Design of the Colorado Ocean Relief Sewer Project

The City of Santa Monica embarked on this project to expand the capacity of its sewer system. The project is located in downtown Santa Monica within 1/4 mile of City Hall, the City Mall, and the Santa Monica Pier. An existing 33-inch sewer is an integral part of the City's sewer system, as it collects and conveys 2/3 of the City's sewer flows. The existing sewer, with a peak capacity of 29.7 cfs (840 L/s), is in need of an upgrade due to damage from an earthquake and being undersized for anticipated future flows. This new Colorado Ocean Relief Sewer will accommodate existing and future wastewater flows, provide operational flexibility, and address the City's desire for a redundant system for future emergencies. The design involved a triple barrel inverted siphon that runs beneath a major highway. This paper will describe design constraints, considerations, and construction challenges associated with the new pipeline.