erosion of this bank. If there is such an abnormality, the buffer width should 

 be increased from the standard minimum buffer width for the downstream end of 

 the site given in Section V A 5b. In this example, assume no abnormality 

 exists; use a standard minimum buffer width increased by 25 percent to account 

 for the increased design life (25 years instead of 20 years) to derive a 19 m 

 width in zone B. For zone A, an annual migration of 3 m per year over 25 years 

 would prescribe a 75-m wide buffer. No change in the average erosion rate is 

 expected from, for example, a meander cutoff developing upstream, and the 

 historical period is longer than the design life, thus, the user can feel 

 confident with the prediction. A safety factor of 1.2 can be used resulting in 

 a recommended buffer width of 90 m. 



Sinuous Conf igurat ion . A river with a sinuous channel configuration is 

 expected to behave in a similar manner to that of the meandering rivers with a 

 few exceptions: erosion rates are often less in sinuous rivers than in mean- 

 dering rivers; and the erosion zone may extend farther upstream on the outside 

 of a sinuous river meander (Figure A-IO). Otherwise, similar procedures can be 

 used to estimate the recommended buffer zones. Safety factors as low as 1.2 

 can be applied to the buffers in zones of erosion on these relatively stable 

 rivers. See the discussion on meandering rivers for a hypothetical example of 

 estimating buffer sizes. 



Straight Configuration . A river with a straight configuration will likely 

 have a similar erosion pattern to that of sinuous rivers, only less pro- 

 nounced. Straight rivers typically exhibit a sinuous pattern in their thalweg 

 with the inside meanders being formed by alternate bars or side channel bars. 

 Thus, what little bank erosion takes place in a straight river would occur 

 opposite and slightly downstream from these gravel bars, which may be sub- 

 merged under most flow conditions (Figure A-ll). Safety factors as low as 1.0 

 may be appropriate on straight rivers. The reason for the straight alignment 

 should be considered before evaluating the buffer requirements. For example, 

 if the straight reach resulted from meander cutoffs, a much larger buffer 

 would be required than if the straight reach is due to erosion resistant 

 banks. 



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