Flood Frequency Analysis 



Flood frequency curves for each of the study sites were generated 

 by applying a regional analysis technique described by Lamke (1979). 

 Discharges for the I. 25-, 2-, 5-, I0-, 25-, 50-, and 100-year recur- 

 rence intervals were computed. In order to improve these estimates, 

 flood frequency data based on the application of the Log Pearson Type 

 III distribution were requested from the U.S. Geological Survey for 17 

 gaging stations on or in the general area of the study sites. The re- 

 gression equations presented by Lamke were also used on these gaged 

 rivers and the ratio of the Log Pearson Type III discharges to the 

 discharges calculated from the regression equations were computed. 

 These ratios were then applied to the study sites if the sites were (I) 

 on the same river but upstream or downstream from the gaging site, (2) 

 a similar size to that of the gaged river, and (3) if the drainage 

 basin characteristics such as headwaters location, aspect, and drainage 

 basin shape were similar. The resulting discharges were used to develop 

 flood frequency curves for each of the study sites. 



HYDRAUL ICS 



Three analyses were included in the hydraulic investigation: back- 

 water analysis, uniform flow analysis, and hydraulic geometry analysis. 

 Each of these are discussed in the following separate subsections. 



Backwater Analysis 



A backwater analysis was performed for most of the rivers included 

 in the study using the standard step method (Chow 1959). Input data to 

 the program included a selected discharge, a corresponding water sur- 

 face elevation at the control section, cross-sectional geometry of each 

 cross section in the study reach, distances between cross sections, and 

 roughness coefficients for each subsection of each cross section. 



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