Aerial photographs frequently are the most useful sources of informa- 

 tion. Stereo pairs are needed to show relief (e.g., height of banks) and a 

 scale of not more than 1:12,000 is preferred. Color photographs are avail- 

 able for some areas of the State, and black and white photography is avail- 

 able for most areas of the State. For some areas, pre-existing aerial photo 

 coverage can be purchased from local aerial survey companies. However, it is 

 frequently worthwhile to have the area in question flown and photographed in 

 order to obtain the needed coverage. From adequate aerial photographs, one 

 can normally distinguish such features as the physical characteristics of 

 the floodplain (e.g., channel configurations, flow regime, gravel availa- 

 bility, vegetation patterns) and can select potential access routes and 

 f ac i I i ty locat i ons. 



Preliminary Selection Procedure 



The procedure for selecting a gravel removal site usually involves 

 identifying two or three alternative sources that appear to have sufficient 

 quantities of gravel. These alternates are then compared either in an in- 

 formal basis (usually minimizing haul distance) or in a more formal pro- 

 cedure involving establishing criteria, evaluating significant factors, and 

 ranking sites. The criteria would be specific to the situation, however, 

 factors that may be considered include physical properties of the material 

 available, haul distance, material site size and configuration needed to 

 produce desired quantities, equipment available and equipment needed, re- 

 quired site preparation (e.g., ramps, berms, dikes, overburden), river 

 hydraulics, and floodplain access from nearest point. At this stage the 

 anticipated life-span of the material site also should be considered. If it 

 is desired to use the site for several consecutive years, or for two or more 

 periods separated by inactive periods, the potential bed-load replenishment 

 rate should be incorporated into site selection. It is generally assumed 

 (See EFFECTS OF GRAVEL REMOVAL ON RIVER HYDROLOGY AND HYDRAULICS) that 

 rivers of glacial and mountain origin, particularly near their headwaters, 

 have greater potential for gravel replenishment than streams of foothill or 

 coastal plain origin. Non-engineering aspects of site selection are dis- 

 cussed in other sections of this report. 



316 



