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Rivers move!  A healthy river maintains a balance between eroding and depositing sediments. Over time, this process leads to the river channel migrating across the river valley bottom, threatening any structures and developments in its path.


  • Understand that rivers are dynamic and move over time – an area may look safe for development now but in ten years it may not be
  • Locate structures outside the channel migration zone
  • Outside bends of rivers are most vulnerable to erosion

Thankfully, experts can predict where rivers are likely to move in the next hundred years and have created maps called Channel Migration Zones (CMZs). For the long-term safety of your investment, locate buildings and permanent structures outside the CMZ. Many rivers and streams in Montana, like the Yellowstone and Musselshell, have completed CMZ maps. Contact your local conservation district to obtain CMZs for your area.

Keeping buildings outside the CMZ will reduce the need for costly bank armor.  Bank armor harms fisheries and ecological health by interfering with erosion and deposition processes. Bank armor has local benefits however, it prevents the dissipation of energy, intensifying downstream floods and erosion for your neighbors–in essence, bank armor only transfers the problem downstream.

Example of a channel migration zone map


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