Moab presents 30% design for Third South bridge replacement; estimate near $10 million

Moab City staff and project engineers presented a 30% design update Oct. 28 for the 300 South (Third South) bridge replacement, describing a bridge and channel redesign intended to pass a 100-year flood with two feet of freeboard while working inside a constrained right-of-way.

The presentation said the current construction estimate is just under $10 million and could rise as the design is finalized. Designers are proposing a continuous bridge span (no intermediate culvert columns), a deeper channel section with a concrete-lined channel, and a shared-use path on one side with a sidewalk on the other. Because of the required structural depth, the road deck will rise roughly 4.5 feet at its center, requiring longer ramps and grade transitions on either side.

Why it matters: the Third South bridge is a known bottleneck for flood flows through downtown Moab. Staff said a plugged culvert at this location can cause urban overtopping and downstream impacts; the replacement aims to increase capacity and reliability while adding pedestrian connectivity.

Key details and tradeoffs - Capacity and elevation: the design target is to pass the 100-year storm with 2 feet of freeboard. The two‑foot freeboard…