The Project
In the aftermath of Hurricane Katrina, the U.S. Army Corps of Engineers (USACE) was faced with the inconceivable task of rebuilding the New Orleans levee system. The first step in this process was to map existing and damaged levees as well as flood control structures associates with the levee system. Survey firms from across the nation were contracted to provide critical information about the existing condition of the levees.

The Rock Island District of the U. S. Army Corps of Engineers had contracted Stanley Consultants, with Martin & Whitacre Surveyors & Engineers, Inc. as a survey subcontractor, to perform a comprehensive six (6) mile topographic survey of the levees. The project began at the 17th Street Canal and followed Lakeshore Drive East to the Inner Harbor Canal. Beyond the scope of a traditional topographic survey, was the request by the USACE to use cutting edge High Definition Laser Scanning (HDS) to capture point cloud data for the Flood gates along the route. Martin Whitacre and the USACE had agreed that HDS was the perfect tool to map the intricate details of the flood gates for later production of 3D CAD models. Martin Whitacre being one of the pioneers in HDS, decided to focus their efforts in mapping the flood gates and began the search for a sub consultant who could focus on the traditional topographic surveying needs of the six (6) mile survey.

Fenstermaker HDS Team Called In
In September of 2006 C. H. Fenstermaker & Associates, Inc. was subcontracted by Martin & Whitacre, to conduct the topographic survey of the six (6) mile stretch of the Lake Ponchartrain levee system. The topographic survey requirements were demanding due to the level of urban development along the route and complex utilities from many years of development and poor conditions due to the flooding by hurricane Katrina.

Figure 1

The task of preparing for a six mile comprehensive topographic survey required an efficient workflow. Based on site conditions, it was decided that a combination of three different technologies would be needed to maximize production; Conventional, GPS and HDS. Required levee cross-sections and profiles were conducted with RTK GPS procedures while control was carried out using GPS observed control points. Each control point was observed for two, six minute sessions. The USACOE Interagency Performance Evaluation Task Force determined that NGS monument ALCO would be held as control.

The pivotal difference for collecting 90% of the topographic features was making the decision to expand the use of HDS beyond structural elements of mapping flood gates. This decision became a viable option thanks to the latest release by Leica called the Scan Station high definition laser scanner. Because of the Scan Station's ability to traverse like a traditional survey instrument, approximately ¾ mile of topography along the levee was collected in a day's work (Figures 1 & 2)

Each setup included a 360º scan and complete digital photography at that location. Point cloud density was in the range of 10 inches horizontal by 1.5 inches vertical at a distance of 300 feet. Accuracy of the scans varied from 3mm at 150 feet to potentially 8mm at a distance of beyond 450 feet from scanner. On an average day, Fenstermaker surveyors completed 10 scans with about 400 feet between setups. In areas with many obstructions, and tall vegetation, traditional total stations were utilized.

Figure 2

On a project of this magnitude and complexity, the use of HDS offers distinct advantages. As shown in Figure 2, the level of detail provided by the scanner virtually eliminated return trips for missed data in areas ware the scanner was used. Figure 1 is a good illustration of the comprehensive surface model generated from the point clouds. We were able to map every slight variation in elevation relief. Using tools like Virtual Surveyor included in Leica's Cyclone Software, traditional survey data was extracted to prepare the required submittals of topographic plan/profile maps. Because the USACE has not yet received training in Cyclone, we were able to extract a 5 ft grid of the entire six (6) mile levee for DTM creation in Inroads.

The ScanStation proved to be a valuable tool in the data collection aspect of this project and will continue to be at the forefront of Fenstermakers emerging technologies.

About the Author
Ryan Fuselier is a Registered Professional Civil Engineer in Louisiana and a Professional Land Surveyor in the States of Louisiana and Texas. He is currently the Past President of the Louisiana Society of Professional Surveyors and is an Engineering and Surveying Director for C. H. Fenstermaker.

Published in the June 2007 issue of SAME Vicksburg newsletter

Fenstermaker is a regional company providing engineering, surveying and mapping, and environmental services to federal, state and local governments, the oil and gas industry and private enterprise. Fenstermaker's offices are located in Lafayette, New Orleans, Baton Rouge, and Shreveport, Louisiana and Houston, Texas.