Mat-Su map indicates little known streams

A hydrology mapping project in the Matanuska Susitna Borough indicates that the area’s watershed contains more miles of streams than previously known. That’s good news for the Borough, because it sheds light on salmon habitat.

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The total miles of Mat Su’s streans has doubled as a result of a two-year stream mapping project. Jim DePasquale is a “spatial ecologist” .. that’s geographer for the uninitiated.. with the Nature Conservancy.

“We ended up adding over 27 thousand linear miles of streams to our existing body of knowledge of Mat Su freshwater maps,” DePasquale said. “And that was an extremely exciting discovery.”

DePasquale formerly worked with the Borough’s GIS [geographical information systems] department. After severe floods hit the Mat Su in late 2102, the Borough decided that more up -to- date information was needed to understand floods.

DePasquale’s $300 thousand mapping project piggybacked on the Borough’s LiDAR map information. LiDAR uses planes to send a signal to the landscape. The signal bounces back, allowing mappers to determine elevations in an area. Aerial photos imposed over the elevation data results in a 3D model. DePasquale said he used the detailed elevation data from the entire 25 thousand square miles of the Mat Su watershed in his work.

DePasquale said the information will have a variety of uses, although defining salmon habitat is the primary one.

“Because the elevation data that we used was so detailed, and because it was brand new, it was literally only a year old when we initiated the project, that allowed us, for the first time, to be able see those little, tiny streams, streams you can step across, in the data itself,” said DePausqaule.

The new data is already being used in a project to pinpoint streams, or portions of streams, that support salmon during the early life stages of the fish.

Other uses of the data include defining flood plain boundaries, or storm water drainages. But after two extremely dry winters in the Mat Su, the mapmakers took climate change into account, too.

“Understanding where their channels are is integral to making those predictions of whether or not water flow or abundance or volume is affected by climate change,” DePasqaule said. “So this type of data would be very important or useful for climate modeling.”

Importantly, the new stream charts meet national map accuracy standards, and are now available to the public through the USGS database.