Summary:

Scour at bridge substructure units can cause undermining of footings and exposure of piles, which can lead to bridge failure. Monitoring of the streambed elevations around a scour critical bridge to identify whether or not scour is occurring during a high-flow event is critical. Working on or near the water may be dangerous during these events.

The study investigated various techniques to monitor bridge scour during high-flow events.

Sonar has been the leading technique when completing underwater investigations. Different sonar devices were compared: single-beam echo sounder, multi-beam echo sounder, and side-scan. Based on parameters of cost, water depths less than 30 feet, data retrieval, processing, and quality, a single-beam echo sounder, sidescan, and the post-processing software SARHawk, was recommended.

Multiple access techniques were assessed based on personnel safety, ease of deployment, and efficient mobilization. Research concluded that a remotely operated unmanned surface vessel (USV) can best complete the following:

• Operate in turbulent waters with high current near substructure units or debris

• Obtain depth readings in water 3 to 30 feet deep

• Transmit real-time images and data to shore station

• Deploy rapidly and transport easily

Several USVs on the market were compared by means of a rating system and equipment testing. The USVs were rated on parameters outlined in specification sheets, in-person testing, and cost. The rating system identified the company and model of USV recommended.

The USV from Hydronalix called Sonar EMILY, equipped with single-beam sonar for water depths, sidescan sonar to obtain images of substructure units below water, topside camera to view the underside of bridges and performance characteristics to operate in turbulent waters with high current near substructure units or debris. The purchase cost for the USV, data acquisition laptop, and running gear is approximately $50,000. 

Publications:

• Final Report
• Spotlight

Additional Resources:

• Sonar EMILY User Manual - MDOT specific
• EMILY User Manual
• Kinexsis User Manual
• Sonar EMILY Autopilot Setup
• Flysky Transmitter Pairing and Programming
• Hummingbird Operations Guide
• SAR HAWK User Manual

Multimedia:

• Remote Controlled Vessels for Bridge Inspections

Research Manager	Project Manager	Performing Organization
Michael Townley	Chad Skrocki	Ayres Associates Inc.