Design-Storm Analysis Extrapolated to Estimate Long-Term Performance

Design storms provide the discrete conditions needed to begin the design of a collection system. These short-duration events facilitate small and quick model runs, but do not demonstrate the long-term performance of the system. To evaluate long-term performance of systems that were tested and designed with design storms, CH2M HILL, in conjunction with other consultants and the Metropolitan Sewer District of Greater Cincinnati (MSDGC), developed a process that applies design storm model run data to historical rainfall records to estimate a sewer system's long-term performance. This process has been nick-named “annualization” and was developed as part of the Capacity Assurance Program Plan (CAPP) for MSDGC.