RESUMO
In this study, the risk analysis is used to determine the return period in which the design cost plus the damage risk cost is minimum. The damage includes the roads and traffic, the lawn areas, and the residential and commercial buildings. The traffic damage is based on two factors, time of delay and social negative impacts. The nonlinear reservoir model is used to convert the rainfall into runoff and the dynamic wave model is utilized to perform the network hydraulic simulation in stormwater management model (SWMM) software. This model is defined as an appropriate model. This model was applied in the risk analysis of a region in Tehran to obtain the optimal return period design. The results indicated that the optimal return period is 10 years. The rational method was also applied to the same region and same return period, but the total design cost of the rational method was greater by 5%. The damage due to the traffic include financial damages due to delays and loss of fuel resources in addition to the dissatisfaction of people due to the psychological burden.
