textbooks (Chow 1959), and in other references (Bovee and Milhous 1978; 

 U. S. Army Corps of Engineers 1976). 



• A flood frequency analysis provides an estimate of the recurrence 

 interval or probability of exceedance of the discharge which just 

 overtops the buffer. Detailed discussion of flood frequency analyses 

 are included in most hydrology textbooks, U. S. Water Resources Council 

 (1977), and Lamke (1979). Lamke (1979) provides equations for deter- 

 mining flood discharges for rivers in Alaska for the following recur- 

 rence intervals and corresponding exceedance probabilities: 



Recurrence interval Exceedance probability 

 (years) (%) 



I . 25 80 



2 50 



5 20 



10 10 



25 4 



50 2 



100 



With the discharge and its frequency of occurrence known, the probability 

 of that flood occurring over the design life of the buffer is needed. Table 

 A- I below provides the probability of occurrence of a flood of a specified 

 recurrence interval during a specified buffer design life. 



100 



