Table A-l. Probability of Occurrence (%) of a Specified Flood During 



a Specified Design Life 



Flood Buffer design life 



( years) 



Recurrence Exceedance 

 interval probab i I i ty 

 (years) (%) 2 5 8 10 20 25 50 100 



99+ 99+ 99+ 99+ 99+ 99+ 99+ 



99+ 99+ 99+ 99+ 99+ 99+ 



89 99 99+ 99+ 99+ 



65 88 95 99 99+ 



54 56 64 87 98 



18 55 40 64 87 



10 18 22 59 65 



a ^ J „ ^ ^..-^ Design Life 



Probability of Occurrence = I - (I - Exceedance Probability) 



With the known probability of flow through the site during the design 

 life of the buffer, the user can evaluate the consequences. If the probability 

 is low, the width of the buffer can be designed based on lateral migration 

 alone. If the probability is high, one of several design options are recom- 

 mended. 



• If the buffer is heavily vegetated, and if flow through the material 

 site is acceptable, riprap the upstream edge of the material site 

 to prevent headward erosion; or, increase the width of the buffer to 

 allow for erosion loss (Figure A- 1 2a). 



