The purpose of this risk and uncertainty analysis is to evaluate the project performance for the implemented Lower and Downtown Guadalupe River Project and for the proposed Upper Guadalupe River Project. The HEC-RAS and HEC-FDA models were used in this analysis. Both the existing conditions with the Lower and Downtown Guadalupe River Project, and the proposed Upper Guadalupe River Project design plans were investigated.

The three bypass projects in the downtown area of San Jose were incorporated into the existing HEC-RAS models for Guadalupe River. The new models were calibrated using the data from the physical models. The normal (50% probability) water surface profiles along the river were predicted using the new HEC-RAS models. The variation ranges of the water stages were computed by adjusting the model parameters, from which the standard deviations of the stage-discharge uncertainties were determined. Using the computed stage-discharge relation with the standard deviation of error and the discharge probability function with the statistical uncertainty, the HEC-FDA model was used to compute the conditional non-exceedance probabilities for the 100-year flood event. The project performances for the implemented projects and for the proposed project alternatives were evaluated based on the freeboard requirements for the 90% or 95% probability of non-exceedance in the 100-year flood event for the floodwalls, levees and incised channels, respectively.