Table 1 1 shows the relationship between the range of stages Ra calculated at 

 any return period and a , (Beyers 1966). 



Table 11 

 Estimate of Standard Deviation from Range 



Sample Size Estimate of a 



2 0.8862 Ra 



3 0.5908 Ra 



4 0.4857 Ra 



113. A single stage-frequency curve with probable error bands at se- 

 lected return periods was produced using the following process. First, at 

 each return period where error bounds were desired, the range of simulated 

 stages was determined by ranking the three values and subtracting the smallest 

 from the largest. Second, the PE was estimated using Table 11 and Equa- 

 tion 18. Third, a single curve was produced by processing all 150 events as 

 one set using the methods discussed in Part VI. Finally, the PE bounds were 

 placed upon this combined curve. Figures 60 and 61 show the combined curves 

 with error bounds which correspond to the three curves shown in Figures 58 and 

 59, respectively. Probable error curves are not presented for any still-water 

 locations. The probable error of the selection process is too small to be 

 seen for the still-water locations because of the small variability shown in 

 Figure 57. 



Assessing the Impact of the Standard Project Northeaster 



114. The Standard Project Northeaster (SPN) definition can be deter- 

 mined from the definition for the Standard Project Storm (Headquarters, De- 

 partment of the Army, Office of the Chief of Engineers, 1952) as the north- 

 easter which results from the "most severe combinations of meteorologic" and 

 tidal "conditions that are considered reasonably characteristic of the geo- 

 graphical region involved, excluding extremely rare combinations." For this 

 report two processes are important in considering the specification of an SPN, 

 still-water level and wave overtopping. It is possible that a separate SPN 

 would have to be defined for each process. The SPN which would produce the 



89 



