Erosion 



Deposition 



Deposition 



Erosion 



Figure A-5. Completed schematic showing bank 

 lines and zones of erosion and deposition from 

 which rates of erosion can be measured. 



the historical migration rates were estimated, that migration rate may be 

 projected into the future. Otherwise, different locations on the floodplains 

 should be selected for obtaining estimates. Any change in the alignment of the 

 channel should be accounted for, with erosion rates increasing for increasing 

 angles of the channel to the bank. A factor of safety should be applied to the 

 result, its value depending on the confidence one has in the estimate for a 

 given system. 



As a hypothetical example, consider the length of bank labeled A in 

 Figure A-6. The dashed line shows the channel as it appeared in 1950 and the 

 solid line represents the location of the 1975 river channel. Assume that the 

 lateral migration of bank A was measured to be 100 m, or 4 m per year. Assume 

 it is desired to have a buffer lasting at least 8 years to protect a scraped 

 gravel removal area in the inactive floodplain. Projecting the past into 

 the future results in 4 m per year for 8 years, or 32 m. 



89 



