hydraulic regime of the channel. In the other cases, induced erosion of the 

 disturbed banks has had more prolonged effects than where this erosion has 

 not occurred. Again, of prime concern with material sites on islands, as 

 with other sites separated from the channel, is maintenance of the natural 

 hydraulic geometry of the river channel. If natural hydraulic forces erode 

 islands in a given reach of a river, the presence of a material site, 

 whether a pit or scrape, wi I I weaken the integrity of the island after 

 natural bank erosion reaches the perimeter of the site. 



Development of material sites on islands where the perimeters of the 

 sites are separated from the channel, will have little effect on water 

 quality and aquatic biota. If the material site is flooded because it was 

 deeply dug, the contained water will be different than the water in the 

 active channel, as discussed under pit sites. If the site is flooded regu- 

 larly during high-flow conditions there is a potential for fish entrapment 

 as the water recedes. The long-term effect on aquatic biota depends on 

 whether the site is permanently flooded and the depth of the water. If the 

 site becomes connected to the active channel by breaching of the buffer 

 zone, the effect may be development of a braided section with the accom- 

 panying changes. Flooding of depressions in the disturbed area could cause 

 fish entrapment before the establishment of a braided pattern. 



Terrestrially, the loss of vegetated habitat would result in loss of 

 both small mammals and perhaps some larger ones. Loss would depend on the 

 size relationship of the material site to the island, but would occur regu- 

 larly where a large proportion of the island is disturbed for the material 

 site. The mortality would occur as a result of animals not being able to 

 cross the river channel (s) to adjacent floodplain habitat. 



The loss of vegetation on an island reduces the amount of bird nesting 

 habitat. This could affect the total productivity of an area more than if an 

 equivalent amount of vegetation were removed along the edges of the flood- 

 plain. This assumes that the island provides some protection from mammalian 

 predators unable to cross the intervening channels. Otherwise, the mobility 



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