ETL 1110-2-367
31 Mar 95
(2) Diversions are used to transfer all or portions of the
elevations protect structures and their contents until the design
runoff from one location to another. They may collect flow for
limits are exceeded. These measures, applied to individual or
pressure conduits, transfer flow out of the basin (reduce the
small groups of structures, are generally less environmentally
contributing area), and collect flow from areas to gravity outlets
disruptive than structural alternatives. The measures do not
and pumping stations, thereby requiring fewer facilities. They
reduce damage to vital services (i.e., water, gas, power), streets,
may be designed to permanently alter conveyance systems or to
bridges, and landscaping, and only slightly reduce the social
operate only for discharges above (and below) certain values.
impact and disruption associated with flood events. Seals,
Diversions may be operated as part of a coordinated system.
walls, and dikes are often significantly less reliable than other
They may also be used to bypass flow around damage centers.
permanent measures.
h.
Measures that manage future development.
(3) Remote detention basins (reservoirs) have
characteristics similar to those described for detention basins
adjacent to the line-of-protection. Bottomland detention basins
(1) Management of future development reduces losses by
may be natural sinks, oxbow lakes, or excavated sumps, or may
requiring floodplain development and activities to be operated
be formed by levees. Hillside or bluff basins are really
or located in a specific manner commensurate with the flood
conventional reservoirs. Implementation of the remote basins
hazard. Land use development can be controlled by regulations
may regulate flow to reduce the size of downstream interior
such as zoning ordinances, building codes and restrictions,
flood loss reduction measures. Damage reductions at several
taxation, or the purchase of land in fee or by the purchase of a
downstream locations may be achieved, in contrast to local
flood easement. Structures not precluded from floodplain
protection works that are effective only at their individual
locations by these measures may locate on the floodplain if
damage center. Detention basins may also retain sediment from
constructed and maintained to be compatible with the
the hillside or bluff areas and thus eliminate it as an interior area
recognized flood hazard.
problem.
(2) Regulatory actions and land acquisition can also cause
(4) Interior levees and walls along conveyance channels
new use of the floodplain. The measures are attractive from the
may be implemented as local interior protection features. These
perspective of managing development to reduce the future
barriers are normally lower in height than the conventional main
damage potential of the area and use of the floodplain for
levees and thus failure is less likely to result in catastrophic loss.
compatible purposes.
If the barriers are of sufficient height, and damage potential from
failure is great, they are considered the same as the main line
(3) Measures that manage future development are
levees or walls. The interior levees may create secondary
generally compatible with implementation of other structural
interior flooding problems that must be considered, though the
and nonstructural measures. Regulatory actions may be
magnitude would likely be minor. Implementation of these
incorporated as part of the agreements with local agencies or the
measures must meet criteria defined by "Flood Plain
local sponsor. For example, implementation of regulatory
Management" (ER 1105-2-100) and other existing federal
policies to preserve the storage and functional integrity of
policy. Flood forecasting emergency-preparedness plans should
detention basins over the life of the project may be employed.
be an integral part of implementation of interior levees and walls
to reduce the potential for loss of life and property when the
(4) The HEC-IFH analysis of the impact of implementing
situation warrants.
these measures and actions is performed similar to that for other
alternatives. An exception is the most likely future condition
g. Measures that permanently
modify
damage
development assumptions, which may be adjusted to reflect the
susceptibility of existing structures.
management policies.
i.
Flood forecasting-emergency preparedness plans.
(1) Several types of nonstructural measures are designed
to permanently modify damage potential of existing structures.
They include: flood proofing (seals, earthen dikes, and walls),
(1) Flood emergency preparedness plans are flood
raising existing structures, and relocating of occupants and/or
emergency management actions and activities that reduce flood
structures (damage potential) from the specified threatened area.
losses, minimize social disruption, and assist in recovery and
The measures are designed to modify the damage potential of an
reoccupation of flooded areas. The measures should not be
area. They are typically implemented on a localized scale (such
considered instead of other feasible permanent structural or
as a neighborhood) as opposed to structural and other types of
nonstructural alternatives due to their temporary nature and
nonstructural measures that often are designed to function for
uncertain reliability during flood episodes. Preparedness plans,
larger areas.
however, should be considered as interim measures until other
flood loss reduction measures are implemented; as companions
(2)
Flood proofing and raising of structures to target
to, or enhancements of, such other measures; and as a means of
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