Developing Realistic Design Storms for St. Louis - Saving Big $ Thoughout a Long-term Capital Improvement and Replacement Program

摘要

The Metropolitan St. Louis Sewer District (MSD) is in the midst of planning and implementing a large Capital Improvement and Replacement Program (CIRP), with assistance from a team of consultants. An important aspect of the planning process was to develop design storms that would realistically reflect local meteorology, and would result in facilities appropriately sized for to meet the District's Cease and Desist agreement with the EPA. Because the meteorology in the St. Louis County region is dominated by cloudburst-type events that are comprised of fastmoving cells with intense cores, it was necessary to define and separate these high-intensity events from the longer-duration synoptic-scale events in the long-term record. Statistical analyses were then performed on the separated datasets to develop two unique Depth-Duration- Frequency (DDF) curves. In addition, it was necessary to apply Depth-Area-Reduction Factors (DARFs) to the cloudburst-type design storms in order to avoid over-sizing sewer replacement pipes. In general, the cloudburst design storms are being used to size relief sewers within MSD subsystems, while the synoptic design storms are used for sizing larger-diameter trunk sewers and storage facilities. The MSD design storms will result in a significant CIRP savings over the 30-year life of the program.