Grid 



Figure A-3. Schematic showing the development of a grid on each 

 photo. 



The accuracy of this technique is sufficient for estimating the expected 

 life of the buffer zone or, conversely, the required width of the buffer 

 to meet the design life expectations. The accuracy of the average annual 

 migration is greater for longer time periods between photo dates. Brice (1971) 

 notes that the accuracy depends on the original scale and definition of the 

 photos, the scale of the enlargement, the degree of scale distortion in the 

 photo, the numbers and reliability of features used as reference points, 

 and the care used in matching. It is generally not advisable to use the edge 

 of lakes or rivers as reference match points or as bank lines for migration 

 estimates because of the variability of this feature with water level changes. 



Channel Configuration 



Channel configuration is an important parameter in evaluating the poten- 

 tial for extending past records into the future. Each configuration is dis- 

 cussed separately in the following sections. The effects of buffer height 

 are discussed in a different section. 



Braided Configuration . Braided river channels are often very active 

 laterally within the active floodplain. When a major active channel is flowing 

 along a vegetated cut bank, substantial bank erosion can take place. If the 

 major channel was flowing along the bank during the entire period over which 



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