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Using a Model River to Investigate How Wood Moves During Floods

By: Josie Welsh (Graduate Student, CU GEOG), and Bridget Mendel (communications at Saint Anthony Falls Laboratory (SAFL))

In a large windowless room and with the hum of a motor steadily pumping water, brightly painted sticks are dropped one at a time into the top of a model river system. Carried by the flow of water, these sticks travel downstream and bump into vertical dowels which form an artificial floodplain forest. Sometimes the sticks bounce off of the dowels and continue their trip. Other times, they get stuck. Slowly, large accumulations of sticks are trapped behind the model trees. Nearby, Master’s student Josie Welsh watches her computer monitor: each dropped stick generates new data that she will spend the upcoming months analyzing.

er’s student Josie Welsh monitoring the physical experiment during an experiment in January 2024.
Figure 1: Master’s student Josie Welsh monitoring the physical experiment during an experiment in January 2024.

Josie is finishing her first year as a graduate student in the geography department at CU Boulder, under advisor Dr. Katherine Lininger, who leads the Riverine Ecogeomorphology Lab at CU. Her work is part of a larger NSF funded project that seeks to answer the question: How does wood move through floodplains, where does it accumulate, and what controls the resulting patterns we observe on floodplains?

Figure 2: A wood jam on the West Creek floodplain near Estes Park, CO.
Figure 2: A wood jam on the West Creek floodplain near Estes Park, CO. 

To answer these questions, Josie travels to the in Minneapolis, MN. SAFL has specialized equipment and expert engineers that have made Josie’s experiments possible, allowing her to isolate and explore particular relationships in complicated natural systems. For each experiment, she models different forest, floodplain, and flow scenarios, like larger floods, more or less dense forest stands, or a narrower or more topographically varied floodplain. In the coming months, Josie will analyze the data from these experiments and determine relationships between these scenarios and the behavior of wood.

Josie hopes her findings will be useful to those working on river restoration projects. Adding wood habitat into landscapes is an increasingly popular restoration technique, but, like sediment, wood moves within the system. This poses a challenge for restoration experts who want their designs to be effective in the long run. How big does a flood need to get to move the wood, how does it move, and where does it go?

Figure 3: Image from above of the physical model after an experiment was conducted. Orange, white, and green pieces are scattered around the model. Flow is from left to right.
Figure 3: Image from above of the physical model after an experiment was conducted. Orange, white, and green pieces are scattered around the model. Flow is from left to right. 

Is it as fun as it looks? “This is just like something I would have done as a child," says Josie, "Except now I have to keep track of a lot of numbers.â€