of exposed gravels, which necessitates the disturbance of adjacent vegetated 

 areas. The magnitude of effect increases with a decrease in river size. 



In general, the rarity of straight channel rivers probably is fortunate 

 from the standpoint of gravel requirements. The relatively few exposed 

 gravel deposits and the narrow floodplains suggest the major problems that 

 can result from gravel removal operations in these systems. Major distur- 

 bances probably will occur in any river of this type unless precautions are 

 taken to protect the area. When mining is restricted to exposed gravel 

 deposits a major length of floodplain will be disturbed if gravel require- 

 ments are large. The latter problem can be prevented by restricting mining 

 to the adjacent vegetated floodplain. Straight channel systems should be 

 avoided where it is possible to select alternate areas to mine. 



DRAINAGE BASIN SIZE (CHANNEL WIDTH) 



Drainage basin size and channel width are closely related from a hydro- 

 logical standpoint and analysis of only the former would be sufficient 

 for assessing change from gravel removal activities. However, channel width 

 was included in the Major Variable Matrix (Table I) because it is a measure- 

 ment easily obtainable in the field while drainage basin must often be 

 estimated from topographical maps. Because of the close relationship between 

 these two parameters, the following discussion applies to both. 



Drainage basin size (channel width) was considered to be the second 

 most important Physical Site Characteristic influencing the amount of change 

 in a floodplain from gravel removal activities. In general, the effects 

 of mining were considerably greater on sma I I rivers than on large ones. The 

 determining factor is the amount of exposed gravel material available within 

 the floodplain. In larger systems, gravel deposits can be numerous and any 

 given deposit usually contains a large quantity of material. The situation 

 is the opposite in a sma I I river - the few exposed deposits general ly do not 

 contain much material. 



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