Fenstermaker launches its underwater acoustic survey vessel at the Boh Bros. facility in New Orleans.

Along with the rest of the nation, we at C.H. Fenstermaker & Associates watched in shock as Hurricane Katrina and the flooding that followed devastated New Orleans and the surrounding area in August 2005. The event hit especially hard for us because Louisiana is our home. Fenstermaker is a multidisciplinary firm headquartered in Lafayette, La., offering expertise in engineering, surveying and environmental consulting.

Our New Orleans office was shut down when Katrina hit. Our employees there were displaced and many suffered major losses. Throughout the devastation and turmoil, our firm remained committed to assisting our employees and making our services available for clients. When the time came to pick up the pieces, we were geared up to help.

We were called on to provide underwater acoustic services in support of recovery operations performed by Boh Bros. Construction Co. LLC, a marine, road, and bridge construction firm headquartered in New Orleans, under contract to the U.S. Army Corps of Engineers. We performed underwater acoustic imaging and acoustic profiling to provide obstruction detection, location and mapping; localized water bottom and obstruction relief profiling; and underwater bridge inspection.

Underwater acoustic visualization of sunken dry dock barge at Florida Street Bridge.

Locating Underwater Wreckage

Our first task was to locate and define the size and position of a sunken barge and sailboat in the Inner Harbor Canal, also known as the Industrial Canal. Fenstermaker's Surveying & Mapping Division mobilized a three-person acoustic survey crew, which I led. Our underwater acoustics team arrived in New Orleans in the early morning hours of Sept. 18, approximately two weeks after Hurricane Katrina's storm surge breached the levee system that protected New Orleans from Lake Pontchartrain and the Mississippi River. It was eerie and uncomfortable arriving in a major metropolitan area that seemed to be empty and devoid of all normal activity. We picked our way along debris-strewn streets to the Boh Bros. yard on the Mississippi River-Gulf Outlet. From there, we launched our survey vessel by crane since debris had jammed nearby launch facilities, rendering them unusable.

To locate and provide images of the two wreckages, we used our proprietary high-resolution steered beam sonar coupled with Differential GPS (DGPS) positioning obtained using Trimble (Sunnyvale, Calif.) 5700 survey grade receivers. The high-resolution steered beam sonar, which was developed under the direction of Fenstermaker by manufacturer Kongsberg Mesotech, uses system integration and data acquisition to provide superior underwater visualization in shallow underwater environments. One of the advantages to using a steered beam technique is the ability to limit the impact of surface noise (inherent in shallow water environments) on the data by directing the vertical path of the acoustic beam. In addition, the ability to mount the sonar so it sweeps ahead of the survey vessel increases safety and provides multiple perspective ensonification (energizing with an acoustic pulse) of the water bottom and targets resting there.

The sunken barge was located close to the Florida Street Bridge and actually sat on the water bottom under a construction derrick barge being used in recovery efforts. We determined the dimensions of the barge were 30 feet by 66 feet, which made it clear that a larger recovery vessel than the one currently available onsite would not be necessary.

We then moved on to locate the sunken sailboat. We performed a sonar sweep scan of the water bottom from the survey vessel as we tracked northward in the canal toward the Almonaster Bridge. Our crew defined targets of interest in an area 800 feet to 1200 feet south of the bridge. Stationary deployments of the steered beam sonar sensor let us perform a detailed investigation of the defined targets. We established that one of the defined targets was the sailboat we were looking for. It was located 1,100 feet south of the Almonaster Bridge and 125 feet from the west bank of the canal. The 60-foot sailboat was oriented southeast to northwest with the mast projecting north from the sailboat hull. The wreckage was marked with a buoy and geographic position reference. The next day we observed a salvage spud barge (a barge moored by two vertical tubes from the barge to the water bottom used for salvage and recovery operations) position itself so it could successfully salvage the sailboat with the assistance of divers.

Our efforts then turned to marking the extremities of a partly submerged dry-dock barge partially blocking the canal at the Florida Street Bridge. We scanned the water bottom with the steered beam sonar to visualize the position and attitude of the dry-dock wreckage. The wrecked dry-dock barge was approximately 300 feet long by 160 feet wide. It had been pushed against the bank of the canal with one end projecting 225 feet into the canal. A cargo barge straddled the top of the dry dock's exposed section and the bank. We performed acoustic profiling to determine the extent of the navigable gap on the east side of the canal. We used our proprietary steered beam narrow footprint acoustic profiling system to profile the wreckage and cavities inside the wreckage. We were also able to direct the acoustic beam to profile the water bottom underneath suspended portions of the wreckage.

The objective of our work was to facilitate at least limited usage of the canal for barge and boat traffic. The profiling indicated that there was a 95-foot-wide gap with a water depth of 34 feet between the barge and the east side bridge pilings and coffer dams (a system of pilings used to isolate an area in a body of water from the water), which could be used for navigation.

Departing New Orleans after dark at the end of an interesting day of surveying was as disconcerting as our arrival. There was no electrical power in the core of the city at that time, which meant there were no lights. The city was darker and more desolate than I ever could have imagined. The only noticeable activity came from the National Guard Troops who worked various checkpoints.

Underwater acoustic visualization of submerged barge and wharf pilings near Florida Street Bridge.

Returning to the City

We returned to New Orleans a few weeks later in the aftermath of Hurricane Rita. This time we were contracted to redefine the vertical profile of the sunken dry dock at the Florida Street Bridge and inspect the pilings, underwater support bridge structure and surrounding water bottom for the Seabrook, Almonaster and Florida Street railroad bridges. We were also asked to conduct a total "post salvage" scan of the Inner Harbor Canal water bottom to find possible obstructions to navigation that might have been missed during the initial salvage and wreckage recovery.

Working conditions were less than desirable and slightly hindered productivity. There was significant concern about the level of biological and chemical contamination in the water, and an extremely unpleasant odor of rotting poultry from a large, formerly refrigerated warehouse filled the air. To get the job done, we obtained respirators with filters that reduced the odor to a bearable level. Concerns about contaminant levels in the water were later declared by government agencies to be unfounded, as contaminant levels were reported to be within established guidelines.

To allow the director of salvage operations to position recovery barges above the wreckage without causing damage to them, we began to redefine the vertical profile of the submerged dry-dock wreckage. We performed acoustic profiling over the wreckage using a steered, narrow beam acoustic profiling system integrated with pitch and roll attitude sensors, a heading sensor and Trimble 5700 RTK GPS receivers. From the acoustic profile data acquired, we produced a map depicting the elevations across the surface of the wreckage, relative to the NAVD88 vertical datum, which the operations director then used to plan the positioning of the salvage barges.

Working on the Bridges

Our next task was to inspect the pilings and surrounding water bottom at the Seabrook and Almonaster railroad bridges. To do this, we implemented the same technology and procedures used to map the profile of the sunken dry-dock. We performed the visualization and profiling of the underwater bridge support structure at the bridges over a two-day period. The profiling and imagery data we acquired enabled us to generate an image of the underwater support structure and the surrounding water bottom as well as cross sections at 20-foot intervals along the canal.

The cross sections depicted the water bottom profile across the canal on the approach to the bridge as well as the profile of the bridge support pilings and coffer dams on the embankment side. This was of interest because, during the storm and shortly after, stray barges drifted against the bridges, blocking the water flow through the canal and forcing the majority of the flow to go between the backside of the bridge supports and the embankment. There was concern that this may have caused scouring of the water bottom around the bridge support pilings, but the acoustic imagery showed no evidence of significant scour impact. The profile data illustrated various irregularities in the water bottom but no consistent pattern that might indicate scour.

At this time we were also asked to inspect the underwater structure of the Florida Street railroad bridge. However, we couldn't perform this task until the wreckage of the sunken dry-dock had been salvaged, which took another two months.

Digital elevation model of water bottom at Florida Street Bridge.

Profiling for Destruction

We then proceeded to scan the entire length of the canal from Lake Pontchartrain to the Mississippi River, primarily looking for any obstructions to navigation that remained on the water bottom. We did this over a two-day period in mid-October, defining 41 targets, two of which were disqualified upon review. Of the remaining 39 targets, only one corresponded to a significant obstruction. The object was an overturned lift-boat at the entrance to the slip of a boatyard 4,000 feet south of the Seabrook Bridge at Lake Pontchartrain. It was near the canal bank, west of the main path of travel and was not a hazard to navigation. The remaining targets, while indicating a significant amount of debris scattered down the length of the canal, did not indicate a profile that would be a hazard to navigation. From the results of the water bottom scan and visual observations of conditions on the surface, it was evident that the majority of the damage and resulting wreckage was strewn along the banks of the Inner Harbor Canal, where there were dozens of grounded vessels ranging in class from small pleasure craft to yachts to large cargo barges.

Back to the Bridge

On Dec. 6, 2005, we returned to complete the underwater survey of the Florida Street railroad bridge, which was not an easy task. Because it is on the same platform as a road bridge, it could only be kept open for short periods of time. Since our survey boat needed to be under the bridge during much of our work, we surveyed small sections of the underwater bridge support structure during times when the bridge was open. It took two-and-a-half days to complete approximately four hours of work, but the bridge survey task was finally complete. The data showed an extremely disturbed water bottom, but no indication of a scour pattern around the bridge support structure.

This was an incredible experience for us. We observed extreme devastation reminiscent of a war zone, coupled with a complete lack of activity and life, especially in the eastern New Orleans area. We saw destroyed and abandoned buildings strewn with debris that included cars, trucks and boats on buildings and in trees. We saw toppled power poles and transmission lines. In the early days of our work in the Inner Harbor canal, the only life we saw other than National Guard troops and recovery personnel was the odd emaciated dog and a group of swans swimming in the Inner Harbor Canal. We are proud that C.H. Fenstermaker & Associates was able to provide the technology and services that helped move the destroyed area a little closer to recovery. Our firm continues to provide acoustic services as well as engineering, surveying and environmental services to support hurricane recovery and storm protection rebuilding efforts.

Composite image from underwater acoustic survey of Huey P. Long Bridge.

Sidebar: Improving the Future

In addition to providing underwater acoustic imaging services for the recovery effort, Fenstermaker has aided in verifying the structural integrity of the Huey P. Long Bridge. This bridge, which spans the Mississippi River in New Orleans, has been in service since 1935, and is set to undergo a major expansion.

The Huey P. Long Bridge widening project is part of the Louisiana Department of Transportation's TIMED (Transportation Infrastructure Model for Economic Development) Program, the single largest transportation program in state history. The project is designed to improve traffic flow while increasing safety for the motoring public.

Because the bridge expansion will require extensive modification to the upper section of the bridge piers, Fenstermaker was commissioned to evaluate and record the condition of the bridge piers using underwater acoustic imaging technology, and to establish a base line of the pier condition.