M3 Engineering Group provided hydraulic modeling-related services as a Subconsultant to Jacobs Engineering, Inc. on the Watershed Facility Planning Program for the Metropolitan St. Louis Sewer District. MSD used HYDRA to perform detailed modeling of the separate sewer collection system and to develop project-specific preliminary plans, preliminary designs and designs. M3 Engineering managed the updates to the Gravois Creek and the Lower Merammec Subbasin & models. M3 served as the modeling resource on assigned service area and watershed teams created for execution of the SSO Control Plan. The HYDRA basin models were refined and re-calibrated as preliminary plans, pre-designs and designs were prepared. The aggressive schedule for preparing preliminary plans and the need for incorporating the results of I/I investigations required that modeling activities were well organized and coordinated with the MSD Modeling lead to prioritize tasks and establish task deliverable dates. The HYDRA-modeled network was extended to include all bypasses, which required adding smaller-diameter pipes to the model and redefining the sewersheds (HYDRA service areas).  Re-calibration made use of radar rainfall data and/or the use of multiple rainfall gages. In addition, recalibrating the models  included incorporating detailed defects data collected by MSD’s I/I consultants.