sible that subsequent high flows will cause erosion due to the hydraulic 

 forces acting on the once protected banks. This could significantly alter 

 the local reach of a river. 



This effect is less likely to occur in straight and perhaps sinuous 

 river systems because the flow is relatively unidirectional down the flood- 

 plain and direct hydraulic forces on the banks would be less than in a 

 meandering system. The effect on a meandering river could be to facilitate 

 the formation of cutoffs by increasing the hydraulic force on the inside 

 bank at the upstream end of a meander. 



Removal or lowering of gravel bars will facilitate the spreading of 

 river flow when water levels are higher than during the gravel removal opera- 

 tion. This flow spread has the effect of reducing the depth and velocity of 

 the water and will increase sedimentation rates of both bed load and suspen- 

 ded materials. Additional ly, water temperature and dissolved oxygen contents 

 could change. Benthic communities would develop that are adapted to riffles 

 and less stable substrate. Fish would become redistributed with younger age 

 classes perhaps being attracted to the disturbed site where currents would 

 be less. 



The effects to the terrestrial environment, of removing gravel from a 

 bar, are minimal if the integrity of the bar is basically maintained. The 

 only changes that could be expected are if the hydraulic regime of the river 

 channel is altered, thus, causing changes in adjacent vegetated areas. The 

 spreading of flow between the banks when bars are removed might attract 

 shorebirds for purposes of feeding. These effects would only be expected in 

 single-channel systems. 



Removing gravel from isolated material sites using accepted mining 

 techniques from bars in braided river systems would have little or no effect 

 on the scenic quality of a floodplain. The lateral instability of the chan- 

 nels that characterize these systems would cause any changes resulting from 

 gravel removal to blend in with natural processes. Removal of bars in a 

 single channel system wi I I local ly affect the appearance of the river sys- 



369 



