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Bank Armor

Takeaways

  1. Rip-rap should be a last resort
  2. Consider alternative practices wherever possible
  3. Rip-rap causes serious damage to river health and landowners

 

 

 

 

Rip-rap is often landowners’ first choice when their bank starts eroding. However, rip-rap carries many negative consequences for the river and for other landowners. These consequences include:

  • Rip rap is very expensive ($100 to $500 per foot), and permitting can result in hundreds of thousands of dollars in mitigation fees
  • Increased flow velocity, putting your downstream neighbors at increased risk of erosion and flooding
  • Interfering with stream dynamics, causing more erosion on adjoining banks
  • Destroying riparian vegetation necessary for healthy ecosystems and fisheries
  • Improperly constructed rip-rap will eventually fail and is very expensive to fix

Rip-rap should be considered a last resort for protecting banks. If you select a construction site taking floodplains and channel migration zones into account, rip-rap should not be necessary. Some of the problems with rip-rap can be mitigated by adding woody vegetation to the engineered structure.

Rip-rap requires permits from the local conservation district and the US Army Corps of Engineers. Learn more about what permits you need.

Only use rip-rap when:

  • Long-term durability is needed
  • Design discharge and shear stress is high
  • There is substantial threat to high-value property
  • Impacts to channel stability and fisheries would be minimal
  • Effective alternative practices are unavailable

Some guidelines for rip-rap engineering and construction:

  • Use bioengineering and vegetative plantings to stabilize the upper bank.
  • The key must be placed below scour depth.
  • The toe is the most important part of a rip-rap project. This is the zone of highest erosion.
  • Rock is unnecessary above high water mark.
  • 2:1 is the recommended slope. 1.5:1 is the steepest slop on which rip-rap will stabilize.
  • Rock must be angular, not rounded, for greatest strength.
  • Rock is sized according to shear stress criteria for engineered designs.
  • Rip-rap is flexible and not impaired by slight movement from settlement.
Protecting My Investments
1. Erosion Control
2. Failing Bank Protection
3. Alternatives to Bank Armor
4. Bank Armor
5. Vegetation and Landscaping
6. Flood Insurance
7. Protecting My Investment
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