ICE CHARACTERISTICS 



Two ice characteristics were identified as potentially being increased 

 as a result of gravel removal activity. They are ice jamming and auf e i s 

 formation. These can be affected by a widening of the channel followed 

 by a rapid reduction in width, a reduction in depth, obstructions in the 

 floodplain, and relocating the channel through an area which was previously 

 dry. Aufeis formation was observed at four study sites. 



HYDROLOGY 



The only characteristic related to the hydrology of the river which 

 was identified as potentially changing as a result of gravel removal opera- 

 tions was a change from surface flow to groundwater flow or vice versa. 

 This change, although relatively minor at most sites, can have a local 

 effect on the mean annual flow, flow duration curve, and potentially, 

 on the flood frequency curve. Significant reduction of surface flow occur- 

 red at two study sites. 



RECOMMENDATIONS 



Listed below are several recommendations concerning gravel removal 

 operations, the purpose of which is to reduce the number or magnitude 

 of changes to the physical characteristics of rivers: 



1. Small rivers should not be considered as gravel sources. 



2. Braided rivers should be considered as primary gravel sources; 

 other river configurations, listed in order or likelihood of caus- 

 ing the least physical change, are split, meandering, sinuous, 



and s tr ai gh t . 



3. Pit excavations should be located on terraces or possibly inactive 

 floodplains and should be separated from the active floodplain 



by a buffer designed to maintain this separation for two or more 

 decades . 



136 



