SUMMARY AND CONCLUSIONS 



EFFECTS OF GRAVEL SCRAPING ON RIVERINE HABITATS 



Gravel removal by scraping in floodplains resulted in a number of 

 alterations to aquatic habitats with the biota showing a variety of re- 

 sponses to these habitat alterations. Important habitat alterations in- 

 cluded: (I) the creation of braided channel areas with associated changes in 

 various habitat parameters, (2) removal of bank and instream cover, (3) 

 increased habitat diversity, (4) creation of potential migration blockages, 

 and (5) creation of potential entrapment areas. 



Increased Braiding Characteristics 



This habitat alteration occurred at 15 study sites where active channel 

 deposits were scraped to below the water line or where flow subsequently 

 increased to inundate the mined area. The main effect of braiding on spe- 

 cific habitat parameters was to reduce velocity and depth by spreading flow 

 over a wider area. The populations of both aquatic macro i nvertebrates and 

 fish utilizing these areas were altered with shifts in species and life 

 history stages. The reduction in velocity led to increased detrital accum- 

 ulation, deposition of fine materials, and often altered the temperature and 

 dissolved oxygen regime. The altered temperature regime led to altered 

 emergence periods of aquatic insects; the effect of this alteration on 

 reproductive success and overall population stability is unknown. 



Fish populations responded to increased braiding in a number of ways, 

 but the general pattern was a reduction in the diversity of the fish com- 

 munity. The number of species and age groups usually decreased in the braid- 

 ed areas. 



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