The Magazine for Underwater Professionals

May/Jun 2019

UNMANNED VESSELS

USVs - a solution for bathymetric dam imaging

The ability to use commercial off-the-shelf technology to conduct rapid and accurate hydrographic surveys has the potential to save lives, writes George Galdorisi

An appropriately equipped USV can be the ideal solution to examine a dam and provide precise underwater structural imaging. Photo: Jack Rowley

Many nations suffer from crumbling infrastructure. Bad roads, old bridges, archaic railways, outdated power grids and the rest are putting a genuine brake on the global economy. Most have only a general notion of the extent of the challenge of dealing with this issue, and rarely give infrastructure a second thought until they hear about a bridge collapse, a highway buckling, or other local catastrophe.

 

Deteriorating infrastructure is an issue for most countries – both developed and less so. Many nations have systems in place to evaluate and grade the state of their national infrastructure. In the United States, the nation’s civil engineers provide an assessment of the nation’s 16 infrastructure categories using an A-to-F school report card format. The latest report card assigned a D+ grade to the 16 US infrastructure categories.


Among these 16 categories, America’s 90,000-plus dams fared worse, attaining an overall grade of D. The condition of dams gets a great deal of attention – and it should. While a road buckling or a bridge collapsing might injure or even kill several people, a dam failing could suddenly flood entire communities, potentially causing scores or even hundreds of deaths and untold financial loss. The January 2019 failure of a Brazilian iron-ore mining company dam – the second dam failure in just over three years – flooded the town of Brumadinho. The initial death toll of 60 people is sure to rise with some 300 people still unaccounted for.

 

HAZARD
Part of the challenge of managing and sustaining this part of the United States infrastructure is the fact that the average age of dams in America is over 57 years old. Therefore, it is no surprise that the nation’s civil engineers identified over 15,000 dams as “high-hazard”, while over 11,000 more were listed as “significant hazard” potential, meaning a failure might not cause a loss of life, but could result in significant economic losses.


Most are only vaguely aware of what dams do for their local communities. Dams provide essential benefits such as hydropower, flood control and irrigation. When the public considers dams, they most commonly think of large engineering marvels rather than smaller structures that provide power for a small city, or ensure flood control for a valley. No matter how large or small, dams are typically overlooked until failure occurs.


By 2025, seven out of 10 dams in the United States will be over 50 years old. Fifty years ago dams were built with the best engineering and construction standards of the time, not the more-stringent design criteria that are used today. But while the “want” is often there to determine the condition of a dam, the “how” is a bit more daunting. A major challenge in deciding if and how to upgrade a dam is the lack of ability to survey that portion of the dam that is underwater. Surveying with divers is slow, expensive and hazardous.


The danger of using humans to survey the underwater portion of dams is often not well-understood. Many dams have violent, high-speed, high-volume currents that even the strongest divers cannot cope with. Until recently, the technology needed to do a proper survey of the underwater portion of dams without putting humans at undue risk simply did not exist. Today it does, through the use of emerging technologies such as sturdy and reliable unmanned surface vehicles equipped with echosounders and sonars.

 

SURVEY
A recent example of how emerging technology has been employed to survey dams in the United States involved marrying an unmanned surface vehicle with a high-resolution multibeam imaging echosounder to conduct an underwater survey of the Keokuk Dam on the Mississippi River near Keokuk, Iowa. This survey work was successful and is being studied by many US municipalities which are concerned about their local dams.


The Keokuk Dam/Energy Plant presented an extreme challenge as it is considered a nine out of ten on the scale of danger and difficulty due to the high currents and eddies caused by water flowing through the dam. This made an appropriately equipped USV the ideal solution to examine the dam and provide precise underwater structural imaging.


Due to the age of the Keokuk Dam, as well as the high-risk to divers due to strong currents and eddies, the facility’s owner and operator, Ameren Missouri, contracted with a Florida unmanned surface vehicle manufacturer, Maritime Tactical Systems (MARTAC), to conduct a comprehensive survey of the underwater portions of this dam. MARTAC produces a family of MANTAS unmanned vessels built on a catamaran hull. Ameren Missouri selected a 12-foot (3.7-metre) MANTAS for this underwater bathymetric imaging. For this task, the MANTAS was equipped with a Teledyne RESON (Denmark) T20 multibeam echosounder.

  • MANTAS USV equipped with Teledyne RESON T20 multibeam underway. Photo: Jack Rowley

The objective of the Keokuk Dam hydrographic survey was to develop the capability to map and inspect underwater structures with an unmanned surface vehicle followed by the USV performing the survey of the upstream and downstream sections of the dam. The deliverable was a comprehensive, on-location hydrographic survey which further evolved into a complete high-resolution bathymetric map and inspection report necessary to achieve the imaging and scanning requirements for the Ameren Dam Safety Group.


Earlier maps were developed using divers and manned surface vehicles. Not only did this technique put divers and other operators in harm’s way, but the resulting data obtained lacked the resolution to adequately detect and identify all areas of scouring, defects or structural problems. Use of the USV equipped with the multibeam echosounder was expected to correct these issues.


The USV solution performed as expected with excellent resolution. The final survey took less than two days to complete and was performed through the joint effort of a MANTAS remote operator seated next to a hydrographer. Operating as a team, the real-time USV track and the real-time display of the received echosounder imaging was coupled to achieve the best dam and bottom images possible.

 

PROOF
Based on the results of the Keokuk Dam hydrographic survey, additional proof of concepts were requested and demonstrated. As a result, other dam imaging has been performed and more are scheduled. With over 26,000 dams in the United States deemed structurally unsound, the market for such surveys that do not put people at risk is virtually unlimited. These US best-practices can readily be extrapolated to other nations, many of which have dams as old – or older than – those in the United States.


The dam failure that flooded the Brazilian town of Brumadinho is not a “one off” event. In 2018 alone there were major dam failures in Kenya, Afghanistan, Laos and Myanmar with a total of almost 100 fatalities. Having the ability to use commercial off-the-shelf technology to conduct rapid and accurate bathymetric dam imaging is a life-saving solution that all nations should consider adopting today.


The continued introduction of unmanned surface vehicle technology into the commercial arena will further spread the need for USVs in a number of other areas. In the United States, given the “D+” grade for the nation’s infrastructure, USVs will likely be in increasing demand for survey operations for bridges, ports, inland waterways, dams, levees, canals and other infrastructure that cannot be safely or effectively inspected by humans.

  • Real-time video display. Photo: Jack Rowley

Using low-cost, off-the-shelf unmanned vehicles to replace human operators when inspecting this infrastructure wherever and whenever possible will likely be a key factor in successfully undertaking needed infrastructure upgrades. All nations with aging dams would be well-served to study the results of the Keokuk Dam survey as a best-practices example of surveying this part of their infrastructure.

 

As readers of this magazine know, the commercial uses of unmanned surface vehicles are growing rapidly. This is due to the fact that these USVs are proving to be increasingly adept at doing the same “dull, dirty and dangerous” work in commercial applications as they do in the multiple military missions. Using unmanned surface vehicles like MANTAS that have been “wrung out” in military exercises, experiments and demonstrations is one way to achieve a low-cost solution to critical missions like infrastructure inspection and survey.

 

 

George Galdorisi is a former US Navy officer and holds a master’s degree in oceanography. He is currently the director of Strategic Assessments and Technical Futures at the US Navy’s Command and Control Center of Excellence in San Diego, California.

 

 

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