[Code of Federal Regulations]
[Title 23, Volume 1]
[Revised as of April 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 23CFR650.105]

[Page 228-229]
 
                           TITLE 23--HIGHWAYS
 
 CHAPTER I--FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
 
PART 650_BRIDGES, STRUCTURES, AND HYDRAULICS--Table of Contents
 
Subpart A_Location and Hydraulic Design of Encroachments on Flood Plains
 
Sec. 650.105  Definitions.

    (a) Action shall mean any highway construction, reconstruction, 
rehabilitation, repair, or improvement undertaken with Federal or 
Federal-aid highway funds or FHWA approval.
    (b) Base flood shall mean the flood or tide having a 1-percent 
chance of being exceeded in any given year.
    (c) Base flood plain shall mean the area subject to flooding by the 
base flood.
    (d) Design Flood shall mean the peak discharge, volume if 
appropriate, stage or wave crest elevation of the flood associated with 
the probability of exceedance selected for the design of a highway 
encroachment. By definition, the highway will not be inundated from the 
stage of the design flood.
    (e) Encroachment shall mean an action within the limits of the base 
flood plain.
    (f) Floodproof shall mean to design and construct individual 
buildings, facilities, and their sites to protect against structural 
failure, to keep water out or to reduce the effects of water entry.
    (g) Freeboard shall mean the vertical clearance of the lowest 
structural member of the bridge superstructure above the water surface 
elevation of the overtopping flood.
    (h) Minimize shall mean to reduce to the smallest practicable amount 
or degree.
    (i) Natural and beneficial flood-plain values shall include but are 
not limited to fish, wildlife, plants, open space, natural beauty, 
scientific study, outdoor recreation, agriculture, aquaculture, 
forestry, natural moderation of floods, water quality maintenance, and 
groundwater recharge.
    (j) Overtopping flood shall mean the flood described by the 
probability of exceedance and water surface elevation at which flow 
occurs over the highway, over the watershed divide, or through 
structure(s) provided for emergency relief.
    (k) Practicable shall mean capable of being done within reasonable 
natural, social, or economic constraints.
    (l) Preserve shall mean to avoid modification to the functions of 
the natural flood-plain environment or to maintain

[[Page 229]]

it as closely as practicable in its natural state.
    (m) Regulatory floodway shall mean the flood-plain area that is 
reserved in an open manner by Federal, State or local requirements, 
i.e., unconfined or unobstructed either horizontally or vertically, to 
provide for the discharge of the base flood so that the cumulative 
increase in water surface elevation is no more than a designated amount 
(not to exceed 1 foot as established by the Federal Emergency Management 
Agency (FEMA) for administering the National Flood Insurance Program).
    (n) Restore shall mean to reestablish a setting or environment in 
which the functions of the natural and beneficial flood-plain values 
adversely impacted by the highway agency action can again operate.
    (o) Risk shall mean the consequences associated with the probability 
of flooding attributable to an encroachment. It shall include the 
potential for property loss and hazard to life during the service life 
of the highway.
    (p) Risk analysis shall mean an economic comparison of design 
alternatives using expected total costs (construction costs plus risk 
costs) to determine the alternative with the least total expected cost 
to the public. It shall include probable flood-related costs during the 
service life of the facility for highway operation, maintenance, and 
repair, for highway-aggravated flood damage to other property, and for 
additional or interrupted highway travel.
    (q) Significant encroachment shall mean a highway encroachment and 
any direct support of likely base flood-plain development that would 
involve one or more of the following construction-or flood-related 
impacts:
    (1) A significant potential for interruption or termination of a 
transportation facility which is needed for emergency vehicles or 
provides a community's only evacuation route.
    (2) A significant risk, or
    (3) A significant adverse impact on natural and beneficial flood-
plain values.
    (r) Support base flood-plain development shall mean to encourage, 
allow, serve, or otherwise facilitate additional base flood-plain 
development. Direct support results from an encroachment, while indirect 
support results from an action out of the base flood plain.