Boxelder Basin mapped with high-tech LiDAR

Technology that has been used to map the mountains on Mars and the jungles of Mexico is helping engineers map and model Northern Colorado’s newest flood-control project — for a fraction of the cost of a traditional survey.

The North Poudre Irrigation Co. received $80,000 from the federal Natural Resources Conservation Service in 2011 to update the contour maps of the area of Larimer County stretching from the Soil Conservation Service dams north of Wellington south to Timnath. The update allows NRCS to study the possible impact of a potential breech of the SCS dams and what areas would be inundated in the event of such a dam break.

Ayres Associates, an engineering firm based in Madison, Wis., was hired to perform the NRCS mapping. In addition to taking new aerial photos, Ayres scanned the terrain with computerized LiDAR (Light Detection and Ranging) equipment. LiDAR can create topographic images accurate down to one-third of a foot, according to Jason Krueger, project manager for Ayres.
“LiDAR is much quicker than traditional mapping from aerial photography,” he said. “It also collects more data that we can put together in higher resolution. It shows surface features in higher definition.”

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The area north of Wellington mapped using LiDAR.

Ayres’ Fort Collins office is the engineering consultant for the Boxelder Basin Stormwater Authority based in Wellington. The authority spent $11,000 to access the portion of the data showing the drainage of Boxelder Creek, which is being modified to lessen the effects of flooding in the basin. Larimer County also contributed toward the study to update its own maps of the northern portion of the county.

“The LiDAR maps are nice for design purposes,” said Andrea Faucett, Ayres project manager for Boxelder. “And partnerships make the data available for a relatively low cost per square mile.”

How it works

LiDAR works in air like sonar works in water. The LiDAR equipment is mounted on the underside of an airplane. As the plane flies at low altitude over the study area, the LiDAR sends pulses of infrared light toward the earth. The signals bounce back from the ground at varying speeds, depending on the height of the objects encountered. That data is then processed into 3D maps showing geographic contours in minute detail.

For the NRCS mapping project, a plane carrying Ayres’ LiDAR equipment flew over 183 square miles of Northern Colorado at less than 3,000 feet for a day in October.

“The flight was very successful,” Krueger said. “It was a good time of year to do it, because the leaves were off the trees. That makes it easier to collect the data.”

Because the technology does not rely on the visible spectrum, LiDAR can be used in weather conditions that would interfere with normal photography — even at night — as long as there’s no snow on the ground to skew the reflection. It can also capture images hidden by a forest canopy, if necessary.

Colorado State University researchers used LiDAR last summer to reveal detailed architectural features of an ancient city “lost” in the deep jungles of western Mexico. In addition to outlining buildings and plazas, the LiDAR found changes in landscape elevation that suggest the city had a complex water management system.

It’s that accuracy of measuring elevation changes that was of the most interest to the Boxelder engineers.

“Optical bounce-back technology has come a long way in a short time,” Faucett said. “It’s greatly improved in weeding out extraneous data and showing only what’s important, and that makes it easy for us to get extremely accurate data.”

Colorized maps give engineers and project designers a visual representation of drainage patterns, down to the micro scale. They can use that information to create models to predict where floodwater would naturally flow – and the most efficient courses to reroute it.

Ayres began using LiDAR technology to update Federal Emergency Management Agency floodplain maps several years ago following the catastrophic floods in the Midwest, according to Krueger. Now the firm is building partnerships with other agencies across the country, like the Boxelder Authority.
“Accurate maps can help prevent disasters down the road,” Krueger said. “They make people aware of where the water wants to go.”

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