Channel Constrictions 



A stream channel's cross 

 section reflects the amount 

 of water and sediment 

 carried by the stream. If 

 you change the stream's 

 width by either narroioing 

 or widening it, you alter its 

 ability to transport water 

 and sediment. Such 

 changes cause other 

 problems both upstream 

 and downstream. 



How We Impact Stream Channels 



• Building bridges, berms, levees, roads, 

 and railroads 



• Cutting off side channels 



• Installing culverts 



• Placing debris or riprap along the banks 



Effects of Our Impact 



• Can increase the erosive energy at a 

 particular location, which: 



— Increases erosion of stream bed and banks 



— Creates down-cutting (incision) of channel, 

 which leads to lowering of local water tables 

 and loss of riparian vegetation 



• Creates low-energy backwater 

 — Increases filling of sediment 

 — Increases bank erosion 



— Elevates flood flows 



Lessening Our Impact 



• Avoid confining channel 



• Ensure that stream crossings, 

 such as bridges and culverts, are 

 large enough to pass flood flows 



• Replace undersized stream 

 crossings 



• Stabilize erosive areas that add 

 sediment to the water 



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