At work on the river

Follow a day in the life of a hydrographic surveyor as he navigates the Mighty Mississippi.

Instead of staring at the cubicle wall, picture watching the sun rising over the glassy water of the Mississippi, 60-degree weather, no traffic except for an occasional deer swimming across the water or an eagle flying toward a treetop perch. Such is the office life for a hydrographic surveyor.

On the other hand, it’s not the simple life of Huck Finn. Ray Armstrong explains that surveyors also experience cold and rainy days when 20 to 25 mph winds are whipping the boat around, the waves are 2 feet high, ice is forming on the front of the boat making visibility almost zero, or getting caught at the end of the day in a fog bank.

Armstrong heads up Hanson’s hydrographic surveying unit based in St. Louis, Mo. Although his territory extends across the country, he personally knows the 300 miles of the Mississippi River from Cairo, Ill., to Saverton, Mo., like the back of his hand.

Hydrographic surveying is performed to determine the underwater topography of a project site (body of water).

Information is collected on:

• depth of water;
• configuration, nature and thickness of the bottom;
• directions and forces of currents;
• heights and time of tides and water stages; and
• the location of fixed objects for survey and navigation purposes.

Armstrong says his crew needs to know more in addition to hydrographic surveying. They need to know a lot about working on the water, the boat and the equipment.

“For example, if you have a car problem, you pull over to the side of the road, fix it or call for help. If you have a boat problem, you can’t just pull over and thumb for a ride. You have to be prepared for anything and be able to react to a problem immediately. Problems like swift currents, high water, unknown water hazards, and river traffic,” he says.

The surveying work they do is highly technical. Hanson has an extensive history of offering electronic hydrographic and bathymetric surveys for clients in the private and public sector.

To ensure precise measurements, Hanson provides automated differential global positioning systems (DGPS) and Real-Time Kinematic/On-the-Fly (RTK/OTF) hydrographic surveys using two fully equipped survey vessels. Hanson has the capability to receive DGPS corrections broadcast by the U.S. Coast Guard, receive the DGPS corrections nationwide, or generate, transmit and receive our own DGPS corrections locally using RTK/OTF.

Hanson has provided single-track hydrographic surveys and automated multibeam single transducer channel sweep hydrographic surveys for the U.S. Army Corps of Engineers under several indefinite delivery order contracts.

Examples of multibeam surveys include work on the stilling basin and outlet channel at the Harry S. Truman Reservoir Dam, the largest flood control reservoir in Missouri, to determine its extent and depth of erosion. From there, the surveying team developed a computer-generated digital terrain model for measuring the amount of scour, horizontally and vertically, of the concrete floor, so that corrective measures could be properly engineered.

For the Vicksburg (Mississippi) District Corps of Engineers, they conducted detailed (full-bottom coverage) hydrographic surveys of 15 miles of river bends on the Mississippi River to determine existing river bottoms.

Other surveys of lakes, rivers, channels and harbors include the Indiana Harbor and Canal for the Chicago District Corps of Engineers and work on the Melvin Price Lock and Dam. For this dam near Alton, Ill., surveyors also monitor the structure for movement using instruments capable of millimeter accuracy.

Crews also have conducted surveys to determine locations of sunken barges, towboats and unknown underwater obstructions.

Surveying the damage

Sometimes the ordinary work is interrupted by emergencies. Armstrong remembers getting a call at home at 8 a.m. one Sunday in 1993. It was the St. Louis District Corps of Engineers requesting an immediate boat ride to inspect damaged levees and to determine how to survey through the breaches while the water was still flowing through the levee.

“We took the survey vessel from river to farm field, gliding along through flooded farm fields at 20 mph,” Armstrong says.

As a result of the 1993 floods, several Corp districts, including Kansas City and Omaha, had their rivers re-surveyed.

“We were under contract with the Kansas City District at the time. Their district covers 500 miles of the navigable reach of the Missouri River. Omaha had Kansas City contract with us to do their portion of 250 miles of the navigable reach of the Missouri River. Through a consultant who had a contract with the Omaha District, we also surveyed from mile 750 to 801 (non-navigable reach). These were hydrographic surveys only, no over bank work, from water’s edge to water’s edge, at 500-foot intervals perpendicular to the river.”

Armstrong explains that the main purpose of the survey was to determine the change in the river bottom due to the flooding and to create an updated hydrographic book map, but he adds that there were other byproducts, such as hydraulic analysis and engineering design.

A day in the life

During normal situations, each day the party chief is responsible for making sure there’s enough fuel in the truck, boat and generator (electricity on the boat). He hauls the boat to the nearest ramp to the project, launches it, and ensures working condition of motors, generator, computer, positioning and sounding equipment.

The next step is to locate and read the nearest river gauges to the project area. On the Mississippi, they are approximately 10-15 miles apart. Armstrong says the party chief knows where they are by memory, or he will read the water surface elevation from a previously established project benchmark. If he is working in view of a lock and dam, he has to notify the lockmaster, via marine band radio, of his position and work plan. He also monitors the radio for any barge traffic.

Once at the project location, the surveyor performs quality control checks and begins his work.

Horizontal positioning is done using global positioning systems in real time. It tells him his position every second and he compares the position with a known horizontal control station. Soundings are performed using a survey fathometer. To check the sounder’s depth, he lowers a “bar” to a pre-defined depth in the water to calibrate the sounder.

Normally pre-determined lines are established in the computer for him to navigate and are usually perpendicular to the river flow, go bank to bank, and are at sufficient intervals for the task at hand. Using real time navigation and a computer monitor, he navigates along reach “range,” collecting positions and depths until the process is completed.

Armstrong says “this is probably the most tedious part of the job.”

Although the work can be tedious, the surveyor, while collecting data, has to stay on line while the current is sweeping the boat downstream, adjust steering for changes in the river flow, adjust throttle for changing flows, monitor the river depths so he doesn’t run aground in shallow water, and continue to monitor river traffic.

Once he has collected the day’s work, he does a quick screen plot to ensure he has not missed any areas, and downloads the data to a CD-ROM. He then re-reads the river gauges and heads back to the boat ramp, finished for another day.

That field data is then transmitted to office personnel for further processing. Plan views, cross-sections, contours, and 3-D views can then be generated for engineering analysis.

For more information, contact Ray Armstrong, PLS, at (314) 209-0006 or at rarmstrong@hanson-inc.com.

Ray Armstrong takes precise measurements to the dam to determine horizontal movement. The information is used with other data collected at the site to ensure there are no problems with the structure, such as settling.

A hydrographic surveying boat heads toward the Hanson-designed Clark Bridge on the Mississippi River.

For the St. Louis District Corps of Engineers, the hydrographic surveying crew works at the Melvin Price Lock and Dam near Alton, Ill.