Horner & Shifrin was the lead consultant on a three-phase study undertaken by the Metropolitan St. Louis Sewer District (MSD) to set the course for the future in handling stormwater issues. This work was performed by a team of five major stormwater consultants, assisted by other firms for public relations and data acquisition. As MSD assumes complete responsibility for stormwater throughout the entire service area of 524 miles, it has examined every aspect of that responsibility, from design criteria to construction inspection and from capital improvement plans through financing methods.

Phase I included the following major tasks applicable to the entire District:

Development of a Public Involvement and Information Program to gain the input of the public at large and to build understanding and communication during the planning effort.

The policies and standards of the District and of the municipalities within it were reviewed and compared with others nationwide. Goals and objectives were set for new District policies and standards and specific technical methods and design procedures were investigated.

Information about stormwater facilities and problems was acquired from St. Louis County and the 92 municipalities within the District. A computer data management system was developed in which the material received was cataloged for follow-up use. Additional material was assembled by direct contact with Federal, state and county agencies and from material which they publish or distribute. Watershed data assessments provided an overview and description of the known problems and information available for each watershed.

Phases II and III involved assembling extensive and detailed models of watersheds throughout the District. The EPA Stormwater Management Model (SWMM) was used in these analyses using RUNOFF to model rainfall/runoff relationships for existing and future conditions and the Extended Transport (EXTRAN) Model for detailed hydraulic modeling of unsteady flow conditions. Where possible, data was imported from existing HEC 1 and HEC 2 models used by FEMA in previous flood insurance studies (FIS). Additional materials utilized in the Phase II and III analyses included new air photo maps, digitally prepared photogrammetric stream cross sections, and extensive field reconnaissance and elevation surveys.

Phase II of the project consisted of computer analyses of selected "pilot" watersheds; during this phase the effectiveness of proposed policies and standards were tested to determine which ones should be implemented throughout the remainder of the watersheds in the District. In Phase III, all watersheds in the District were analyzed using the methods established in the pilot watershed models and Watershed Management Plans were developed for each, utilizing Stormwater Policies and Design Criteria established during Phase I.

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