The environment surrounding urban streams imposes constraints upon stream e
nhancement projects. Constraints include bridges, culverts, highways, sewer
and water lines, lack of easements, and other floodplain structures. The c
onsequences of failure of these infrastructure constraints can be significa
nt and should be considered in the design process. Fault tree analysis prov
ides a systematic technique for analyzing the interactions of events that c
ould lead to infrastructure failure. A case study of a stream in Pittsburgh
, Pennsylvania, shows that fault tree analysis can effectively model the in
teractions between the stream system and the infrastructure constraints and
predict the most likely modes of failure. In addition, the relative succes
s of alternative designs and failure mitigation techniques can be assessed
using this analysis tool, lending insight into the urban stream enhancement
design process. The method could also provide justification in the design
permitting process and input for risk assessment.