Downtown Study Combined Sewer System Model

Comprehensive Mapping and Inventory Study and Hydraulic Analysis of Downtown Systems

The Boston Water and Sewer Commission (BWSC) selected Weston & Sampson to perform a comprehensive mapping and inventory study and hydraulic analyses of the water distribution, fire protection, wastewater collection, and drainage systems in the “Downtown Area.” The downtown area is that area bounded by the Charles River, Massachusetts Avenue, Southeast Expressway, Fort Point Channel, and Boston Harbor.

The mapping and inventory work of the wastewater collection and drainage systems included pipe size, invert elevations, rim elevations, material, and installation data. The completed maps and inventory served as the basis for a computer‑generated hydrologic/hydraulic (H/H) analysis of the downtown area’s West Side Interceptor, East Side Interceptor, and Boston Main Interceptor systems.

Weston & Sampson utilized the PCSWMM program for the hydrologic and hydraulic modeling component of the project. The model contained over 2000 node and conduit elements, 850 subcatchment delineations, and covered approximately 1,800 acres in project area. Wastewater flow estimations were developed from BWSC’s Utility Billing Information System (UBIS) database listing. The UBIS list contains information on all known water services in the city. Water demands were generated through manipulation of information in the UBIS list using various database programs. We then transferred these demands to the PCSWMM wastewater system model input files. Stormwater flow estimation was developed for each subcatchment based on hydrologic characteristics. Model calibration was obtained through the utilization of a flow metering program, with installation of 14 meters.

Weston & Sampson made final recommendations on various plans for rehabilitating and/or replacing the existing facilities. Prioritized for a 20‑year implementation period to meet current and projected future needs, the recommended program investigated the impact on the water, sewer, and drainage systems due to the construction of the proposed third Boston Harbor Tunnel and the depression of the Central Artery.


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