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For nearly a century, two dams on the Elwha River blocked the natural flow of sediment and wood, leading to a highly altered river environment. Removal of the dams unleashed large quantities of sediment and wood that had been trapped behind the reservoirs. This debris was carried downstream, reshaping the river’s course and impacting its ecosystems.

In a new USGS-led study, scientists have leveraged cutting-edge remote sensing and Artificial Intelligence (AI) technology to measure the movement and storage of large wood along the Elwha River in Washington State. This research, which followed the historic removal of two major dams on the river, provides new insights into how natural materials like wood and sediment shape river ecosystems over time.

Researchers relied on aerial imagery collected from 2012 to 2017 as part of interdisciplinary before-after/control-impact studies of dam-removal response. The images were generated using structure-from-motion photogrammetry using a digital camera mounted in the wing of a small airplane.

Four-panel image showing example aerial orthoimagery of wood along Elwha River
Example orthoimagery at a typical location (located in the middle reach of the Elwha River), showing the variation in color and brightness, as well as the nature of the channel, wood deposition, and bar growth.
Elwha River - Humes Ranch Area

Developing the Deep-Learning Approach

Using the aerial imagery, researchers created an AI model capable of identifying and measuring large wood deposits along the river corridor. The model tracked changes in the Elwha River over several years, providing highly accurate measurements of wood and sediment movement—within 15% of true values.

One of the study’s key findings was the relationship between large wood deposits and the formation of sediment bars. As wood accumulated on the river's banks, it helped trap and build up sediment, playing a critical role in reshaping the river channel. This natural process, which was disrupted by the dams, is now restoring the river’s dynamic riparian ecosystems. 

Example annotated orthoimagery of woody debris along the Elwha River
Example annotated aerial images (left column) and resulting label images (right column) made using the software program Doodler.
Multi-paneled graph of orthoimagery shows example model output of woody debris along Elwha River
Example model outputs for the first (2012-04-07) and last (2017-09-22) aerial survey from a selection of bars in the middle reach (MR) and lower reach (LR).

The AI model developed for this study could have far-reaching applications beyond the Elwha River. The researchers suggest that this technology could be used to identify large wood and sediment deposits in other river systems worldwide, potentially aiding in the restoration and management of rivers affected by human intervention.

Moreover, the datasets and AI models from the study have been made publicly available to encourage further research into river dynamics and the interactions between water flow, wood, sediment, and riparian ecosystems. 

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