METHODS OF DATA ANALYSIS 



The evaluat-ion of changes resulting from gravel removal operations 

 at the 25 study sites was based primarily on subjective judgement. A few 

 hydrologic and hydraulic analyses were performed to enhance the data base 

 for making further evaluations and biological analyses. A table was prepared 

 that listed quantitative values for the subjective evaluation of changes, 

 and was used to compare sites and, thereby, to evaluate the relative change. 

 The following subsections describe briefly the methods used in th« analys«s. 



HYDROLOGY 



Mean annual flows and flood frequency curves were developed for the 

 25 study sites. There were no U. S. Geological Survey gaging stations ^t 

 the study sites. Nine sites were near enough to gaging stations to use 

 the gaging station data, although none of the station records exceeded 

 12 years in length. Standard regional regression techniques were difficult 

 to use because of the sparse gaging station network in arctic and subarctic 

 Alaska. The hydrologic analyses thus include a significant amount of judge- 

 ment; thus, the results should be considered as rough estimates. 



Mean Annual Flow 



The mean annual flows at six U. S. Geological Survey gaging stations 

 were used as a basis for the analysis. The unit mean annual flow (mean 

 annual flow per square kilometer of drainage basin) was computed for these 

 stations. Nine of the study sites were near enough to the stations to use 

 the station's unit mean annual flow. At the remaining 16 sites, the unit 

 mean annual flow from the nearest gaging station was modified after con- 

 sidering the difference in mean annual precipitation of the drainage basins 

 for the gaged river and the study site. 



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