Aerial photos courtesy of Tara Gregg
Drone images show how rivers change at different times of year, from low water, to flood stage, to where springs run even in winter.

Videos shot from drone offer valuable perspectives

By Marcy Stamper

A river is part of a complex ecosystem, but that can be hard to grasp from the limited view on a riverbank. But get a few hundred feet above the ground and follow a river as it meanders, and you get an invaluable understanding of the flow, sheltered pools, and fertile wetlands.

For the past year, Tara Gregg, a drone pilot and cartographer, has been using a small drone to capture these elements — the current, eddies and side channels — and how they interact. Through her company Tabula Geographica, Gregg shoots both video and still photos for river-habitat and salmon-recovery organizations.

“It’s amazing the different things you notice from the sky. You just don’t have that perspective from the ground,” where you can see only 15 feet around you — even less if there’s lots of vegetation, said Gregg.

Drones are relatively new in river-restoration work, but they’re becoming an increasingly common tool, said Gregg. The flexibility of drones and the ability to deploy them quickly and relatively inexpensively has made a big difference in the accuracy and applicability of information about river flow, said Chris Johnson, president of the Methow Salmon Recovery Foundation.

“We used to need a helicopter — and a videographer who hung out of the helicopter — to take images,” said Jessica Goldberg, MSRF’s program coordinator. Not only was that costly, but it had to be scheduled weeks in advance.

Nimble and quick

By contrast, a drone is nimble and can go out on short notice. A drone can be sent out to check on an eroding bank or a logjam during high water, whereas hiring a surveyor and going out in boats could take weeks, said Johnson.

Before MSRF had access to a drone, aerial footage was done every 10 years or so. With a drone, it’s possible to see regular changes in the river and landscape. “If I can do it every year or every month, I have this amazing opportunity to show a funder or permitter what’s going on,” Johnson said. MSRF implements river and habitat projects to aid in the recovery of endangered salmon.

When a recovery or habitat group first starts looking at a project site, doing a flyover at different water levels will show areas of inundation and those that dry up later in the summer, said Gregg. The aerial perspective provides a broader view of the project area, including patterns that are not immediately visible from the ground, she said.

Videos are beneficial because they show the direction and the force of the water. Still imagery lets them focus on wet and dry areas and vegetation, said Gregg. They can figure out where to put calm pools that provide a refuge for tiny fish during high water. They can even see salmon holding in a pool, or redds along the river bottom.

Winter benefits

Drone imagery shot in the winter is particularly valuable, because the contrast of the snow provides a perfect backdrop for revealing how rivers work. For example, observers can see where a year-round spring melts snow and provides winter habitat, said Johnson. With no leaves on the trees, it’s easier to see water seeping into floodplains, said Gregg.

Gregg controls the drone from her smartphone. She can program it to follow a particular flight pattern, or to take photos in a grid. Gregg combines these photos through a process called orthorectification, which removes all perspective distortion so that it always looks like you’re directly above the image. It’s the same process used by applications such as Google Earth, she said.

MSRF has used Gregg’s drone imagery to help design a floodplain project on the Twisp River, and to monitor habitat changes on the Methow and Twisp rivers.

Project designers use the photos as a base map, and can draw right on it to show where a log structure would be installed. Engineers have said it gives them a better understanding of project sites, said Gregg. With more accurate information, the drone imagery lets them modify their hydraulic models.

The photos make the work easier for everyone to grasp — the public generally wants to see fish, not data and spreadsheets, said Goldberg.

Assessing flood damage

Over the past several weeks, Johnson has been working with a property owner on the Methow River who lost several feet of riverbank during recent high water. Drone imagery has proven indispensable in figuring out how to respond to concerns about flooding and bank erosion, said Johnson.

“It’s nice to talk to a landowner in a way they can engage in,” he said. “It’s usually ‘engineering-ese’ or ‘river-restoration-ese’ — tech-talk that makes most people’s eyes glaze over.”

Having accurate imagery also helps shape an appropriate response. When their property is threatened by erosion, people typically want a barrier right there to protect their house, even though the problem could actually be upstream, said Johnson.

“It’s really cool to put an iPad on the table to show a landowner, and to be able to draw in real time,” he said.

MSRF is considering using drone imagery to provide status updates to agencies like the Washington Department of Ecology, but thus far that has been limited by the state’s privacy concerns, said Johnson.

People are often uneasy about drones because they don’t know what they’re being used for, said Gregg. When she works for MSRF, they coordinate directly with landowners, but people passing through the area may see a drone and not understand what it’s doing, she said.

Gregg is certified by the Federal Aviation Administration to operate a commercial drone, also called an unmanned aerial vehicle, or UAV. She typically flies the drone between 200 and 300 feet above the ground. The drone flies relatively slowly and can stay airborne for about 20 minutes until its battery runs out. Gregg must notify local airports if she’s flying within 5 miles.

Groups that work on rivers are finding more uses for the tiny aircraft. Drone footage saved a beaver project researcher hours of difficult, messy bushwhacking, and it’s been used to observe habitat changes over time and to measure recovery after a wildfire.

“To be able to do that is really a giant step forward, compared to how hard it was five years ago,” said Johnson.