Comprehensive Flood Hazard Assessment

DOE-STD-1023-95

(3)

Reliability of flood protection devices

(4)

Acceptable level of risk.

The flood hazard is defined in terms of the annual probable frequency of exceeding specified

elevations. All uncertainties in estimating flood levels shall be propagated in the flood hazard

analysis.

A comprehensive flood hazard assessment shall consider detailed meteorologic, hydrologic, and

hydraulic assessments of the potential flood hazards determined by the flood screening and an

evaluation of the reliability of flood protection systems (e.g., dams, levees), if present. This includes:

(1)

Estimation of rainfall and snowfall frequency in watersheds.

(2)

Overland flow assessment due to precipitation (Crawford and Kinsley, 1966).

(3)

Hydrologic modeling of watershed responses using validated models (IACWD, 1986) and

(U.S. Army Corps of Engineers, 1986).

(4)

Assessment of discharge (flow rates) and flood elevations using detailed hydraulic modeling

techniques, e.g., HEC (1986).

(5)

Estimation of joint natural hazard events frequency. For example, a joint probability analysis

shall be performed to assess surge level frequencies (Ho, et al., 1987).

(6)

Assessment of the likelihood of upstream dams and levees failures. All causes of dam failures

should be accounted for (McCann and Boissonnade, 1988b).

(7)

Assessment of the uncertainty due to the limited data for estimating model parameters, the

modeling of physical processes, and interpretation of the available data.

A full-scope probabilistic approach to model river flooding shall include temporal and spatial

frequency estimates of the random meteorological parameters that contribute to precipitation and

runoff and an estimate of the modeling uncertainty of the watersheds (NRC, 1988).

Three of the acceptable approaches are available to evaluate the frequency of extreme flows and/or

levels due to hydrologic events (NRC, 1988) and (IACWD, 1986) are:

(1)

statistical methods

(2)

probabilistic hydrologic modeling (including, Bayesian analysis, joint probability methods,

etc.)

(3)

paleohydrologic analysis (i.e., evaluating ancient evidence using age dating techniques to

deduce early extreme hydrologic events).