Flood Evaluation Process

DOE-STD-1020-2002

combination of flood hazards (e.g., river flooding and wind-wave action)

given in Table 4-2, and

Corresponding loads associated with the DBFL peak-hazard level and

applicable load combinations (e.g., hydrostatic and/or hydrodynamic

forces, debris loads).

The first item is determined as part of the probabilistic flood hazard assessment. Limited

flood hazard assessments for some DOE sites have been conducted (see Refs. 4-4, 4-5, and 4-6).

Flood loads are assessed for the DBFL on a SSC-by-SSC basis.

Table 4-2 defines the flood design basis events that must be considered. The events

listed in Table 4-2 should be considered as part of the site flood hazard assessment. For

example, if a river is a source of flooding, wind waves must be considered. The DBFL is

determined by entering the flood hazard curve which includes the combination of events in Table

4-2. For example, at a site located on an ocean shore, the flood hazard curve should include the

effects of storm surge, tides and wind-waves.

If the hazard annual probability for a primary flood hazard is less than the design basis

hazard annual probability for a given Performance Category (see Table 4-1), it need not be

considered as a design basis event. For instance, if the hazard annual probability for

Performance Category 1 is 2x10-3 per year, failure of an upstream dam need not be considered if

it is demonstrated that the mean probability of flooding due to dam failure is less than 2x10-3.

4.1.2 Flood Evaluation Process

The following describes the steps involved in the evaluation of SSCs. The procedure is

general and applies to new and existing construction. It is oriented toward the evaluation of

individual SSCs. However, due to the nature of flood events (i.e., river flooding may inundate a

large part of a site and thus many SSCs simultaneously), it may be possible to perform an

evaluation for the entire site or a group of SSCs.

The flood evaluation process is illustrated in Figure 4-1. It is divided into the

consideration of regional flood hazards and local precipitation. For new construction, design

practice (see Section 4.1.3) is to construct the SSC above the DBFL, thus avoiding the flood

hazard and eliminating the consideration of flood loads as part of the design. The design of the

site stormwater management system and structural systems (i.e., roofs) for local precipitation

must be adequate to prevent flooding that may damage a SSC or interrupt operations to the

extent that the performance goals are not satisfied.

4-4