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WEB-BASED HANDBOOK (Legacy Edition). CLICK HERE to submit comments.
Because of staff changes and Randolph Langenbach's retirement from FEMA, these handbooks were never published on the FEMA website.  These are the only copies available.



A. High Velocity Flows




High velocity flows impact an irrigation facility causing erosion that either undermines support or directly damages the facility.

Mitigation Objective:

To prevent damage by reducing high velocity flows that will reduce erosion.

A.1 Install an Inverted Siphon

Construct an inverted siphon to transport irrigation water under a stream or canal in order to prevent floodwaters and debris from damaging the at-grade flume or culvert crossing.

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  • Very effective in preventing debris impact damage and floodwater causing overfill to irrigation facilities.


  • Depth of stream and geology may preclude this option.


A.2 Line Earthen Canals

After repairing erosion-damaged irrigation earthen canals, apply cement concrete to the canal walls. Lining is accomplished by pumping and spraying the mixture over reinforcing wire in areas that are exposed to highly erosive flows. (Shotcrete and Gunite are examples). The concrete and reinforcing wire should be applied from concrete structure to concrete structure, or from an upstream cut-off wall installed to prevent flows from scouring under the upstream edge of the installation.

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  • Very effective
  • Lining limits scour damage to canal walls.
  • Lining also limits canal water loss from percolation through canal soils.


  • Aquifers or wetlands may be impacted due to loss of groundwater percolation.



B.3 Place Riprap

(SEE 1.B.5)

B.4 Install Flow Diverters

(SEE 2.D.4)



NOTE:  None of the mitigation measures in these Handbooks should be considered ‘pre-approved’ or otherwise automatically eligible for FEMA funding. Only FEMA staff can determine eligibility, once they have determined that an applicant is eligible and they have reviewed a project proposal.

FEMA HAZARD MITIGATION HANDBOOKS                                                                        Updated: June 13, 2002