Replacing San Antonio River Walk Flood Gates with a 650-Ton Crane: A Practical Engineering Retrofit

Overview

In this episode of Practical Engineering, Grady Hillhouse documents a major flood control upgrade in downtown San Antonio. Crews replace aging flood gates on the San Antonio River, install a hydraulic gate system, and repurpose a downstream pump area to keep the River Walk flowing while work continues. The project centers on preserving the riverfront as a public asset while updating critical infrastructure.

What you’ll learn: how a city maintains a constant upstream water level, the sequence of gate removal and installation, and the role a large crane plays in complex urban lifts.

Introduction: Setting the Scene

Grady Hillhouse introduces a high-profile civil engineering effort in downtown San Antonio. The River Walk is described as a below-street-level park that anchors a major tourist district, with the Alamo and other attractions nearby. The video frames a long‑planned replacement of two aging flood gates installed in 1983. These gates regulate the upstream water level in a critical bend of the river, allowing floodwaters to pass downstream when needed while keeping the downtown channel from draining during sunny weather.

Background: Why Gate Replacement Was Necessary

One gear box on a flood gate wore out, eventually causing misalignment and inoperability. The city installed stop logs to block flow and prevent the riverwalk from dropping, but the dam could no longer lower the gate in a flood. This triggered a modernization effort to design and install new gates that fit within the existing structure, increasing reliability and capacity without draining the River Walk.

The Bypass and Pump Room: Keeping the River Moving

The project includes a bypass system downstream of the dam to recirculate water and prevent stagnation. An original screw pump, Archimedes screw, was installed to lift water upstream if flows drop, but a flood bypass tunnel later allowed downtown flows to bypass the area, rendering the old pump obsolete. The bypass improves circulation, reduces sediment buildup, and helps flush debris when needed.

Construction Phases: Gate Removal and New Gate Installation

Initial work focuses on removing the damaged leaf and its attachments. Large equipment is staged in a nearby parking lot to minimize disruption to pedestrians. The crew detaches the drive shaft and the top hinge assembly, using a crane to lift out heavy components. A sequence of cutting, grinding, and bolting is performed with rigorous safety planning, including spotters and a lift plan. The first gate is removed and placed in a staging area, while the second gate follows a similar process, now completed more quickly because the new design could be fitted faster.

The New Gate: Hydraulics, Not Electric Motors

Unlike the old gates that relied on electric motors, the new system uses hydraulic cylinders powered by a dedicated power unit. Piers are retrofit to accept hydraulic actuation, and the top beam and hinge points are installed to link the cylinders to the leaf. The two halves of the new gate are joined with sealant and bolts before installation at the dam, then torqued to specification on both upstream and downstream sides.

Oil, Concrete, and Safety: Supporting the Final Assembly

After the gate is landed on its base plates, the team completes concrete modifications to ensure a perfect fit. An overhead crane in the adjacent pump room helps position the new gate into place, showcasing how urban projects rely on coordinated space and equipment. The hydraulic power unit and control tower enable operators to adjust the gate’s position from a central location that overlooks the dam and bypass tunnels.

Testing and Commissioning: First Movements, Then Confidence

With the system wired, operators perform a controlled test lift to verify linear movement and avoid binding. The test is described as successful, though the team proceeds with care to avoid destabilizing the River Walk. Finally, old stop logs are removed in stages, and the site transitions to a near-complete retrofit, with two new gates and a bypass ready to serve the city for decades to come.

Reflection: Significance for Urban Infrastructure

The video closes with thanks to the City of San Antonio, the River Authority, engineers, and the contractor. The author emphasizes the beauty and complexity of large-scale civil engineering and the importance of maintaining critical infrastructure without disrupting public spaces. The episode also notes how independent creators bring a fresh perspective to heavy construction, making complex projects accessible to a broad audience.