tion is long-term but, in fact, could blend more with the i nterspers i on of 

 cutoffs and lakes occurring naturally in the floodplain. 



Adjoining Channel Locations 



The Major Variable Matrix (Table I) includes four subdivisions under 

 adjoining channel locations. These are: point bar, lateral bar, mid-channel 

 bar, and bank. To thoroughly characterize the 25 study sites it was neces- 

 sary to utilize all of these subdivisions but the gravel removal effects are 

 similar for some. Therefore, the following discussion combines the three bar 

 locations and discusses banks separately. Remember, at a given material site 

 these bars and banks are associated with one of the three channel types 

 discussed in the previous section. 



Point, Lateral, and Mid-Channel Bars . This discussion only considers 

 removing gravel from unvegetated bars with exposed gravel deposits. All 

 three gravel bars are usually numerous in braided systems but, in single 

 channel systems, usually only point and lateral bars are found. 



The effect of removing gravel from a bar is to lower the elevation of 

 the bar thus allowing flow to inundate an area that was previously above 

 the low-flow water line. These sites are usually scraped. Maintenance of the 

 integrity and conformation of the bar will cause little permanent change to 

 channel hydraulics and will facilitate replenishment of the gravel during 

 subsequent high flows. Changes in the active channels can and probably will 

 occur where bar integrity is not maintained. In a braided river system this 

 change will be similar to the natural processes and the long-term effects 

 will be minimal. In a single-channel system redistributing flow by removing 

 bars can have long-term effects by changing the local hydraulics of the 

 channel. This hydraulic change could either decrease the lateral stability 

 of the channel or widen or deepen the flow because the cross-sectional area 

 is larger. Where the banks are stable, the river eventually will equilibrate 

 itself by reforming gravel bars as upstream bed load materials become avail- 

 able during subsequent high flows. Where banks are less stable it is pos- 



368 



