The general conclusion reached was that proper site selection and 

 project design facilitate gravel mining with minimal effects on the habi- 

 tats and fauna of floodplains. The key to the successful mitigation of 

 potential detrimental effects is to carefully match the material site design 

 and operation (site location, configuration, profile, schedule, and rehabil- 

 itation) with the Physical Site Characteristics of the selected floodplain. 



VARIABLES INFLUENCING MINING EFFECTS 



Physical Site Characteristics 



Among the Physical Site Characteristics, channel configuration was 

 the most important. Potential floodplain change is least for a braided river 

 and greatest for a straight river. Size of channel is an important factor, 

 with the least change to be expected in a large system and the greatest in a 

 small system (assuming equally-sized material sites). Combining these two 

 variables (channel configuration and size), gravel removal operations can be 

 expected to have the least effect on large braided rivers and the greatest 

 effect on small straight rivers. 



Other influencing Physical Site Characteristics, which are related to 

 configuration and size, are the availability and size of unvegetated gravel 

 bars, floodplain width, and the distance that can be maintained between the 

 mining site and the active channel. For example, in a small straight river 

 system the floodplain is narrow and gravel bars are neither plentiful nor 

 large. Thus, to extract gravel, either a significant length of active flood- 

 plain or the adjacent inactive floodplain and terrace must be disturbed. In 

 the latter case the narrowness of the floodplain forces the operation to 

 closely encroach upon the active channel. In large river systems these 

 problems can be less significant because gravel bars are larger and, if the 

 inactive floodplain or terrace are used, the wider floodplain allows mainten- 

 ance of a broader undisturbed buffer zone between the material site and 

 act i ve f I oodp lain. 



IV 



