permitting assessment of the effects of various gravel removal procedures on 

 sites with different physical and biological characteristics. 



The major variables were again reviewed following the field inves- 

 tigation, when detailed site characteristics were available to determine 

 which were still suitable for comparing the 25 material sites. The seven 

 variables selected for the final Major Variables Matrix included: 



• Drainage basin size, 



• Channe I > width, 



• Channel configuration, 



• Channel slope, 



• Stream origin, 



• Type of gravel removal, and 



• Location of gravel removal. 



These parameters were categorized as either Physical Site Characteristics 

 or Gravel Removal Area Characteristics. Each of the sites was characterized 

 according to these variables (Table I). Definitions of these variables 

 are included in the Glossary. 



Physical Site Characteristics. Drainage basin size and channel width 

 are significant because the impact of gravel removal could differ depending 

 on the amount of disturbance in proportion to the size of stream and flood- 

 plain. Also, systems having greater discharge and bed load movement could 

 be expected to regenerate a material site more rapidly than a system with 

 sma I ler discharge and less bed load movement assuming the amount of mining 

 disturbance is proportionate in the two streams. Categories used were small, 

 medium, and large based on the drainage area above the site and sma I I, 

 medium, and large based on the channel top width within the study reach 

 at mean annual flow. Although from a hydrological standpoint categorization 

 only according to drainage basin area would have been sufficient, we con- 

 sidered it important to include channel width because width is a tangible 

 measurement that can be observed at a site location. 



14 



