Flood Design Strategies

DOE-STD-1020-2002

Since it may not always be possible to construct a new SSC above the DBFL level,

alternate design strategies must be considered. The following lists the hierarchy of flood design

strategies:

Situate the SSC above the DBFL level,

Modify the flood, or

Harden the site or SSC to mitigate the effects of the DBFL such that the

performance goals are satisfied, and

Establish emergency operation plans to safely evacuate employees and

secure areas with hazardous, mission-dependent, or valuable materials.

If an SSC is situated above the DBFL, the performance goals are readily satisfied. If an

SSC is located below the DBFL, alternatives can be considered to modify the magnitude of the

flood or mitigate its effects such that the likelihood of damage and interruption of operations is

acceptably low (i.e., performance goals are satisfied). In addition, emergency operation plans

must be developed that establish the procedures to be followed to recognize/identify the flood

hazard in a timely manner and provide for occupant safety and secure areas that may be

vulnerable to the effects of flooding. The implementation of emergency operation plans is not,

in general, an alternative to satisfy the performance goals. While they are necessary to provide

for occupant safety, generally they do not adequately limit the level of damage and interruption

to facility operations.

Under certain circumstances the flood can be modified to limit the magnitude of the

hazard. Alternatives include the construction of detention ponds that provide for the collection

and controlled release of runoff on-site, modification of stream channels, etc.

The strategy of hardening a SSC or site and providing emergency operation plans is

secondary to siting facilities above the DBFL level because some probability of damage does

exist and SSC operations may be interrupted. If it is determined that a SSC may be impacted by

the DBFL and thus must be hardened, the designer must determine the flood loads associated

with the DBFL. The design of flood mitigation systems (i.e., exterior walls, flood-proof doors,

etc.) must be conducted in accordance with the requirements specified in applicable regulations.

The evaluation of the site stormwater management system and roof design (i.e., drainage

and structural capacity) differs somewhat from that for other flood hazards. First, all sites must

be designed for the effects of local precipitation. Secondly, from the perspective of the

performance goals, the adequacy of the site stormwater management system is measured in terms

of the impact of local flooding on SSCs at the site. For example, the initial design of the site

stormwater management system may correspond to the 25-year rainfall 6-hour storm. If the

DBFL for a SSC corresponds to a 5x10-4 rainfall, the site stormwater management system

design clearly does not meet this criterion. However, at this point the only conclusion that can

be reached is that the system (i.e., storm sewers, etc.) will be filled to capacity. The actual

impact of the DBFL precipitation on the SSC is assessed by conducting a hydrologic evaluation

for the site that accounts for natural and man-made watercourses on site, roof drainage, etc. The

analysis may conclude that flooding is limited to streets and parking lots. If temporary flooding

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