You are not on the FEMA website.  TOUCH FEMA home to go to the FEMA official website.

[CONSERVATIONTECH.COM-Home]     [ FEMA home (www.FEMA.gov) | FEMA Library (www.fema.gov/library/index.jsp)]


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.


 

 

 FEMA HAZARD MITIGATION
 HANDBOOK SERIES

-----HOME PAGE-----


 

 FLOOD HANDBOOK
________________________________ 
 
    Introduction

    Symbols and Keywords
 
     Mitigation Alternatives
 
 I.       ROADS
     A.     Ditch Erosion
     B.     Embankment Erosion
     C.     Roadway Erosion
 
 II.       CULVERTS
     A.      Insufficient capacity
     B.      Plugging
     C.      Embankment Erosion
     D.      Misalignment
 
 III.       BRIDGES
     A.      Misalignment
     B.      Insufficient Flow Capacity
     C.      Erosion (Approaches)
     D.      Scour (Piers & Abutments)
     E.      Debris Impact
 
 IV.       BUILDINGS
     A.     Inundation
     B.      High Velocity Flows
 
 V.       UTILITIES
     A.      High Velocity Flows
     B.      Soil Settlement
 
 VI.       IRRIGATION FACILITIES
     A.      High Velocity Flows
  
 VII.       MISCELLANEOUS FACILITIES
     A.      Inundation
     B.      High Velocity Flows
 
 Appendices
     A.      Regulations
     B.      Glossary &
  
         Keyword Index
     C.      Acronyms
     D.      References
     E.      List of Contributors

Chapter 1:

Roads


Introduction

Roads are the most commonly damaged facility in a flood event.  Damage to roads may be caused by floodwaters overtopping and eroding road surfaces, shoulders, and embankment slopes, and by washing out roadway prisms.  Mitigation measures identified may also be applicable to railroads or other embankment facilities damaged by flood events.  Damages to roads and other embankment facilities can be mitigated by:

  • Protecting ditches from erosion and increasing the capacity for ditches to carry side flow;
  • Constructing protection from embankment slope erosion; and

  • Protecting road surfaces and shoulders from erosion.

 image001.jpg (47032 bytes) CLICK ON IMAGES TO ENLARGE

Assessing the Causes of Road Damage

Selection of appropriate mitigation measures for damaged road facilities depends upon the flow conditions that caused the damage.  Some observations of these flow conditions can be made during or immediately after the damage occurrence. 

If the elevations of the upstream and downstream high water marks are nearly the same, the flow conditions across the road were tranquil or streaming, and scour of the entire road surface and shoulders will be evident.  Erosion of the upstream embankment may have also occurred and there may be deposition of gravel across the road surface.  Appropriate mitigation for this flow condition includes:· 

  • Hardening the entire road surface and shoulders in the road overflow section, and

  • Armoring the top of the upstream embankment.

If the upstream and downstream high water marks are significantly different, the flood flow was likely in a 'supercritical' state (rapid and turbulent flow) at the downstream side of the road, and scour of the downstream road shoulder and embankment will be evident.  Appropriate mitigation for this flow condition includes:

  • Hardening the downstream road shoulder, and

  • Armoring the entire downstream face of the embankment.

If the road prism was washed out, a determination of the flow conditions will be critical in order to appropriately design the restoration and mitigation.  To identify the flow conditions that caused damage to roads and their embankments, determine:

  • The upstream and downstream water surface elevations, and

  • The scour and erosion features on the remaining road surfaces, shoulders, and embankments.

 

 

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