adjacent to the channels. Such locations, when excavated for gravel, tend to 

 increase channel width, decrease depth, and allow for freezing down to the 

 channel bed. 



As noted earlier, large areas of aufeis were observed in the Washington 

 Creek and Oregon Creek study sites. Both of these sites had been extensively 

 scraped and that caused numerous channels to form and loss of surface flow 

 to intergravel flow because of loosely compacted gravels. The aufeis may be 

 retarding the recovery of the surface flow by protecting the loose gravels 

 from the flood flows during the snowmelt runoff period. At both sites, the 

 channels flowing during the survey were not flowing where the channel had 

 previously been; it is thus likely that the talik was not as deep beneath 

 the newly formed channels, thereby providing the auf e i s requirement of a 

 subsurface constriction. The shallow channels would likely freeze to the 

 bed, thereby satisfying another requirement for aufeis formation. The third 

 requirement, a water source, was already available. Thus, at these two 

 sites the gravel removal operation changed the channel location and cross 

 section sufficiently to provide two of the three requirements for aufeis 

 format i on . 



HYDROLOGY 



Hydrology is the study of the origin, distribution, and properties 

 of water during the time it is at or near the earth's surface. Of concern 

 in this section is the distribution of the water. More specif ical ly, this 

 section discusses briefly the quantity of water that can be expected at 

 the 25 material sites during low flow and flood flow conditions and poten- 

 tial effects on the quantity due to the removal of gravel. 



Undisturbed Condition 



The mean annual flow of a river at a specific point is, as the term 

 implies, the mean flow during any 12 month period. It is an indication 

 of total annual runoff and may also be used as an approximation of the 

 typical low summer flow. Estimates of mean annual flow for the 25 study 



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