approximately 30 m to 40 m wide vegetated buffers. The main ctiannel of 

 the Tanana River has the capability to erode through such a buffer in less 

 than a year. The side channel at the Tanana R i ver-Upstream site (Figure 

 27) eroded 3 m of the widest part of the buffer between early June and 

 mid-September of 1978. At either of the Tanana River sites, it could take 

 several years or several decades for the river to breach the buffer and 

 flow through the pit, the length of time depending on the lateral direction 

 of travel of the main channels. 



The Prospect Creek and West Fork Tolovana River sites were judged 

 to have a moderate potential for all of the flow to divert through the 

 pits. Both sites had vegetated buffers that included portions of abandoned 

 channels. The upstream end of the abandoned channel, in both cases, causes 

 a zone of weakness in the buffer. Even though, at both sites, the width 

 and height of the buffers were likely sufficient to prevent breaching for 

 several decades, zones of weakness in the buffers at the abandoned channels 

 and channel aufeis development in the active channel may cause earlier 

 flow diversion and buffer breaching. At the West Fork Tolovana River site, 

 the upstream end was diked off and heavily riprapped; however, in spring 

 of 1979, flow apparently overtopped the dike and scoured the channel lead- 

 ing into the pit, leaving a large delta gravel deposit in the pit. Flood 

 stage was probably high because of aufeis development in the channel. 

 Channel aufeis development also influenced the Prospect Creek site (Figure 

 28). Aufeis developed in the channel reach upstream from the material site, 

 reducing the channel capacity during the snowme I t runoff period. The runoff 

 thus flowed directly down the valley, rather than following the ice-filled 

 channel. The water flowed through the pit causing headcutting of the up- 

 stream edge. The edge was subsequently riprapped to prevent further head- 

 cutting. Doyle and Childers (1976) documented this April 1976 occurrence. 



HYDRAULICS 



Hydraulics, as used in this investigation, is the study of those param- 

 eters which influence the mechanics of water flow through the study reach. 

 The hydraulic parameters which were considered include hydraulic geometry. 



99 



