during high flows, and in some cases forms a braided configuration through 

 the disturbed site. When this occurs on unvegetated gravel bars in braided 

 systems, the effect on the f I oodp I a i n is relatively minor because the ef- 

 fects are similar to natural hydraulic processes. After site closure, unless 

 stockpiles or dikes are present, the disturbed site can return to a rather 

 natural configuration within a maximum of a few years. This, however, is not 

 the case where lateral bars are excavated to include removal of adjacent 

 banks. Bank removal is discussed in the subsequent section. 



The potential for causing braiding from scraping operations within the 

 active floodplain, is usually insignificant in a river system that already 

 has a braided channel configuration. However, in split channel and single 

 channel systems braiding constitutes a significant change to the aquatic 

 environment and alters the aquatic biota; species which benefit are those 

 better adapted to riffle areas, to less stable substrates and, perhaps, to 

 substrates less granular than those found in the natural system. These 

 habitat changes primarily affect the distribution of organisms. This study 

 general ly found a local decreased diversity of the fish community as a 

 result of braiding. There is a potential of blockage to fish passage, at 

 least during low flow conditions, as occurred at the Aufeis Creek site 

 because the water flows over a wider area than in the undisturbed channel. 

 Blockage is most severe if the entire active floodplain is disturbed, not 

 just the lateral bars. Entrapment of fish, in depressions created by scrap- 

 ing, is also possible during periods when water is receding from high flows. 



Effects on the terrestrial environment depend greatly on the river type 

 involved and on the location of the work area within the floodplain. In 

 braided systems mined in the active floodplain, there essentially is no 

 effect. However, on split and single channel systems, braiding caused by 

 gravel mining can provide feeding habitat for shorebirds that utilize ben- 

 thic organisms. Destruction of banks with associated vegetation removes 

 habitat used by terrestrial fauna; the effects are the same as removal of 

 vegetation for pit sites. 



361 



