Using High Definition Laser Scanning in the Face of the Anticipated El Niño
By James Nicolau IV, PLS
Since California is in the midst of a severe drought, the forecasted El Niño for this fall and winter suggests a long-awaited reprieve—the rainfall is much needed. However, danger lies within the prospect of this drought-easing weather. Shorelines, coastline structures, and areas that have had recent wildfires are at risk from the forecasted El Niño storms, with the strong possibility that life-threatening damage could occur.
The drought has sapped moisture and soil adhesion, and once the soil becomes over saturated, swelling or expansion could lead to unstable cliff faces or, worse case, structural failure and collapse. There is also a danger to the structural integrity of piers and storm walls along the shoreline from increased surf, combined with the natural winter regression of the supporting beach sand.
These types of damages will not be isolated to the communities along our coastlines. Inland drainage structures, bridges and dams will also be vulnerable to a rapid increase in water flow and potential “flash flooding,” as we saw in the recent collapse of the “Tex Wash” bridge on Interstate 10 near the Arizona border in July. This bridge was host to more than 20,000 cars per day and, during the time that the bridge was out of service, drivers had to travel hundreds of miles around this route. The bridge was listed as being functionally obsolete in 2014, however no structural defects were known.
To proactively identify these kinds of risks, systematic scanning of vital structures in the natural and built environment would provide a comprehensive review with the ability for more diligent inspections.
We are fortunate that modern laser scanning is superior to conventional surveying methods in a number of significant ways. A laser scanner is capable of obtaining upwards of 100,000 shots per second, which allows for a much denser and richer point cloud model. Rip rap, for instance, is very difficult to measure accurately and cost effectively, but not for a laser scanner, which can capture anything the eye can see. Once the scan is complete, that data can be saved and then compared year-to-year to accurately measure and track sediment build up.
Laser scanning can efficiently create a baseline of existing conditions for successive monitoring campaigns. Modern scanners are able to obtain accuracies to within +/-2mm, providing phenomenal resolution for monitoring and change detection. An added benefit is that once that data has been collected, there is a complete as-built report and, should a failure occur, there is the ability to precisely recreate the pre-failure conditions.
Laser scanning is also a non-intrusive means of collecting data—data can be collected safely and without disturbing the local environment. This allows the user to document sensitive areas without causing harm to the local ecosystem. Once data has been collected in the field, project-specific measurements can be made from the office by analyzing the resulting point cloud. Scanning also provides design-quality as-built data while not impeding traffic needs.
The added benefit of performing laser scanning is that once the scans have been captured, you can always return to the model and extract more data as you or your clients’ needs evolve through the scope of the project, without the need to go back into the field.
With the El Niño season fast approaching, the proactive use of laser scanning could be essential in protecting and enhancing our communities’ safety.
James Nicolau IV, PLS is a Project Manager in the Psomas San Diego Survey team.