A risk indexing tool is proposed to assist in the prioritization of mainten
ance, repair, and evaluation tasks on embankment dams that are generally le
ss than 33 m (100 ft) high and for which there is little or no instrumentat
ion. limited or no information concerning as-built conditions, and little o
r no information on the performance history. Under such circumstances, ther
e may not be enough information available to perform anything other than an
"indexing" type of analysis to assist in prioritization. The risk indexing
tool is based upon identifying potential deficiencies in the physical cond
ition of the dam and rating the overall importance of these deficiencies to
the safety of the structure. It is meant as an index of risk (indication)
and not as a direct measure of risk. Checklists are presented for onsite in
spections to determine current physical condition. Condition is defined in
terms of a condition function that is based upon a condition indexing scale
. Four potential failure modes are considered: (1) overtopping; (2) externa
l erosion: (3) piping; and (4) mass movement (slope instability). Absolute
probabilities are specifically not factored into the analysis. Conditional
probabilities are estimated for each failure mode using a Bayesian updating
procedure based on dam attributes. A simple failure criticality analysis i
s performed wherein specific changes in physical condition of the dam are c
onsidered to contribute to the probability of failure for each mode. From t
his failure criticality analysis and the conditional probabilities of failu
re, the relative importance of the various changes in physical condition is
determined. The physical condition and the relative importance are then co
mbined for each observable deficiency to form a risk index. These risk indi
ces are used to prioritize expenditures for improvements on the premise tha
t actions to address the most significant physical deficiencies are preferr
ed.