Streams on Chichagof Island mapped using high resolution digital elevation data. (Photo courtesy of TerrainWorks)

There could be up to five times as many streams in Alaska than previously thought, according to a group of scientists and programmers who have spent nearly a decade mapping the state.

Lee Benda runs Terrain Works, a company that maps natural landscapes. He says many state and federal agencies rely on the National Hydrography Dataset which charts known waterways.

“The problem with the datasets is that the mapping accuracy is fair to poor,” said Benda. “They lack large numbers of streams and rivers because they were drawing them from photographs and interpreting their location even under thick vegetation.”

Benda’s team built new maps, based on cutting-edge high resolution digital elevation data gathered by aircraft. And that has led to some dramatic discoveries.

“On North Chichagof Island, west of Juneau, we discovered a 518% increase in the channel length of the networks in that island, based on the high-resolution digital data,” said Benda. “It was eye opening to see all the streams that are missing on the current maps.”

Benda’s new maps have already revealed nearly 200,000 miles of new streams across Alaska. That’s enough streams to go around the world seven times! And so far, they’ve only mapped half of the state. Benda says all of this matters for two big reasons. Firstly, fish habitats.

“Well, if you’re going to protect fish habitat, you have to know where the habitat is,” said Benda. “And so with the advanced mapping and the discovery of all these, what I would call missing streams, there’s also missing salmon habitats that are identified as well.”

And secondly, natural disasters. 

“Floodplains are also mapped at the same time, so that can show you where you’re exposed to flooding,” said Benda. “And also, the small tributaries coming out of the mountains are those that carry the landslide debris and hit homes on the lower gradient ground.”

Terrain Works is now collaborating with the U.S. Geological Survey to improve mapping in the Yukon territory and St. Lawrence Island. They will also be working with the U.S. Forest Service in the coming months to uncover hidden streams on the islands off Prince of Wales.

You can hear more about Benda’s work during his presentation, “Searching for Missing Streams and Salmon Habitats,” which will take place at the Petersburg Public Library on Thursday, August 17th at 6:30 p.m.