Uniform Flow Analysis 



In addition to the flood flow computations performed in the backwater 

 analysis, values of some geometric and hydraulic parameters at low flows 

 were computed in order to relate these parameters to the corresponding 

 discharge and to provide data for the aquatic habitat evaluation. Use of the 

 backwater program was not appropriate for low flows because of the small 

 number and wide spacing of cross sections in the study reaches. The flows at 

 the surveyed cross sections were assumed to be uniform and computations were 

 made using the Manning equation (Chow 1959). 



The input data to the uniform flow program included the cross-sectional 

 coordinates, roughness coefficients, energy slopes, selected discharges, and 



initial estimates of stage. The surveyed water surface slope was used as an 

 estimate of the energy slope because most surveys took place when rivers 

 were carrying flow similar in magnitude to the mean annual flow. Similarly, 

 the roughness coefficient was calculated from the measured discharge and 

 geometry rather than from estimates used in the backwater analysis. This 

 calculation technique was used because roughness would likely be greater at 



low flows than that at flood flows due to the greater influence of the bed 

 roughness at sma I I depths. 



Hydraulic Geometry Analysis 



Values of the coefficients and exponents in the power relations for the 

 hydraulic geometry (including mean velocity) at a cross section were com- 

 puted for disturbed and undisturbed cross sections at five selected study 

 sites. Power curve fitting was completed for the geometric and corresponding 

 discharge data which were determined by the hydraulic analyses discussed in 

 the previous subsections. The resulting coefficients and exponents were 

 compared with the values obtained for other rivers in Alaska and other parts 

 of the United States. In addition to this quantitative comparison, a quali- 

 tative comparison of power relation coefficients and exponents for disturbed 

 and undisturbed cross sections was made based on plots of the power curves 

 for each cross section of other sites having insufficient data range for a 

 quantitative analysis. 



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