Risk for a given analysis year is measured as expected annual damage (EAD) or average annual equivalent damage when computed on an annual basis over the period of analysis. EAD expresses risk as a combination of the likelihood and consequence of an event. Expected annual damages are the most tangible measure of the severity of the existing flood problem.
Expected Annual Damage is derived by combining the information from three basic relationships: the stage-frequency relationship, the stage-damage relationship and the damage-frequency curve. HEC-FDA combines stage frequency relationship curves with stage damage curves to develop the damage frequency curve which is then integrated to determine the area under the curve aka EAD. EAD is then interpolated between analysis years, discounted to the base year, and amortized to calculate Average Annual Equivalent Damage.