GRAVEL REMOVAL AREA CHARACTERISTICS 



In the preceding section on Physical Site Characteristics it was ap- 

 parent that not all characteristics were important in evaluating the po- 

 tential floodplain change caused by gravel removal activities. In contrast, 

 all of the factors discussed in this section were found to greatly influence 

 the amount of change to a river system. The three main features discussed 

 are type of gravel removal (pit or scrape), location of the material site 

 relative to the active channel (s), and the occurrence of dikes and stock- 

 piles. Singularly and in combination these factors caused varying degrees of 

 change at the 25 study sites, in some cases, irrespective of the specific 

 physical site characteristics. 



TYPE OF GRAVEL REMOVAL 



There are two basic types of material sites: pits and scrapes. Pits 

 are dug deeply, usually with draglines or backhoes, and are flooded year- 

 round after site closure. In many cases pits are flooded during gravel 

 extraction unless water is pumped out to keep the site relatively dry. Eight 

 pit sites were studied and they represented two types, those connected 

 to an active channel and those completely separated from an active channel 

 by a buffer zone. Pits usually are situated away from an active channel. 



In a scraping operation, gravel deposits are removed with bulldozers 

 or scrapers in active and inactive floodplains and terraces. Gravel is 

 extracted by successive removal of thin layers, and scraping depths usually 

 are sufficiently shallow to minimize the occurrence of surface water. At 

 certain study sites, gravel was extracted below the water table, thus water 

 ponded in the site. This situation is not conducive to a scraping operation 

 and, therefore, is usually avoided unless it is required for other reasons. 



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