2.1 Flume configuration
Flume experiments took place at Colorado State University’s Engineering Research Center using a 9-m long and 1.2-m wide flume with a rectangular cross section and smooth sidewalls (Figure 1). Flow was delivered to the flume via pipes and pumps from a reservoir of water. A cobble‐filled baffle dissipated flow energy at the upstream end of the flume and a reinforced 250-micron mesh screen at the downstream end of the flume trapped any mobilized sediment. We sized sediment to maintain an immobile bed and used a gravel subsurface sediment with a pebble topcoat. A summary of all flume attributes is included as Supplemental Information.
We used natural wood pieces of varying size to create logjams in the flume (Figure 1). We ensured a similar wood load per jam by quantifying the wood volume and number of large wood pieces per each jam. Each constructed jam was pinned by one large immobile key piece of wood to avoid jam mobility. To change the permeability of a single jam, we added coarse particulate organic matter, mainly in the form of leaves, pine needles, and bark. We also added a plastic impermeable material to the jam to further reduce its permeability (Figure 1).