Assessing Flood Damage with UAS
In this feature guest post, Geospatial Engineering Magazine discusses how fixed-wing drones helped a Canadian town identify and prevent flood damage. This mission was performed by Chris Healy, owner and operator of IN•FLIGHT Data.
Flooding in Canada is an ongoing concern, especially since the Alberta Floods in 2013, which cost an estimated $5bn. So, when rain raised river levels in Okotoks by 300% in just six hours, what was intended to be a typical mapping project quickly turned into a disaster management effort.
The project was being carried out in collaboration with senseFly, a fixed wing UAV manufacturer, to assess the success of recent upgrades at a wastewater treatment plant on Sheep River, Okotoks, Alberta. One of the indicators of the effectiveness of the upgrades was the temperature of the effluent. To help environmental scientists and evaluators collect samples at locations where there was a variant in the temperature, rather than taking random samples, we wanted to identify areas downstream of the wastewater plant where effluent was pooling.
As the length of the river running through the town was 8km, some of the mission was to be flown beyond visual line of sight (BVLOS) and so the senseFly eBee X fixed wing UAV was used. One of three senseFly UAVs on Transport Canada’s list of those eligible for advanced operations, the eBee X was employed alongside senseFly’s Duet T thermal mapping camera to provide a complete unmanned aerial system (UAS) that could meet all project requirements. Because the Duet T includes both a high-resolution thermal infrared camera and a senseFly sensor optimised for UAS applications [S.O.D.A.] RGB camera with a one-inch sensor, it was selected for a project looking to map both the land and temperature variants.
The planned mission involved a full RTK survey of the river valley. With eight ground control points, the set up included a pilot station on a ridge that overlooked the entire area, ensuring a continuous radio line of sight even though it was flying BVLOS. At its greatest distance the aircraft was 4km from the pilot and at that distance it would be landing blind.
The changing scope
24 hours before the flight was planned, a major rain event raised the water level of the river from 30m3 3/s to 90m3 3/s, meaning the temperature of the effluent could no longer be measured. Instead, the town now wanted to know how the rapid increase in water flow was affecting the river and parks, as well as its critical infrastructure.
As such, the mission was very quickly retooled to carry out a high streamflow surveillance of the river to assess the condition of the river itself, as well as the shore, and make sure there weren’t any issues that needed to be addressed by other departments. Working directly with the town of Okotoks, its engineering department, emergency services and the municipal police force, we coordinated a new mission to identify where high watermarks were as a result of the increased stream flow across an 8km stretch of river.
The eBee X flew for over 100km, capturing over 5,000 images in HD RGB and thermal IR in just two hours. The RGB function of the Duet T identified areas where the water was causing overland flooding within the river valley and showed where the new high-water marks were, at a resolution of 2.7cm/px. Using the orthomosaics that were captured, the team also created a full 3D model of the entire river valley. This was particularly valuable to the town as it could be used to update the municipality’s raster files within its GIS systems to show how the river had changed as a result of the high stream flow.
The town also wanted to pinpoint areas where there were temperature anomalies that may have been caused as a result of the flood, using the Duet T’s thermal camera. It was from these results that a new hot spring was discovered, which had been feeding the Sheep River. A team of experts examined whether the effluent was a result of anything else, but was unable to identify any other possible causes and concluded that the hot spring was more than likely caused by additional pressure on the hydrologic system as a result of the rain event, which was forcing underground hot water to the surface.
Although the flight unveiled critical information, many municipalities are budget-strapped and simply don’t have the finances to be able to carry out projects like this, especially in the timescales involved. If the original mission hadn’t been planned, then the disaster management assessments wouldn’t have happened. In this project, although being able to update the GIS and raster systems is important, the main benefit is that there is now an established baseline against which streamflow changes can be measured in the future.
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