Multiple Survey Technologies Speed Flood Response
The rain hit on an early summer Friday. In June 2017, a freakish storm, later described as a once-in-500-year rain event, dropped more than seven inches of water on central Michigan in just 36 hours. The storm was concentrated over a relatively small area. Midland County, home to roughly 83,000 people, was hit especially hard.
Near the city of Midland, the Tittabawasse River quickly rose to flood stage and beyond. On Saturday the river crested at 32.15 feet, more than eight feet above flood stage. It reached the second-highest level in more than 30 years. In less than two days, the river flow jumped from 3,200 cubic feet per second (cfs) to more than 39,000 cfs. The flooding inundated homes, businesses and infrastructure, inflicting millions of dollars in damage.
The county’s roads were hit especially hard. By Saturday morning, the Midland County Road Commission (MCRC) had closed roads in more than 120 locations throughout the county. The reasons for closures emphasized safety and ranged from standing water to washouts, damaged pavement and loss of culverts and drainage structures. The MCRC needed to act quickly to assess the damage and get repairs underway. The effort included identifying areas requiring immediate attention and developing plans for temporary or permanent repairs. The amount of urgent work was overwhelming. But there was good news: MCRC had a solid partner who was ready to go to work.
Led by Terry Palmer, MCRC managing director, the response to the crisis began immediately. “On Monday morning, we took stock, prioritized the damage and determined which roads we could open with minor repairs,” Palmer said. “There were over a dozen water crossings that would require more major repairs—which is when OHM Advisors called and offered to assist. They had a team ready to assess our crossings and start the process of obtaining topographic data for the major failures.” Craig Schripsema, manager of OHM Advisors’ office in Midland, deployed the firm’s survey teams to the affected area.
The relationship between MCRC and OHM Advisors had developed over many years. A Michigan-based firm providing architecture, engineering and planning for clients in the public and private sectors, OHM Advisors employs more than 500 people in 16 offices across three states. “We work alongside Midland County on many projects,” said OHM Advisors Survey Practice Leader Ray Lillibridge. “We don’t offer typical solutions; we bring forth the best solution customized for the county and not what’s most profitable for us. That approach to innovation has really helped strengthen our partnership.”
By Monday, the county emergency services were in the field identifying washed out bridges and culverts. The locations were marked on a paper at the MCRC office. Lillibridge quickly added the locations to a GIS application so the information could be readily shared among OHM Advisors’ teams. “Once we started plotting known washouts, we were logistically able to create a plan of attack,” he said. “We knew a couple of sites had no access, in which case we had to wait for the county to bring in temporary solutions.”
On Tuesday morning, two OHM Advisors field crews began surveying the damaged areas. They needed to gather data that would enable their engineers to evaluate the damage and develop plans to repair or rebuild the sites. In addition to often-circuitous routes to the sites, the two-person field crews faced soggy conditions and unstable, potentially dangerous slopes near the edges of the washouts. Lillibridge determined that the best and safest approach to producing accurate information quickly would be a blend of field technologies including unmanned aerial systems (UAS), GNSS and total stations.
At each site, OHM Advisors surveyors conducted a quick walkaround before setting ground control points (GCP) for the aerial imagery. They marked the points using chevron targets. The crews set a minimum of four GCPs at each site, placing two on each side of the washout. One point was set as close as safely possible to the washout, and the second on the road up to 400 feet away.
OHM Advisors captured the location of the GCPs using Trimble R10 GNSS receivers with Trimble TSC3 controllers running Trimble Access software. Connected by NTRIP (Network Transmission via Internet Protocol) to the Michigan DOT real time GNSS network, the R10s produced precise positions for each GCP. The R10 delivered coordinates tied directly to the required Michigan state plane coordinate zone. “We can connect our R10 receivers to the MDOT network anywhere we have cellular coverage,” Lillibridge said. “That way we can be confident that everything we collect can be used in the future.” At each site the crews used GNSS to collect a handful of check points needed to verify the accuracy of the aerial data.
With control in place, OHM employed a DJI Phantom 4 Pro to capture aerial imagery. Where vegetation prevented aerial work, they used a Trimble S7 total station to capture details of the washout. On average, the crews spent roughly one hour surveying at each site and completed 12 sites in two days. “Those were long days,” Lillibridge recalled. “Once we were actually on a location, things went quickly. It was the logistics of getting between the sites that presented a problem. At some places we had to go miles out of our way to get back into the other side of the sites.” Over the course of the next week and a half, the county identified an additional six sites that had been compromised. OHM Advisors crews surveyed them as well.
Integrating the Data
At the end of each day Lillibridge downloaded each site’s photos (roughly 60 images) to Esri Drone2Map for ArcGIS software. The GNSS data for control and check points was exported in CSV format directly to the Esri software, which produced a georeferenced point cloud. Lillibridge then transferred the point cloud to Trimble Business Center software (TBC). “We’re familiar with TBC for point cloud manipulation, so we were able to clean up the clouds and pull contours,” he said. “Then we exported all of that to Civil3D. Our work flow is such that no matter where the data was coming from, our CAD technicians would see the same thing and have the same thing to manipulate, whether it was from the drone software or TBC as GNSS points or total station points. Once it gets to the CAD techs it looks identical.” Because TBC supports all common industry data standards, transfers were accomplished via simple drag and drop of project files.
Lillibridge also used TBC to check the accuracy of the aerial work. “For this project, our tolerance was 0.15 ft vertical,” he said. “But I cannot recall any being over a tenth in vertical difference. These projects hit their checkpoints with minimal error.”
Preparation of deliverables moved quickly. OHM Advisors’ in-house engineering teams reviewed the field data and developed plans for rebuilding or replacing damaged structures. The firm had previously worked with the county to develop a design for Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) that provide flexible design and low maintenance. They provided sizes for the replacement bridges and the county’s contractors could then mold the road to fit the structure. As a result, aside from re-verifying the control, OHM Advisors did not need to provide any construction surveying.
As construction wrapped up, OHM Advisors used the opportunity to incorporate the Microsoft HoloLens 3D mixed reality headset. To do this, they exported design models from TBC to Trimble SketchUp software. Next, they used Trimble Connect to load the design data polylines into HoloLens along with a decimated version of the original washout surface model. In the field, they used Trimble Connect to orient to the site. They could then visually compare the finished conditions with the original surfaces. “It was really interesting on the HoloLens to see the base surface from when the washout occurred. The original data looked like a cliff in the new road where the washout had been,” Lillibridge said.
OHM Advisors has used HoloLens, SketchUp and Trimble Connect on other projects as well, primarily for pre-construction design and conception. For example, they recently did a project for a community firefighter memorial. The client wanted to see how planned flagpoles impacted the park site and how the monument sizes would fit the park. OHM Advisors’ experts visited the site with local officials, each using the HoloLens to visualize the finished project. The design work was done using Autodesk products and loaded into Trimble Connect for the field visualization.
In reviewing lessons learned from the Midland County flooding, Lillibridge said the effort confirmed what OHM Advisors has been doing. The approach of using UAS to supplement traditional survey methods proved to be stable and efficient.
MCRC’s Palmer emphasized the speed of the work. As the floodwaters receded, the commission set a goal to rebuild and reopen four key sites by the end of October. Palmer said that they completed the structure replacements with new GRS-IBS’ designed by OHM Advisors.
“I was amazed by the efficiency and professionalism of the OHM Advisors survey team,” Palmer said. “With minimal direction, they prioritized the areas to obtain data, collected data on multiple sites in one day and began delivering topographic data to the engineering design team in less than 72 hours. We then authorized data collection at additional sites and that information was delivered within three days. This allowed the engineering team to accurately assess the cost to restore nine road crossings, making our applications for emergency funds faster and more accurate.”
The performance of OHM Advisors was recognized by the industry. The company received the 2018 Eminent Conceptor Award from the American Council of Engineering Companies and the 2018 Project of the Year Award from the Michigan Chapter of the American Public Works Association.
Lillibridge credits OHM Advisors multiple technologies as the key to success. “Using a mix of technologies and methods is really beneficial in emergency situations. A lot of people think that traditional surveying is sufficient. But from a safety perspective, that’s not the best way. You can keep your personnel out of harm’s way, and because of the built-in efficiencies, you’re able to provide solutions much faster than with traditional methods.”