Project Background

The Water Authority’s First Aqueduct contains six tunnels to convey water by gravity. This project will involve three of them delivering treated water to the northern portion of San Diego County. Each tunnel contains two buried concrete bifurcation structures, one at the upstream and the other at the downstream end of the tunnel. The upstream bifurcation structures combine flows from Pipelines 1 and 2 into a single tunnel. The downstream structures split the flow from the single tunnel back into the two pipelines. Pipelines 1 and 2 are 48 inches in diameter and the tunnels are typically 72 inches in the horse-shoe shape. Also included in this project are two above-grade concrete vent structures that are part of the aqueduct system allowing air entry and release at high points.

The project will use cast-in-place concrete to provide seismic upgrades at five bifurcation structures and two vent structures. New, precast panels will be needed to seal the tops of the modified bifurcation structures. At-grade concrete pads will be poured around or adjacent to the structures and new chain link fencing will be installed. Other improvements may include adding reinforcement, removing the existing stop log (metal) guides, and repairing concrete inside and outside the structures. The Water Authority has planned for an aqueduct pipeline shutdown in early 2025 to facilitate the rehabilitation work inside the structures.