Inexpensive Sonars Changing the Game for Rapid Detection of Bridge Scouring

Vincent J. Capone

President, Black Laser Learning


Technological improvements are enabling DOT teams to quickly and economically assess bridge scour damage after, or even during, high-water events.   A combination of innovations in three different fields work together to create sonar systems which can be easily and rapidly deployed when and where they are needed.

Sonar systems used to come in two flavors; effective but expensive, complex towed units or cheap, easy-to-use fish finders with minimal functionality and poor resolution. Towed side scan sonar or very complex multibeam systems have historically been the only choice for projects requiring high quality data. These systems cost tens of thousands of dollars, plus require extensive training and manned surface craft, limiting the number of surveys conducted. Towed units have the further drawbacks of often getting snagged by submerged debris and being difficult to maneuver in tight areas.

In the past few years, the imagery and data quality generated by hull-mounted sonars (fish finders) have improved exponentially. In shallow water (typically under 75ft), they offer high resolution images of bottom structure, pilings and obstructions as well as depth soundings. Hull-mounted units have the advantages of being affordable, mobile, easy to use, and less prone to damage. They also offer both Down Imaging (DI) and Side Imaging (SI). Down Imaging sonar can provide detailed images of vertical structures such as bridge piers or exposed footers and measurements from DI images have been shown to compare extremely well with diver measurements. Alternatively, Side Imaging hull-mounted systems offer quick and easy overhead views of scour and debris. The hull mounted systems also provide single beam depth data which allows engineers to see the depth of scour in addition to bottom profiles. Having all these sensors combined in a small, single hull mounted transducer enables teams to rapidly assess damage after, or even during, high water events.


Humminbird(r) down and side images of dam intake structure — Courtesy of Colorado Parks and Wildlife


The second game changing innovation is the commercial availability of sophisticated data processing software capable of importing Humminbird® sonar data (a leading hull-mounted sonar system), analyzing targets, creating mosaic maps of the survey area and exporting xyz coordinates. SAR HAWK® Surveyor software enables detailed analysis either in the field or on a high-resolution screen in the office, allowing engineers to zoom in on areas of concern, ensure they are looking at the same exact spot on multiple passes, measure targets and export data in GIS compatible formats.

Finally, we have entered the robotic age. Small, portable autonomous surface vehicles (ASVs) can now be procured with built-in sonar capability. For example, at five feet in length weighing about 50 lbs, a Sonar EMILY can be transported in a standard vehicle and deployed from just about any shore. ASVs offer not just convenience but safety as the survey is conducted from the shore by remote control or automated search pattern. Surveys can be conducted during high-water events without endangering personnel.

Two Sonar EMILYs survey a bridge pier


The Michigan DOT engaged Ayres Associates Inc. of Michigan to conduct a study of various systems to determine effectiveness based on the criteria of bridge scour detection, ruggedness, safety, and ease of use, transport and deployment. The study recommends the use of hull-mounted sonar systems, especially the Sonar EMILY/Humminbird®/SAR HAWK® software combination. (Ayres Associates study)


Image of a bridge pier — EMILY equipped with Humminbird(r) sonar — Courtesy of Michigan DOT


With our nation’s aging infrastructure, the need to monitor the integrity of bridges and waterways will only increase the demand for surveys. These innovations make those surveys easier, safer and more affordable.

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