Pits 



Pits are usually excavated away from an active channel and cause little 

 or no change to the natural hydraulic processes of the channel. Where pits 

 are connected to a channel, either year-round or seasonally, some change to 

 the hydraulics of a river can occur. The most obvious alteration occurs when 

 spring breakup or other high water flows spread throughout the floodplain; 

 much of the water can flow out of the channel because it is often filled 

 with ice. A pit in the floodplain probably would fill during high flows and 

 then, through erosional processes at the upper and lower ends, function as a 

 channel. The inlets or outlets (or both) connecting the pit to the channel 

 could enlarge significantly and reroute flow through the excavated pit. 

 Depending on site conditions this could be only temporary, for example, 

 where a pit is adjacent to a relatively straight reach of channel. In this 

 case, following high breakup flows, the water would again flow down the 

 original channel because the downvalley distance is shorter than if the 

 water flowed through the channel formed by the pit. 



A permanent alteration to flow is more likely to occur where a pit is 

 located on the inside bend of a meandering stream. Even with undisturbed 

 buffer zones separating the pit from the channel, spring breakup flows can 

 overflow the pit and exit into the downstream reach of the meander surround- 

 ing the pit. If the stability of the buffer zone is low, erosion can breach 

 the buffer zone, thus, connecting the pit to the active channel. The down- 

 val ley distance is shorter through the pit, consequently, there would be a 

 tendency for permanent redirection of flow through the pit and eventual cut 

 off of the meandering channel. 



Excavation of a pit separate from the channel does not affect the water 

 quality of the active channel. As would be expected, however, the water qual- 

 ity is different in a flooded pit than in the channel. In comparison to 

 channel waters, pit waters typically have higher temperatures during ice 

 free conditions, the dissolved oxygen levels are lower, and sometimes there 

 is stratification of both temperature and dissolved oxygen. Differences in 

 water quality parameters could be less in situations where channel flow is 



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