rather are controlled by geological and morphological features of the val- 

 ley. Mountainous rivers commonly have very little or no floodplain and 

 consequently, have small quantities of gravel. Alluvial fans develop when 

 a steep gradient stream flows onto a substantially less steep terrain; its 

 sediment transport capacity is significantly reduced causing sediments to be 

 deposited. This deposition fills the channel, thus forcing the flow to 

 develop a new channel. This may occur by a gradual migration process or by a 

 rapid abandonment of one channel to develop a new channel. Such processes 

 develop a partial cone-shaped deposit of gravels with the apex being near 

 the end of the steep gradient river val ley (Figure 24). The fan may or may 

 not be vegetated; denser vegetation implies greater stability. 



Changes Due to Gravel Removal 



The most common change to the channel configuration resulting from 

 gravel removal was a shift towards a more braided configuration as indi- 

 cated, in part, by an increase in the number of channels. A decrease in 

 lateral stability of the channels was often associated with changes to 



