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.


 

Chapter 7: MISCELLANEOUS FACILITIES

B. High Velocity Flows

 

Introduction

Problem:

Damage to miscellaneous facilities, such as fences and boat ramps, can be due to high velocity flows that erode supporting materials, or carry debris that impacts and then damages the facility.

Mitigation Objective:

To protect miscellaneous facilities from future damage due to high velocity flows.

B.1 Install Sacrificial Fence Sections

Install sacrificial (break-away) fence sections in boundary or other fences (i.e. fence sections designed to fail at strategic locations) to allow floodwaters to pass, relieving pressure on adjacent fence sections, preventing major damage to the fence. Sacrificial sections should be designed so that the failed sections do not become loose in the floodwaters and create additional debris or cause collateral damage.

image136.png (45120 bytes)

Effectiveness:

  • Allows the passage of high velocity flows as well as debris in restricted drainages.

Limitations:

  • Sacrificial fence sections may require repairs after flood events.
  • May not be effective in preventing damage in situations where floodwater velocities cover a larger area than within the traditional flood channel.

Considerations:

B.2 Replace Boat Ramp Material With Concrete

When boat ramps are damaged by erosion, replace the eroded gravel boat ramp or the foundation material eroded from under a concrete boat ramp with concrete

image139.png (13988 bytes)

Effectiveness:

  • Replacement of eroded material with concrete may be very effective in areas of infrequent, minor erosion damage
  • Other measures, such as riprap or other slope protection techniques applied to the downstream side of the ramp, may increase the effectiveness of this mitigation alternative

Limitations:

  • May not be effective in situations where the boat ramp is frequently inundated and damaged by high velocity flows.
  • Relocation of the ramp, if possible, or other alternatives such as construction of a jetty to protect the ramp should be considered in these instances.

Considerations:

B.3 Construct a Jetty to Protect Boat Ramp

Construct a jetty upstream from the boat ramp to protect it from high velocity flows.

image142.png (16413 bytes)

Effectiveness:

  • Construction of a jetty upstream from the boat ramp may be very effective in areas of moderate to high velocity flows.
  • Other measures, such as riprap or other slope protection techniques, applied to the downstream side of the ramp may increase the effectiveness of this mitigation alternative

Limitations:

  • Consider relocating the ramp to the slackwater bay.

Considerations:

 

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