It’s World Hydrography Day! What better way to celebrate than by highlighting the professionals of the Galveston District’s Hydrographic Survey Section?
First things first: what is hydrography? It is the science of surveying and charting bodies of water, such as seas, lakes, channels, bays, and rivers.
As Galveston’s Hydrographic Survey Section Chief Erin Diurba tells it, hydrography—a very math and physics heavy science—helps the U.S. Army Corps of Engineers Galveston District manage important waterways by determining the physical features of an underwater area.
That’s where Diurba, her team at the Jadwin Building, and the three other Hydrographic Survey Sections across the District come in.
So what exactly does the Hydrographic Survey Section do?
The ‘Hydro’ team—as Diurba likes to call it—primarily assists marine construction by monitoring the condition of the navigation channels and determining how much material is removed after dredging work. Dredging is the removal of material from the bed of a harbor, river, or other body of water.
[If you've been keeping up with local news, you'll know the District has been doing a lot of dredge work lately.]
“We collect surveys to try to figure out the volumetric change between [the sea floor] before dredging and after, so that we know how much to pay the contractor for removal,” Diurba said.
Conducting a hydrographic survey isn’t as easy as doing a survey on land because of the characteristics of water. “You are transmitting and receiving acoustic signals through a material that is constantly moving and changing,” Diurba said. “There are an incredible number of components that must work together seamlessly in order to track position, compensate for movement, map the speed of sound, and mathematically determine the depth and location of the ensonified patch of seafloor.”
No two bodies of water are going to be the same, she explained. The unconsolidated sediment and mud-rich waters surrounding Galveston and most of South Texas make it difficult to get an accurate depth measurement of the sea floor. The Hydro team uses a combination of high and low frequency sonars to help isolate the unconsolidated layers and determine the location of the hard upper surface.
“Our professionals have to use their training and their understanding of how sonar technology works, and its limitations, to make the best decision possible,” Diurba said.
Consistency is the key to getting as accurate a measurement as possible, she said. This means using the same boat, the same equipment, and the same survey team. “That way, you can minimize the number of variables in the system and ensure repeatability,” said Diurba, who’s one of only five certified hydrographers within the Corps of Engineers.
The Hydrographic Survey Section also provides a critical service during emergencies.
Leading up to a hurricane, some ports shut down and stop all marine traffic because they’re not safe for navigation, Diurba explained. Getting the ports back up and running is crucial for the economy. According to 2020 statistics, Texas is home to six of the top 20 ports in the country. “Houston is number one on that list,” Diurba said. “They’re losing millions of dollars every day they’re down, if not more.”
During a navigation restoration response, the Hydro team, under the direction of the Corps of Engineers Navigation Restoration Team, works with local Coast Guard Sectors, the National Oceanic and Atmospheric Administration, and local stakeholders to conduct an effective, consistent, safe, and speedy restoration.
“This means making sure the channels have not shoaled in and are safe, meaning there are no obstructions or debris in the water,” Diurba said. The team provides hydrographic surveys to help port authorities determine if the channels are safe for navigation to resume.
This mission has a significant impact considering that a major portion of the trade economy comes through the Gulf Coast of the United States, Diurba stated. In fact, 98% of overseas trade moves through Corps of Engineers projects: 48% of the goods Americans buy pass through harbors maintained by the Corps of Engineers.
Tools of the trade
Hydrographic survey teams rely on agile boats and very sophisticated sonar equipment to get the job done.
In 2021, the Galveston District Hydro teams received three new 27-foot aluminum boats that are equipped with side-scan, multibeam, and single beam sonar systems. Each type of sonar performs a specific function to help paint a clear picture of what’s going on beneath the ocean surface.
- Single beam sonar: uses a single transducer to transmit and receive acoustic energy signals, or “pings.” It’s mainly used for figuring out average depths on the ocean floor, Diurba said.
- Multibeam sonar: sends out multiple, simultaneous sonar beams (or sound waves) at once in a fan-shaped pattern to create a full coverage 3D model of the seafloor.
- Side-scan sonar: emits pulses that measure the intensity of the signal return to locate objects and provide an understanding of the differences in material and texture of the ocean floor.
Hydrographic survey technology is constantly improving, Diurba said. “Most of our equipment has up to a seven-year shelf life,” Diurba said. “Technology changes so fast. We have to evolve with the times.” To ensure mission success the Galveston District’s Hydrographic Survey Section just underwent a $3 million equipment overhaul, she explained.
[To see the work the Galveston Hydro Team does for all the local ship channels, visit their webpage.]
Getting new gear has had immediate benefits, Diurba added. Standardized gear allows for standard operating procedure development, consolidates training and contracting actions, simplifies repairs and replacements, shared lessons learned, and flexibility to share equipment between staff without an extreme learning curve, she said.
“Somebody from Galveston can go to the District’s Port Arthur office and still be able to use their equipment just as well,” she said. Having the same gear across the District will also shorten response times during critical operations, Diurba said.
With new gear and a whole lot of dredging work in their near future, the Hydro team looks forward to continuing working with the Galveston District to maintain the safety of the Coastal Texas waterways.
In the past 10 years, the team has responded to seven hurricanes, giving them plenty of experience in their field. The rest of the Corps of Engineers hydrography section has taken note of the Galveston District’s professionalism as well. The Galveston District’s Hydro team recently hosted the Hydrographic Survey Techniques course. It was the biggest turnout in the course’s nearly 50-year history.
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