Removing gravel from within the channel is accomplished either by 

 dredging or by scraping the bed after flow has been diverted. Either method 

 can result in a deepening of the thalweg and, if the edges of adjacent 

 gravel bars or banks are removed, a widening of the channel. Depending on 

 the location of the material site, this operation could alter the pool: 

 riffle ratio in the river. 



Where the channel is dredged, turbidity in and downstream of the site 

 will increase greatly during mining. Turbidity should reduce quickly after 

 the operation has ceased. If the channel is diverted during mining, the 

 effects on water quality entail suspension of the fines exposed during 

 mining when water is diverted back through the site. This suspension will 

 result in a temporary increase in turbidity. 



Reduction in the velocity of water entering the excavated hole will 

 cause sedimentation of both bed load and suspended materials. This will aid 

 in rapid replenishment of the gravel materials removed from the site. Being 

 in the active channel, the replenishment rate is considered high compared to 

 other areas in the f I oodp I a i n . 



Excavation of the channel bed can remove spawning areas. During a 

 dredging operation fish probably will redistribute to less turbid waters. 

 Benthic organisms adapted to silt-laden areas will establish following 

 excavation and remain until the natural gravel bed becomes established. 



Assuming that the disturbances resulting from gravel removal are re- 

 stricted to the channel, and do not include the banks or edges of gravel 

 bars, little long-term effect on the terrestrial environment is expected. 

 Changes could occur if hydraulic changes in the channel affect adjacent 

 banks. 



Aesthetically, the in-channel material site has little or no effect. 

 Hydraulic changes resulting from in-channel disturbance that affects banks 

 can cause some effect. 



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