hydraulic forces erode newly exposed 



370 



